fix(agent-manager): clear stale child activity

[marius-kilocode]

What Problem This Solves

Agent Manager worktrees could remain In Progress after a background child completed while another project was active.

Why This Change Was Made

Released child sessions were removed from active tracking before their terminal status reached the owning project provider. The provider now retains bounded ownership for running children and accepts only matching terminal status events.

User Impact

Completed background worktrees show their green completion badge instead of a stale running indicator. Unrelated project events remain filtered.

Evidence

• Reproduced the issue on the installed snapshot with a real two-project background-agent flow.
• Repeated the same flow with this fix and observed the green completion badge.
• Full extension unit suite: 4,724 passed, 1 skipped.
• Typecheck, lint, build, Knip, and merge-marker checks passed.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (4 files)

• .changeset/fix-stale-worktree-status.md
• packages/kilo-vscode/src/KiloProvider.ts
• packages/kilo-vscode/tests/unit/kilo-provider-followup.test.ts
• packages/kilo-vscode/tests/unit/kilo-provider-load-messages.test.ts

Previous Review Summary (commit d842b97)

Current summary above is authoritative. Previous snapshots are kept for context only.

Previous review (commit d842b97)

Status: No Issues Found | Recommendation: Merge

Files Reviewed (4 files)

• .changeset/fix-stale-worktree-status.md
• packages/kilo-vscode/src/KiloProvider.ts
• packages/kilo-vscode/tests/unit/kilo-provider-followup.test.ts
• packages/kilo-vscode/tests/unit/kilo-provider-load-messages.test.ts

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_{Reviewed by grok-4.6 · Input: 67.4K · Output: 4.3K · Cached: 183.9K}

_{Review guidance: REVIEW.md from base branch main}