fix(preview): reconnect automation hosts after stream eviction

[waffleflopper]

What Changed

Re-register preview automation 250 ms after its stream completes or is remotely interrupted, even while the WebSocket stays connected. Cancel pending recovery on unmount or session replacement, and leave transport failure handling with the existing supervisor. Timed-out commands are not replayed.

Why

An unanswered preview request can evict the only desktop automation host, leaving later browser tools unavailable until the app restarts.

Fixes #12146. Complements #12279, which addresses the optional 500 ms metadata timeout in #12273. This PR contains only host recovery.

Validation

• 60 focused tests passed across subscription, preview state, broker, and request-consumer tests.
• Client-runtime typecheck, targeted lint/format checks, and diff checks passed.
• Isolated macOS Electron: real 15-second timeout, temporary no-host error, then successful click/evaluation in the original tab. No new WebSocket or renderer reload; the timed-out action ran once.

The recording shows actual MCP requests/responses in T3’s terminal alongside the preview. It was captured with #12279 applied on the local validation branch; that change is excluded here. Cross-machine relay behavior was not tested.

Recording

recovery-terminal.mp4

Model: GPT-6 (Astra) · Harness: Codex in T3 Code

Summary by CodeRabbit

• Bug Fixes
  • Preview automation connections now reconnect automatically after a stream ends, with a brief delay to improve reliability.
  • Automation sessions can resume after completion or interruption while retaining the active session.
  • Pending reconnections are cancelled when the preview is closed or the active session changes, preventing unwanted reconnects.

[macroscopeapp]

Approvability

Verdict: Approved at 75786f0

Macroscope's review found this PR approvable — This is a contained preview automation recovery fix: only the explicitly configured automation subscription retries after remote stream eviction, while existing subscriptions and cancellation behavior remain unchanged. The added behavior is covered by focused tests and introduces no schema, deployment, security, billing, or static-analysis changes.

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📥 Commits

Reviewing files that changed from the base of the PR and between 3fd5d64 and 75786f0.

📒 Files selected for processing (3)

• packages/client-runtime/src/rpc/client.test.ts
• packages/client-runtime/src/rpc/client.ts
• packages/client-runtime/src/state/preview.ts

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📝 Walkthrough

Walkthrough

The preview automation subscription now uses a callback with delayed resubscription after stream completion. RPC client tests cover reopening, session preservation, and cancellation during interruption or session replacement.

Changes

Preview automation resubscription

Layer / File(s)	Summary
Preview automation subscription wiring packages/client-runtime/src/state/preview.ts	automationRequests now subscribes to previewAutomationConnect with PreviewAutomationHost input and resubscribes 250 milliseconds after stream completion.
Delayed resubscription tests packages/client-runtime/src/rpc/client.test.ts	Tests cover delayed reopening after completion or interruption, session preservation, and cancellation during consumer interruption or session replacement.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~15 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: juliusmarminge

Merge Risk: ⚪ Minimal · up to 75786

The recovery path reconnects preview automation after stream termination while avoiding stale reconnections when the consumer or session changes. No actionable merge-blocking risk remains.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 3 files.	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 summarizes the primary change: reconnecting preview automation hosts after stream eviction.
Description check	✅ Passed	The description clearly explains what changed, why it changed, validation results, scope, and limitations. It omits the template Checklist section, but the required change rationale and validation det…
Linked Issues check	✅ Passed	Issue #12146 requires preview automation to recover during the existing session after the host disappears. packages/client-runtime/src/state/preview.ts now resubscribes to previewAutomationConnect…
Out of Scope Changes check	✅ Passed	The changes remain within issue #12146. The production change adds delayed resubscription for the preview automation stream. The test changes validate delayed resubscription, session preservation, and…

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[juliusmarminge]

Superseded by #12535 (merged), which lands the same host-registration recovery after request/stream timeouts. Closing this open PR as wash.