[marksftw]

Stacked on #1282 (Search), which builds on #1236 (rail/header).

Animate sidebar collapse and expansion over 200 ms while keeping the single sidebar toggle fixed beside the window controls. New task, Search, the divider and title spacing follow the transition. Reversing direction continues from the current position; reduced-motion settings switch layouts immediately.

Keep Settings visible throughout the transition and in both settled layouts, centered within the 48 px collapsed rail. Search keeps its existing command/focus behavior; Settings has its own keyboard tab position. Existing endpoint tests opt into reduced motion so their layout assertions remain immediate.

Sync with current master preserves the new draft-attachment/upload state alongside the sidebar animation state. No attachment behavior is changed by this PR.

Validation (2026-10-26): the prior combined stack at 1bdec838 was manually tested and approved. After syncing onto d35ea98d, the pinned Agent Dev debug build passed (9m 21s), with development attestation and hosted Dev API/billing settings.

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[marksftw]

Stack 1 UI testing completed on October 26, 2026.

Manual UI testing: passed. The refreshed Dev build was manually tested and approved by the human tester.

Automated computer-use UI testing: passed for the scoped Stack 1 flows. Codex drove the native app through pointer and keyboard interactions and verified results with screenshots and accessibility observations.

Tested the combined stack #1236 → #1282 → #1248, at eeb75093b7979a553c6637000d5d4c61967d1423 (this PR's current head). The lower heads were #1236 b8bfdd13 and #1282 902e891c. Individual layers were not launched separately. Environment: macOS, Maple Work Debug 0.0.8, hosted Dev API/billing, native attestation PCR development. The pinned Agent Nix build succeeded.

Coverage relevant to this PR passed:

• Repeated collapse/expand reversals and Cmd-B; the toggle retains its fixed screen position.
• Settings stays visible in both layouts and centered in the collapsed rail; pointer and keyboard/Space activation work.
• Collapsed Tab navigation through the rail mark, toggle, New task, Search and Settings, without submitting the draft.
• Unsent text and a synthetic 53-byte attachment survive toggles, Search and a Settings round trip.
• Cross-stack checks: all Search entry points, filtering/result navigation, two-step Escape and composer focus restoration, context menus, popup dismissal on collapse, long-title truncation, and a disposable Dev chat returning the expected response.

The synthetic attachment was removed before sending the separate QA prompt. The QA task was archived, Search cleared, and the original window size restored.

Out-of-scope observations for possible future issues

These are retained separately from this stack's acceptance scope. Source evidence suggests they may predate this stack; no running baseline comparison was performed. No issues have been opened.

1. Narrow-window composer clipping. Resize to approximately 1706×1204 screenshot pixels and expand the sidebar. In both new-task and conversation views, the composer right edge and Send button extend beyond the window. Collapsing restores visibility. Expected: controls stay visible at supported widths.
2. Cached sidebar accessibility omission. Expand the sidebar or activate Search, then inspect native AX after a cached redraw. Visible task/sidebar controls and open task menus can disappear from AX, making exposed element actions stale; screenshot-coordinate interactions still work. Expected: visible controls retain their accessibility nodes. Source review points to pinned GPUI cached-view AX replay.

No unit/integration suites or test-running hooks ran. Light appearance, OS reduced motion, VoiceOver, large/deeply scrolled lists, other platforms, actual attachment sending and release frame-time performance were not exercised.

[AnthonyRonning]

Reviewed at eeb75093b7979a553c6637000d5d4c61967d1423. The bounded, reversible sidebar transition honors reduced motion and preserves cached sidebar ownership. The always-visible Settings control reuses the existing Settings path and adds no persistence contract.

No substantive blockers found. Hosted Agent CI passed, and the combined stack passed the local human smoke test, including Vim mode.

The merge-base changed after approval.