feat: keep background agents running when the main agent stops

[marius-kilocode]

What Problem This Solves

In the VS Code extension, Esc and the main Stop button cancelled asynchronous subagents along with the parent. Interrupting the parent to send a correction could therefore discard background work.

Why This Change Was Made

Separate parent interruption from deliberate background cancellation. The abort endpoint accepts scope=session to stop the current turn and foreground work while preserving asynchronous children. The default scope=tree remains unchanged for lifecycle shutdowns and other clients.

A per-session pause gate retains completed background results without restarting an interrupted parent. Sending a message or using Continue resumes the parent with those results. The review fixes also keep paused background injections inactive across a later continuation and prevent an invalid slash command from unpausing a stopped session.

User Impact

• Esc, main Stop, and retry cancellation preserve background agents.
• The existing top background-agent bar gains a direct Stop all (N) action for that session's running background jobs. It does not stop the parent or ask for confirmation.
• No new composer count, extra spinner, shared UI provider, toast, or transcript status is added. Existing progress indicators and layout remain unchanged.

Evidence

• Six focused backend regression tests cover scoped interruption, retained results, continuation, default/tree cancellation, foreground-child cleanup, and the two pause-gate review findings.
• Existing task model-selection tests pass after merging the current base.
• The Stop-all browser test reuses the existing TaskHeader story and verifies exact cancellation targets with no parent abort. Existing pointer-accessibility and spinner-stability checks cover the unchanged agent bar.
• Package typechecks, lint, focused unit tests, and the shared-code annotation and Promise-facade guards pass.

The earlier isolated VS Code run verified parent-only interruption and retained results against a local test model. The reduced UI is covered by browser tests; the isolated VS Code relaunch failed in the local test harness, so there is no claim of a fresh native-editor end-to-end run.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (2 files)

• packages/kilo-vscode/tests/fixtures/session-provider-activity.tsx
• script/architecture-allowlist.json

Previous Review Summary (commit 9d2a4ac)

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

Previous review (commit 9d2a4ac)

Status: No Issues Found | Recommendation: Merge

Files Reviewed (4 files)

• packages/kilo-docs/public/img/screenshot-tests/kilo-vscode/visual-regression/chat/task-header-background-agents-200-chromium-linux.png
• packages/kilo-docs/public/img/screenshot-tests/kilo-vscode/visual-regression/chat/task-header-background-agents-420-chromium-linux.png
• packages/kilo-vscode/tests/fixtures/session-provider-activity.tsx
• script/architecture-allowlist.json

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_{Reviewed by grok-4.6 · Input: 194.8K · Output: 4.8K · Cached: 82.2K}

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