[juliusmarminge]

Problem

Open thread A, then B, open and close Settings, then use navigation Back. Back returned to Settings instead of A because closing Settings pushed a duplicate B history entry. Reproduced in the real Linux web app on a12d6ed942, using Ctrl+[ as the reported macOS Cmd+[ equivalent.

Change

Remember the last main-app history position and traverse to that existing entry when leaving a utility page. When traversal could have overwritten the remembered entry, keep the existing href fallback. The shared hook covers Settings Back/Escape and sidebar Back on Usage, Pull Requests, and project settings. Browser history is not globally filtered.

Include deterministic stopped-thread fixtures and capture helpers as required by the triage evidence workflow; no provider turns are started.

Scope and approval

Fixes #16542
GitCafe: https://git.cafe/pingdotgg/t3code/issues/16542
Triaged bug via the automated issue flow: #16542. No merge authorization; dispatcher/Julius owns landing. Native macOS/Electron needs verification.

Verification

• Regression failed on base: expected A after closing Settings then Back, got Settings. A second red regression covered an overwritten remembered history entry (expected A, got Usage).
• cd apps/web && vp test run --project browser src/components/sidebar/mainAppLocation.browser.test.tsx: 2/2 pass, 15.62 seconds.
• Changed-file lint and formatting: pass, including fixture scripts. vp run --filter @t3tools/web typecheck: pass with existing Effect suggestions.
• Primary integrated real-app check on 5f983b4e2c: A(1) → B(2) → Settings(3) → Back B(2) → Ctrl+[ A(1) → Ctrl+] B(2). Runtime transcript.
• Fresh isolated GPT-6.1-Sol and Claude Opus 5.5 reviewers: both MERGE, no confirmed production regressions.

Evidence — partial, strict capture contract incomplete. Index and all recordings, fixture matrix, authoritative manifest, all visible differences.

Script: A → B → Settings → sidebar Back → history Back → Forward → further Forward. Per-action timestamps and narrated checkpoints are in each recording's JSON in the index. Before is a12d6ed942; inherited after runtime is 915e03dc90, with identical navigation code at 5f983b4e2c. The new revalidation recording and primary transcript use merged head. Inherited artifacts do not prove an exact final-head rebuild.

Desktop light, history Back checkpoint	Before	After	Diff0 (8×)	DiffT (>16/255)
Chromium/Linux, DPR 2; video 2880×1800, still 1280×800
Runtime SHA	a12d6ed942	915e03dc90	same pair	same pair
Recording	Before	After

What else changed: history Back now shows thread A and its sidebar selection/composer instead of Settings. Inherited same-route pairs also contain clock/layout drift; 64 same-href checkpoints have nonzero pixel deltas. No claim of pixel-identical rendering is made. 204 paired checkpoints include zero and threshold differences; 84 are zero-identical. Videos were decoded at first/middle/last frames; MP4 extensions correct the inherited filenames.

Unverified: strict 1440/390 × light/dark × DPR1 geometry and frozen-clock gates; cross-utility chains; complete project-alias coverage; real-app truncation/equality/conservative invalidation and cold/reload lifecycle; baseline/other-profile revalidation pairs; exact final-head paired rebuild. The regression tests cover truncation logic. Usage captures show empty limits, PR captures an unavailable-tool state. Native macOS Cmd+[ / Cmd+], Electron/hash history, and remote/relay/tunnel remain unverified. React Native mobile is unaffected. An initial hash-pairing attempt produced invalid history indices and failed the flow; it is excluded from pass claims, while a fresh tab paired through the form passed with finite indices. Proof audit pass 2: INSUFFICIENT A1–A8. The auditor independently rebuilt the core head flow successfully and confirmed the served hook matches head; all 204 pixel counts recompute. Required variants/pairings, strict geometry/DPR/clock, and the exact-head paired rebuild remain incomplete. The capture report’s “opaque sources” claim is incorrect: 102 paired source references include alpha below 255. Keep this PR draft for dispatcher/Julius; it is not merge-ready.

Models: Claude Opus 5.5 and GPT-6.1-Sol through T3 Code (Claude Agent and Codex harnesses).

[github-actions]

Thread transfer impact

⚠️ The latest CI run did not produce a thread transfer result for 5f983b4.

This comment will update automatically after the next completed run.