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#2450 · Split right-panel panes have no close action when their only tab is fixed

Bug Priority: Medium Effort: Low–Medium ui open on GitHub 2026-08-27 · base ad79bbb5ec909524f8f281e62d860c588a86f332

Verdict: REPRODUCED · Root-cause confidence: high

1. TL;DR

A user can put the fixed Info and Diff tabs in separate right-panel panes. Neither pane then has a direct remove action. The fixed tabs also have no tab-close action. The layout has no transition that removes a nonempty pane and keeps its tabs.

The browser reproduction showed two panes and zero direct pane controls. PR #2486 adds the required layout transition and a button for each pane.

2. Claims vs findings

3. Environment

• bb base commit: ad79bbb5ec909524f8f281e62d860c588a86f332.
• OS: Ubuntu Linux, kernel 7.0.0-30-generic, x86-64.
• Node: v24.18.0, ABI 137.
• Browser: Headless Chrome 152.0.7977.64, viewport 1440 × 900.
• Provider used for the fixture thread: Codex CLI 0.150.1.
• App: http://localhost:13242. Server: http://localhost:21242. Host daemon: 29242.
• Data directory: /home/sawyer/.bb-dev/bb-report-worktrees-bb-report-2450-revise-bnt2t7-0f0733c24d86.

4. Minimal reproduction

Prerequisites: Use Node v24.18.0 with ABI 137. Install pnpm, Git, curl, and Codex.

1. Run these commands from the base checkout. They create a private app instance and a scratch repository.

   test "$(node --version)" = "v24.18.0"
   test "$(node -p 'process.versions.modules')" = "137"
   pnpm install --frozen-lockfile --prefer-offline --package-import-method=copy
   pnpm exec turbo run build
   export BB_DEV_NODE_BIN_DIR="$(dirname "$(command -v node)")"
   export npm_config_package_import_method=copy
   scripts/bb-dev-app current
   eval "$(scripts/bb-dev-app env)"
   
   qa_repo=$(mktemp -d /tmp/bb-2450-repro-XXXXXX)
   git -C "$qa_repo" init -q
   git -C "$qa_repo" config user.name "Issue 2450 QA"
   git -C "$qa_repo" config user.email "qa@example.invalid"
   git -C "$qa_repo" commit --allow-empty -qm "fixture"

2. Select the connected isolated host. Then create the project through the isolated server.

   machine_json=$(node packages/scripts/dist/commands/run-cli.js machine list --json)
   host_id=$(printf '%s' "$machine_json" | node -e '
   let s="";
   process.stdin.on("data", d => s += d).on("end", () => {
     const host = JSON.parse(s).find(h => h.status === "connected");
     if (!host) process.exit(1);
     process.stdout.write(host.id);
   });')
   payload=$(node -e '
   process.stdout.write(JSON.stringify({
     name: "Issue 2450 QA",
     source: { type: "local_path", path: process.argv[1], hostId: process.argv[2] },
   }));' "$qa_repo" "$host_id")
   project_json=$(curl -fsS -X POST "$BB_SERVER_URL/api/v1/projects" \
     -H 'content-type: application/json' --data "$payload")
   project_id=$(printf '%s' "$project_json" | node -e '
   let s="";
   process.stdin.on("data", d => s += d).on("end", () => {
     process.stdout.write(JSON.parse(s).id);
   });')

3. Create the fixture thread. Wait for it. Then print its local URL.

   thread_json=$(node packages/scripts/dist/commands/run-cli.js thread spawn \
     --project "$project_id" --environment "$qa_repo" --provider codex \
     --permission-mode accept-edits --title "Issue 2450 QA" \
     --prompt "Reply only with ok." --json)
   thread_id=$(printf '%s' "$thread_json" | node -e '
   let s="";
   process.stdin.on("data", d => s += d).on("end", () => {
     process.stdout.write(JSON.parse(s).id);
   });')
   node packages/scripts/dist/commands/run-cli.js thread wait "$thread_id" \
     --status idle --timeout 120000
   app_url=$(scripts/bb-dev-app status | sed -n 's/^App: //p')
   printf '%s/projects/%s/threads/%s\n' "$app_url" "$project_id" "$thread_id"

   The run printed Thread thr_pzp45wdan7 reached status idle. It printed a URL under http://localhost:13242.

4. Open the printed URL. Then open the right panel if the app hides it.
5. Drag the fixed Diff tab into the panel body.
6. Release the tab on the Split bottom target.
7. Inspect the visible controls or run this browser-console check.

   ({
     panes: document.querySelectorAll('[data-split-pane-id]').length,
     closePane: document.querySelectorAll('[aria-label="Close pane"]').length,
     removeSplit: document.querySelectorAll('[aria-label="Remove split"]').length,
     tabClose: document.querySelectorAll('[aria-label^="Close "]').length,
     hidePanel: document.querySelectorAll('[aria-label^="Hide right panel"]').length,
   })

Expected:

{ panes: 2, removeSplit: 2 }

Actual:

{ panes: 2, closePane: 0, removeSplit: 0, tabClose: 0, hidePanel: 1 }

Regression test

The test saves a fixed-tab split. It then requires one direct action for each pane.

expect(document.querySelectorAll("[data-split-pane-id]")).toHaveLength(2);
expect(
  screen.getAllByRole("button", { name: "Remove split" }),
).toHaveLength(2);

Copy the report artifact into the checkout. Then run it from apps/app.

cp /home/sawyer/.bb/reports-work/issues/2450/repro/issue2450.repro.test.tsx \
  apps/app/src/components/secondary-panel/issue2450.repro.test.tsx
cd apps/app
pnpm exec vitest run src/components/secondary-panel/issue2450.repro.test.tsx

Base result:

Test Files  1 failed (1)
Tests       1 failed (1)
Unable to find an accessible element with the role "button" and name "Remove split"
src/components/secondary-panel/issue2450.repro.test.tsx:94:14
exit_code=1

Repro files: test, base log, and browser checks.

5. Root cause

The split feature added pane creation, tab movement, and empty-pane cleanup. It did not add a direct nonempty-pane removal action.

Fixed tabs receive select and drag actions only. They receive no close action in ThreadSecondaryPanel.tsx.

Each split pane also sets onRequestClose to null in SidebarSplitContainer.tsx.

The layout can remove a pane only after its group becomes empty. The guard rejects all nonempty groups in sidebarSplitLayout.ts.

A fixed-only pane never becomes empty through the user interface. Therefore, the three contract choices create the dead end.

6. Proposed fix (first principles)

1. Add a layout action that removes one pane without closing its tabs.
2. Move each removed tab into the focused survivor.
3. Keep the removed pane selection when the removed pane had focus.
4. Keep the survivor selection when another pane had focus.
5. Show one keyboard-focusable Remove split button for each pane only when a split exists.
6. Keep the fixed Info and Diff tab rules unchanged.

This is an app-only state change. It does not change a server or host-daemon message. It needs no protocol-version increase.

7. PR review

#2486 · Fix right-panel split removal and drop bounds

Verdict: MERGE. The PR fixes the root cause and keeps fixed-tab behavior unchanged.

Detailed evidence: PR regression log, merged validation log, and PR data.

8. Related issues

• #1841 added the right-panel split feature. It did not specify a direct pane-remove action.
• #1337 concerns moves from the sidebar into the main view. It does not cover this control gap.

9. Appendix

• All principal commands
• Raw issue data
• Regression test source
• Base regression test log
• PR regression test log
• PR merged validation log
• Browser state checks
• Screenshot PNG

Verification

The verifier found that the old browser steps lacked a fixture. The old test command also lacked the linked file.

This revision created a scratch Git repository, a project, and a Codex thread in a fresh isolated instance. A real pointer drag reproduced the split. A second pointer drag verified the center-drop workaround.

This revision also copied the linked test into the stated source path. The exact command failed at line 94 with exit code 1.