feat(waybar): show the layout indicator only when the layout is ambiguous (#109)

The indicator answers "which layout am I typing in?", so it is worth bar
space exactly when that question has more than one answer. It was gated on a
per-device override merely *existing*, which is the trap this box walked
into: the junk rows a keyboard's extra HID collections leave behind are all
remembered at the session layout, so they added no second answer and still
raised an indicator that could only ever show one value.

Gate on layouts rather than devices, and read the runtime-remembered
settings.keyboard.devices alongside the declared option — the new-keyboard
watcher writes those without a rebuild and they only graduate into
keyboard.devices later, so a bar reading the option alone was wrong for
exactly as long as the memory was fresh, which is when it matters most.

keyboard.layouts is now excluded on purpose: hyprland.nix keeps it as the
pool the picker offers first and deliberately never merges it into kb_layout,
so listing candidates cannot make the current layout ambiguous. A device
actually using one of them still does.

All four whole-swaps list the module unconditionally, so a single-layout
setup saw on a swapped bar what the generated bar hides — the parity rule was
already broken. Filter a swap through the same answer instead of asking four
hand-written files to re-derive it.

Logic is pure in modules/home/waybar-language.nix, matching monitor-rules /
dock-audio-rules; checks.waybar-language unit-tests both halves against
boreal's real swap, including a fixture-drift guard so the parity assertion
cannot pass vacuously.

Verified V2: new check passes, docking-ux and theme-wholeswap still pass,
`nix flake check` is clean, and the live config's generated bar now resolves
modules-right without hyprland/language on its single-layout default.

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

docs/ROADMAP.md

@@ -500,6 +500,52 @@ Design/decision records and a running log of shipped work (items marked
   the internal-first recovery before deletion and leaves real cable-removal
   timing to V3. V3 is queued as round 4; no speculative audio power policy was
   added.
+  ✓ **Docking rounds 4–5 — the hotplug event is not the truth (2026-07-14):**
+  the dev-box dock pass failed on wallpaper, dock mode, docked audio and a
+  four-times keyboard prompt. Three causes, and a process lesson. `socat -T 1`
+  closed Hyprland's IPC socket after a second of *inactivity* — a dock is
+  normally plugged into an idle desktop, so `monitoradded` was routinely lost
+  in the reconnect gap, and wallpaper, profile and audio all hung off that one
+  event. The connection is now long-lived with the tick coming from a 1s
+  `read` timeout, and the *output set* is the source of truth: `reconcile`
+  diffs it on ticks and events alike, so an event only makes the reaction
+  instant. A newly-present external is as unambiguous a plug as the event, so
+  it may still override a manual sink choice. Automatic dock mode never
+  existed — the watcher auto-*undocked* but on plug only matched display
+  profiles, so with none saved it did nothing while `Dock mode` stayed
+  menu-only; the pair is now symmetric, with a matched profile winning as the
+  more specific layout. Hyprland calls every key-capable evdev node a
+  "keyboard" (lid/power buttons, a monitor's control channel, each extra HID
+  collection), so udev's `ID_INPUT_KEYBOARD` is now the filter and the prompt
+  is once per physical keyboard, applied to every node it brings. Audio to the
+  BenQ was unreachable *by any means* because WirePlumber had the GPU's DP
+  card pinned to `pro-audio`, whose raw `pro-output-N` sinks have no ports,
+  no routing and no volume — and card profiles persist, so it survived
+  forever; a plug that finds nothing routable now repairs cards carrying an
+  *available* HDMI/DP port (the monitor asking for audio over the cable),
+  which keeps the internal analog card and considered pro-audio setups
+  untouched. On UCM cards headphones are a sink rather than a route, and a
+  stored default outranks every priority rule, so the jack is now followed
+  explicitly; unplug needs no undo since the pin goes stale by itself. The
+  process lesson: both watchers are `exec-once`, so `nomarchy-home` leaves the
+  *old* processes running and two of the four reports were never testing the
+  fix — **relogin before testing a watcher**. V3 is queued as round 6.
+  ✓ **Conditional layout indicator + swap parity (#109, 2026-07-14):** the
+  indicator answers "which layout am I typing in?", so it earns bar space
+  exactly when that has more than one answer — not when a device merely
+  exists. Counting devices was the trap: the junk rows a keyboard's extra HID
+  collections leave behind are all remembered at the session layout and added
+  no second answer. The gate reads the runtime-remembered
+  `settings.keyboard.devices` alongside the declared option, since the watcher
+  writes them without a rebuild and they only graduate later — reading the
+  option alone was wrong for exactly as long as the memory was fresh.
+  `keyboard.layouts` is excluded on purpose: hyprland.nix keeps it as the
+  picker's candidate pool and never merges it into `kb_layout`, so it cannot
+  make the current layout ambiguous by itself. All four whole-swaps list the
+  module unconditionally and so used to show what the generated bar hid; they
+  are filtered through the same answer rather than re-deriving it by hand
+  (the parity rule). Logic is pure in `modules/home/waybar-language.nix`;
+  `checks.waybar-language` unit-tests both halves against boreal's real swap.
   ✓ **Parallel fingerprint-or-password (2026-07-12, Bernardo promoted
   from PROPOSED):** `nomarchy.hardware.fingerprint.parallel` (default
   **true** — the better UX is what opting into fingerprint PAM gets you;