fix(web): keep the parent thread highlighted while viewing its subagent

[saphid]

Opening a subagent cleared every sidebar highlight because subagents have no row. The sidebar now represents an open subagent with its nearest loaded ancestor that has a row, within the same environment. Forks stop the ancestor walk. This row also remains visible in collapsed shelves and anchors search highlighting and next/previous navigation.

Draft indicators, parent PR actions, settle and snooze still use the exact route thread. Missing parents and cycles leave the row unmatched.

Taken over from @saphid's #15163, preserving the contributor's commits and adding maintainer commits. Kept one lineage regression test (one before → one after in Sidebar.logic.test.ts); removed two redundant assertions and simplified the traversal.

Verification at 5fe80b4:

• 235 tests pass across Sidebar.logic, drag, snooze and pointer suites. The former motion test file no longer exists on main.
• Web typecheck, targeted lint (three existing unused-import warnings), formatting and diff checks pass.
• One parallel adversarial review round: Claude Opus 5.5 and Codex GPT-6-Sol, no blocking findings. Opus noted the ancestor row's existing aria-current page semantics as a non-blocking refinement.
• Live headless Linux Chromium: direct and nested subagent routes highlight the parent; clicking the highlighted parent still opens its own route. Disposable stopped fixtures; no provider turns started. Exact main Sidebar.tsx baseline and candidate captured at matching route/data/viewport.
• macOS, Windows, iOS, Android and Electron desktop were not verified. Native mobile is outside this web change. Shelf/search/PR/draft paths were source-reviewed; they were not all exercised live. CI and configured bot results must be checked on this pushed head before merging.

Before — main leaves the parent unhighlighted:

After — parent stays highlighted while the subagent is open:

Resumed and published with GPT-6.1-Sol in the Codex harness through T3 Code. Independent reviews: Claude Opus 5.5 and Codex GPT-6-Sol.

[macroscopeapp]

Approvability

Verdict: Approved at 5fe80b4

Macroscope's review found this PR approvable — This is a focused sidebar bug fix that maps an open subagent to its existing ancestor row while preserving exact-route behavior for drafts and pull-request actions. The production changes are localized, edge cases are covered by tests, and there are no schema, security, deployment, default, or static-analysis changes.

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Dismissing prior approval to re-evaluate 51943d4

[coderabbitai]

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 31a9da1 and 51943d4.

📒 Files selected for processing (3)

• apps/web/src/components/Sidebar.logic.test.ts
• apps/web/src/components/Sidebar.logic.ts
• apps/web/src/components/Sidebar.tsx

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📝 Walkthrough

The sidebar resolves routed subagents to their nearest loaded, non-subagent ancestor in the same environment. It uses that ancestor’s row for route-aware visibility, sorting, navigation, search, and highlighting while retaining the exact routed thread identity for row actions.

Changes: Sidebar route rows

Layer / File(s)	Summary
Resolve the visible ancestor row apps/web/src/components/Sidebar.logic.ts, apps/web/src/components/Sidebar.logic.test.ts	Adds resolveSidebarRowThreadId to follow parent links within the same environment. Tests cover ancestors, forks, missing or cross-environment parents, and lineage cycles.
Use the representing row across sidebar navigation apps/web/src/components/Sidebar.tsx	Uses the resolved route row key to retain rows in shelves and settled-tail paging, and to drive sorting, keyboard navigation, and search-result activation.
Separate active row from exact routed thread apps/web/src/components/Sidebar.tsx	Separates row highlighting from exact route matching. Draft decoration and pull-request actions now use the exact-route flag.

Priority: ⬇️ Low

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

Change: Bug fix

Suggested reviewers: juliusmarminge

Merge Risk: ⚪ Minimal · up to 51943

The change is mergeable after normal checks. No actionable regression in sidebar highlighting or navigation is established.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

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.
Title check		The title clearly and concisely describes the primary fix: keeping the parent thread highlighted while viewing its subagent.
Description check		The description clearly explains the problem, implementation, route-specific behavior, verification results, limitations, and before/after screenshots. It does not provide an explicit maintainer appro…

Full details: Description check

Explanation

The description clearly explains the problem, implementation, route-specific behavior, verification results, limitations, and before/after screenshots. It does not provide an explicit maintainer approval comment or explain why the change qualifies without prior approval, but the description is otherwise mostly complete and focused.

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[saphid]

Review requested

Date (UTC)	Reviewer	Where
2026-10-06	Maria	Discord DM

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Dismissing prior approval to re-evaluate 591e8af

[juliusmarminge]

Taking over this one. I'll trim the tests to the minimum, rebuild the implementation to current conventions, run adversarial reviews, and push the result here.

Dismissing prior approval to re-evaluate 5fe80b4