Extract independent web cleanup from mobile stack

[t3dotgg]

Summary

• Extract independent web correctness fixes and small UI/performance cleanups from T3 Code Mobile [WIP] #2013.
• Preserve zero-usage context snapshots, avoid oversized LRU entries, and make thread ordering robust to invalid timestamps.
• Keep the mobile/client-runtime PR focused on platform, runtime, and protocol changes.

Validation

• bun fmt
• bun lint (passes with existing warnings)
• bun typecheck
• bun run test --filter=@t3tools/web --filter=@t3tools/shared

Stack

• This PR -> main
• T3 Code Mobile [WIP] #2013 -> this PR after restack
• feat(cloud): Add managed relay tunnels and APN service #2837 -> T3 Code Mobile [WIP] #2013

Note

Fix thread sorting, LRU cache, and context window snapshot handling in web app

• deriveLatestContextWindowSnapshot in contextWindow.ts now accepts usedTokens === 0 as valid instead of skipping it.
• LRUCache.set in lruCache.ts rejects entries whose size exceeds the memory budget, preserving any existing entry for that key.
• Thread sorting in threadSort.ts now falls back to the first valid timestamp when createdAt or updatedAt is invalid.
• ChatHeader in ChatHeader.tsx is made responsive, wrapping and truncating on small screens.
• Several Array.includes membership checks are replaced with Set.has in ChatView.tsx and OpenInPicker.tsx.

^{Macroscope summarized 3ca1460.}

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Note

Low Risk
Targeted client-side logic and styling with added unit tests; no auth, API, or protocol changes.

Overview
This PR pulls web-only correctness and polish out of a larger mobile stack: behavior fixes, small performance tweaks, and responsive UI adjustments—without platform/runtime protocol work.

Data & sorting: deriveLatestContextWindowSnapshot now accepts usedTokens === 0 so empty usage still shows in the composer. LRUCache.set skips entries larger than the memory budget and leaves existing keys intact on oversized updates. sortThreads / getThreadSortTimestamp use getFirstSortableTimestamp so invalid ISO dates fall back (created_at → updatedAt, and the reverse where needed).

State & attachments: uiStateStore dedupes persisted project order and per-logical-key cwd lists with **Set**s. handoffAttachmentPreviews and OpenInPicker use Set membership instead of Array.includes.

UI: ChatHeader stacks on narrow viewports (title, badge, actions). Sidebar thread rows are slightly shorter on mobile; remote cloud icon and thread list padding are toned down.

Tests: New coverage for zero-usage context snapshots, LRU oversized entries, thread sort fallbacks, and stable trace file ordering in shared observability tests.

^{Reviewed by Cursor Bugbot for commit 3ca1460. Bugbot is set up for automated code reviews on this repo. Configure here.}

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[macroscopeapp]

Approvability

Verdict: Approved

Low-risk cleanup PR containing mechanical performance optimizations (Array.includes → Set.has), minor responsive CSS tweaks, and small bug fixes with accompanying tests. All changes are self-contained with clear intent.

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