feat(text-injection): use IBus on unbridged compositors when ibus-wayland runs

[eiseleb47]

Closes #607.

What

_IBUS_UNBRIDGED_COMPOSITORS assumes nothing sits between the compositor and ibus-daemon. Since IBus 1.5.32 that is no longer safe: IBus ships ibus-wayland, which implements zwp_input_method_v2 and relays commits to native Wayland clients speaking text-input-v3. Every compositor on the denylist exposes zwp_input_method_manager_v2, so with the bridge running they are bridged — and skipping IBus drops to a slower path for no reason.

This adds a live pgrep -x ibus-wayland probe and lets it override the denylist.

Scope

The probe is checked only inside the denylist branch. GNOME and the KDE VirtualKeyboard path (#574) are untouched — there is a test asserting the probe is never even consulted for bridged desktops.

Properties:

• Strictly additive. With no bridge running, behaviour is byte-for-byte what it is today.
• Self-disabling. A live probe rather than configuration, so it degrades back to the denylist by itself if the bridge dies or was never started. There is no way to assert a bridge that isn't there.
• Cost is one pgrep per TextInjector construction, not per injection.

Evidence

Hyprland 0.56.1, IBus 1.5.34:

$ wayland-info | grep -E 'text_input|input_method'
interface: 'zwp_text_input_manager_v1',    version: 1, name: 20
interface: 'zwp_text_input_manager_v3',    version: 1, name: 21
interface: 'zwp_input_method_manager_v2',  version: 1, name: 28

$ strings /usr/lib/ibus/ibus-wayland | grep zwp_input_method
zwp_input_method_manager_v2
zwp_input_method_v2
...

With the bridge started, dictation commits through IBus in VSCodium, Claude Desktop, another Electron 41 app and kitty — 303 chars in ~200 ms, versus 16.8 s for 415 chars via ydotool type (-d 20 -H 20 defaults = 40 ms/char).

Caveat worth documenting either way: Chromium only opens a zwp_text_input_v3 seat when launched with --enable-wayland-ime. Without it the bridge runs and the app still receives nothing — possibly part of why IBus has looked unusable with Electron.

VOCALINUX_FORCE_BACKEND

Folded in per your note on #607. Accepts ibus / wtype / ydotool / auto; unknown values fall back to auto with a warning rather than silently pinning a backend.

The motivation is that autodetection has to infer whether IBus commits reach the focused app and cannot verify it — commit_text() reports success even when the text is dropped — so an escape hatch is useful when the inference is wrong, and it makes the two paths A/B-testable without editing code.

This overlaps #476 / #402. Happy to drop it from this PR if you would rather it follow the design there — the probe stands alone and I would rather that not wait on it.

Two existing tests changed

Both asserted the unbridged outcome without pinning the probe, so both were implicitly host-dependent once a probe exists:

• test_cosmic_skips_ibus_and_uses_wtype blanket-mocks subprocess.run to returncode=0, which the probe reads as "bridge found".
• test_unbridged_wayland_skips_ibus_when_engine_is_xkb shells out for real, so it depended on whether the machine running the suite had the bridge up.

Both now state the "no bridge" precondition explicitly. Their intent is unchanged.

Tests

10 added: denylisted compositors with and without the bridge, probe not consulted for bridged desktops, probe argv, probe resilience to missing/hung pgrep, and the VOCALINUX_FORCE_BACKEND parsing matrix. No new flake8 findings and no test failures unique to this branch against main.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.85%. Comparing base (4fad897) to head (c9501d1).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #614      +/-   ##
==========================================
+ Coverage   85.78%   85.85%   +0.06%     
==========================================
  Files          35       35              
  Lines        6375     6405      +30     
  Branches     1035     1041       +6     
==========================================
+ Hits         5469     5499      +30     
  Misses        683      683              
  Partials      223      223              

Files with missing lines	Coverage Δ
src/vocalinux/text_injection/text_injector.py	88.67% <100.00%> (+0.47%)	⬆️

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[jatinkrmalik]

Nice. Keeping the ibus-wayland probe inside the denylist branch is the right shape so the KDE path stays alone, and leaving force-backend in here is fine. Tests cover the host-dependent cases well. LGTM.