Give drag feedback a native Liquid Glass appearance (v2)#86

Draft type: visual design and implementation. Source: feedback point 10. Release scope: v2.

What to build

Replace the visually separate drag-placement line with feedback that uses a native Liquid Glass appearance. Keep the insertion target clear while matching macOS materials, transitions, and interaction behavior. Use this drag interaction as the first bounded improvement toward Sam's broader native UI goal.

Acceptance criteria

• Use native macOS materials and documented drag feedback conventions while preserving the existing placement behavior.
• Distinguish insertion into a stack from creation of a new column.
• Keep valid, refused, and cancelled drops visually understandable.
• Use a consistent native appearance in light and dark modes, with screenshots or recordings in the PR.
• Remain legible with Reduce Transparency, Increase Contrast, and Reduce Motion enabled.
• The indicator does not steal focus, intercept the drag, or remain after the drag ends.
• Preserve placement accuracy and interaction responsiveness across each connected display.
• Record other UI, animation, and behavior inconsistencies as bounded follow-up tickets.

Verification

Inspect real title-bar drags over light and dark application content on each connected display. Check stack insertion, new columns, refused drops, cancellation, and display boundaries. Compare recordings before and after the change.

Related work

Issue #43 defines drag placement behavior. This draft changes its presentation while preserving that behavior.

Blocked by

None for implementation once the existing drag interaction is available to reproduce and verify. Routine material, radius, and transition choices belong to the implementing agent. Changing drop semantics, permissions, or accepted accessibility behavior requires a separate product decision.