docs(backlog): design pass for display profiles (item 15)

The item required a written plan before coding. Option shape reuses the
existing monitorType submodule (attrsOf (listOf monitorType)); active
profile is in-flake state (settings.displayProfile) on the night-light
instant+bake pattern; whole-entry-by-name rebuild overlay with a
disable-guard so a stale menu resolution pick can't resurrect a
disabled panel; self-gated System > Display profile row; sliced a/b/c
with hotplug auto-switch and workspace binding deferred behind the
core picker. kanshi remains a non-goal.

Verified: V0 (docs-only change).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

agent/BACKLOG.md

@@ -47,11 +47,38 @@ job: the `checks.*` VM suite + real toplevel/HM builds on every push
 (also upgrades item 14's bump gate from eval-only to the full suite).
 
 ### 15. Display profiles — docked/undocked switching
-ROADMAP § Display / monitor management, remaining: true profile
-switching of the *same* outputs (multi-layout toggles, beyond
-per-output hotplug rules), optionally workspace-to-monitor binding.
-Design first (state-file shape, menu surface) — write the plan into
-this entry before coding.
+ROADMAP § Display / monitor management, remaining: profile switching of
+the *same* outputs. **Plan (designed 2026-07-05, iteration #27):**
+- **Option:** `nomarchy.displayProfiles` (HM) = `attrsOf (listOf
+  monitorType)` — each profile is a named list reusing the existing
+  monitor submodule verbatim (no second schema). Example: `docked =
+  [ { name="eDP-1"; resolution="disable"; } { name="DP-3"; … } ]`.
+- **State:** `settings.displayProfile = "<name>"` (absent = base
+  config), menu-written with `--no-switch` — the night-light pattern:
+  instant now, baked at the next rebuild. Add the key to
+  nomarchy-theme-sync's known-settings list (item 11's validator warns
+  on unknowns).
+- **Rebuild overlay** (hyprland.nix): active profile's entries replace
+  base `nomarchy.monitors` entries whole, by name; the existing
+  `settings.monitors` resolution overlay then applies field-level on
+  top, EXCEPT onto entries whose profile resolution = "disable" (a
+  stale resolution pick must not resurrect a disabled panel).
+- **Instant apply** (menu): System › Display gains a self-gated
+  "Profile: <active>" row (only when profiles are declared) → pick →
+  `hyprctl keyword monitor <rule>` per entry (rules baked into the
+  dispatcher at build, like everything else in rofi.nix) + state write
+  + toast. Outputs the profile doesn't name keep their base rules.
+- **Slices:** (a) option + overlay + menu picker + template example
+  (opt-in ⇒ commented `templates/downstream/home.nix` block) — V1 +
+  a checks.* grep of the rendered hyprland conf, V3 real dock; (b)
+  opt-in hotplug auto-switch: a socket2 watcher on monitoradded/
+  removed picks the profile whose named-output set matches connected
+  outputs (exact match, else largest subset, ties = no switch) —
+  decide the flag shape (`settings.displayProfile = "auto"` vs a
+  separate boolean) at implementation; (c) optional per-profile
+  `workspaces = { "1" = "DP-3"; }` → Hyprland `workspace` keywords.
+- **Non-goals:** no kanshi (fights Hyprland's output management —
+  decided in ROADMAP), nwg-displays stays a find-the-values helper.
 
 ### 16. Greeter theming from the JSON
 ROADMAP § Greeter. tuigreet themed from theme-state.json at system