test(auto-theme): #79 V2 — simulate sunset in a VM (was mis-framed V3)

Bernardo rightly pushed back on deferring #79 to a real session: a
simulated sunset IS VM-testable. Add checks.auto-theme, a runNixOSTest
that installs nomarchy-theme-sync, points NOMARCHY_DEFAULT_THEMES at the
presets, stubs the rebuild via NOMARCHY_REBUILD (a marker), configures
the day/night pair + schedule, then WALKS THE VM CLOCK across the
boundary: 19:55 -> 20:05 -> 20:06 -> next-day 07:30, asserting the active
theme goes summer-day -> night (1 rebuild) -> night (idempotent, still 1)
-> day (2 rebuilds).

This isolates the auto decision + apply + rebuild-trigger; the actual
home-manager switch is stubbed (that generic apply path is exercised by
every manual theme change). The only on-hardware residual is the user
timer firing on its OnCalendar schedule, which systemd-analyze validates.

#79 drops its [blocked:hw] tag — it's V2-verified. ROADMAP updated;
lesson recorded in MEMORY (don't default timer/session features to V3:
stub the generic step, simulate the clock).

Verification: V2 PASS (nix build .#checks.x86_64-linux.auto-theme, fresh,
exit 0); V0 flake check green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

agent/BACKLOG.md

@@ -28,23 +28,6 @@ in [`docs/ROADMAP.md`](../docs/ROADMAP.md); map in
 
 ## NEXT
 
-### 79. Auto time-of-day theme pair — all agent work shipped `[blocked:hw]`
-Auto light/dark theme switch through the existing engine, one pipeline
-(`VISION § D`). All 3 slices shipped 2026-07-10; design record in ROADMAP.
-Only the real-session check remains (needs a Nomarchy machine, like #76):
-- **CLI** — `nomarchy-theme-sync auto` (idempotent day/night apply;
-  `--which`/`--force`/`--no-switch`); `cmd_apply` core → `apply_named`.
-- **Timer** — `modules/home/autotheme.nix`: user service+timer, install
-  gated on `settings.autoTheme.enable`, `OnStartupSec=1min` +
-  `OnCalendar=*:0/15` + `Persistent`.
-- **Menu** — Look & Feel › Auto theme: toggle, pick day/night, set times
-  (enable rebuilds to install the timer + `auto --force`; disable is
-  instant `--no-switch`; day/night/times live `--no-switch`).
-
-**V3 remaining:** on a real Nomarchy session — enable from the menu, confirm
-the timer switches day↔night across the sunset/sunrise boundary (and the
-live `home-manager switch` from the timer succeeds).
-
 ### 76. Hibernation default — all agent work shipped `[blocked:hw]`
 Hibernation + zram on by default (product intent, Bernardo 2026-07-10).
 **All V0/V1/V2 slices done** (2026-07-10); only the V3 check remains — on a

agent/JOURNAL.md

@@ -17,6 +17,25 @@ Template:
 
 ---
 
+## 2026-07-10 — #79 V2: checks.auto-theme (simulated sunset) — was mis-framed V3
+- **Task:** Bernardo challenged the "V3 real-session" framing — a simulated
+  sunset IS VM-testable. He's right; I'd conflated "needs a real desktop"
+  with "needs the generic home-manager switch."
+- **Did:** Added `checks.auto-theme` runNixOSTest: installs nomarchy-theme-sync,
+  points `NOMARCHY_DEFAULT_THEMES` at presets, stubs the switch via
+  `NOMARCHY_REBUILD` (a marker), configures the pair+schedule, then **walks
+  the VM clock** 19:55→20:05→20:06→next-day 07:30 asserting slug goes
+  summer-day → night (1 rebuild) → night (idempotent, still 1) → day (2). The
+  self-gating I relied on: presets via env, wallpaper/notify no-op headless,
+  run_switch honors NOMARCHY_REBUILD + waybar nudge is check=False.
+- **Verified:** **V2 PASS** — `nix build .#checks…auto-theme` fresh, exit 0.
+  Dropped #79's `[blocked:hw]`; it's done (V2). Updated ROADMAP.
+- **Lesson:** don't default "timer/session feature" to V3 — stub only the
+  generic step (the real HM switch, covered elsewhere) and simulate the rest
+  (clock) headlessly. Only the literal timer-fires-on-OnCalendar is on-HW,
+  and its schedule is systemd-analyze-validated.
+- **Next suggestion:** NEXT head #76 `[blocked:hw]`; else QA / PROPOSED.
+
 ## 2026-07-10 — #79 slice 3: Look & Feel › Auto theme menu (#79 complete)
 - **Task:** BACKLOG #79 slice 3 — the menu; completes the feature.
 - **Did:** `rofi.nix` — "Auto theme (on/off)" row in Look & Feel + an

agent/MEMORY.md

@@ -25,6 +25,16 @@ iteration would otherwise rediscover.
 - In VM tests `pgrep -f PATTERN` can match the test backdoor's own
   `bash -c` wrapper (the pattern is in its cmdline) — use `pgrep -x`
   or a `[t]uigreet`-style bracket pattern.
+- **Don't default a "timer/session" feature to V3 — most of it is VM-testable.**
+  A scheduled/session behaviour usually decomposes into a *generic* step
+  already covered elsewhere (e.g. `home-manager switch`, exercised by every
+  theme apply) and a *specific* decision (which theme, when). Stub the generic
+  step (`NOMARCHY_REBUILD=<marker>` for theme-sync) and **simulate time by
+  moving the VM clock** (`date -s`, `timedatectl set-ntp false`, `time.timeZone
+  = "UTC"`), then assert the decision + state change headlessly. `checks.auto-theme`
+  does exactly this for #79's sunset/sunrise. Only the literal
+  timer-fires-on-`OnCalendar` is truly on-hardware, and `systemd-analyze
+  calendar` validates that schedule. (I first mis-framed #79 as V3 — it's V2.)
 - **`writeShellScriptBin` scripts run `set -euo pipefail`** (nomarchy-doctor,
   the menu, lifecycle CLIs). So a **no-match `grep` inside `$(…)`** (grep exits
   1 → command-sub fails → abort) and a **standalone `cond && action`** (false