[hogeheer499-commits]

Queued preview actions can run after their caller has timed out, causing stale clicks or navigation after control resumes. Capture one monotonic request deadline and check it immediately before a queued action starts. Already-started work retains its normal timeout and queue reservation. The historical suggestion to cap navigation by the remaining caller budget is intentionally omitted: this change revokes actions before dispatch and lets started actions settle under their normal bounds. Recording stop still drains after expiry so capture is cleaned up, and initial navigation stays tracked for human handoff.

Rebuilt from #16941; thanks @hogeheer499-commits for the deadline/cleanup model. Contributor history is preserved, with main merged. The independent implementation pass retained the production approach because it is already the smallest correct model; duplicate tests were removed. Adversarial review also caught initial navigation tracking blocking user-opened tabs; strong tracking is now limited to agent-owned tabs, preserving main’s viewer responsiveness.

Validation at e7bc457af8:

• PR-added cases 9 → 5 in existing SessionControl and ServerBrowser suites; 65 tests pass. The queue and public click regressions fail against main; deliberate removal of navigation tracking or the recording-stop exception also fails the retained tests.
• Scoped lint, formatting and server typecheck pass.
• Fresh independent Claude Opus 5.5 and Codex GPT-6 Sol whole-diff reviews: two rounds; the first found the user-tab initial-navigation regression described above, now fixed. Both second-round reviews found no confirmed defects.

Live proof used the real PreviewAutomationBroker → ServerBrowser → Playwright/CDP → Chrome Headless Shell 154.0.8037.92 with a synthetic loopback page and isolated temporary state. A held navigation blocks the queue. After callers time out, release it: main fires the expired click once; this head never fires it; both execute the valid follow-up once. A second real recording scenario confirms an expired stop still executes after the blocker, and another stop reports no active recording.

A real user-opened tab with its initial HTTP response held also accepts a corrected viewer URL before that initial response is released. One focused regression failed on the first reviewed revision and passes after the agent-only tracking fix.

The harness uses updateCurrentTab:false after opening to keep deliberately timed-out broker requests from disconnecting the host; deadline dispatch and browser actions remain the production path. This proves the service/browser integration, not the complete client or MCP transport.

Before — main 5569a42bff, expired click fires:

After — rebuilt head, expired click skipped and follow-up runs:

Before recording:

https://gh-file-drop-api-prod-mi5fy3sowv63ufte.pinglabs.workers.dev/f/d81de83e2d77cd35/before.mp4

After recording:

https://gh-file-drop-api-prod-mi5fy3sowv63ufte.pinglabs.workers.dev/f/22d59608670f2ddb/after.mp4

Reproducible harness, exact-head results, focused checks and full review reports.

Not verified: native macOS, Windows, iOS, Android, Electron desktop, physical devices, relay/tunnel, or full client/MCP transport. No native implementation changed. The shared server queue and real browser behavior were verified on headless Linux; the focused tests cover initial-open/human-handoff ordering.

Implemented with Codex GPT-6.1 Sol in T3 Code; tests by GPT-6 Astra; adversarial reviews by Claude Opus 5.5 and GPT-6 Sol.

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📒 Files selected for processing: 3

• apps/server/src/preview/ServerBrowser.test.ts
• apps/server/src/preview/ServerBrowser.ts
• apps/server/src/preview/SessionControl.ts

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📝 Walkthrough

Browser requests now calculate absolute deadlines and pass them to controlled session operations. SessionControl rejects queued actions at dispatch when their deadlines have arrived. Running actions retain their queue reservation. Tests cover dispatch boundaries and browser operations queued behind snapshots or captures.

Changes: Preview operation deadlines

Layer / File(s)	Summary
Session dispatch deadline checks apps/server/src/preview/SessionControl.ts, apps/server/src/preview/SessionControl.test.ts	SessionControl accepts an optional deadline and rejects queued actions when dispatch occurs at or after it. Tests cover deadline boundaries and confirm that running work retains its queue reservation.
Browser request deadline propagation apps/server/src/preview/ServerBrowser.ts, apps/server/src/preview/ServerBrowser.test.ts	ServerBrowser computes a deadline from the request timeout and passes it to controlled tab operations. Tests cover queued clicks, screenshot captures, and a recording stop that executes after its deadline.

Priority: ➖ Normal

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

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant ServerBrowser
  participant SessionControl
  Client->>ServerBrowser: send request with timeout
  ServerBrowser->>ServerBrowser: compute deadline and run operation
  ServerBrowser->>SessionControl: invoke controlled operation with deadline
  SessionControl->>SessionControl: check deadline at dispatch
  SessionControl-->>ServerBrowser: run action or reject expired action
  ServerBrowser-->>Client: return operation result

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Suggested reviewers: juliusmarminge

Merge Risk: ⚪ Minimal · up to 76614

The queued-action deadline change is ready to merge after normal checks; no actionable issue remains from this review.

Security architecture risk: 🟡 Moderate · up to 76614

Queued expiry generally preserves ownership checks and prevents late actions. However, opening a tab can start navigation before expiry is checked. Rejecting that opening operation can then remove the wait that normally keeps subsequent actions and control handoffs behind the navigation.

Retained concerns

• Medium · reliability · inferred: If tab initialization consumes the request budget, createTab can already have started initialNavigation when the new deadline check rejects the opening action. Rejection skips the callback's await of initialNavigation, and that navigation is not registered with SessionControl.track. Subsequent actions or ownership handoffs can therefore drain the queue while the earlier navigation remains active. Before this PR, an otherwise-authorized opening callback awaited that navigation even after caller timeout. This introduces an ordering and failure-containment gap on an agent-owned tab; cross-identity exploitation is not established.

Security review details

Security Blast Radius

• inferred — The identified ordering failure affects a newly created preview tab accessible to its owning agent and authorized viewers. Existing admission checks apply per-agent and server-wide tab limits, and unviewed agent tabs have idle cleanup. These controls constrain resource retention but do not restore navigation ordering.

Trust Boundaries and Controls

• observed — Agent mismatch, human control, epoch changes, and closed state remain independent dispatch barriers. The flagged boundingBox and scrollIntoViewIfNeeded declarations are locator mocks inside a regression test, not newly exposed production entrypoints.

Resilience and Maintainability Implications

• inferred — Keeping a created tab after caller failure is preexisting behavior, not sufficient evidence of a newly introduced resource leak. The material regression is narrower: deadline rejection bypasses the initial-navigation wait that previously reserved the queue, weakening orderly recovery and control handoff.

Hardening Proposals

• proposed — Represent already-started initial navigation in the tab's drain lifecycle independently of whether the opening callback remains eligible to dispatch, so expiry cannot release subsequent actions or ownership handoffs ahead of that work.

Pre-merge checks: 4

Check name	Status	Explanation
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Description check		The description clearly explains the problem, implementation, scope, verification results, test coverage, limitations, and agent usage. It does not explicitly link a triaged issue with maintainer appr…
Title check		The title is concise, specific, and accurately summarizes the primary change, including the recording-stop exception.

Full details: Description check

Explanation

The description clearly explains the problem, implementation, scope, verification results, test coverage, limitations, and agent usage. It does not explicitly link a triaged issue with maintainer approval or explain an approval exemption.

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[hogeheer499-commits]

Superseded (14 Oct). This snapshot-compatibility reply concerned the earlier c8201d7 patch. Its contract, MCP-output and capture-preference changes are outside the current PR diff. See the PR description for current scope and verification. The original reply is preserved in the edit history.

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🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
set -euo pipefail
git rev-parse HEAD
cat packages/contracts/package.json
rg -n -C2 '\bPreviewAutomationSnapshot\b' .
ast-grep outline apps/server/src/mcp/McpHttpServer.ts --match registerPreviewSnapshot --view expanded
ast-grep outline apps/server/src/mcp/McpHttpServer.test.ts --items all
ast-grep outline apps/server/src/mcp/toolkits/preview/handlers.ts --items all
ast-grep outline packages/contracts/src/previewAutomation.ts --match 'PreviewAutomationSnapshot' --view expanded
gh api repos/pingdotgg/t3code/pulls/16941/comments --paginate --jq '.[] | select(.user.login == "coderabbitai" and (.body | test("compatib|consumer|optional|schema"; "i"))) | {id,path,line,body}'

Length of output: 11663

---

🏁 Script executed:

#!/bin/bash
set -euo pipefail
sed -n '451,565p' apps/server/src/mcp/McpHttpServer.ts
sed -n '205,225p' apps/server/src/mcp/toolkits/preview/handlers.ts
sed -n '696,715p' packages/contracts/src/previewAutomation.ts
rg -n -C3 'snapshot|older host|includeImage|saved|outputSchema' apps/server/src/mcp/McpHttpServer.test.ts
git show --format=short --stat c8201d7
git show --format= -- apps/server/src/mcp/McpHttpServer.test.ts
gh api repos/pingdotgg/t3code/issues/16941/comments --paginate --jq '.[] | select(.user.login == "coderabbitai" and (.body | test("compatib|consumer|optional|schema"; "i"))) | {id,body}'

Length of output: 30104

---

@hogeheer499-commits Thanks for clarifying the compatibility boundary. I inspected c8201d7 and withdraw the snapshot compatibility finding.

The code and tests support these conclusions:

• @t3tools/contracts is private. The reference search found no web, mobile, or desktop decoder of PreviewAutomationSnapshot.
• registerPreviewSnapshot advertises no outputSchema. Its structured metadata excludes PNG data, so the external MCP result is not the full internal snapshot shape.
• Only includeImage: false without save: true requests capture omission. Default, explicit-image, and saved snapshots retain capture.
• The tests cover both omitted screenshots and older hosts that still return PNG data. They check metadata preservation, image suppression, and the next default request.

This evidence resolves my concern for the identified consumers and older-host response path. It does not establish compatibility for arbitrary custom consumers.

I verified the code and test assertions, not the reported test execution. The maintainer review requirement remains unchanged.

---

✏️ Learnings added

Learnt from: hogeheer499-commits
URL: https://github.com/pingdotgg/t3code/pull/16941

Timestamp: 2026-10-07T20:58:32.839Z
Learning: In pingdotgg/t3code, t3tools/contracts is a private TypeScript workspace package. PreviewAutomationSnapshot is an internal host-result schema used by server code. apps/server/src/mcp/McpHttpServer.ts registers preview_snapshot without an external MCP outputSchema and excludes PNG data from structured metadata. Do not treat the external MCP result as the full PreviewAutomationSnapshot shape. apps/server/src/mcp/toolkits/preview/handlers.ts requests capture omission only when includeImage is false and save is not true. Default, explicit-image, and saved snapshots retain capture. apps/server/src/mcp/McpHttpServer.test.ts covers older hosts that ignore the capture preference and return PNG data, while the formatter suppresses image content as requested.

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Pre-merge checks failed. Please resolve the failing checks before merging.

[hogeheer499-commits]

Superseded (14 Oct): this describes an earlier, broader revision of this PR. The current scope and evidence are in the PR description.

@juliusmarminge The fix for #16921 is ready for maintainer review, based on your merged #16939. CodeRabbit withdrew its snapshot compatibility finding; its remaining Approvability gate requires a maintainer review because the change spans the server and contracts.

CI, Mobile Fingerprint Check, Mobile EAS Preview and Web Preview are all action_required, with zero jobs started. Could you approve the fork workflow runs and review the PR?

Current head: c8201d7. The production changes passed 181 focused tests and native Windows checks; the tests-only compatibility follow-up passed all 24 MCP server tests. The PR documents the remaining hidden-guest PNG capture limitation.

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Actionable comments posted: 1

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Inline comments:
Review comments at @apps/server/src/preview/ServerBrowser.ts:
- Line 1786: Cap both navigation calls in handleRequest with the remaining
request budget at the time navigation starts, including the call using
navigationTimeout and the call using navigateInput.timeoutMs or
request.timeoutMs. Pass remainingTimeoutMs through runOperation to the open
callback so both paths can apply the cap.

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📥 Commits

Reviewing files that changed from the base of the PR and between 1ead03a and 2368541.

📒 Files selected for processing (8)

• apps/server/src/mcp/McpHttpServer.test.ts
• apps/server/src/mcp/McpHttpServer.ts
• apps/server/src/mcp/toolkits/preview/handlers.ts
• apps/server/src/mcp/toolkits/preview/tools.ts
• apps/server/src/preview/ServerBrowser.test.ts
• apps/server/src/preview/ServerBrowser.ts
• apps/server/src/preview/SessionControl.ts
• packages/contracts/src/previewAutomation.ts

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[hogeheer499-commits]

Superseded (14 Oct). This reply concerned navigation-budget changes in the earlier e9f5f2d patch. Those changes are outside the current PR diff. Started operations keep their full operation timeout; bounding them by the remaining budget is left for a follow-up. See the PR description for the boundary and verification. The original reply is preserved in the edit history.

[coderabbitai]

@hogeheer499-commits Thanks for the update. I’ll resume automatic reviews and review the updated head, including the navigation-budget changes in e9f5f2d.

I have not independently verified the fix or the reported test results. The maintainer review requirement remains unchanged.

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[juliusmarminge]

Taking over this one. I’ll rebuild the dispatch-time deadline check against current main, reduce the tests to the expired-action/recording-cleanup regressions, and verify queue serialization with the real headless browser before pushing to this branch.