perf(desktop): keep cached transcript visible while session resumes

[helix4u]

What does this PR do?

Desktop can already have the exact remembered session's bounded transcript snapshot before backend/profile hydration and session.resume finish binding a live runtime. Without an early navigation claim, the cold / route can expose a usable fresh composer during that window and later replace what the user was doing when remembered navigation resolves.

This claims remembered navigation before first paint, restores only the exact connection/profile-scoped transcript snapshot, and keeps that presentation provisional until the live session list validates ownership. Cached text may remain visible while the runtime binds, but the composer and fresh-session intro remain unavailable until the remembered route owns a live runtime.

Current main also keeps the loader visible when the session list says a routed session has history but no display-authoritative transcript has arrived. The rebased implementation preserves that behavior: a brand-new routed draft with a bound runtime may be empty, while known history, route mismatch, missing runtime binding, or unresolved remembered navigation remains pending. The transcript loader is suppressed only when cached text is already visible; the composer gate remains active.

The explicit last-opened session is authoritative when a torn shutdown left the remembered route and session ID disagreeing. The route is healed only after live validation. Cached text never creates or impersonates a runtime, and stale, missing, cross-profile, or unnameable remote targets fail closed and clear only the provisional paint.

Desktop performance series

This change is one independently reviewable layer of the same Desktop startup and first-interaction performance pass.

• perf(cli): dispatch serve without the full parser tree #96749 removes unrelated CLI parser work from the hermes serve entry path.
• perf(serve): overlap cached startup preparation #96750 overlaps independent cached startup preparation before the existing readiness join.
• perf(serve): move Desktop runtime services after bind #96751 lets the verified local Desktop control socket bind before nonessential runtime services finish loading.
• perf(desktop): start the backend before first-window setup #97032 starts the backend before first-window setup and defers noncritical Electron integrations.
• perf(desktop): make the shell interactive before startup hydration #97027 releases the renderer boot barrier once the gateway socket and active profile are ready, while noncritical hydration continues.
• perf(desktop): paint cached shell state before live refresh #96717 paints connection/profile-scoped session and project navigation from bounded snapshots while live refresh continues.
• perf(desktop): keep cached transcript visible while session resumes #96721 paints the exact connection/profile-scoped remembered transcript before backend/profile hydration, then keeps it visible while the live runtime resumes.
• fix(desktop): retain the largest cacheable transcript tail #96921 prevents the existing transcript cache from discarding a complete suffix that still fits its storage bound.
• perf(desktop): warm common route chunks while idle #97037 warms common lazy route code serially during idle time in the connected primary window, without prefetching route data.
• perf(desktop): progressively hydrate Bot Mode roster #96728 progressively hydrates Bot Mode roster presentation without changing canonical chat identity.

This PR owns remembered-session presentation and pending-runtime gating. It does not change backend startup, session-list caching, transcript snapshot bounds, or Bot Mode roster behavior.

Related Issue

None.

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

• Claim remembered startup navigation during layout so / cannot expose a competing fresh composer before session hydration.
• Restore a bounded transcript tail only for the exact remembered connection/profile/session scope.
• Keep cached transcript presentation visible while live ownership validation and session.resume bind the runtime.
• Keep the composer and fresh-session intro unavailable throughout that pending state.
• Preserve current main's distinction between a legitimately empty new draft and a known-history session whose transcript has not arrived.
• Treat the explicit last-opened session as the chat authority when route/session persistence was torn, then heal the route after live validation.
• Fail closed for stale, cross-profile, or unnameable legacy remote ownership and clear only provisional state owned by startup restore.
• Add behavioral coverage for pre-profile paint, torn persistence, ownership rejection, runtime binding, fresh-route gating, cached-transcript loading, known-history loading, and exhausted recovery.

How to Test

1. From apps/desktop, run npx vitest run --project ui --maxWorkers=4 src/app/contrib/hooks/use-desktop-integrations.test.tsx src/app/session/hooks/use-route-resume.test.tsx src/app/chat/index.test.tsx src/app/chat/thread-loading.test.ts.
2. Run npm run typecheck.
3. Run ESLint over the ten changed renderer and store files.

Expected result: the exact scoped cached transcript can paint before live hydration; cached text stays visible while runtime binding is pending; the composer remains gated; known-history sessions do not flash blank; new empty drafts remain usable after runtime binding; and invalid ownership fails closed.

Focused result: 4 Vitest files passed with 56 tests. Desktop renderer, Electron, and E2E typechecks passed. Affected-file ESLint and git diff --check passed.

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features)
• I've tested on my platform: Windows 11

The Python suite was not run because this is a renderer-only change.

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — or N/A
• I've updated cli-config.yaml.example if I added/changed config keys — or N/A
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — or N/A
• I've updated tool descriptions/schemas if I changed tool behavior — or N/A

Screenshots / Logs

Not applicable. This changes loading behavior without changing the visual design.

[helix4u]

[teknium1]

Thanks — reviewed against current origin/main. Main already paints the durable transcript-tail cache on cold resume (f8767d1 / #89206, profile-scoped by #94828): transcript visible at ~1.43-1.48 s, under the boot overlay until ≥2.1 s, so a pre-boot prepaint cannot be seen. The early setMessages()/$selectedStoredSessionId claim from a useLayoutEffect also bypasses the persisted-display provenance gate (b6eb17d), and the prefetched-REST early paint landed via #101227. Closing as redundant.