fix(web): keep floating preview anchored after panel closes

[AksharP5]

What Changed

Closing the side panel no longer leaves an untouched floating preview near the middle of the chat. It stays anchored to the top-right corner. Previews that the user moved still keep their explicit position.

Validated with the focused preview-layout tests, the web typecheck, targeted lint, and an integrated before/after pass.

Why

When the side panel narrows the chat, the layout observer converts the preview's default right-anchored position into an explicit left coordinate. Closing the panel then reuses that coordinate in the wider layout.

The default position now stays responsive until the user moves the preview. The initial placement also uses the existing shared edge-gap value.

Fixes #6546

UI Changes

Before

floating-preview-panel-close-before-omarchy.mp4

After

floating-preview-panel-close-after-omarchy.mp4

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

Built with GPT-5.6-Sol via the Codex harness.

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Note

Low Risk
Scoped UI behavior in the preview mini player; no auth, data, or API changes.

Overview
Fixes the floating thread preview drifting away from the top-right when the right panel closes after layout changes.

The resize observer no longer calls move when there is no stored user position—it only clamps size and bumps a defaultLayoutVersion keyed on parent dimensions so BrowserSurfaceSlot still relayouts. User-moved previews still get position clamping on resize.

Default placement now uses PREVIEW_MINI_PLAYER_EDGE_GAP instead of hardcoded 16px. Resize drag seeds position from the player’s offset at pointer-down (playerX/playerY) rather than position ?? offsetLeft, avoiding accidental persistence of layout-derived coordinates.

^{Reviewed by Cursor Bugbot for commit a356052. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Fix floating preview mini-player anchor position after panel closes

• When no saved position exists, ThreadPreviewMiniPlayer now records the offset parent's dimensions and skips moving based on DOM offsets, preventing positional jumps when a panel closes.
• On resize start, the handler captures the player's coordinates relative to its offset parent and uses those for position clamping during the drag, rather than potentially stale DOM offsets.
• The default top/right inset now uses PREVIEW_MINI_PLAYER_EDGE_GAP instead of a hardcoded 16.
• BrowserSurfaceSlot layoutVersion now includes parent dimensions when position is unset, so a relayout triggers when container size changes.

^{Macroscope summarized a356052.}

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[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 2 potential issues.

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[macroscopeapp]

Approvability

Verdict: Approved a356052

Self-contained UI positioning fix for a floating mini-player component. Changes are isolated to visual layout behavior with no broader runtime implications.

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[CDVolvik]

Default layout used offsetLeft/offsetTop when the store had no position, so closing the side panel jumped the floater. Capturing playerX/Y from bounding rects at resize-start, and versioning the overlay with parent size, is the right clamp.

PREVIEW_MINI_PLAYER_EDGE_GAP replaces the magic 16. MERGEABLE. No test file in the diff.