feat(web): add parent thread breadcrumb navigation

[maria-rcks]

child threads show only the project and current thread in the header, so returning to the parent requires finding its timeline link. add the immediate parent as a clickable breadcrumb, collapsing its label to a clickable ellipsis when space runs out and keeping its full title in the tooltip.

verification:

• exercised parent navigation, narrow collapse, wide expansion, project draft creation, title menu, and rename/restore against real stopped child data; light and dark were inspected.
• existing chatheader tests, scoped web types, and targeted lint passed remotely; final formatting check passed on Blacksmith.
• native desktop/mobile and relay/tunnel paths remain unverified.

font changes also remeasure the parent breadcrumb. verified the same 850px header switching from monospace to arial; the full parent fits at 499.52px within 506px.

model: gpt-6.1-sol; harness: codex.

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This PR introduces new automatic parent-thread navigation and responsive breadcrumb behavior in the production web UI. The implementation is localized and does not change schemas or product defaults, but the new user-facing capability warrants human review.

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• apps/web/src/components/chat/ChatHeader.tsx

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📝 Walkthrough

Walkthrough

ChatView passes parent-thread navigation data to ChatHeader. ChatHeader displays a parent-thread breadcrumb and collapses its title to an ellipsis when the breadcrumb exceeds the available width.

Changes

Parent Thread Breadcrumb

Layer / File(s)	Summary
Parent-thread breadcrumb navigation apps/web/src/components/chat/ChatHeader.tsx, apps/web/src/components/ChatView.tsx	ChatHeader accepts a parent-thread link and navigation callback. It measures breadcrumb width and displays the parent title or an ellipsis. The parent link opens that thread and shows its full title in a tooltip. ChatView passes the link and callback to ChatHeader.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Feature

Suggested reviewers: juliusmarminge

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Merge Risk: ⚪ Minimal · up to 658e7

The breadcrumb change has no established issue requiring correction before merge. Normal checks remain appropriate.

Pre-merge checks | 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: adding parent thread breadcrumb navigation in the web application.
Description check		The description explains the problem, implementation, verification steps, screenshots, test results, and unverified paths. It does not include an explicit scope and approval section, but the overall d…
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.

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Actionable comments posted: 1

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🤖 Prompt to fix review comments

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Inline comments:
Review comments at @apps/web/src/components/chat/ChatHeader.tsx:
- Line 108: Update the breadcrumb fit calculation in ChatHeader so it measures
the project label at its rendered width and excludes its hidden overflow; retain
hidden-width adjustments only for labels the layout should show in full,
including WorkspaceBreadcrumbText’s capped project title.

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📒 Files selected for processing (2)

• apps/web/src/components/ChatView.tsx
• apps/web/src/components/chat/ChatHeader.tsx

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