fix: don't resurrect completed sub-agents from history rescan (v0.2.4)

[psh4607]

Summary

• Bug: After plugin load or TUI restart, the sidebar briefly displays phantom rows like `explore Done 1230m 35s` / `librarian Done 1231m 29s` for sub-agents that ran in earlier turns, before retention prunes them.
• Fix: `upsertToolPart` and `handleBackgroundStatusText` no longer resurrect entries when no in-flight tracking exists.
• Bumped to v0.2.4.

Root cause

`scanSessionState` re-walks every message part of the session on every reactive tick (it's invoked from inside the panel's `insert(...)` accessor, which depends on `now()` and `version()`). It was designed to bootstrap state on plugin load.

For a background tool part already in `status: "completed"` — meaning the launch finished before this scan ran — we never observed the prior `pending` / `running` events. The old code did three things in sequence on rescan:

1. `upsertToolPart` (status="completed", isBackground=true): no existing entry → unconditionally created one with `status: "running"` and `startedAt = part.state.time.start` (potentially hours old).
2. On the next tick `handleBackgroundStatusText` matched the same message's `[BACKGROUND TASK COMPLETED]` / `[ALL BACKGROUND TASKS COMPLETE]` system reminder text.
3. It called `completeEntry(entry, "completed", completedAt)` with `completedAt = Date.now()` (system reminders have no `time` field, so the fallback chain landed on the current time).

Result: `elapsed = Date.now() - startedAt` ≈ 1230 minutes. The v0.2.3 "stamp once" fix kept the row from getting worse, but the very first stamp itself was bogus on history rescans.

Why early-return is safe

Live launches deterministically pass through `pending` → `running` → `completed`. By the time a `status: "completed"` event is observed live, the entry is already in the `active` map (created by the `pending` / `running` branch a few hundred ms earlier). The only path that hits "`completed` with no existing entry" is a history rescan, where the entry has no business existing on the sidebar in the first place.

The same reasoning applies to `handleBackgroundStatusText`'s prior fallback that fabricated a row from an `[ALL BACKGROUND TASKS COMPLETE]` summary line alone.

Change

```diff
const bgKey = makeKey("background", bgID);
const promoted = active.get(bgKey);
if (promoted) return touchEntry(promoted, agent, description);
-active.set(bgKey, {

• key: bgKey,
• sessionID,
• kind: "background",
• agent,
• description,
• status: "running",
• startedAt,
• bgID,
• callID,
  -});
  -return true;
  +// Live launches always pass through pending/running before reaching
  +// completed, so observing status="completed" with no in-flight entry
  +// means scanSessionState is replaying a historical message. Resurrecting
  +// here would stamp startedAt to part.time.start (potentially hours old)
  +// and let handleBackgroundStatusText finalize completedAt = Date.now()
  +// on the next tick, producing a spurious "Done 1230m" row before
  +// retention prunes it.
  +return false;
  ```

Verification

• `bun run typecheck` ✅
• `bun run build` ✅ (dist/ regenerated)
• LSP diagnostics clean on `src/tui.ts`
• Foreground completed branch already had the same `if (!existing) return false` guard, so no symmetric change needed there.

Files changed

• `src/tui.ts` — fix + version bump
• `package.json` — 0.2.3 → 0.2.4
• `dist/tui.js`, `dist/tui.js.map`, `dist/tui.d.ts.map` — regenerated build output

Related

• Follow-up to fix: freeze elapsed timer for completed entries + 3s retention (v0.2.3) #1 (v0.2.3) — that PR froze re-stamping; this one prevents the bogus first stamp.

[Copilot]

Pull request overview

Fixes a sidebar UI bug where completed background sub-agents could be temporarily “resurrected” during session history rescans (e.g., after plugin load / TUI restart), causing phantom “Done 1230m” rows until retention pruning removed them.

Changes:

• Prevent upsertToolPart from creating a new background entry when it observes status="completed" without any in-flight tracking entry (treat as historical replay).
• Prevent handleBackgroundStatusText from fabricating completed background entries from summary reminder text when no in-flight entry exists.
• Bump plugin/package version to v0.2.4 and regenerate dist/ outputs.

Reviewed changes

Copilot reviewed 2 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/tui.ts	Adds guards to avoid resurrecting historical completed background entries during rescans; bumps plugin version constant.
package.json	Version bump to 0.2.4.
dist/tui.js	Regenerated build reflecting the rescans/guard changes and version bump.
dist/tui.js.map	Regenerated sourcemap output.
dist/tui.d.ts.map	Regenerated types sourcemap output.

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