feat(desktop): keep running threads synced in the background

[t3dotgg]

When you open a thread that is running, "Syncing messages..." flashes in the composer. Since #9740 (#9740), a thread's live stream closes when the last view leaves, so opening a running thread must replay the events it missed. A cold open is worse, because the disk cache never saves a thread mid-turn.

Now the desktop app keeps each running thread subscribed in the background. When you open one, its state is already live, so no sync status shows.

How it works:

• RunningThreadKeepAlive mounts one atom at the app root. It uses useAtomMount, so it never reads the value and thread updates cause zero React renders.
• That atom reads the shell data that is already loaded and mounts the same thread state atom the thread view uses, for each thread whose session is starting or running. The thread view shares that stream.
• The running set keeps its identity until a thread starts or stops. Ordinary shell updates do not rebuild the set.
• When a thread stops, its mount drops and the stream closes through the idle TTL 0 path from perf(client): stop thread streams when unused #9740. The scope finalizer then saves the settled state to disk (it uses committed state, not the 500ms debounce).
• The shell and detail streams are independent, so the shell can report a stop before the detail loads or catches up. If it does, the thread stays mounted until its own stream is live and shows the stop too. A deleted or failed stream releases at once. Without this, the stream could close before it applies the stop, and the settled state would not reach the disk cache.

Scope limits:

• Desktop only (isElectron). Web and mobile do not change.
• Every enabled environment: local, remote, relay, and tunnel. An environment that connects gets its running threads picked up. An environment that goes away drops all of its mounts, including a thread still waiting for its stop.
• Only threads with session status starting or running, the same rule the disk cache uses. Idle threads do not change, and their disk cache is already current.

I updated the thread detail section of docs/internals/connection-runtime.md with the keep-alive rule.

Tests: vp test run apps/web/src/state/threads.test.ts covers which threads are kept, the stop handoff, and environments that connect and go away. The existing threads-sync and threads-atoms suites pass. Typecheck passes for apps/web and packages/client-runtime. I did not test in a real client. The main agent can do a desktop pass on request.

Made by Claude Opus 5.5 in Claude Code, running in T3 Code.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • The desktop app now keeps threads available while their sessions are starting or running, so opening an active thread doesn’t require replaying its activity.
• Bug Fixes
  • Stopped threads now remain available until their final state is received, helping ensure the displayed thread state is up to date.
• Documentation
  • Clarified how thread availability differs across desktop, web, and mobile.

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.5 KiB	13.5 KiB	+35 B (+0.3%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.1 KiB	7.1 KiB	+6 B (+0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.4 KiB	6.5 KiB	+29 B (+0.4%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	56.2 KiB	56.3 KiB	+44 B (+0.1%)	66.4 KiB	✅
Codex	Live turn messages	9	10	+1 (+11.1%)	21	✅
Claude	Total thread wire	13.5 KiB	13.5 KiB	−13 B (−0.1%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.1 KiB	0 B (0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.4 KiB	−13 B (−0.2%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.0 KiB	57.0 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	9	9	0 (0.0%)	21	✅

Baseline: ebdcda1 · PR result: d85f586 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 114.0 KiB
• Claude decoded thread snapshot: 114.7 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This PR adds automatic desktop background synchronization by maintaining live detail streams for every running thread across enabled environments, along with associated state processing and persistence. Because it changes default product behavior and introduces substantial ongoing runtime work, human review is appropriate.

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📝 Walkthrough

Walkthrough

The change adds session-running detection and desktop keep-alive tracking for threads in enabled environments. Electron mounts the tracking component. Tests cover thread and environment updates, and documentation describes the connection behavior.

Changes

Desktop thread keep-alive

Layer / File(s)	Summary
Running-session tracking packages/client-runtime/src/state/threads.ts, apps/web/src/state/threads.ts, apps/web/src/state/threads.test.ts	The shared predicate identifies starting and running sessions. The keep-alive atom tracks running threads and retains detail state until it is done. Tests cover shell updates, detail state, and environment removal.
Desktop mounting and runtime documentation apps/web/src/components/desktop/RunningThreadKeepAlive.tsx, apps/web/src/routes/__root.tsx, docs/internals/connection-runtime.md	The route mounts the keep-alive component in Electron. The documentation describes when desktop thread streams remain mounted and states that web and mobile do not keep threads alive.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant RootRouteView
  participant RunningThreadKeepAlive
  participant runningThreadKeepAliveAtom
  participant EnvironmentCatalog
  participant ThreadShellAtoms
  participant ThreadDetailAtoms
  RootRouteView->>RunningThreadKeepAlive: render when isElectron is true
  RunningThreadKeepAlive->>runningThreadKeepAliveAtom: mount
  runningThreadKeepAliveAtom->>EnvironmentCatalog: read enabled environment IDs
  runningThreadKeepAliveAtom->>ThreadShellAtoms: track running thread IDs
  runningThreadKeepAliveAtom->>ThreadDetailAtoms: mount detail state for tracked threads
  ThreadDetailAtoms-->>runningThreadKeepAliveAtom: report settled detail state
  runningThreadKeepAliveAtom->>ThreadDetailAtoms: release completed mounts

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Suggested reviewers: juliusmarminge

Merge Risk: 🔵 Low · up to d85f5

A recently completed turn may temporarily disappear from the local thread view. This is recoverable, but the stop handoff should be corrected before relying on it.

Security Architecture Review

Security architecture risk: 🟡 Moderate · up to d85f5

Background syncing improves thread continuity, but it also keeps more connections active and may start them outside the usual primary-authenticated path. The access controls and capacity limits for that broader behavior need confirmation; no unauthorized access was established.

Retained concerns

• Medium · security · inferred: Hosted-static Electron can start background subscriptions for enabled environments without the root's primary-authenticated condition. Whether each detail connection independently enforces the intended environment identity and authorization is unresolved; this is not an established bypass.
• Medium · security · inferred: Desktop subscription count now grows with the running-thread set across all enabled environments, rather than just threads being viewed. A connected environment that reports many running sessions can increase concurrent detail-stream work; effective connection limits and failure containment were not established.

Security review details

Security Blast Radius

• inferred — A connected environment's shell data can now cause background detail subscriptions for each of its reported running threads on desktop. Exposure is bounded by enabled environments but is no longer bounded by the currently viewed thread.

Security Findings and Attack Paths

• inferred — Many running sessions reported by an enabled environment could amplify concurrent detail-stream work. No unauthorized read or demonstrated exhaustion was established; actual impact depends on transport authorization and capacity behavior not verified here.

Trust Boundaries and Controls

• observed — The root excludes ordinary unauthenticated states and the first-run gate can withhold its children. Hosted-static is an allowed root state, however, and the new Electron mount is not conditional on primaryEnvironmentAuthenticated.

Resilience and Maintainability Implications

• observed — Stable running-set identity avoids rebuilding mounts on ordinary shell updates. Stream-scope owner checks prevent an older scope from persisting over its successor, while the stop-confirmation test covers shell/detail ordering.

Hardening Proposals

• proposed — Confirm per-environment authorization for hosted-static background detail streams and bound or monitor aggregate stream concurrency. Verify disk-cache recovery when a failed stream or environment removal interrupts stop confirmation.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 12 functions across 5 files. (1 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: desktop-only background synchronization for running threads.
Description check	✅ Passed	The description clearly explains what changed, why it was needed, implementation details, scope limits, tests, and the known limitation that real-client testing was not performed. It does not include …
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 12 functions across 5 files. (1 skipped: 1 unsupported.)

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✨ Finishing Touches 💡 1

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Actionable comments posted: 1

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🤖 Prompt to fix review comments

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Inline comments:
In `@apps/web/src/state/threads.ts`:
- Line 63: Update the keep-alive release condition using isDetailDone so it
carries the stopped shell turn identity through the handoff and releases the
mount only when detail confirms that same turn is settled; do not accept
retained detail from a previous turn.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository: pingdotgg/t3code/.coderabbit.yaml

Review profile: CHILL

Plan: Advanced

Run ID: df4d231a-0762-4477-9ace-72dfdbb0414f

📥 Commits

Reviewing files that changed from the base of the PR and between ebdcda1 and d85f586.

📒 Files selected for processing (6)

• apps/web/src/components/desktop/RunningThreadKeepAlive.tsx
• apps/web/src/routes/__root.tsx
• apps/web/src/state/threads.test.ts
• apps/web/src/state/threads.ts
• docs/internals/connection-runtime.md
• packages/client-runtime/src/state/threads.ts

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