feat(solo): smooth chat recency reordering - #3502

Overview

Category: improvement
User Impact: Solo chats move between recent-activity positions with the same short slides and fades as Team channels.

Problem: Activity-sorted Solo chats jump abruptly when another conversation becomes active, making it difficult to follow a row.

Solution: Reuse the existing channel sidebar motion for each Solo workspace's chat list. Nearby moves slide, distant moves fade at their endpoints, and reduced motion applies the new order immediately.

Changes

Coverage audit

Production is +28/−14 lines ignoring indentation (+71/−57 including the wrapped row map); help adds two lines. The current test total includes the +12/−5-line adaptation of existing rename journeys and a +50-line lifecycle regression update: ten lines extend the existing conversion case, and one 40-line journey covers native focus handoff with both motion preferences and the no-steal guard. The earlier consolidation reduced duplicate motion executions from four to two; the focus regression adds two distinct engine executions. The two component cases exercise different host compositions. Shared controller tests already cover batching bounds, cancellation, removal/reappearance and media-subscription teardown; this port does not duplicate those cases.

Removed assertion mapping:

• Duplicate nearby/distant order, identity and focus checks remain in the single motion-enabled browser journey.
• Reduced-motion “no transform, no fade, immediate order” moves to a live preference change in that journey. A frozen clock prevents a delayed animation from passing as immediate; standalone/combined component cases retain the pending-batch flush contract. Existing channel browser coverage retains startup reduced motion.
• The distant row's zero-translation check remains alongside its endpoint geometry check. Nearby siblings may still slide into their slots.

The five-chat fixture is the minimum used here to express a greater-than-two-slot distant move. No existing browser journey was removed, no engine was skipped, and no assertion tolerance or timeout was relaxed.

Validation

• Hosted CI run 43498574843 passed at 75beb4f7a38ae60e7883fcb6c70964c748a8c3a4, including CI required, DCO, all Chromium/WebKit journeys and flake checks. Windows native validation was skipped by the existing workflow.
• At 75beb4f7a38ae60e7883fcb6c70964c748a8c3a4, mandatory pre-commit and pre-push checks passed: TypeScript/related units (33.12 s), design types/guards (6.31 s), and scope/policy gates. The untouched Rust lane correctly skipped.
• Chromium and WebKit: all 20 executions in the existing Solo chat journey file passed after mainline integration; both executions of the consolidated motion journey passed with the final test source. Production sources match the published head in both runs.
• Falsifiability: removing the Solo wrapper fails both host component cases; removing active-copy filtering fails the workspace-move focus assertion. In an isolated checkout, disabling the production reduced-motion gate makes both engines fail the consolidated journey's frozen-clock immediate-order assertion.
• The complete rename file passes all 24 Chromium/WebKit executions with the final 75beb4f7a38ae60e7883fcb6c70964c748a8c3a4 source. The original CI rename failure reproduced in both engines before the selector repair; a conversion followed immediately by another rename also exposed a missing actual-unmount boundary. Both preserve their full original assertions.
• Browser cases added relative to main: 2 journeys / 4 engine executions. Existing cases removed: 0. Both engines and the original geometry tolerance remain enabled.

The initial CI repair changed tests only. Both previously failing WebKit shards now pass; toolbar code and its geometry tolerance remain unchanged. Native/human acceptance, a complete theme/width/text-scale inspection and fresh performance profiling remain unverified.

Exit lifecycle validation

• Rename draft discard: the changed-draft conversion probe failed in Chromium and WebKit at 75beb4f7a38ae60e7883fcb6c70964c748a8c3a4, each recording an unwanted signing request. The presence guard prevents both signing and publication.
• Focus handoff: both engines failed the new native-focus journey before the presence-aware cleanup. The fixed journey covers handoff to the surviving selected chat and preserving focus moved to the composer, with normal and reduced motion in the same mounted app.
• At clean acfd1ce3cb947f4a3b1b16a55e887c0850c00b02, all 26 executions of the complete solo-rename.spec.mjs file passed in Chromium and WebKit (36.6 s total runner time). Mandatory push gates passed: TypeScript/related units (32.41 s), design types/guards (5.93 s), and policy gates; unchanged Rust inputs correctly skipped Clippy. Hosted CI for this new head is pending; the earlier green run above applies only to 75beb4f7a3.

Reproduction

1. Open Solo with several chats listed in a workspace. Cause activity in a chat one or two slots below the top: it should slide into its new position without scaling, fading or losing keyboard focus.
2. Cause activity in a chat more than two slots away: it should fade between its endpoints rather than sweep across the list.
3. Enable reduced motion while the app is open, then cause more activity: the order should update immediately.

Additions/removals retain the controller's existing row fades, while neighboring rows reflow immediately. Creating/removing the first/last unfiled chat mounts/unmounts the whole Chats section and still bypasses the row fade; this PR does not expand that behavior.

Screenshots / demos

The selected Solo chat slides up one position after new activity.