[matt2e]

Summary

Closing a routed panel tab calls history.go(-1) to retire its visit, and that return lands on a later popstate. Until it lands, the navigator still shows the closing visit, but the opener already has focus. If a Profile was reopened from the opener in that window, it was hidden when the return arrived, because entering the channel visit restored that visit's saved selection. This PR treats a reopen made before the return lands as superseding the close, so the panel stays open with a fresh visit of its own.

fix(channels): keep a panel reopened before its close's return lands

Problem

Two WebKit journeys lost a Profile that was reopened right after its tab closed. Both failed on attempt 1 on unrelated branches, and the same SHA passed on rerun.

• profiles.spec.mjs:321 "profile plumbing: exact avatar/mention targets, thread enrichment, lifecycle and recovery", branch peon/participant-collator, run 41752442750 (webkit 13/14): https://github.com/block/buzz-app/actions/runs/41752442750/job/126320885261. After the Mic tab closed, Space on the focused mention never reopened the Profile, and the test failed at :479.
• solo-workspace.spec.mjs:159 "Solo chat Activity opens the agent's profile locally, restores per conversation and retires on plugin disable", branch peon/dnd-stable-transform, run 41757728323 attempt 1 (webkit 5/14): https://github.com/block/buzz-app/actions/runs/41757728323/job/126338025674. After the agent's Profile closed, Enter on the focused Activity trigger never brought back "Profile details".

Cause

• Closing a routed panel tab removes it locally. dismissContent then calls navigator.dismiss. The browser driver retires the visit and calls history.go(-1), which lands on a later popstate. Until then the navigator still shows the retiring visit, while afterClose has already focused the opener.
• A reopen in that window runs open() and then visitPanel. visitPanel sees the navigator already on that Profile's detail, so it doesn't navigate. When the return lands, the route effect enters the channel visit, and enterVisit restores that visit's saved selection, which hides the reopened panel. Reopening a different panel pushes its visit on top of the retiring one, and the late return then removes it.
• Both traces show this sequence:
  • Profiles run: the close finished at 80128 ms and Space ran at 80148–80193 ms with the URL still on Mic's detail. By 80383 ms the URL was the channel and the dock was closing.
  • Solo run: the close finished at 251783 ms and Enter ran at 251808–251872 ms. By 251999 ms the URL was the channel and the dock was hidden.
• The dock isn't the cause. PanelDock keeps a reopened subtree through its exit (PanelDock.test.tsx).

Fix

• When a dismissal retires the current visit and the navigator hasn't moved yet, dismissContent records a pending return. A synchronous driver or a replacing dismissal moves the navigator at once, so neither records anything.
• While that return is pending, visitPanel records the panel as the reopen instead of navigating.
• When the return lands on the dismissal's fallback, the route effect checks whether that panel is still selected. If it is, the effect reselects and opens it, which gives it its own visit. If the panel has closed again, or the return landed somewhere else, nothing is revived.
• A later close before the return lands, such as closing the thread beneath a closed Profile, moves where the return lands. The record follows the latest fallback and keeps the reopen.
• While the return is pending, the route effect no longer reapplies the retiring visit's detail. Otherwise a re-render could reopen the panel that was just closed.
• Two new cases in profiles.spec.mjs hold history.go and pause the dock's exit while a Profile closes. One reopens Mic by click and by Space. The other closes a thread's Profile and then the thread, and opens Mic. Each asserts that the Profile shows while the return is held, the navigator stays on the closed visit with exactly one return held, a fresh Mic visit lands after the release, and Back returns to the channel and closes the panel.

The existing journeys are unchanged, and no assertions are loosened.

Residual limit

Thread and other explicit navigation during a pending return is not deferred, so a late return can still undo it. #2113 lists the same limit.

Validation

Local Linux workstation, Playwright 1.63.0, --no-deps --retries=0:

• New cases without the fix: 4/4 failed. The reopen case failed at :406 (no fresh visit). The thread case failed at :442, with the click stacking a visit on the closed one. With the fix but without the latest-fallback step, the thread case failed 2/2 at :452. With the fix, all pass.
• Adversarial ordering, with temporary changes that delayed history.go calls from click or key handlers by 250 ms, 6 repeats per engine:
  • Without the fix: 9/24 failed, seven with the CI signatures.
  • With the fix: 24/24 passed, twice.
• Natural contention, with 4 CPUs shared with 4 busy loops, 2 workers and 10 repeats per engine: 40/40 passed with the fix.
• The 38 browser specs that close panel tabs, both engines: all passed at 6 workers. At 12 workers, 42 failed on timeouts because the test server had stopped serving under load, and those 42 passed on rerun.
• Vitest for channels, panels, navigation and channel-navigation: 87 files, 1539 tests passed.
• Rebased on main f4805605f5:
  • tsc --noEmit, biome check --error-on-warnings on the changed files and git diff --check are clean.
  • Vitest src/bundled/channels: 61 files, 1097 tests passed.
  • profiles.spec.mjs and solo-workspace.spec.mjs in full, WebKit and Chromium, --workers=4 --retries=0: 48/48 passed.

A green run doesn't prove the flake is gone. Hosted CI covers broad validation.

Coordination

• fix(people): open profiles from Solo Share access and "N others" lists #2415 (open) rewrites the same route effect in ChannelsPage.tsx around a dismissalReturn record. Its head 9555c2ed conflicts textually with this branch. Whichever PR lands second should fold this PR's pending reopen, and the guard against reapplying the retiring visit's detail, into the other's record.
• fix(channels): restore panel opener focus after history returns #2113 (open) restores panel opener focus after history returns. It doesn't overlap these hunks, its head merges cleanly with this branch, and it lists the same residual limit described above.
• Draft feat(channels): restore tab workspaces across refresh #1793 (stale since 2026-10-29) also edits ChannelsPage.tsx, and its head conflicts textually with this branch.

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