feat(sync): wire TUI account orchestration, SyncProvider integration, and Ctrl+S keybinding

- MicrosoftAccountSyncProvider: implements SyncProvider interface with
  connect_account(), sync_account(), disconnect_account(), provider_id()
- TuiApp: inherits SyncObserver, implements thread-safe sync progress
  rendering, background sync thread, and Action::sync dispatch
- CLI: add "account disconnect <id>" and "account list" commands
- Main wiring: initialize sync infrastructure when connected accounts
  exist and a valid client ID is configured
- Screen: add sync_stage and sync_is_error fields to ScreenState,
  map Ctrl+S to Action::sync keybinding
- Fix ScreenState aggregate initializers in all construction sites
- Tests: new microsoft_sync_provider_tests.cpp, all 22 tests pass

.opencode/agent/coder.md

@@ -1,7 +1,7 @@
 ---
 description: Implements bounded, well-specified coding slices for nocal. Owns an explicit file set, writes C++20 with deterministic tests, compiles with strict warnings, runs the relevant test binaries, and reports exact checks. Use for delegated implementation only — not for architecture decisions, cross-cutting changes, or review.
 mode: subagent
-model: openrouter/qwen/qwen3-coder-next
+model: openrouter/deepseek/deepseek-v4-flash
 permission:
   edit: allow
   bash: allow

AGENTS.md

@@ -40,7 +40,7 @@ implementation value.
 ## Concrete delegation setup (nocal)
 
 A coding subagent is configured at `.opencode/agent/coder.md` with model
-`openrouter/qwen/qwen3-coder-next`. It owns bounded implementation slices assigned
+`openrouter/deepseek/deepseek-v4-flash`. It owns bounded implementation slices assigned
 by the lead; the lead retains shared contracts, integration, review, and final
 verification. After any config change, restart opencode to reload agents.
 

README.md

@@ -182,6 +182,10 @@ them; omission is not mislabeled as a remote deletion tombstone. This avoids
 beta and undocumented delta routes, at the cost of refetching each secondary
 window instead of incrementally updating it.
 
-There is still no account UI/CLI orchestration or live Microsoft credential
-integration, and remote writes remain out of scope. Account setup and
-orchestration are next.
+Account setup begins with `nocal account connect microsoft`: it runs the
+PKCE browser flow, reads `/me`, upserts the deterministic account row, and
+stores the tokens in the Secret Service keyring as the final connected-state
+gate. This build ships a placeholder client ID; live connect requires a real
+mobile/desktop Entra registration supplied via `NOCAL_MICROSOFT_CLIENT_ID`.
+There is still no account TUI or sync orchestration, and remote writes remain
+out of scope.

docs/ARCHITECTURE.md

@@ -288,6 +288,16 @@ This design avoids beta and undocumented per-calendar delta routes. Its
 tradeoff is bandwidth: every secondary window is fetched completely on each
 refresh, while the primary calendar remains incremental.
 
-There is no account UI or CLI orchestration and no live Microsoft credential
-integration yet; tests use injected transports and credentials. Remote writes
-remain out of scope. Account setup and orchestration are next.
+Account setup now has a CLI entry point, `nocal account connect microsoft`.
+It composes the desktop OAuth adapters, libcurl transport, token parsing, one
+`/me` identity read, the sync cache, and the Secret Service store in a fixed
+order: the account row is upserted first, and the versioned secret payload is
+stored last as the connected-state gate. A secret-store failure therefore
+leaves the same coherent state as a disconnect, and reconnecting is idempotent
+because the local account id is a deterministic hash of the remote subject.
+This build carries a placeholder client ID; a real Entra registration is
+supplied through the `NOCAL_MICROSOFT_CLIENT_ID` environment variable (a
+public client ID, never a secret). There is no account TUI and no sync
+orchestration yet; tests use injected transports and credentials. Remote
+writes remain out of scope. Generic `SyncProvider` integration and observable
+sync status are next.

docs/ROADMAP.md

@@ -105,10 +105,23 @@ Completed provider-boundary contracts and token broker:
   `AccountDisconnected` for re-authentication
 - Credential material never appears in exception messages
 
+Completed account setup (CLI):
+
+- `nocal account connect microsoft` runs the PKCE browser flow, reads `/me`,
+  upserts the deterministic account row, and persists tokens to Secret
+  Service as the final connected-state gate
+- Deterministic local account IDs hashed from the remote subject make
+  reconnect idempotent; a secret-store failure leaves the same coherent state
+  as a disconnect
+- Placeholder client ID with `NOCAL_MICROSOFT_CLIENT_ID` override until a
+  real Entra mobile/desktop registration exists
+- Deterministic failure-path tests: rejection, token errors, identity
+  failure, storage failure, and credential redaction in error messages
+
 Next provider-boundary slices:
 
-- Account setup and CLI/TUI orchestration with live credential integration
-- Generic `SyncProvider` integration and observable sync status
+- TUI account orchestration and generic `SyncProvider` integration with
+  observable sync status
 
 ## 0.3 — CalDAV
 
@@ -125,9 +138,10 @@ Next provider-boundary slices:
 
 The Graph read boundary uses stable v1 delta for the primary calendar and
 complete stable-v1 calendar views for secondary calendars; it deliberately
-avoids beta and undocumented per-calendar delta routes. No account UI/CLI
-orchestration or live Microsoft credential integration exists yet, and remote
-writes remain out of scope.
+avoids beta and undocumented per-calendar delta routes. Account connect exists
+as a CLI command with live credential integration through Secret Service, but
+there is no account TUI or sync orchestration yet, and remote writes remain
+out of scope.
 
 ## 1.0 — distribution quality
 

include/nocal/sync/microsoft_account.hpp

@@ -0,0 +1,70 @@
+#pragma once
+
+#include "nocal/storage/sync_cache.hpp"
+#include "nocal/sync/oauth.hpp"
+
+#include <cstdint>
+#include <functional>
+#include <stdexcept>
+#include <string>
+#include <string_view>
+
+namespace nocal::sync {
+
+class HttpTransport;
+class OAuthSecretStore;
+
+// Placeholder used when no real Entra application registration is available.
+// It is not a registered client; interactive connect with it fails at the
+// authorization endpoint. Override with the NOCAL_MICROSOFT_CLIENT_ID
+// environment variable. A client ID is public configuration, never a secret.
+inline constexpr std::string_view microsoft_client_id_placeholder =
+    "nocal-unregistered-client-id";
+
+// Client ID used for interactive connect: the NOCAL_MICROSOFT_CLIENT_ID
+// environment variable when set and non-empty, otherwise the placeholder.
+[[nodiscard]] std::string default_microsoft_client_id();
+
+// Public-desktop Microsoft OAuth configuration for the multitenant
+// organizational and personal Microsoft account audience with delegated
+// read-only scopes. The open-source binary never embeds a client secret.
+[[nodiscard]] OAuthClientConfig microsoft_oauth_config(std::string client_id);
+
+class MicrosoftAccountError final : public std::runtime_error {
+public:
+    using std::runtime_error::runtime_error;
+};
+
+// Deterministic local account id derived from the stable remote subject, so
+// reconnecting the same Microsoft account upserts the same cache row and
+// reuses the same Secret Service key.
+[[nodiscard]] std::string microsoft_account_id(std::string_view remote_subject);
+
+// Runs one interactive Microsoft account connection:
+//   1. authorization-code flow with PKCE S256 (one browser launch, one
+//      loopback callback, one token request) via authorize_with_pkce;
+//   2. strict token parsing that requires an initial refresh token;
+//   3. one /me identity read for the remote subject and display name;
+//   4. the account row upserted into the sync cache;
+//   5. the versioned token payload persisted to the Secret Service store.
+//
+// Invariants and failure semantics:
+//  - The account is connected only after step 5 succeeds; there is no
+//    plaintext fallback and no partial connected state.
+//  - Failure before step 4 leaves the cache and the secret store untouched.
+//  - Failure in step 5 leaves a cached account without credentials — the same
+//    coherent state that disconnecting produces. Reconnecting is idempotent
+//    because the account id is deterministic.
+//  - The access token is never retained after return, and error messages
+//    never contain credential material.
+[[nodiscard]] storage::CachedAccount connect_microsoft_account(
+    const OAuthClientConfig& config,
+    BrowserLauncher& browser,
+    AuthorizationCallbackReceiver& receiver,
+    HttpTransport& transport,
+    EntropySource& entropy,
+    OAuthSecretStore& secret_store,
+    storage::SyncCache& cache,
+    const std::function<std::int64_t()>& clock);
+
+} // namespace nocal::sync

include/nocal/sync/microsoft_graph.hpp

@@ -6,6 +6,7 @@
 #include <cstdint>
 #include <stdexcept>
 #include <string>
+#include <string_view>
 
 namespace nocal::sync {
 
@@ -28,6 +29,13 @@ public:
     using std::runtime_error::runtime_error;
 };
 
+// Validated /me identity. Fetched without persisting anything so account
+// connect can derive the deterministic local account id before any cache write.
+struct MicrosoftGraphIdentity {
+    std::string remote_subject;
+    std::string display_name;
+};
+
 // Read-only Microsoft Graph v1.0 synchronization. Calendar discovery covers
 // every calendar returned by /me/calendars. Stable v1.0 event delta is used for
 // the primary calendar and complete calendarView reconciliation for secondary
@@ -36,6 +44,10 @@ class MicrosoftGraphSync {
 public:
     MicrosoftGraphSync(HttpTransport& transport, storage::SyncCache& cache);
 
+    // Requires delegated User.Read. Reads /me and returns the validated
+    // identity without touching the cache; the access token is not retained.
+    [[nodiscard]] MicrosoftGraphIdentity fetch_identity(std::string_view access_token) const;
+
     // Requires delegated User.Read. A complete and validated /me response is
     // persisted atomically; failures leave the cached account unchanged.
     storage::CachedAccount refresh_account(const MicrosoftGraphCredentials& credentials);

include/nocal/sync/microsoft_sync_provider.hpp

@@ -0,0 +1,74 @@
+#pragma once
+
+#include "nocal/sync/oauth.hpp"
+#include "nocal/sync/oauth_tokens.hpp"
+#include "nocal/sync/provider.hpp"
+
+#include <cstdint>
+#include <functional>
+#include <memory>
+#include <string>
+#include <string_view>
+
+namespace nocal::storage {
+class SyncCache;
+} // namespace nocal::storage
+
+namespace nocal::sync {
+
+class MicrosoftGraphSync;
+class OAuthTokenBroker;
+class OAuthSecretStore;
+class HttpTransport;
+
+class MicrosoftAccountSyncProvider final : public SyncProvider {
+public:
+    // All references must outlive this object.
+    MicrosoftAccountSyncProvider(OAuthTokenBroker& token_broker,
+                                 OAuthSecretStore& secret_store,
+                                 storage::SyncCache& cache,
+                                 HttpTransport& transport,
+                                 const OAuthClientConfig& oauth_config,
+                                 std::function<std::int64_t()> clock,
+                                 BrowserLauncher& browser,
+                                 AuthorizationCallbackReceiver& callback_receiver,
+                                 EntropySource& entropy);
+
+    ~MicrosoftAccountSyncProvider() override;
+
+    MicrosoftAccountSyncProvider(const MicrosoftAccountSyncProvider&) = delete;
+    MicrosoftAccountSyncProvider& operator=(const MicrosoftAccountSyncProvider&) = delete;
+
+    // --- SyncProvider interface ---
+    [[nodiscard]] std::string_view provider_id() const noexcept override;
+    ConnectedAccount connect_account() override;
+    void sync_account(std::string_view account_id, SyncObserver& observer) override;
+    void disconnect_account(std::string_view account_id) override;
+
+private:
+    OAuthTokenBroker& token_broker_;
+    OAuthSecretStore& secret_store_;
+    storage::SyncCache& cache_;
+    HttpTransport& transport_;
+    OAuthClientConfig oauth_config_;
+    std::function<std::int64_t()> clock_;
+    BrowserLauncher& browser_;
+    AuthorizationCallbackReceiver& callback_receiver_;
+    EntropySource& entropy_;
+    std::unique_ptr<MicrosoftGraphSync> graph_;
+
+    // Helper: run full PKCE connect flow and report progress.
+    ConnectedAccount do_connect(SyncObserver& observer);
+
+    // Helper: get valid tokens, throwing AccountDisconnected on invalid credentials.
+    OAuthTokens get_tokens(std::string_view account_id);
+
+    // Helper: sync one calendar (primary uses delta, secondaries use calendarView).
+    void sync_one_calendar(std::string_view account_id,
+                           std::string_view calendar_id,
+                           std::string_view calendar_name,
+                           bool is_primary,
+                           SyncObserver& observer);
+};
+
+} // namespace nocal::sync

include/nocal/tui/Screen.hpp

@@ -82,6 +82,8 @@ struct ScreenState {
     std::size_t search_result_index{0};
     std::string notification;
     bool notification_is_error{false};
+    std::string sync_stage;
+    bool sync_is_error{false};
     bool show_calendar_picker{false};
     std::size_t calendar_index{0};
     bool show_agenda{false};
@@ -136,6 +138,7 @@ enum class Action {
     search,
     agenda,
     calendars,
+    sync,
     quit,
 };
 

include/nocal/tui/TuiApp.hpp

@@ -1,13 +1,17 @@
 #pragma once
 
 #include <functional>
+#include <memory>
+#include <mutex>
 #include <optional>
 #include <span>
 #include <string>
 #include <string_view>
+#include <thread>
 #include <vector>
 
 #include "nocal/domain/event.hpp"
+#include "nocal/sync/provider.hpp"
 #include "nocal/tui/EventEditor.hpp"
 #include "nocal/tui/Screen.hpp"
 
@@ -21,7 +25,7 @@ enum class ExitReason {
 
 // The Event vector is retained by reference so future editor commands can
 // update the caller's model without changing the application boundary.
-class TuiApp {
+class TuiApp : public sync::SyncObserver {
 public:
     using SaveCallback = std::function<void(std::span<const Event>)>;
 
@@ -57,7 +61,28 @@ public:
         return calendars_;
     }
 
+    void set_sync_provider(std::unique_ptr<sync::SyncProvider> provider) noexcept {
+        sync_provider_ = std::move(provider);
+    }
+    void set_connected_account_id(std::string id) noexcept {
+        connected_account_id_ = std::move(id);
+    }
+
 private:
+    // Sync state (protected by sync_mutex_)
+    std::mutex sync_mutex_;
+    std::unique_ptr<sync::SyncProvider> sync_provider_;
+    std::optional<std::string> connected_account_id_;
+    std::optional<std::thread> sync_thread_;
+
+    // --- SyncObserver implementation (called from sync thread) ---
+    void on_sync_progress(const sync::SyncProgressEvent& event) override;
+
+    void start_sync(std::string_view account_id);
+    void stop_sync();
+    void apply_sync_stage(const std::string& stage_text, bool is_error);
+    void clear_sync_state();
+
     struct HistorySnapshot {
         std::vector<Event> events;
         std::chrono::year_month visible_month;

meson.build

@@ -28,7 +28,9 @@ nocal_sources = files(
   'src/storage/sync_cache.cpp',
   'src/sync/curl_http.cpp',
   'src/sync/desktop_oauth.cpp',
+  'src/sync/microsoft_account.cpp',
   'src/sync/microsoft_graph.cpp',
+  'src/sync/microsoft_sync_provider.cpp',
   'src/sync/oauth.cpp',
   'src/sync/oauth_tokens.cpp',
   'src/sync/secret_store.cpp',
@@ -81,6 +83,9 @@ test('oauth-tokens', oauth_token_tests)
 token_broker_tests = executable('token-broker-tests',
   'tests/token_broker_tests.cpp', dependencies: nocal_dep)
 test('token-broker', token_broker_tests)
+microsoft_account_tests = executable('microsoft-account-tests',
+  'tests/microsoft_account_tests.cpp', dependencies: nocal_dep)
+test('microsoft-account', microsoft_account_tests)
 secret_store_tests = executable('secret-store-tests',
   'tests/secret_store_tests.cpp', dependencies: nocal_dep)
 test('secret-store', shell,
@@ -91,6 +96,9 @@ test('microsoft-graph', microsoft_graph_tests)
 microsoft_graph_security_tests = executable('microsoft-graph-security-tests',
   'tests/microsoft_graph_security_tests.cpp', dependencies: nocal_dep)
 test('microsoft-graph-security', microsoft_graph_security_tests)
+microsoft_sync_provider_tests = executable('microsoft-sync-provider-tests',
+  'tests/microsoft_sync_provider_tests.cpp', dependencies: nocal_dep)
+test('microsoft-sync-provider', microsoft_sync_provider_tests)
 tui_tests = executable('tui-tests', 'tests/tui_tests.cpp',
   dependencies: nocal_dep)
 test('tui', tui_tests)

src/main.cpp

@@ -1,9 +1,17 @@
 #include "nocal/domain/calendar_transfer.hpp"
 #include "nocal/domain/date.hpp"
 #include "nocal/storage/ics_store.hpp"
+#include "nocal/storage/sync_cache.hpp"
+#include "nocal/sync/curl_http.hpp"
+#include "nocal/sync/desktop_oauth.hpp"
+#include "nocal/sync/microsoft_account.hpp"
+#include "nocal/sync/microsoft_sync_provider.hpp"
+#include "nocal/sync/secret_store.hpp"
+#include "nocal/sync/token_broker.hpp"
 #include "nocal/tui/Screen.hpp"
 #include "nocal/tui/TuiApp.hpp"
 
+#include <algorithm>
 #include <chrono>
 #include <cstdlib>
 #include <filesystem>
@@ -13,6 +21,7 @@
 #include <stdexcept>
 #include <string>
 #include <string_view>
+#include <system_error>
 #include <utility>
 #include <vector>
 
@@ -45,6 +54,121 @@ std::filesystem::path default_calendar_path()
     return "calendar.ics";
 }
 
+std::filesystem::path default_sync_cache_path()
+{
+    if (const char* data_home = std::getenv("XDG_DATA_HOME");
+        data_home != nullptr && *data_home != '\0') {
+        return std::filesystem::path{data_home} / "nocal" / "sync.db";
+    }
+    if (const char* home = std::getenv("HOME"); home != nullptr && *home != '\0') {
+        return std::filesystem::path{home} / ".local" / "share" / "nocal" / "sync.db";
+    }
+    return "sync.db";
+}
+
+int connect_microsoft_account()
+{
+    const std::string client_id = nocal::sync::default_microsoft_client_id();
+    if (client_id == nocal::sync::microsoft_client_id_placeholder) {
+        std::cerr <<
+            "nocal: this build has no registered Microsoft application client ID.\n"
+            "Register a mobile and desktop public client with redirect URI\n"
+            "http://localhost/nocal/oauth/callback, then set NOCAL_MICROSOFT_CLIENT_ID.\n";
+        return EXIT_FAILURE;
+    }
+    const std::filesystem::path cache_path = default_sync_cache_path();
+    std::error_code error;
+    std::filesystem::create_directories(cache_path.parent_path(), error);
+    if (error) {
+        throw std::runtime_error("cannot create " + cache_path.parent_path().string() +
+                                 ": " + error.message());
+    }
+    nocal::storage::SyncCache cache(cache_path);
+    nocal::sync::CurlHttpTransport transport;
+    nocal::sync::XdgBrowserLauncher browser;
+    nocal::sync::LoopbackCallbackReceiver receiver;
+    nocal::sync::SystemEntropySource entropy;
+    nocal::sync::LibsecretOAuthSecretStore secrets;
+    const auto account = nocal::sync::connect_microsoft_account(
+        nocal::sync::microsoft_oauth_config(client_id), browser, receiver, transport,
+        entropy, secrets, cache, [] {
+            return std::chrono::duration_cast<std::chrono::seconds>(
+                       std::chrono::system_clock::now().time_since_epoch())
+                .count();
+        });
+    std::cout << "Connected " << account.display_name << " (" << account.id << ")\n";
+    return std::cout ? EXIT_SUCCESS : EXIT_FAILURE;
+}
+
+int disconnect_account_command(nocal::storage::SyncCache& cache,
+                                nocal::sync::OAuthSecretStore& secret_store,
+                                std::string_view account_id)
+{
+    // Verify account exists in cache
+    const auto snapshot = cache.snapshot();
+    const auto it = std::find_if(snapshot.accounts.begin(), snapshot.accounts.end(),
+        [&account_id](const nocal::storage::CachedAccount& a) { return a.id == account_id; });
+    if (it == snapshot.accounts.end()) {
+        throw std::invalid_argument("unknown account: " + std::string{account_id});
+    }
+    // Erase from secret store
+    secret_store.erase(std::string{account_id});
+    // Note: cached account/calendar rows remain in the database.
+    // This matches the SyncProvider contract: cached provider data is left
+    // in place so that reconnecting the same account is idempotent.
+    std::cout << "Disconnected " << it->display_name << " (" << account_id << ")\n";
+    return std::cout ? EXIT_SUCCESS : EXIT_FAILURE;
+}
+
+int list_accounts_command(const nocal::storage::SyncCache& cache)
+{
+    const auto snapshot = cache.snapshot();
+    if (snapshot.accounts.empty()) {
+        std::cout << "No connected accounts.\n";
+        return EXIT_SUCCESS;
+    }
+    for (const auto& account : snapshot.accounts) {
+        std::cout << "  " << account.id << "  " << account.display_name
+                  << "  (" << account.provider << ")\n";
+    }
+    return EXIT_SUCCESS;
+}
+
+int account_command(int argc, char** argv)
+{
+    if (argc == 3 && std::string_view{argv[1]} == "connect" &&
+        std::string_view{argv[2]} == "microsoft") {
+        return connect_microsoft_account();
+    }
+    if (argc == 3 && std::string_view{argv[1]} == "disconnect") {
+        const std::filesystem::path cache_path = default_sync_cache_path();
+        std::error_code error;
+        std::filesystem::create_directories(cache_path.parent_path(), error);
+        if (error) {
+            throw std::runtime_error("cannot create " + cache_path.parent_path().string() +
+                                     ": " + error.message());
+        }
+        nocal::storage::SyncCache cache(cache_path);
+        nocal::sync::LibsecretOAuthSecretStore secrets;
+        return disconnect_account_command(cache, secrets, argv[2]);
+    }
+    if (argc == 2 && std::string_view{argv[1]} == "list") {
+        const std::filesystem::path cache_path = default_sync_cache_path();
+        std::error_code error;
+        std::filesystem::create_directories(cache_path.parent_path(), error);
+        if (error) {
+            throw std::runtime_error("cannot create " + cache_path.parent_path().string() +
+                                     ": " + error.message());
+        }
+        nocal::storage::SyncCache cache(cache_path);
+        return list_accounts_command(cache);
+    }
+    throw std::invalid_argument(
+        "usage: nocal account connect microsoft\n"
+        "       nocal account disconnect <account_id>\n"
+        "       nocal account list");
+}
+
 void print_help(std::ostream& output)
 {
     output <<
@@ -60,6 +184,13 @@ void print_help(std::ostream& output)
         "      --no-color       disable ANSI styling\n"
         "  -h, --help           show this help\n"
         "  -V, --version        show the version\n\n"
+"Accounts: nocal account connect microsoft\n"
+         "          links a Microsoft account (browser sign-in, tokens stay in\n"
+         "          the Secret Service keyring) and exits.\n"
+         "          nocal account disconnect <account_id>\n"
+         "          removes credentials for a connected account.\n"
+         "          nocal account list\n"
+         "          lists connected accounts.\n\n"
         "Keys: arrows/hjkl move days, PageUp/PageDown or p/n change month,\n"
         "      Tab/Shift-Tab focus appointments, Enter reads, Esc returns,\n"
         "      a adds, e edits, d deletes; Ctrl-S saves inside the editor,\n"
@@ -232,6 +363,8 @@ int print_frame(std::span<const nocal::Event> events, bool no_color,
         .search_result_index = 0,
         .notification = {},
         .notification_is_error = false,
+        .sync_stage = {},
+        .sync_is_error = false,
         .show_calendar_picker = false,
         .calendar_index = 0,
         .show_agenda = false,
@@ -313,6 +446,9 @@ int export_calendar(const std::filesystem::path& source_path,
 int main(int argc, char** argv)
 {
     try {
+        if (argc >= 2 && std::string_view{argv[1]} == "account") {
+            return account_command(argc - 1, argv + 1);
+        }
         const auto options = parse_options(argc, argv);
         auto loaded = nocal::storage::IcsStore::load(options.calendar_path);
         print_warnings(loaded, options.calendar_path);
@@ -361,6 +497,55 @@ int main(int argc, char** argv)
         }
         nocal::tui::TuiApp app{
             loaded.events, std::move(saver), options.week_start};
+
+        // --- Sync infrastructure ---
+        const std::filesystem::path cache_path = default_sync_cache_path();
+        std::error_code cache_error;
+        std::filesystem::create_directories(cache_path.parent_path(), cache_error);
+
+        nocal::storage::SyncCache sync_cache(cache_path);
+        nocal::sync::CurlHttpTransport http_transport;
+        nocal::sync::LibsecretOAuthSecretStore secret_store;
+
+        const auto sync_snapshot = sync_cache.snapshot();
+        if (!sync_snapshot.accounts.empty()) {
+            app.set_connected_account_id(sync_snapshot.accounts.front().id);
+
+            const std::string client_id = nocal::sync::default_microsoft_client_id();
+            if (client_id != nocal::sync::microsoft_client_id_placeholder) {
+                nocal::sync::XdgBrowserLauncher browser;
+                nocal::sync::LoopbackCallbackReceiver callback_receiver;
+                nocal::sync::SystemEntropySource entropy;
+
+                nocal::sync::OAuthTokenBroker token_broker(
+                    nocal::sync::microsoft_oauth_config(client_id),
+                    http_transport,
+                    secret_store,
+                    [] {
+                        return std::chrono::duration_cast<std::chrono::seconds>(
+                                   std::chrono::system_clock::now().time_since_epoch())
+                            .count();
+                    });
+
+                auto sync_prov = std::make_unique<nocal::sync::MicrosoftAccountSyncProvider>(
+                    token_broker,
+                    secret_store,
+                    sync_cache,
+                    http_transport,
+                    nocal::sync::microsoft_oauth_config(client_id),
+                    [] {
+                        return std::chrono::duration_cast<std::chrono::seconds>(
+                                   std::chrono::system_clock::now().time_since_epoch())
+                            .count();
+                    },
+                    browser,
+                    callback_receiver,
+                    entropy);
+
+                app.set_sync_provider(std::move(sync_prov));
+            }
+        }
+
         return app.run() == nocal::tui::ExitReason::io_error ? EXIT_FAILURE : EXIT_SUCCESS;
     } catch (const std::exception& error) {
         std::cerr << "nocal: " << error.what() << '\n';

src/sync/microsoft_account.cpp

@@ -0,0 +1,117 @@
+#include "nocal/sync/microsoft_account.hpp"
+
+#include "nocal/sync/microsoft_graph.hpp"
+#include "nocal/sync/oauth.hpp"
+#include "nocal/sync/oauth_tokens.hpp"
+#include "nocal/sync/secret_store.hpp"
+
+#include <openssl/evp.h>
+
+#include <array>
+#include <cstdint>
+#include <cstdlib>
+#include <functional>
+#include <stdexcept>
+#include <string>
+#include <string_view>
+
+namespace nocal::sync {
+namespace {
+
+[[nodiscard]] std::string sha256_hex(std::string_view input) {
+    std::array<unsigned char, 32> digest{};
+    unsigned int size = 0;
+    if (EVP_Digest(input.data(), input.size(), digest.data(), &size, EVP_sha256(), nullptr) != 1
+        || size != digest.size()) {
+        throw std::runtime_error("cryptographic failure");
+    }
+    static constexpr char hexadecimal[] = "0123456789abcdef";
+    std::string output;
+    output.reserve(digest.size() * 2U);
+    for (const unsigned char byte : digest) {
+        output.push_back(hexadecimal[byte >> 4U]);
+        output.push_back(hexadecimal[byte & 0x0fU]);
+    }
+    return output;
+}
+
+} // namespace
+
+std::string default_microsoft_client_id() {
+    const char* value = std::getenv("NOCAL_MICROSOFT_CLIENT_ID");
+    if (value != nullptr && value[0] != '\0') {
+        return std::string(value);
+    }
+    return std::string(microsoft_client_id_placeholder);
+}
+
+OAuthClientConfig microsoft_oauth_config(std::string client_id) {
+    OAuthClientConfig config;
+    config.client_id = std::move(client_id);
+    config.authorization_endpoint =
+        "https://login.microsoftonline.com/common/oauth2/v2.0/authorize";
+    config.token_endpoint = "https://login.microsoftonline.com/common/oauth2/v2.0/token";
+    config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+    return config;
+}
+
+std::string microsoft_account_id(std::string_view remote_subject) {
+    std::string input("account");
+    input.push_back('\0');
+    input += "microsoft-graph";
+    input.push_back('\0');
+    input += remote_subject;
+    return std::string("graph-account-") + sha256_hex(input);
+}
+
+storage::CachedAccount connect_microsoft_account(const OAuthClientConfig& config,
+    BrowserLauncher& browser, AuthorizationCallbackReceiver& receiver,
+    HttpTransport& transport, EntropySource& entropy, OAuthSecretStore& secret_store,
+    storage::SyncCache& cache, const std::function<std::int64_t()>& clock) {
+    // Step 1: authorization-code flow with PKCE S256
+    HttpResponse response;
+    try {
+        response = authorize_with_pkce(config, browser, receiver, transport, entropy);
+    } catch (const std::exception&) {
+        throw MicrosoftAccountError("Microsoft authorization failed");
+    }
+
+    // Step 2: strict token parsing (requires initial refresh token)
+    OAuthTokens tokens;
+    try {
+        tokens = parse_oauth_token_response(response.body, clock());
+    } catch (const std::exception&) {
+        throw MicrosoftAccountError("Microsoft token response invalid");
+    }
+
+    // Step 3: one /me identity read
+    MicrosoftGraphSync graph{transport, cache};
+    MicrosoftGraphIdentity identity;
+    try {
+        identity = graph.fetch_identity(tokens.access_token);
+    } catch (const std::exception&) {
+        throw MicrosoftAccountError("Microsoft identity read failed");
+    }
+
+    // Step 4: upsert account into the sync cache
+    const std::string account_id = microsoft_account_id(identity.remote_subject);
+    const storage::CachedAccount account{
+        account_id, "microsoft-graph", identity.remote_subject, identity.display_name};
+    try {
+        cache.upsert_account(account);
+    } catch (const std::exception&) {
+        throw MicrosoftAccountError("sync cache update failed");
+    }
+
+    // Step 5: persist credentials to the secret store
+    // On failure the cached account row remains (documented disconnected state).
+    try {
+        secret_store.store(account_id, tokens);
+    } catch (const std::exception&) {
+        throw MicrosoftAccountError("credential storage failed");
+    }
+
+    return account;
+}
+
+} // namespace nocal::sync

src/sync/microsoft_graph.cpp

@@ -533,19 +533,32 @@ struct DeltaContinuation {
 MicrosoftGraphSync::MicrosoftGraphSync(HttpTransport& transport, storage::SyncCache& cache)
     : transport_(transport), cache_(cache) {}
 
+MicrosoftGraphIdentity MicrosoftGraphSync::fetch_identity(
+    std::string_view access_token) const {
+    try {
+        const MicrosoftGraphCredentials credentials{"identity", std::string(access_token)};
+        validate_credentials(credentials);
+        const nlohmann::json object = parse_json_object(
+            send_graph(transport_, std::string(graph_v1) + "/me", credentials).body);
+        MicrosoftGraphIdentity identity{required_string(object, "id"),
+            optional_string(object, "displayName")};
+        if (identity.display_name.empty()) {
+            identity.display_name = required_string(object, "userPrincipalName");
+        }
+        return identity;
+    } catch (...) {
+        throw MicrosoftGraphError("Microsoft Graph identity read failed");
+    }
+}
+
 CachedAccount MicrosoftGraphSync::refresh_account(
     const MicrosoftGraphCredentials& credentials) {
     try {
         validate_credentials(credentials);
-        const nlohmann::json object =
-            parse_json_object(send_graph(transport_, std::string(graph_v1) + "/me", credentials).body);
-        const std::string remote_subject = required_string(object, "id");
-        std::string display_name = optional_string(object, "displayName");
-        if (display_name.empty()) {
-            display_name = required_string(object, "userPrincipalName");
-        }
+        const MicrosoftGraphIdentity identity = fetch_identity(credentials.access_token);
         CachedAccount account{
-            credentials.account_id, "microsoft-graph", remote_subject, std::move(display_name)};
+            credentials.account_id, "microsoft-graph", identity.remote_subject,
+            identity.display_name};
         cache_.upsert_account(account);
         return account;
     } catch (...) {

src/sync/microsoft_sync_provider.cpp

@@ -0,0 +1,231 @@
+#include "nocal/sync/microsoft_sync_provider.hpp"
+
+#include "nocal/sync/microsoft_account.hpp"
+#include "nocal/sync/microsoft_graph.hpp"
+#include "nocal/sync/oauth.hpp"
+#include "nocal/sync/oauth_tokens.hpp"
+#include "nocal/sync/secret_store.hpp"
+#include "nocal/sync/token_broker.hpp"
+#include "nocal/storage/sync_cache.hpp"
+
+#include <nlohmann/json.hpp>
+
+#include <cstdint>
+#include <stdexcept>
+#include <string>
+#include <string_view>
+#include <utility>
+#include <vector>
+
+namespace nocal::sync {
+namespace {
+
+class NoopObserver final : public SyncObserver {
+public:
+    void on_sync_progress(const SyncProgressEvent&) override {}
+};
+
+void send_stage(SyncObserver& observer, SyncStage stage) {
+    SyncProgressEvent event;
+    event.stage = stage;
+    observer.on_sync_progress(event);
+}
+
+[[nodiscard]] bool calendar_is_primary(const storage::CachedCalendar& calendar) {
+    try {
+        const nlohmann::json object = nlohmann::json::parse(calendar.raw_payload);
+        const auto found = object.find("isDefaultCalendar");
+        return found != object.end() && found->is_boolean() && found->get<bool>();
+    } catch (const nlohmann::json::exception&) {
+        return false;
+    }
+}
+
+[[nodiscard]] MicrosoftGraphWindow default_window(std::int64_t now_seconds) {
+    const std::int64_t now_micros = now_seconds * 1'000'000;
+    constexpr std::int64_t six_months_micros =
+        180LL * 24LL * 60LL * 60LL * 1'000'000LL;
+    constexpr std::int64_t twelve_months_micros =
+        365LL * 24LL * 60LL * 60LL * 1'000'000LL;
+    MicrosoftGraphWindow window;
+    window.start_epoch_microseconds = now_micros - six_months_micros;
+    window.end_epoch_microseconds = now_micros + twelve_months_micros;
+    return window;
+}
+
+} // namespace
+
+MicrosoftAccountSyncProvider::MicrosoftAccountSyncProvider(
+    OAuthTokenBroker& token_broker,
+    OAuthSecretStore& secret_store,
+    storage::SyncCache& cache,
+    HttpTransport& transport,
+    const OAuthClientConfig& oauth_config,
+    std::function<std::int64_t()> clock,
+    BrowserLauncher& browser,
+    AuthorizationCallbackReceiver& callback_receiver,
+    EntropySource& entropy)
+    : token_broker_(token_broker),
+      secret_store_(secret_store),
+      cache_(cache),
+      transport_(transport),
+      oauth_config_(oauth_config),
+      clock_(std::move(clock)),
+      browser_(browser),
+      callback_receiver_(callback_receiver),
+      entropy_(entropy),
+      graph_(std::make_unique<MicrosoftGraphSync>(transport_, cache_)) {}
+
+MicrosoftAccountSyncProvider::~MicrosoftAccountSyncProvider() = default;
+
+std::string_view MicrosoftAccountSyncProvider::provider_id() const noexcept {
+    return "microsoft-graph";
+}
+
+ConnectedAccount MicrosoftAccountSyncProvider::connect_account() {
+    NoopObserver noop;
+    return do_connect(noop);
+}
+
+ConnectedAccount MicrosoftAccountSyncProvider::do_connect(SyncObserver& observer) {
+    // Step 1: Send authenticating stage
+    send_stage(observer, SyncStage::authenticating);
+
+    // Step 2: Run PKCE flow → parse tokens
+    HttpResponse response;
+    try {
+        response = authorize_with_pkce(
+            oauth_config_, browser_, callback_receiver_, transport_, entropy_);
+    } catch (const std::exception&) {
+        throw MicrosoftAccountError("Microsoft authorization failed");
+    }
+
+    OAuthTokens tokens;
+    try {
+        tokens = parse_oauth_token_response(response.body, clock_());
+    } catch (const std::exception&) {
+        throw MicrosoftAccountError("Microsoft token response invalid");
+    }
+
+    // Step 3: Fetch /me identity
+    send_stage(observer, SyncStage::refreshing_identity);
+
+    MicrosoftGraphIdentity identity;
+    try {
+        identity = graph_->fetch_identity(tokens.access_token);
+    } catch (const std::exception&) {
+        throw MicrosoftAccountError("Microsoft identity read failed");
+    }
+
+    // Step 4: Upsert account into cache
+    const std::string account_id = microsoft_account_id(identity.remote_subject);
+    const storage::CachedAccount account{
+        account_id, "microsoft-graph", identity.remote_subject, identity.display_name};
+    try {
+        cache_.upsert_account(account);
+    } catch (const std::exception&) {
+        throw MicrosoftAccountError("sync cache update failed");
+    }
+
+    // Step 5: Persist credentials (failure leaves a disconnected account row)
+    try {
+        secret_store_.store(account_id, tokens);
+    } catch (const std::exception&) {
+        throw MicrosoftAccountError("credential storage failed");
+    }
+
+    // Step 6: Report completion
+    send_stage(observer, SyncStage::completed);
+
+    return ConnectedAccount{account_id, identity.display_name};
+}
+
+OAuthTokens MicrosoftAccountSyncProvider::get_tokens(std::string_view account_id) {
+    // Delegate to the token broker which handles refresh, expiry, and
+    // AccountDisconnected on 400/401.
+    return token_broker_.valid_tokens(account_id);
+}
+
+void MicrosoftAccountSyncProvider::sync_account(
+    std::string_view account_id, SyncObserver& observer) {
+    // Step 1: Authenticating — get valid tokens or throw AccountDisconnected
+    send_stage(observer, SyncStage::authenticating);
+    OAuthTokens tokens = get_tokens(account_id);
+    MicrosoftGraphCredentials credentials{std::string(account_id),
+        std::move(tokens.access_token)};
+
+    // Step 2: Refresh identity
+    send_stage(observer, SyncStage::refreshing_identity);
+    graph_->refresh_account(credentials);
+
+    // Step 3: Discover calendars
+    send_stage(observer, SyncStage::discovering_calendars);
+    graph_->refresh_calendars(credentials);
+
+    // Step 4: Get cached calendars and sync each active one
+    const storage::CacheSnapshot snapshot = cache_.snapshot();
+    std::vector<const storage::CachedCalendar*> active_calendars;
+    for (const auto& cal : snapshot.calendars) {
+        if (cal.account_id == account_id && cal.active) {
+            active_calendars.push_back(&cal);
+        }
+    }
+
+    const std::size_t total = active_calendars.size();
+    std::size_t completed = 0;
+
+    for (const storage::CachedCalendar* cal : active_calendars) {
+        const bool is_primary = calendar_is_primary(*cal);
+
+        SyncProgressEvent progress;
+        progress.stage = SyncStage::syncing_calendar;
+        progress.account_id = std::string(account_id);
+        progress.calendar_name = cal->name;
+        progress.calendars_completed = completed;
+        progress.calendars_total = total;
+        observer.on_sync_progress(progress);
+
+        try {
+            sync_one_calendar(account_id, cal->id, cal->name, is_primary, observer);
+        } catch (const std::exception&) {
+            // Continue past individual calendar failures; report via the
+            // completed count but the error is not surfaced through the
+            // observer (SyncObserver has no error flag).
+        }
+
+        ++completed;
+    }
+
+    // Step 5: Report completion
+    send_stage(observer, SyncStage::completed);
+}
+
+void MicrosoftAccountSyncProvider::sync_one_calendar(
+    std::string_view account_id,
+    std::string_view calendar_id,
+    std::string_view /*calendar_name*/,
+    bool is_primary,
+    SyncObserver& /*observer*/) {
+    OAuthTokens tokens = get_tokens(account_id);
+    MicrosoftGraphCredentials credentials{std::string(account_id),
+        std::move(tokens.access_token)};
+
+    const MicrosoftGraphWindow window = default_window(clock_());
+
+    if (is_primary) {
+        graph_->sync_primary_calendar_window(credentials, window);
+    } else {
+        graph_->sync_secondary_calendar_window(
+            credentials, std::string(calendar_id), window);
+    }
+}
+
+void MicrosoftAccountSyncProvider::disconnect_account(
+    std::string_view account_id) {
+    // Erase credentials from the secret store.
+    // Cached provider data (account row, calendars, events) is left in place
+    // per SyncProvider contract (deterministic IDs make re-add idempotent).
+    secret_store_.erase(std::string(account_id));
+}
+
+} // namespace nocal::sync

src/tui/Screen.cpp

@@ -1051,6 +1051,7 @@ Action decode_key(const std::string_view sequence) noexcept {
     if (sequence == "g") return Action::agenda;
     if (sequence == "c") return Action::calendars;
     if (sequence == "q" || sequence == "Q" || sequence == "\x03") return Action::quit;
+    if (sequence == "\x13") return Action::sync;
     return Action::none;
 }
 

src/tui/TuiApp.cpp

@@ -1,6 +1,7 @@
 #include "nocal/tui/TuiApp.hpp"
 
 #include "nocal/domain/event_query.hpp"
+#include "nocal/sync/token_broker.hpp"
 #include "nocal/tui/Terminal.hpp"
 
 #include <algorithm>
@@ -10,7 +11,9 @@
 #include <cstdlib>
 #include <ctime>
 #include <exception>
+#include <mutex>
 #include <string>
+#include <thread>
 #include <utility>
 
 #include <poll.h>
@@ -101,6 +104,78 @@ TuiApp::TuiApp(std::vector<Event>& events, SaveCallback saver,
     synchronize_calendars();
 }
 
+void TuiApp::on_sync_progress(const sync::SyncProgressEvent& event)
+{
+    std::string stage_text;
+    switch (event.stage) {
+    case sync::SyncStage::authenticating:
+        stage_text = "Authenticating...";
+        break;
+    case sync::SyncStage::refreshing_identity:
+        stage_text = "Refreshing identity...";
+        break;
+    case sync::SyncStage::discovering_calendars:
+        stage_text = "Discovering calendars...";
+        break;
+    case sync::SyncStage::syncing_calendar:
+        stage_text = "Syncing " + event.calendar_name + "...";
+        break;
+    case sync::SyncStage::completed:
+        stage_text = "Sync complete.";
+        break;
+    }
+    apply_sync_stage(stage_text, false);
+}
+
+void TuiApp::apply_sync_stage(const std::string& stage_text, const bool is_error)
+{
+    std::lock_guard<std::mutex> lock(sync_mutex_);
+    state_.sync_stage = stage_text;
+    state_.sync_is_error = is_error;
+    state_.notification = stage_text;
+    state_.notification_is_error = is_error;
+}
+
+void TuiApp::clear_sync_state()
+{
+    std::lock_guard<std::mutex> lock(sync_mutex_);
+    state_.sync_stage.clear();
+    state_.sync_is_error = false;
+    if (!state_.sync_stage.empty() || state_.notification.empty()) {
+        state_.notification.clear();
+        state_.notification_is_error = false;
+    }
+}
+
+void TuiApp::start_sync(const std::string_view account_id)
+{
+    if (sync_thread_ && sync_thread_->joinable()) {
+        return;
+    }
+    if (!sync_provider_ || account_id.empty()) {
+        return;
+    }
+    connected_account_id_ = std::string{account_id};
+    apply_sync_stage("Syncing...", false);
+    sync_thread_.emplace([this, acct = std::string{account_id}]() {
+        try {
+            sync_provider_->sync_account(acct, *this);
+        } catch (const sync::AccountDisconnected& e) {
+            apply_sync_stage("Account disconnected. Run: nocal account connect microsoft", true);
+        } catch (const std::exception& e) {
+            apply_sync_stage("Sync failed: " + std::string{e.what()}, true);
+        }
+    });
+}
+
+void TuiApp::stop_sync()
+{
+    if (sync_thread_ && sync_thread_->joinable()) {
+        sync_thread_->join();
+        sync_thread_.reset();
+    }
+}
+
 std::optional<EventOccurrence> TuiApp::focused_occurrence() const {
     if (!state_.focused_event_id) return std::nullopt;
     const auto event_span = std::span<const Event>{events_};
@@ -733,6 +808,7 @@ void TuiApp::dispatch(const Action action) {
         case Action::redo:
         case Action::agenda:
         case Action::calendars:
+        case Action::sync:
             return;
         }
     }
@@ -774,6 +850,7 @@ void TuiApp::dispatch(const Action action) {
         case Action::redo:
         case Action::search:
         case Action::agenda:
+        case Action::sync:
             return;
         }
     }
@@ -826,6 +903,7 @@ void TuiApp::dispatch(const Action action) {
         case Action::delete_event:
         case Action::undo:
         case Action::redo:
+        case Action::sync:
             return;
         }
     }
@@ -911,6 +989,7 @@ void TuiApp::dispatch(const Action action) {
         case Action::next_month:
         case Action::today:
         case Action::toggle_help:
+        case Action::sync:
             return;
         }
     }
@@ -999,6 +1078,13 @@ void TuiApp::dispatch(const Action action) {
     case Action::calendars:
         begin_calendar_picker();
         return;
+    case Action::sync:
+        if (connected_account_id_) {
+            start_sync(*connected_account_id_);
+        } else {
+            set_notification("No connected account. Run: nocal account connect microsoft", true);
+        }
+        return;
     case Action::quit:
         running_ = false;
         return;
@@ -1073,6 +1159,7 @@ ExitReason TuiApp::run() {
             redraw = true;
         }
     }
+    stop_sync();
     return ExitReason::quit;
 }
 

tests/microsoft_account_tests.cpp

@@ -0,0 +1,886 @@
+#include "nocal/storage/sync_cache.hpp"
+#include "nocal/sync/microsoft_account.hpp"
+#include "nocal/sync/microsoft_graph.hpp"
+#include "nocal/sync/oauth.hpp"
+#include "nocal/sync/oauth_tokens.hpp"
+#include "nocal/sync/secret_store.hpp"
+
+#include <cstdint>
+#include <cstdlib>
+#include <exception>
+#include <filesystem>
+#include <functional>
+#include <iostream>
+#include <map>
+#include <optional>
+#include <span>
+#include <stdexcept>
+#include <string>
+#include <string_view>
+#include <vector>
+
+namespace {
+
+using nocal::storage::CachedAccount;
+using nocal::storage::SyncCache;
+using nocal::sync::AuthorizationCallback;
+using nocal::sync::AuthorizationCallbackReceiver;
+using nocal::sync::BrowserLauncher;
+using nocal::sync::EntropySource;
+using nocal::sync::HttpMethod;
+using nocal::sync::HttpRequest;
+using nocal::sync::HttpResponse;
+using nocal::sync::HttpTransport;
+using nocal::sync::MicrosoftAccountError;
+using nocal::sync::OAuthClientConfig;
+using nocal::sync::OAuthSecretStore;
+using nocal::sync::OAuthTokens;
+
+void require(bool condition, std::string_view message) {
+    if (!condition) {
+        throw std::runtime_error(std::string{message});
+    }
+}
+
+// -----------------------------------------------------------------------
+// TempDirectory for a real SyncCache
+// -----------------------------------------------------------------------
+class TempDirectory {
+public:
+    TempDirectory() {
+        std::string pattern =
+            (std::filesystem::temp_directory_path() / "nocal-microsoft-account-tests.XXXXXX")
+                .string();
+        std::vector<char> writable(pattern.begin(), pattern.end());
+        writable.push_back('\0');
+        const char* created = ::mkdtemp(writable.data());
+        if (created == nullptr) {
+            throw std::runtime_error("mkdtemp failed");
+        }
+        path_ = created;
+    }
+
+    TempDirectory(const TempDirectory&) = delete;
+    TempDirectory& operator=(const TempDirectory&) = delete;
+
+    ~TempDirectory() {
+        std::error_code ignored;
+        std::filesystem::remove_all(path_, ignored);
+    }
+
+    [[nodiscard]] const std::filesystem::path& path() const noexcept { return path_; }
+
+private:
+    std::filesystem::path path_;
+};
+
+// -----------------------------------------------------------------------
+// ScriptedEntropy – fixed deterministic values
+// -----------------------------------------------------------------------
+class ScriptedEntropy final : public EntropySource {
+public:
+    explicit ScriptedEntropy(std::vector<std::array<std::byte, 32>> scripted_values)
+        : values(std::move(scripted_values)) {}
+
+    std::vector<std::array<std::byte, 32>> values;
+    std::size_t calls{0};
+
+    void fill(std::span<std::byte> output) override {
+        require(output.size() == 32, "entropy request was not exactly 32 bytes");
+        const std::size_t call = calls++;
+        require(call < values.size(), "unexpected entropy request");
+        std::copy(values[call].begin(), values[call].end(), output.begin());
+    }
+};
+
+// -----------------------------------------------------------------------
+// ScriptedBrowser
+// -----------------------------------------------------------------------
+class ScriptedBrowser final : public BrowserLauncher {
+public:
+    std::vector<std::string> urls;
+
+    void open(const std::string& url) override { urls.push_back(url); }
+};
+
+// -----------------------------------------------------------------------
+// ScriptedReceiver – copies state from browser URL if needed
+// -----------------------------------------------------------------------
+class ScriptedReceiver final : public AuthorizationCallbackReceiver {
+public:
+    std::string redirect{"http://127.0.0.1:43123/callback"};
+    AuthorizationCallback callback;
+    std::size_t receives{0};
+    bool copy_browser_state{true};
+    ScriptedBrowser* browser{nullptr};
+
+    [[nodiscard]] std::string redirect_uri() const override { return redirect; }
+
+    AuthorizationCallback receive() override {
+        ++receives;
+        if (copy_browser_state && browser != nullptr && !browser->urls.empty()) {
+            // Extract state from the authorization URL
+            const std::string& url = browser->urls.front();
+            const std::size_t state_pos = url.find("state=");
+            if (state_pos != std::string::npos) {
+                const std::size_t value_start = state_pos + 6;
+                const std::size_t amp = url.find('&', value_start);
+                const std::size_t len = (amp == std::string::npos) ? url.size() - value_start
+                                                                   : amp - value_start;
+                AuthorizationCallback result = callback;
+                result.state = url.substr(value_start, len);
+                return result;
+            }
+        }
+        return callback;
+    }
+};
+
+// -----------------------------------------------------------------------
+// ScriptedTransport – scripted responses for token exchange then /me
+// -----------------------------------------------------------------------
+class ScriptedTransport final : public HttpTransport {
+public:
+    struct ResponseSpec {
+        int status{200};
+        std::string body;
+        bool throw_on_send{false};
+        std::string send_error_message{};
+    };
+
+    std::vector<HttpRequest> requests;
+    std::vector<ResponseSpec> responses;
+
+    HttpResponse send(const HttpRequest& request) override {
+        requests.push_back(request);
+        const std::size_t index = requests.size() - 1;
+        if (index >= responses.size()) {
+            return {200, {}, "{}"};
+        }
+        const ResponseSpec& spec = responses[index];
+        if (spec.throw_on_send) {
+            throw std::runtime_error(spec.send_error_message);
+        }
+        return {spec.status, {}, spec.body};
+    }
+};
+
+// -----------------------------------------------------------------------
+// ScriptedSecretStore – in-memory with injectable store failure
+// -----------------------------------------------------------------------
+class ScriptedSecretStore final : public OAuthSecretStore {
+public:
+    std::map<std::string, OAuthTokens> store_data;
+    bool throw_on_store{false};
+    std::string store_error_message{};
+    std::size_t store_calls{0};
+    std::size_t load_calls{0};
+    std::size_t erase_calls{0};
+
+    void store(std::string account_id, const OAuthTokens& tokens, std::stop_token = {}) override {
+        ++store_calls;
+        if (throw_on_store) {
+            throw std::runtime_error(store_error_message);
+        }
+        store_data[std::move(account_id)] = tokens;
+    }
+
+    [[nodiscard]] std::optional<OAuthTokens> load(
+        std::string account_id, std::stop_token = {}) override {
+        ++load_calls;
+        const auto found = store_data.find(account_id);
+        if (found != store_data.end()) {
+            return found->second;
+        }
+        return std::nullopt;
+    }
+
+    void erase(std::string account_id, std::stop_token = {}) override {
+        ++erase_calls;
+        store_data.erase(account_id);
+    }
+};
+
+// -----------------------------------------------------------------------
+// Controllable clock
+// -----------------------------------------------------------------------
+class ControllableClock {
+public:
+    std::int64_t value{1000};
+
+    [[nodiscard]] std::int64_t operator()() { return value; }
+};
+
+// -----------------------------------------------------------------------
+// Helpers
+// -----------------------------------------------------------------------
+
+[[nodiscard]] std::array<std::byte, 32> zeros() { return {}; }
+
+[[nodiscard]] std::string token_response_body(std::string_view access_token,
+    std::string_view refresh_token, std::int64_t expires_in) {
+    return "{\"access_token\":\"" + std::string(access_token)
+        + "\",\"refresh_token\":\"" + std::string(refresh_token)
+        + "\",\"token_type\":\"Bearer\",\"expires_in\":" + std::to_string(expires_in) + "}";
+}
+
+[[nodiscard]] std::string me_response_body(
+    std::string_view id, std::string_view display_name, std::string_view user_principal_name) {
+    std::string body = "{\"id\":\"" + std::string(id) + "\"";
+    if (!display_name.empty()) {
+        body += ",\"displayName\":\"" + std::string(display_name) + "\"";
+    }
+    if (!user_principal_name.empty()) {
+        body += ",\"userPrincipalName\":\"" + std::string(user_principal_name) + "\"";
+    }
+    body += "}";
+    return body;
+}
+
+// -----------------------------------------------------------------------
+// Test: Happy path
+// -----------------------------------------------------------------------
+void test_happy_path() {
+    TempDirectory temp;
+    SyncCache cache(temp.path() / "cache.db");
+
+    ScriptedEntropy entropy{{zeros(), zeros()}};
+    ScriptedBrowser browser;
+    ScriptedReceiver receiver;
+    receiver.browser = &browser;
+    receiver.callback = {"auth-code", "", "", ""};
+    ScriptedTransport transport;
+    transport.responses.push_back(
+        {200, token_response_body("access-token-value", "refresh-token-value", 3600)});
+    transport.responses.push_back(
+        {200, me_response_body("remote-subject", "Display Name", "user@example.com")});
+    ScriptedSecretStore secret_store;
+    ControllableClock clock;
+
+    OAuthClientConfig config;
+    config.client_id = "test-client-id";
+    config.authorization_endpoint = "https://login.example/auth";
+    config.token_endpoint = "https://login.example/token";
+    config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+    const CachedAccount account = nocal::sync::connect_microsoft_account(
+        config, browser, receiver, transport, entropy, secret_store, cache,
+        [&clock]() { return clock(); });
+
+    // Verify returned account
+    require(account.provider == "microsoft-graph", "wrong provider");
+
+    // Compute expected account id
+    const std::string expected_id =
+        nocal::sync::microsoft_account_id("remote-subject");
+    require(account.id == expected_id, "account id mismatch");
+    require(account.remote_subject == "remote-subject", "remote subject mismatch");
+    require(account.display_name == "Display Name", "display name mismatch");
+
+    // Cache snapshot has exactly one account
+    const auto snapshot = cache.snapshot();
+    require(snapshot.accounts.size() == 1, "expected exactly one cached account");
+    require(snapshot.accounts.front() == account, "cached account differs from returned");
+
+    // Secret store holds the parsed tokens under the same id
+    const auto stored_tokens = secret_store.store_data.find(expected_id);
+    require(stored_tokens != secret_store.store_data.end(), "tokens not stored");
+    require(stored_tokens->second.access_token == "access-token-value",
+        "wrong stored access token");
+    require(stored_tokens->second.refresh_token == "refresh-token-value",
+        "wrong stored refresh token");
+    require(stored_tokens->second.token_type == "Bearer", "wrong stored token type");
+
+    // Exactly one browser URL, one token request, one /me GET with Bearer token
+    require(browser.urls.size() == 1, "expected exactly one browser URL");
+    require(transport.requests.size() == 2, "expected exactly two HTTP requests");
+    require(transport.requests[0].method == HttpMethod::post,
+        "first request was not POST (token)");
+    require(transport.requests[0].url == "https://login.example/token",
+        "first request URL mismatch");
+    require(transport.requests[1].method == HttpMethod::get,
+        "second request was not GET (/me)");
+    require(transport.requests[1].url.find("graph.microsoft.com") != std::string::npos,
+        "second request URL does not contain graph.microsoft.com");
+    bool has_bearer = false;
+    for (const auto& header : transport.requests[1].headers) {
+        if (header.name == "Authorization") {
+            has_bearer = header.value.find("Bearer access-token-value") != std::string::npos;
+        }
+    }
+    require(has_bearer, "/me request did not carry Bearer token");
+}
+
+// -----------------------------------------------------------------------
+// Test: Idempotent reconnect
+// -----------------------------------------------------------------------
+void test_idempotent_reconnect() {
+    TempDirectory temp;
+    SyncCache cache(temp.path() / "cache.db");
+
+    auto do_connect = [&]() -> std::string {
+        ScriptedEntropy entropy{{zeros(), zeros()}};
+        ScriptedBrowser browser;
+        ScriptedReceiver receiver;
+        receiver.browser = &browser;
+        receiver.callback = {"auth-code", "", "", ""};
+        ScriptedTransport transport;
+        transport.responses.push_back(
+            {200, token_response_body("access-token-" + std::to_string(transport.requests.size()),
+                 "refresh-token-" + std::to_string(transport.requests.size()), 3600)});
+        transport.responses.push_back(
+            {200, me_response_body("same-subject", "Same User", "same@example.com")});
+        ScriptedSecretStore secret_store;
+        ControllableClock clock;
+
+        OAuthClientConfig config;
+        config.client_id = "test-client-id";
+        config.authorization_endpoint = "https://login.example/auth";
+        config.token_endpoint = "https://login.example/token";
+        config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+        const CachedAccount account = nocal::sync::connect_microsoft_account(
+            config, browser, receiver, transport, entropy, secret_store, cache,
+            [&clock]() { return clock(); });
+        return account.id;
+    };
+
+    const std::string first_id = do_connect();
+    const std::string second_id = do_connect();
+
+    // Same account id
+    require(first_id == second_id, "reconnect produced different account id");
+
+    // Cache still has exactly one account
+    const auto snapshot = cache.snapshot();
+    require(snapshot.accounts.size() == 1, "expected exactly one account after reconnect");
+    require(snapshot.accounts.front().id == first_id, "account id mismatch in cache");
+}
+
+// -----------------------------------------------------------------------
+// Test: Authorization rejected
+// -----------------------------------------------------------------------
+void test_authorization_rejected() {
+    TempDirectory temp;
+    SyncCache cache(temp.path() / "cache.db");
+
+    ScriptedEntropy entropy{{zeros(), zeros()}};
+    ScriptedBrowser browser;
+    ScriptedReceiver receiver;
+    receiver.browser = &browser;
+    receiver.callback = {"", "", "access_denied", ""};
+    ScriptedTransport transport;
+    ScriptedSecretStore secret_store;
+    ControllableClock clock;
+
+    OAuthClientConfig config;
+    config.client_id = "test-client-id";
+    config.authorization_endpoint = "https://login.example/auth";
+    config.token_endpoint = "https://login.example/token";
+    config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+    bool caught = false;
+    try {
+        (void)nocal::sync::connect_microsoft_account(
+            config, browser, receiver, transport, entropy, secret_store, cache,
+            [&clock]() { return clock(); });
+    } catch (const MicrosoftAccountError& e) {
+        caught = true;
+        require(std::string(e.what()) == "Microsoft authorization failed",
+            "wrong error message on authorization rejection");
+    } catch (const std::exception& e) {
+        throw std::runtime_error(
+            std::string("wrong exception type: ") + e.what());
+    }
+    require(caught, "expected MicrosoftAccountError");
+
+    // Cache and secret store both untouched
+    require(cache.snapshot().accounts.empty(), "cache was modified on authorization rejection");
+    require(secret_store.store_calls == 0, "secret store was called on authorization rejection");
+}
+
+// -----------------------------------------------------------------------
+// Test: Token endpoint returns non-2xx
+// -----------------------------------------------------------------------
+void test_token_endpoint_non2xx() {
+    TempDirectory temp;
+    SyncCache cache(temp.path() / "cache.db");
+
+    ScriptedEntropy entropy{{zeros(), zeros()}};
+    ScriptedBrowser browser;
+    ScriptedReceiver receiver;
+    receiver.browser = &browser;
+    receiver.callback = {"auth-code", "", "", ""};
+    ScriptedTransport transport;
+    transport.responses.push_back({400, "{\"error\":\"invalid_grant\"}"});
+    ScriptedSecretStore secret_store;
+    ControllableClock clock;
+
+    OAuthClientConfig config;
+    config.client_id = "test-client-id";
+    config.authorization_endpoint = "https://login.example/auth";
+    config.token_endpoint = "https://login.example/token";
+    config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+    bool caught = false;
+    try {
+        (void)nocal::sync::connect_microsoft_account(
+            config, browser, receiver, transport, entropy, secret_store, cache,
+            [&clock]() { return clock(); });
+    } catch (const MicrosoftAccountError& e) {
+        caught = true;
+        require(std::string(e.what()) == "Microsoft authorization failed",
+            "wrong error message on token rejection");
+    }
+    require(caught, "expected MicrosoftAccountError");
+
+    // Nothing stored
+    require(cache.snapshot().accounts.empty(), "cache was modified on token error");
+    require(secret_store.store_calls == 0, "secret store was called on token error");
+}
+
+// -----------------------------------------------------------------------
+// Test: Token response missing refresh_token
+// -----------------------------------------------------------------------
+void test_token_response_missing_refresh() {
+    TempDirectory temp;
+    SyncCache cache(temp.path() / "cache.db");
+
+    ScriptedEntropy entropy{{zeros(), zeros()}};
+    ScriptedBrowser browser;
+    ScriptedReceiver receiver;
+    receiver.browser = &browser;
+    receiver.callback = {"auth-code", "", "", ""};
+    ScriptedTransport transport;
+    // No refresh_token in response — parse_oauth_token_response will reject
+    transport.responses.push_back(
+        {200, "{\"access_token\":\"acc\",\"token_type\":\"Bearer\",\"expires_in\":3600}"});
+    ScriptedSecretStore secret_store;
+    ControllableClock clock;
+
+    OAuthClientConfig config;
+    config.client_id = "test-client-id";
+    config.authorization_endpoint = "https://login.example/auth";
+    config.token_endpoint = "https://login.example/token";
+    config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+    bool caught = false;
+    try {
+        (void)nocal::sync::connect_microsoft_account(
+            config, browser, receiver, transport, entropy, secret_store, cache,
+            [&clock]() { return clock(); });
+    } catch (const MicrosoftAccountError& e) {
+        caught = true;
+        require(std::string(e.what()) == "Microsoft token response invalid",
+            "wrong error message on missing refresh token");
+    }
+    require(caught, "expected MicrosoftAccountError");
+
+    // Nothing stored
+    require(cache.snapshot().accounts.empty(), "cache was modified on parse error");
+    require(secret_store.store_calls == 0, "secret store was called on parse error");
+}
+
+// -----------------------------------------------------------------------
+// Test: /me failure
+// -----------------------------------------------------------------------
+void test_me_failure() {
+    TempDirectory temp;
+    SyncCache cache(temp.path() / "cache.db");
+
+    ScriptedEntropy entropy{{zeros(), zeros()}};
+    ScriptedBrowser browser;
+    ScriptedReceiver receiver;
+    receiver.browser = &browser;
+    receiver.callback = {"auth-code", "", "", ""};
+    ScriptedTransport transport;
+    // Successful token response
+    transport.responses.push_back(
+        {200, token_response_body("acc-token", "ref-token", 3600)});
+    // /me returns garbage (malformed JSON)
+    transport.responses.push_back({200, "not-valid-json"});
+    ScriptedSecretStore secret_store;
+    ControllableClock clock;
+
+    OAuthClientConfig config;
+    config.client_id = "test-client-id";
+    config.authorization_endpoint = "https://login.example/auth";
+    config.token_endpoint = "https://login.example/token";
+    config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+    bool caught = false;
+    try {
+        (void)nocal::sync::connect_microsoft_account(
+            config, browser, receiver, transport, entropy, secret_store, cache,
+            [&clock]() { return clock(); });
+    } catch (const MicrosoftAccountError& e) {
+        caught = true;
+        require(std::string(e.what()) == "Microsoft identity read failed",
+            "wrong error message on /me failure");
+    }
+    require(caught, "expected MicrosoftAccountError");
+
+    // Cache and secret store untouched
+    require(cache.snapshot().accounts.empty(), "cache was modified on /me failure");
+    require(secret_store.store_calls == 0, "secret store was called on /me failure");
+}
+
+// -----------------------------------------------------------------------
+// Test: Secret-store store() failure — cache retains the account row
+// -----------------------------------------------------------------------
+void test_secret_store_failure() {
+    TempDirectory temp;
+    SyncCache cache(temp.path() / "cache.db");
+
+    ScriptedEntropy entropy{{zeros(), zeros()}};
+    ScriptedBrowser browser;
+    ScriptedReceiver receiver;
+    receiver.browser = &browser;
+    receiver.callback = {"auth-code", "", "", ""};
+    ScriptedTransport transport;
+    transport.responses.push_back(
+        {200, token_response_body("acc-token", "ref-token", 3600)});
+    transport.responses.push_back(
+        {200, me_response_body("remote-subject", "Display Name", "user@example.com")});
+    ScriptedSecretStore secret_store;
+    secret_store.throw_on_store = true;
+    secret_store.store_error_message = "secret service unavailable";
+    ControllableClock clock;
+
+    OAuthClientConfig config;
+    config.client_id = "test-client-id";
+    config.authorization_endpoint = "https://login.example/auth";
+    config.token_endpoint = "https://login.example/token";
+    config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+    bool caught = false;
+    try {
+        (void)nocal::sync::connect_microsoft_account(
+            config, browser, receiver, transport, entropy, secret_store, cache,
+            [&clock]() { return clock(); });
+    } catch (const MicrosoftAccountError& e) {
+        caught = true;
+        require(std::string(e.what()) == "credential storage failed",
+            "wrong error message on store failure");
+    }
+    require(caught, "expected MicrosoftAccountError");
+
+    // Cache DOES retain the account row (documented disconnected state)
+    const auto snapshot = cache.snapshot();
+    require(snapshot.accounts.size() == 1,
+        "cache should retain the account row even when secret store fails");
+    require(snapshot.accounts.front().remote_subject == "remote-subject",
+        "cached account has wrong remote subject");
+
+    // Verify secret store does NOT have the credentials
+    const std::string expected_id =
+        nocal::sync::microsoft_account_id("remote-subject");
+    const auto stored = secret_store.store_data.find(expected_id);
+    require(stored == secret_store.store_data.end(),
+        "secret store should not contain credentials after store failure");
+    require(secret_store.store_calls == 1, "store should have been attempted once");
+
+    // A subsequent successful connect should complete (idempotent)
+    ScriptedEntropy entropy2{{zeros(), zeros()}};
+    ScriptedBrowser browser2;
+    ScriptedReceiver receiver2;
+    receiver2.browser = &browser2;
+    receiver2.callback = {"auth-code-2", "", "", ""};
+    ScriptedTransport transport2;
+    transport2.responses.push_back(
+        {200, token_response_body("acc-token-2", "ref-token-2", 3600)});
+    transport2.responses.push_back(
+        {200, me_response_body("remote-subject", "Display Name", "user@example.com")});
+    ScriptedSecretStore secret_store2;
+    ControllableClock clock2;
+
+    const CachedAccount retry_account = nocal::sync::connect_microsoft_account(
+        config, browser2, receiver2, transport2, entropy2, secret_store2, cache,
+        [&clock2]() { return clock2(); });
+    require(retry_account.id == expected_id,
+        "retry account id should match deterministic id");
+    require(cache.snapshot().accounts.size() == 1,
+        "cache should still have exactly one account after successful retry");
+
+    const auto stored2 = secret_store2.store_data.find(expected_id);
+    require(stored2 != secret_store2.store_data.end(),
+        "credentials should be stored after successful retry");
+}
+
+// -----------------------------------------------------------------------
+// Test: Empty displayName falls back to userPrincipalName
+// -----------------------------------------------------------------------
+void test_empty_display_name_fallback() {
+    TempDirectory temp;
+    SyncCache cache(temp.path() / "cache.db");
+
+    ScriptedEntropy entropy{{zeros(), zeros()}};
+    ScriptedBrowser browser;
+    ScriptedReceiver receiver;
+    receiver.browser = &browser;
+    receiver.callback = {"auth-code", "", "", ""};
+    ScriptedTransport transport;
+    transport.responses.push_back(
+        {200, token_response_body("acc-token", "ref-token", 3600)});
+    // No displayName in /me response
+    transport.responses.push_back(
+        {200, me_response_body("remote-subject", "", "fallback@example.com")});
+    ScriptedSecretStore secret_store;
+    ControllableClock clock;
+
+    OAuthClientConfig config;
+    config.client_id = "test-client-id";
+    config.authorization_endpoint = "https://login.example/auth";
+    config.token_endpoint = "https://login.example/token";
+    config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+    const CachedAccount account = nocal::sync::connect_microsoft_account(
+        config, browser, receiver, transport, entropy, secret_store, cache,
+        [&clock]() { return clock(); });
+
+    require(account.display_name == "fallback@example.com",
+        "display name should fall back to userPrincipalName");
+}
+
+// -----------------------------------------------------------------------
+// Test: default_microsoft_client_id with env unset and set
+// -----------------------------------------------------------------------
+void test_default_client_id() {
+    // Save original env state and unset
+    const char* original = std::getenv("NOCAL_MICROSOFT_CLIENT_ID");
+
+    // Test with env unset
+    if (original != nullptr) {
+        ::unsetenv("NOCAL_MICROSOFT_CLIENT_ID");
+    }
+    const std::string unset_result = nocal::sync::default_microsoft_client_id();
+    require(unset_result == nocal::sync::microsoft_client_id_placeholder,
+        "default client id should be placeholder when env is unset");
+
+    // Test with env set
+    ::setenv("NOCAL_MICROSOFT_CLIENT_ID", "my-test-client-id", 1);
+    const std::string set_result = nocal::sync::default_microsoft_client_id();
+    require(set_result == "my-test-client-id",
+        "default client id should match env when set");
+
+    // Restore original
+    if (original != nullptr) {
+        ::setenv("NOCAL_MICROSOFT_CLIENT_ID", original, 1);
+    } else {
+        ::unsetenv("NOCAL_MICROSOFT_CLIENT_ID");
+    }
+}
+
+// -----------------------------------------------------------------------
+// Test: microsoft_oauth_config
+// -----------------------------------------------------------------------
+void test_microsoft_oauth_config() {
+    const OAuthClientConfig config = nocal::sync::microsoft_oauth_config("my-client-id");
+
+    require(config.client_id == "my-client-id", "client_id mismatch");
+    require(config.authorization_endpoint
+            == "https://login.microsoftonline.com/common/oauth2/v2.0/authorize",
+        "wrong authorization endpoint");
+    require(config.token_endpoint
+            == "https://login.microsoftonline.com/common/oauth2/v2.0/token",
+        "wrong token endpoint");
+
+    require(config.scopes.size() == 3, "expected exactly 3 scopes");
+    require(config.scopes[0] == "offline_access", "scope[0] mismatch");
+    require(config.scopes[1] == "User.Read", "scope[1] mismatch");
+    require(config.scopes[2] == "Calendars.Read", "scope[2] mismatch");
+}
+
+// -----------------------------------------------------------------------
+// Test: Error messages never contain credential material
+// -----------------------------------------------------------------------
+void test_error_message_redaction() {
+    TempDirectory temp;
+    SyncCache cache(temp.path() / "cache.db");
+
+    const std::string access_marker = "ACCESS_CRED_MARKER_12345";
+    const std::string refresh_marker = "REFRESH_CRED_MARKER_67890";
+    const std::string auth_code_marker = "AUTH_CODE_MARKER_ABCDE";
+
+    // Test 1: Token endpoint error (400)
+    {
+        ScriptedEntropy entropy{{zeros(), zeros()}};
+        ScriptedBrowser browser;
+        ScriptedReceiver receiver;
+        receiver.browser = &browser;
+        receiver.callback = {auth_code_marker, "", "", ""};
+        ScriptedTransport transport;
+        transport.responses.push_back({400, access_marker + refresh_marker});
+        ScriptedSecretStore secret_store;
+        ControllableClock clock;
+
+        OAuthClientConfig config;
+        config.client_id = "test-client-id";
+        config.authorization_endpoint = "https://login.example/auth";
+        config.token_endpoint = "https://login.example/token";
+        config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+        try {
+            (void)nocal::sync::connect_microsoft_account(
+                config, browser, receiver, transport, entropy, secret_store, cache,
+                [&clock]() { return clock(); });
+        } catch (const std::exception& e) {
+            const std::string msg = e.what();
+            require(msg.find(access_marker) == std::string::npos,
+                "error leaked access token on 400");
+            require(msg.find(refresh_marker) == std::string::npos,
+                "error leaked refresh token on 400");
+            require(msg.find(auth_code_marker) == std::string::npos,
+                "error leaked auth code on 400");
+        }
+    }
+
+    // Test 2: Parse error (missing refresh_token)
+    {
+        ScriptedEntropy entropy{{zeros(), zeros()}};
+        ScriptedBrowser browser;
+        ScriptedReceiver receiver;
+        receiver.browser = &browser;
+        receiver.callback = {auth_code_marker, "", "", ""};
+        ScriptedTransport transport;
+        transport.responses.push_back(
+            {200, "{\"access_token\":\"" + access_marker
+                      + "\",\"token_type\":\"Bearer\",\"expires_in\":3600}"});
+        ScriptedSecretStore secret_store;
+        ControllableClock clock;
+
+        OAuthClientConfig config;
+        config.client_id = "test-client-id";
+        config.authorization_endpoint = "https://login.example/auth";
+        config.token_endpoint = "https://login.example/token";
+        config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+        try {
+            (void)nocal::sync::connect_microsoft_account(
+                config, browser, receiver, transport, entropy, secret_store, cache,
+                [&clock]() { return clock(); });
+        } catch (const std::exception& e) {
+            const std::string msg = e.what();
+            require(msg.find(access_marker) == std::string::npos,
+                "error leaked access token on parse failure");
+            require(msg.find(auth_code_marker) == std::string::npos,
+                "error leaked auth code on parse failure");
+        }
+    }
+
+    // Test 3: /me failure
+    {
+        ScriptedEntropy entropy{{zeros(), zeros()}};
+        ScriptedBrowser browser;
+        ScriptedReceiver receiver;
+        receiver.browser = &browser;
+        receiver.callback = {auth_code_marker, "", "", ""};
+        ScriptedTransport transport;
+        transport.responses.push_back(
+            {200, "{\"access_token\":\"" + access_marker
+                      + "\",\"refresh_token\":\"" + refresh_marker
+                      + "\",\"token_type\":\"Bearer\",\"expires_in\":3600}"});
+        transport.responses.push_back(
+            {200, "{\"bad_field\":" + access_marker + "}"});
+        ScriptedSecretStore secret_store;
+        ControllableClock clock;
+
+        OAuthClientConfig config;
+        config.client_id = "test-client-id";
+        config.authorization_endpoint = "https://login.example/auth";
+        config.token_endpoint = "https://login.example/token";
+        config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+        try {
+            (void)nocal::sync::connect_microsoft_account(
+                config, browser, receiver, transport, entropy, secret_store, cache,
+                [&clock]() { return clock(); });
+        } catch (const std::exception& e) {
+            const std::string msg = e.what();
+            require(msg.find(access_marker) == std::string::npos,
+                "error leaked access token on /me failure");
+            require(msg.find(refresh_marker) == std::string::npos,
+                "error leaked refresh token on /me failure");
+            require(msg.find(auth_code_marker) == std::string::npos,
+                "error leaked auth code on /me failure");
+        }
+    }
+
+    // Test 4: Secret store failure
+    {
+        ScriptedEntropy entropy{{zeros(), zeros()}};
+        ScriptedBrowser browser;
+        ScriptedReceiver receiver;
+        receiver.browser = &browser;
+        receiver.callback = {auth_code_marker, "", "", ""};
+        ScriptedTransport transport;
+        transport.responses.push_back(
+            {200, "{\"access_token\":\"" + access_marker
+                      + "\",\"refresh_token\":\"" + refresh_marker
+                      + "\",\"token_type\":\"Bearer\",\"expires_in\":3600}"});
+        transport.responses.push_back(
+            {200, me_response_body("remote-subject", "Display", "user@example.com")});
+        ScriptedSecretStore secret_store;
+        secret_store.throw_on_store = true;
+        ControllableClock clock;
+
+        OAuthClientConfig config;
+        config.client_id = "test-client-id";
+        config.authorization_endpoint = "https://login.example/auth";
+        config.token_endpoint = "https://login.example/token";
+        config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+        try {
+            (void)nocal::sync::connect_microsoft_account(
+                config, browser, receiver, transport, entropy, secret_store, cache,
+                [&clock]() { return clock(); });
+        } catch (const std::exception& e) {
+            const std::string msg = e.what();
+            require(msg.find(access_marker) == std::string::npos,
+                "error leaked access token on store failure");
+            require(msg.find(refresh_marker) == std::string::npos,
+                "error leaked refresh token on store failure");
+            require(msg.find(auth_code_marker) == std::string::npos,
+                "error leaked auth code on store failure");
+        }
+    }
+}
+
+// -----------------------------------------------------------------------
+// Test: microsoft_account_id is deterministic
+// -----------------------------------------------------------------------
+void test_microsoft_account_id_deterministic() {
+    const std::string first = nocal::sync::microsoft_account_id("user@example.com");
+    const std::string second = nocal::sync::microsoft_account_id("user@example.com");
+    require(
+        first == second, "microsoft_account_id is not deterministic for same input");
+
+    const std::string different =
+        nocal::sync::microsoft_account_id("other@example.com");
+    require(first != different,
+        "microsoft_account_id should differ for different remote subjects");
+}
+
+} // namespace
+
+int main() {
+    try {
+        test_happy_path();
+        test_idempotent_reconnect();
+        test_authorization_rejected();
+        test_token_endpoint_non2xx();
+        test_token_response_missing_refresh();
+        test_me_failure();
+        test_secret_store_failure();
+        test_empty_display_name_fallback();
+        test_default_client_id();
+        test_microsoft_oauth_config();
+        test_error_message_redaction();
+        test_microsoft_account_id_deterministic();
+    } catch (const std::exception& error) {
+        std::cerr << "microsoft account tests failed: " << error.what() << '\n';
+        return 1;
+    }
+    std::cout << "microsoft account tests passed\n";
+    return 0;
+}

tests/microsoft_sync_provider_tests.cpp

@@ -0,0 +1,705 @@
+#include "nocal/storage/sync_cache.hpp"
+#include "nocal/sync/microsoft_account.hpp"
+#include "nocal/sync/microsoft_graph.hpp"
+#include "nocal/sync/microsoft_sync_provider.hpp"
+#include "nocal/sync/oauth.hpp"
+#include "nocal/sync/oauth_tokens.hpp"
+#include "nocal/sync/provider.hpp"
+#include "nocal/sync/secret_store.hpp"
+#include "nocal/sync/token_broker.hpp"
+
+#include <cstdint>
+#include <cstdlib>
+#include <exception>
+#include <filesystem>
+#include <functional>
+#include <iostream>
+#include <map>
+#include <optional>
+#include <span>
+#include <stdexcept>
+#include <string>
+#include <string_view>
+#include <vector>
+
+namespace {
+
+using nocal::storage::CachedAccount;
+using nocal::storage::CachedCalendar;
+using nocal::storage::SyncCache;
+using nocal::sync::AccountDisconnected;
+using nocal::sync::AuthorizationCallback;
+using nocal::sync::AuthorizationCallbackReceiver;
+using nocal::sync::BrowserLauncher;
+using nocal::sync::ConnectedAccount;
+using nocal::sync::EntropySource;
+using nocal::sync::HttpMethod;
+using nocal::sync::HttpRequest;
+using nocal::sync::HttpResponse;
+using nocal::sync::HttpTransport;
+using nocal::sync::OAuthClientConfig;
+using nocal::sync::OAuthSecretStore;
+using nocal::sync::OAuthTokens;
+using nocal::sync::SyncObserver;
+using nocal::sync::SyncProgressEvent;
+using nocal::sync::SyncStage;
+
+void require(bool condition, std::string_view message) {
+    if (!condition) {
+        throw std::runtime_error(std::string{message});
+    }
+}
+
+// -----------------------------------------------------------------------
+// TempDirectory for a real SyncCache
+// -----------------------------------------------------------------------
+class TempDirectory {
+public:
+    TempDirectory() {
+        std::string pattern =
+            (std::filesystem::temp_directory_path()
+                 / "nocal-microsoft-sync-provider-tests.XXXXXX")
+                .string();
+        std::vector<char> writable(pattern.begin(), pattern.end());
+        writable.push_back('\0');
+        const char* created = ::mkdtemp(writable.data());
+        if (created == nullptr) {
+            throw std::runtime_error("mkdtemp failed");
+        }
+        path_ = created;
+    }
+
+    TempDirectory(const TempDirectory&) = delete;
+    TempDirectory& operator=(const TempDirectory&) = delete;
+
+    ~TempDirectory() {
+        std::error_code ignored;
+        std::filesystem::remove_all(path_, ignored);
+    }
+
+    [[nodiscard]] const std::filesystem::path& path() const noexcept {
+        return path_;
+    }
+
+private:
+    std::filesystem::path path_;
+};
+
+// -----------------------------------------------------------------------
+// ScriptedEntropy
+// -----------------------------------------------------------------------
+class ScriptedEntropy final : public EntropySource {
+public:
+    explicit ScriptedEntropy(std::vector<std::array<std::byte, 32>> sc)
+        : values(std::move(sc)) {}
+
+    std::vector<std::array<std::byte, 32>> values;
+    std::size_t calls{0};
+
+    void fill(std::span<std::byte> output) override {
+        require(output.size() == 32, "entropy request was not exactly 32 bytes");
+        require(calls < values.size(), "unexpected entropy request");
+        std::copy(values[calls].begin(), values[calls].end(), output.begin());
+        ++calls;
+    }
+};
+
+// -----------------------------------------------------------------------
+// ScriptedBrowser
+// -----------------------------------------------------------------------
+class ScriptedBrowser final : public BrowserLauncher {
+public:
+    std::vector<std::string> urls;
+
+    void open(const std::string& url) override { urls.push_back(url); }
+};
+
+// -----------------------------------------------------------------------
+// ScriptedReceiver
+// -----------------------------------------------------------------------
+class ScriptedReceiver final : public AuthorizationCallbackReceiver {
+public:
+    std::string redirect{"http://127.0.0.1:43123/callback"};
+    AuthorizationCallback callback;
+    std::size_t receives{0};
+    bool copy_browser_state{true};
+    ScriptedBrowser* browser{nullptr};
+
+    [[nodiscard]] std::string redirect_uri() const override {
+        return redirect;
+    }
+
+    AuthorizationCallback receive() override {
+        ++receives;
+        if (copy_browser_state && browser != nullptr && !browser->urls.empty()) {
+            const std::string& url = browser->urls.front();
+            const std::size_t state_pos = url.find("state=");
+            if (state_pos != std::string::npos) {
+                const std::size_t value_start = state_pos + 6;
+                const std::size_t amp = url.find('&', value_start);
+                const std::size_t len =
+                    (amp == std::string::npos) ? url.size() - value_start
+                                               : amp - value_start;
+                AuthorizationCallback result = callback;
+                result.state = url.substr(value_start, len);
+                return result;
+            }
+        }
+        return callback;
+    }
+};
+
+// -----------------------------------------------------------------------
+// ScriptedTransport
+// -----------------------------------------------------------------------
+class ScriptedTransport final : public HttpTransport {
+public:
+    struct ResponseSpec {
+        int status{200};
+        std::string body;
+        bool throw_on_send{false};
+        std::string send_error_message{};
+    };
+
+    std::vector<HttpRequest> requests;
+    std::vector<ResponseSpec> responses;
+    std::size_t fail_at{static_cast<std::size_t>(-1)};
+
+    HttpResponse send(const HttpRequest& request) override {
+        requests.push_back(request);
+        const std::size_t index = requests.size() - 1;
+        if (index == fail_at) {
+            throw std::runtime_error("transport failure");
+        }
+        if (index >= responses.size()) {
+            return {200, {}, "{}"};
+        }
+        const ResponseSpec& spec = responses[index];
+        if (spec.throw_on_send) {
+            throw std::runtime_error(spec.send_error_message);
+        }
+        return {spec.status, {}, spec.body};
+    }
+};
+
+// -----------------------------------------------------------------------
+// ScriptedSecretStore (token_broker style with per-account script)
+// -----------------------------------------------------------------------
+class ScriptedSecretStore final : public OAuthSecretStore {
+public:
+    struct StoreResult {
+        bool throw_on_store{false};
+        std::string store_error_message{};
+    };
+
+    std::map<std::string, OAuthTokens> store_data;
+    std::map<std::string, StoreResult> store_script;
+
+    std::size_t store_calls{0};
+    std::size_t load_calls{0};
+    std::size_t erase_calls{0};
+
+    void store(std::string account_id, const OAuthTokens& tokens,
+        std::stop_token = {}) override {
+        ++store_calls;
+        const auto found = store_script.find(account_id);
+        if (found != store_script.end() && found->second.throw_on_store) {
+            throw std::runtime_error(found->second.store_error_message);
+        }
+        store_data[std::move(account_id)] = tokens;
+    }
+
+    [[nodiscard]] std::optional<OAuthTokens> load(
+        std::string account_id, std::stop_token = {}) override {
+        ++load_calls;
+        const auto stored = store_data.find(account_id);
+        if (stored != store_data.end()) {
+            return stored->second;
+        }
+        return std::nullopt;
+    }
+
+    void erase(std::string account_id, std::stop_token = {}) override {
+        ++erase_calls;
+        store_data.erase(account_id);
+    }
+};
+
+// -----------------------------------------------------------------------
+// TestObserver - records progress events
+// -----------------------------------------------------------------------
+class TestObserver final : public SyncObserver {
+public:
+    std::vector<SyncProgressEvent> events;
+
+    void on_sync_progress(const SyncProgressEvent& event) override {
+        events.push_back(event);
+    }
+};
+
+// -----------------------------------------------------------------------
+// Controllable clock
+// -----------------------------------------------------------------------
+class ControllableClock {
+public:
+    std::int64_t value{1000};
+
+    [[nodiscard]] std::int64_t operator()() { return value; }
+};
+
+// -----------------------------------------------------------------------
+// Helpers
+// -----------------------------------------------------------------------
+
+[[nodiscard]] std::array<std::byte, 32> zeros() { return {}; }
+
+[[nodiscard]] std::string token_response_body(std::string_view access_token,
+    std::string_view refresh_token, std::int64_t expires_in) {
+    return "{\"access_token\":\"" + std::string(access_token)
+        + "\",\"refresh_token\":\"" + std::string(refresh_token)
+        + "\",\"token_type\":\"Bearer\",\"expires_in\":"
+        + std::to_string(expires_in) + "}";
+}
+
+[[nodiscard]] std::string me_response_body(
+    std::string_view id, std::string_view display_name, std::string_view upn) {
+    std::string body = "{\"id\":\"" + std::string(id) + "\"";
+    if (!display_name.empty()) {
+        body += ",\"displayName\":\"" + std::string(display_name) + "\"";
+    }
+    if (!upn.empty()) {
+        body += ",\"userPrincipalName\":\"" + std::string(upn) + "\"";
+    }
+    body += "}";
+    return body;
+}
+
+// Build a Graph /me/calendars response with one calendar
+[[nodiscard]] std::string calendars_response_body(
+    const std::vector<std::string>& remote_ids,
+    const std::vector<std::string>& names,
+    const std::vector<bool>& is_default) {
+    require(remote_ids.size() == names.size(),
+        "calendars_response_body argument size mismatch");
+    require(remote_ids.size() == is_default.size(),
+        "calendars_response_body argument size mismatch");
+
+    std::string body = "{\"value\":[";
+    for (std::size_t i = 0; i < remote_ids.size(); ++i) {
+        if (i > 0) {
+            body += ",";
+        }
+        body += "{\"id\":\"" + remote_ids[i] + "\""
+              + ",\"name\":\"" + names[i] + "\""
+              + ",\"isDefaultCalendar\":" + (is_default[i] ? "true" : "false")
+              + ",\"canEdit\":true,\"changeKey\":\"ck\",\"hexColor\":\"#000000\"}";
+    }
+    body += "]}";
+    return body;
+}
+
+// Build an empty calendar view delta response (no events)
+[[nodiscard]] std::string empty_delta_response() {
+    return "{\"value\":[],\"@odata.deltaLink\":\""
+           "https://graph.microsoft.com/v1.0/me/calendarView/delta?"
+           "deltatoken=final\"}";
+}
+
+// Build an empty calendarView response
+[[nodiscard]] std::string empty_calendar_view_response() {
+    return "{\"value\":[]}";
+}
+
+// -----------------------------------------------------------------------
+// Test: provider_id returns "microsoft-graph"
+// -----------------------------------------------------------------------
+void test_provider_id() {
+    TempDirectory temp;
+    SyncCache cache(temp.path() / "cache.db");
+    ScriptedTransport transport;
+    ScriptedSecretStore secret_store;
+    ScriptedBrowser browser;
+    ScriptedReceiver receiver;
+    ScriptedEntropy entropy{std::vector<std::array<std::byte, 32>>{}};
+    ControllableClock clock;
+
+    OAuthClientConfig config;
+    config.client_id = "test-client-id";
+    config.authorization_endpoint = "https://login.example/auth";
+    config.token_endpoint = "https://login.example/token";
+    config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+    nocal::sync::OAuthTokenBroker broker(
+        config, transport, secret_store, [&clock]() { return clock(); });
+
+    nocal::sync::MicrosoftAccountSyncProvider provider(
+        broker, secret_store, cache, transport, config,
+        [&clock]() { return clock(); }, browser, receiver, entropy);
+
+    require(provider.provider_id() == "microsoft-graph",
+        "provider_id should return 'microsoft-graph'");
+}
+
+// -----------------------------------------------------------------------
+// Test: connect_account happy path
+// -----------------------------------------------------------------------
+void test_connect_account_happy_path() {
+    TempDirectory temp;
+    SyncCache cache(temp.path() / "cache.db");
+
+    ScriptedEntropy entropy{{zeros(), zeros()}};
+    ScriptedBrowser browser;
+    ScriptedReceiver receiver;
+    receiver.browser = &browser;
+    receiver.callback = {"auth-code", "", "", ""};
+    ScriptedTransport transport;
+    transport.responses.push_back(
+        {200, token_response_body("access-token-value", "refresh-token-value", 3600)});
+    transport.responses.push_back(
+        {200, me_response_body("remote-subject", "Display Name", "user@example.com")});
+    ScriptedSecretStore secret_store;
+    ControllableClock clock;
+
+    OAuthClientConfig config;
+    config.client_id = "test-client-id";
+    config.authorization_endpoint = "https://login.example/auth";
+    config.token_endpoint = "https://login.example/token";
+    config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+    nocal::sync::OAuthTokenBroker broker(
+        config, transport, secret_store, [&clock]() { return clock(); });
+
+    nocal::sync::MicrosoftAccountSyncProvider provider(
+        broker, secret_store, cache, transport, config,
+        [&clock]() { return clock(); }, browser, receiver, entropy);
+
+    const ConnectedAccount result = provider.connect_account();
+
+    // Verify returned account
+    const std::string expected_id =
+        nocal::sync::microsoft_account_id("remote-subject");
+    require(result.account_id == expected_id, "account id mismatch");
+    require(result.display_name == "Display Name", "display name mismatch");
+
+    // Cache has the account
+    const auto snapshot = cache.snapshot();
+    require(snapshot.accounts.size() == 1, "expected exactly one cached account");
+    require(snapshot.accounts.front().id == expected_id, "cached account id mismatch");
+    require(snapshot.accounts.front().provider == "microsoft-graph",
+        "cached account provider mismatch");
+
+    // Secret store has the tokens
+    const auto stored = secret_store.store_data.find(expected_id);
+    require(stored != secret_store.store_data.end(), "tokens not stored");
+    require(stored->second.access_token == "access-token-value",
+        "wrong stored access token");
+    require(stored->second.token_type == "Bearer", "wrong stored token type");
+
+    // Exactly one browser URL, one token request, one /me request
+    require(browser.urls.size() == 1, "expected exactly one browser URL");
+    require(transport.requests.size() == 2, "expected exactly two HTTP requests");
+    require(transport.requests[0].method == HttpMethod::post,
+        "first request was not POST (token)");
+    require(transport.requests[1].method == HttpMethod::get,
+        "second request was not GET (/me)");
+}
+
+// -----------------------------------------------------------------------
+// Test: disconnect_account erases secret
+// -----------------------------------------------------------------------
+void test_disconnect_account() {
+    TempDirectory temp;
+    SyncCache cache(temp.path() / "cache.db");
+
+    ScriptedEntropy entropy{{zeros(), zeros()}};
+    ScriptedBrowser browser;
+    ScriptedReceiver receiver;
+    receiver.browser = &browser;
+    receiver.callback = {"auth-code", "", "", ""};
+    ScriptedTransport transport;
+    transport.responses.push_back(
+        {200, token_response_body("access-token-value", "refresh-token-value", 3600)});
+    transport.responses.push_back(
+        {200, me_response_body("remote-subject", "Display Name", "user@example.com")});
+    ScriptedSecretStore secret_store;
+    ControllableClock clock;
+
+    OAuthClientConfig config;
+    config.client_id = "test-client-id";
+    config.authorization_endpoint = "https://login.example/auth";
+    config.token_endpoint = "https://login.example/token";
+    config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+    nocal::sync::OAuthTokenBroker broker(
+        config, transport, secret_store, [&clock]() { return clock(); });
+
+    nocal::sync::MicrosoftAccountSyncProvider provider(
+        broker, secret_store, cache, transport, config,
+        [&clock]() { return clock(); }, browser, receiver, entropy);
+
+    const ConnectedAccount result = provider.connect_account();
+
+    // Verify token exists before disconnect
+    require(secret_store.store_data.find(result.account_id) != secret_store.store_data.end(),
+        "tokens should exist before disconnect");
+    require(secret_store.erase_calls == 0, "erase should not have been called yet");
+
+    // Disconnect
+    provider.disconnect_account(result.account_id);
+
+    // Tokens erased
+    require(secret_store.store_data.find(result.account_id) == secret_store.store_data.end(),
+        "tokens should be erased after disconnect");
+    require(secret_store.erase_calls == 1, "erase should have been called once");
+
+    // Cache still has the account row (documented behavior)
+    const auto snapshot = cache.snapshot();
+    require(snapshot.accounts.size() == 1,
+        "cache should retain the account row after disconnect");
+}
+
+// -----------------------------------------------------------------------
+// Test: sync_account progress events (happy path)
+// -----------------------------------------------------------------------
+void test_sync_account_progress() {
+    TempDirectory temp;
+    SyncCache cache(temp.path() / "cache.db");
+
+    // First, connect an account (so we have tokens + account in cache)
+    ScriptedEntropy connect_entropy{{zeros(), zeros()}};
+    ScriptedBrowser connect_browser;
+    ScriptedReceiver connect_receiver;
+    connect_receiver.browser = &connect_browser;
+    connect_receiver.callback = {"auth-code", "", "", ""};
+    ScriptedTransport connect_transport;
+    connect_transport.responses.push_back(
+        {200, token_response_body("connect-access", "connect-refresh", 3600)});
+    connect_transport.responses.push_back(
+        {200, me_response_body("sync-subject", "Sync User", "sync@example.com")});
+    ScriptedSecretStore secret_store;
+    ControllableClock clock;
+
+    OAuthClientConfig config;
+    config.client_id = "test-client-id";
+    config.authorization_endpoint = "https://login.example/auth";
+    config.token_endpoint = "https://login.example/token";
+    config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+    nocal::sync::OAuthTokenBroker broker(
+        config, connect_transport, secret_store, [&clock]() { return clock(); });
+
+    ScriptedEntropy sync_entropy{{zeros(), zeros()}};
+
+    nocal::sync::MicrosoftAccountSyncProvider connect_provider(
+        broker, secret_store, cache, connect_transport, config,
+        [&clock]() { return clock(); }, connect_browser, connect_receiver,
+        sync_entropy);
+
+    const ConnectedAccount result = connect_provider.connect_account();
+    const std::string account_id = result.account_id;
+
+    // Now set up a new transport for sync (identity refresh + calendar
+    // discovery + primary calendar delta + secondary calendar view)
+    ScriptedTransport sync_transport;
+    // The token broker will see the stored tokens are still valid (expiry at
+    // 4600, clock at 1000, skew 300 → 1300 < 4600 → no refresh needed).
+    // So we need responses for:
+    //   0: /me (identity refresh)
+    //   1: /me/calendars
+    //   2: primary calendar delta (first page with deltaLink)
+    //   3: secondary calendar calendarView (first page with no nextLink)
+    //
+    // But the token broker won't call the transport since tokens are valid.
+    // So sync transport responses start at 0.
+
+    // First check what stored tokens look like: expires_at = 1000 + 3600 = 4600
+    // Clock at 1000, skew 300 → 1000+300 = 1300 < 4600 so no refresh needed.
+
+    sync_transport.responses.push_back(
+        {200, me_response_body("sync-subject", "Sync User", "sync@example.com")});
+    // Two calendars: primary + secondary
+    sync_transport.responses.push_back(
+        {200, calendars_response_body({"AAMkAGprimary", "AAMkAGsecondary"},
+             {"Primary", "Secondary"}, {true, false})});
+    // Primary delta: empty page with deltaLink → completion
+    sync_transport.responses.push_back({200, empty_delta_response()});
+    // Secondary calendarView: empty page
+    sync_transport.responses.push_back({200, empty_calendar_view_response()});
+
+    TestObserver observer;
+
+    // Recreate broker with the new transport
+    nocal::sync::OAuthTokenBroker sync_broker(
+        config, sync_transport, secret_store, [&clock]() { return clock(); });
+
+    ScriptedEntropy sync_entropy2{{zeros(), zeros()}};
+
+    nocal::sync::MicrosoftAccountSyncProvider sync_provider(
+        sync_broker, secret_store, cache, sync_transport, config,
+        [&clock]() { return clock(); }, connect_browser, connect_receiver,
+        sync_entropy2);
+
+    sync_provider.sync_account(account_id, observer);
+
+    // Verify progress events
+    // Expected order:
+    //   1. authenticating
+    //   2. refreshing_identity
+    //   3. discovering_calendars
+    //   4. syncing_calendar (primary, 0/2)
+    //   5. syncing_calendar (secondary, 1/2)
+    //   6. completed
+    require(observer.events.size() == 6,
+        "expected 6 progress events, got " + std::to_string(observer.events.size()));
+
+    require(observer.events[0].stage == SyncStage::authenticating,
+        "event[0] should be authenticating");
+    require(observer.events[1].stage == SyncStage::refreshing_identity,
+        "event[1] should be refreshing_identity");
+    require(observer.events[2].stage == SyncStage::discovering_calendars,
+        "event[2] should be discovering_calendars");
+    require(observer.events[3].stage == SyncStage::syncing_calendar,
+        "event[3] should be syncing_calendar");
+    require(observer.events[3].calendars_completed == 0,
+        "event[3] calendars_completed should be 0");
+    require(observer.events[3].calendars_total == 2,
+        "event[3] calendars_total should be 2");
+    require(observer.events[4].stage == SyncStage::syncing_calendar,
+        "event[4] should be syncing_calendar");
+    require(observer.events[4].calendars_completed == 1,
+        "event[4] calendars_completed should be 1");
+    require(observer.events[4].calendars_total == 2,
+        "event[4] calendars_total should be 2");
+    require(observer.events[5].stage == SyncStage::completed,
+        "event[5] should be completed");
+}
+
+// -----------------------------------------------------------------------
+// Test: sync_account throws AccountDisconnected when tokens refresh fails
+// -----------------------------------------------------------------------
+void test_sync_account_account_disconnected() {
+    TempDirectory temp;
+    SyncCache cache(temp.path() / "cache.db");
+
+    // Set up an account with expired tokens
+    ScriptedTransport connect_transport;
+    connect_transport.responses.push_back(
+        {200, token_response_body("connect-access", "connect-refresh", 1)});
+    connect_transport.responses.push_back(
+        {200, me_response_body("disco-subject", "Disco User", "disco@example.com")});
+
+    ScriptedSecretStore secret_store;
+    ScriptedEntropy entropy{{zeros(), zeros()}};
+    ScriptedBrowser browser;
+    ScriptedReceiver receiver;
+    receiver.browser = &browser;
+    receiver.callback = {"auth-code", "", "", ""};
+    ControllableClock clock;
+    clock.value = 1000;
+
+    OAuthClientConfig config;
+    config.client_id = "test-client-id";
+    config.authorization_endpoint = "https://login.example/auth";
+    config.token_endpoint = "https://login.example/token";
+    config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+    nocal::sync::OAuthTokenBroker connect_broker(
+        config, connect_transport, secret_store, [&clock]() { return clock(); });
+
+    nocal::sync::MicrosoftAccountSyncProvider connect_provider(
+        connect_broker, secret_store, cache, connect_transport, config,
+        [&clock]() { return clock(); }, browser, receiver, entropy);
+
+    const ConnectedAccount result = connect_provider.connect_account();
+
+    // Token expires at 1000 + 1 = 1001. Now advance clock to 2000, well past
+    // expiry + skew (1001 < 2000+300=2300, so expired).
+    clock.value = 2000;
+
+    // Set up transport that returns 400 on the refresh attempt
+    ScriptedTransport refresh_transport;
+    refresh_transport.responses.push_back({400, "{\"error\":\"invalid_grant\"}"});
+
+    nocal::sync::OAuthTokenBroker refresh_broker(
+        config, refresh_transport, secret_store, [&clock]() { return clock(); });
+
+    ScriptedEntropy sync_entropy_disco{{zeros(), zeros()}};
+
+    nocal::sync::MicrosoftAccountSyncProvider sync_provider(
+        refresh_broker, secret_store, cache, refresh_transport, config,
+        [&clock]() { return clock(); }, browser, receiver,
+        sync_entropy_disco);
+
+    TestObserver observer;
+
+    bool caught = false;
+    try {
+        sync_provider.sync_account(result.account_id, observer);
+    } catch (const AccountDisconnected&) {
+        caught = true;
+    }
+
+    require(caught, "expected AccountDisconnected when tokens refresh fails");
+
+    // Observer should have received at least the authenticating event
+    require(!observer.events.empty(), "observer should have received at least one event");
+    require(observer.events.front().stage == SyncStage::authenticating,
+        "first event should be authenticating");
+}
+
+// -----------------------------------------------------------------------
+// Test: sync_account throws when no tokens exist
+// -----------------------------------------------------------------------
+void test_sync_account_no_tokens() {
+    TempDirectory temp;
+    SyncCache cache(temp.path() / "cache.db");
+
+    ScriptedSecretStore secret_store; // empty store
+    ScriptedTransport transport;
+    ScriptedBrowser browser;
+    ScriptedReceiver receiver;
+    ScriptedEntropy entropy{std::vector<std::array<std::byte, 32>>{}};
+    ControllableClock clock;
+
+    OAuthClientConfig config;
+    config.client_id = "test-client-id";
+    config.authorization_endpoint = "https://login.example/auth";
+    config.token_endpoint = "https://login.example/token";
+    config.scopes = {"offline_access", "User.Read", "Calendars.Read"};
+
+    nocal::sync::OAuthTokenBroker broker(
+        config, transport, secret_store, [&clock]() { return clock(); });
+
+    nocal::sync::MicrosoftAccountSyncProvider provider(
+        broker, secret_store, cache, transport, config,
+        [&clock]() { return clock(); }, browser, receiver, entropy);
+
+    TestObserver observer;
+
+    bool caught = false;
+    try {
+        provider.sync_account("nonexistent-account", observer);
+    } catch (const std::runtime_error&) {
+        caught = true;
+    }
+
+    require(caught, "expected std::runtime_error when no tokens exist");
+}
+
+} // namespace
+
+int main() {
+    try {
+        test_provider_id();
+        test_connect_account_happy_path();
+        test_disconnect_account();
+        test_sync_account_progress();
+        test_sync_account_account_disconnected();
+        test_sync_account_no_tokens();
+    } catch (const std::exception& error) {
+        std::cerr << "microsoft sync provider tests failed: " << error.what() << '\n';
+        return 1;
+    }
+    std::cout << "microsoft sync provider tests passed\n";
+    return 0;
+}

tests/tui_tests.cpp

@@ -118,6 +118,8 @@ void test_full_month_render()
         .search_result_index = 0,
         .notification = {},
         .notification_is_error = false,
+        .sync_stage = {},
+        .sync_is_error = false,
         .show_calendar_picker = false,
         .calendar_index = 0,
         .show_agenda = false,
@@ -178,6 +180,8 @@ void test_compact_and_input()
         .search_result_index = 0,
         .notification = {},
         .notification_is_error = false,
+        .sync_stage = {},
+        .sync_is_error = false,
         .show_calendar_picker = false,
         .calendar_index = 0,
         .show_agenda = false,