Fix thread timeline autoscroll and simplify branch state

[juliusmarminge]

Summary

• Fix timeline autoscroll so the first non-message rows are included in the scroll target.
• Simplify branch and environment-mode handling by removing temporary override paths and stale branch sync logic.
• Tighten editor and branch detection behavior, including dropping Kiro-specific paths and temporary worktree branch handling.
• Update timestamps and toolbar labels to use the current thread state consistently.

Testing

• Not run (PR description drafted from the committed changes).
• Relevant coverage was updated in unit and browser tests across server and web components.
• Project checks required by repo policy: bun fmt, bun lint, and bun typecheck should pass before merge.

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Note

Medium Risk
Adjusts chat timeline empty-state and autoscroll behavior; small but user-visible changes to scrolling could introduce regressions in when the list pins to bottom.

Overview
Fixes MessagesTimeline empty-state handling by removing the hasMessages prop and instead treating the timeline as empty only when there are no rendered rows (so non-message activity rows no longer show the placeholder).

Adds an effect that detects the transition from 0 → >0 rows and forces an immediate snap-to-bottom (requestAnimationFrame + scrollToEnd) while updating onIsAtEndChange, and introduces a new browser test (MessagesTimeline.browser.tsx) covering both the activity-row empty-state case and the 0 → >0 autoscroll behavior.

^{Reviewed by Cursor Bugbot for commit 2666adb. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Fix thread timeline autoscroll when first rows appear in MessagesTimeline

• MessagesTimeline now snaps to the bottom (non-animated) and sets isAtEnd to true when rows first appear after an initially empty render, using a useRef/useEffect to detect the 0→N rows transition and requestAnimationFrame to schedule the scroll.
• Removes the hasMessages prop from MessagesTimeline; empty-state is now derived from rows.length === 0 internally instead of being passed from ChatView.
• Adds browser-based vitest tests in MessagesTimeline.browser.tsx covering the empty placeholder behavior and the autoscroll transition.

^{Macroscope summarized 2666adb.}

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[macroscopeapp]

Approvability

Verdict: Approved

Straightforward bug fix that adds autoscroll behavior when timeline entries first appear after an empty state, with a minor simplification removing a redundant prop in favor of an internal length check. Changes are well-scoped, include proper cleanup, and are covered by new tests.

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