FA-35905 / Tab interfaces / Member archive

Collapse empty pane: active pane transfer · case 05

The tab workspace reports an incorrect active pane transfer.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

A pane disappears only after its last tab closes; promote its sibling subtree, remove the separator, transfer active-pane ownership and retain sibling extent.

Why this case matters

Offline tab/panel workspace behavior; no browser or desktop framework is emulated.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
workspace regression 0	`[true, false, "q", 40, "p", 2540]`	`[true, false, "q", 40, "q", 2540]`	Failed

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This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

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