{"body":"## Summary\n\n- Keep Info and Diff fixed.\n- Add a trailing pane-edge `Remove split` button only while the right panel has multiple panes.\n- Rehome every tab into the surviving pane without invoking the tab close callbacks.\n- Confine tab-split drag targets to the right panel; the web workspace no longer accepts right-panel tab drops.\n\n## Product decision\n\nInfo and Diff remain fixed. Making them closeable would change Cmd+W, Cmd+D, mobile, and persisted-layout behavior. This layer instead preserves the existing two-action model: the tab-pill × closes a closeable tab, while the pane-edge × removes a split without closing its tabs.\n\n## Before\n\nThe fixed Info and Diff panes had no remove-split affordance.\n\n![Before: fixed split without remove controls](https://raw.githubusercontent.com/get-bb/bb/aeb1c3ca65c6417596a88f8833f2fd26b605f1e7/exact/layer1-before-fixed-split.png)\n\n## After\n\nEach split pane exposes a keyboard-focusable, trailing `Remove split` button; no control is present after the layout returns to one pane.\n\n![After: fixed split with trailing remove controls](https://raw.githubusercontent.com/get-bb/bb/aeb1c3ca65c6417596a88f8833f2fd26b605f1e7/exact/layer1-after-remove-controls.png)\n\n## Validation\n\n- Regression coverage: split-only visibility, accessible naming, native-button Enter/Space activation, tab preservation, focus/selection semantics, tab-close independence, and in-panel/out-of-panel drag targeting.\n- Real web flow: mouse and keyboard split creation/removal, closeable tab close behavior, right-panel tab reorder, right-panel split drop, and rejected main-content drop.\n- Real Safari 26.5.2 flow: keyboard-created fixed Info/Diff split, two focusable `Remove split` buttons, Enter removal, and both fixed tabs preserved after unsplitting.\n- `pnpm exec turbo run test --filter=@bb/app --force -- --run ...` — 9 files, 159 tests passed across the stack.\n- `pnpm exec turbo run typecheck --filter=@bb/app` — passed.\n- `pnpm exec turbo run lint --filter=@bb/app` — 0 errors; existing warnings only.\n\nCloses #2450\n\nBB-Thread-ID: thr_q8degf2y66\n\n> AGENT GENERATED: by GPT-5.6-Sol\n","commits":[{"authoredDate":"2026-08-26T06:01:43Z","authors":[{"email":"brsabel.t@gmail.com","id":"MDQ6VXNlcjU3NjgyMDM4","login":"brsbl","name":"Bersabel Tadesse"}],"committedDate":"2026-08-26T14:24:31Z","messageBody":"","messageHeadline":"Fix right-panel split removal and drop 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