feat: implement Monitor tool for streaming shell output

[Flo5k5]

Summary

Implement the Monitor tool — a new tool that executes shell commands in the background and streams stdout line-by-line as notifications to the model. This is the last missing tool implementation from the source snapshot.

What Monitor does

Monitor fills the gap between synchronous Bash and fire-and-forget run_in_background:

Mode	Blocking	Notifications
Bash	Yes	Immediate result
Bash(run_in_background)	No	1 notification at completion
Monitor	No	Streaming (~1s polling)

Use cases: watching logs (tail -f), monitoring builds, observing dev server startup.

Implementation (3 new files + 1 flag flip)

src/tools/MonitorTool/MonitorTool.ts (195 lines)

• Input: { command, description }
• Spawns a LocalShellTask with kind: 'monitor' via exec() + spawnShellTask()
• Returns immediately with { taskId, outputFile }
• Permission checking delegates to bashToolHasPermission
• The existing task polling infrastructure handles streaming output to the model

src/tasks/MonitorMcpTask/MonitorMcpTask.ts (99 lines)

• Registers monitor_mcp task type in the task registry (satisfies import from tasks.ts)
• Exports killMonitorMcpTasksForAgent() for agent cleanup (called from runAgent.ts:866)
• Architecture: MonitorTool creates local_bash tasks with kind='monitor'; the monitor_mcp type exists for forward-compatibility with MCP-based monitoring

src/components/permissions/MonitorPermissionRequest/MonitorPermissionRequest.tsx (170 lines)

• Permission dialog showing command + description
• "Don't ask again" creates a command-prefix rule (like BashTool), not a blanket allow

scripts/build.ts — MONITOR_TOOL: true

Pre-existing infrastructure used

The codebase already had all integration points wired:

• src/tools.ts:39-41 — MonitorTool import slot
• src/tasks.ts:12-14 — MonitorMcpTask import slot
• src/components/permissions/PermissionRequest.tsx:40-41,73-74 — permission mapping
• src/tasks/LocalShellTask/LocalShellTask.tsx:47 — kind: 'monitor' (stall watchdog disabled)
• src/tasks/LocalShellTask/LocalShellTask.tsx:129-143 — monitor-specific notifications
• src/tools/BashTool/prompt.ts — conditional Monitor guidance text
• src/Task.ts:12 — 'monitor_mcp' in TaskType

Self-review fixes (commit 2)

• Permission: "don't ask again" now creates command-prefix rule instead of blanket tool-name rule
• Architecture comments clarified in MonitorMcpTask

Test plan

• bun run build — compiles successfully
• bun run smoke — smoke tests pass
• Self-review: permission rule, architecture docs, integration points verified
• Run Monitor({ command: "echo hello && sleep 1 && echo world", description: "test" }) — verify streaming notifications
• Verify permission dialog appears and "don't ask again" creates command-specific rule
• Verify TaskStop can kill a running monitor
• Verify monitor tasks are cleaned up on agent exit

[Copilot]

Pull request overview

Adds a new Monitor tool to run shell commands asynchronously while streaming stdout back to the model via periodic task-output notifications, filling the gap between blocking Bash and completion-only background tasks.

Changes:

• Introduces MonitorTool that spawns LocalShellTask jobs with kind: 'monitor' and returns { taskId, outputFile } immediately.
• Registers a forward-compatible monitor_mcp task type and adds agent-exit cleanup for monitor-related tasks.
• Adds a dedicated permission dialog for Monitor and enables the MONITOR_TOOL feature flag in the open build.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 6 comments.

File	Description
src/tools/MonitorTool/MonitorTool.ts	Implements the Monitor tool entrypoint that spawns background shell tasks in monitor mode and maps the immediate result payload.
src/tasks/MonitorMcpTask/MonitorMcpTask.ts	Adds the monitor_mcp task registry entry plus agent-scoped cleanup for monitor-related tasks.
src/components/permissions/MonitorPermissionRequest/MonitorPermissionRequest.tsx	Adds the Monitor-specific permission prompt UI and “don’t ask again” flow.
scripts/build.ts	Enables the MONITOR_TOOL feature flag for the open build.

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[Vasanthdev2004]

Review: Monitor tool for streaming shell output

Reviewed on head a9c7206. CI green ✅. 4 files, +471/-1.

This is a clean implementation of the Monitor tool — fills the last missing tool slot from the source snapshot. The architecture is sound: it correctly reuses the existing LocalShellTask infrastructure with kind: 'monitor' for streaming notifications, delegates permissions to bashToolHasPermission, and registers the forward-compatible monitor_mcp task type.

✅ Architecture

The tool sits correctly between synchronous Bash and fire-and-forget run_in_background:

Mode	Blocking	Notifications
Bash	Yes	Immediate result
Bash(run_in_background)	No	1 notification at completion
Monitor	No	Streaming (~1s polling)

All pre-existing integration points are properly filled: tools.ts import, tasks.ts import, PermissionRequest.tsx mapping, LocalShellTask monitor-kind handling, BashTool/prompt.ts conditional guidance, Task.ts type definition.

✅ Permission system

• checkPermissions correctly delegates to bashToolHasPermission — Monitor runs shell commands, so the same rules apply
• "Don't ask again" correctly saves rules under toolName: 'Bash' (not 'Monitor'), because bashToolHasPermission checks rules against BashTool. Saving under 'Monitor' would create a dead rule that never matches. The code comment explains this clearly.
• Prefix extraction uses first 2 tokens → ${prefix}:* format, matching BashTool's shellRuleMatching pattern
• Empty/whitespace commands skip rule creation entirely (empty array passed to onAllow) — prevents wildcard-everything rules

✅ Self-review fixes (commit 2)

All 6 Copilot issues addressed in a9c7206:

1. expression → ruleContent (correct schema field) ✅
2. Empty command guard (skip rule creation) ✅
3. toolName: 'Bash' for permission rules ✅
4. Removed unused useTheme() ✅
5. Removed unused logError import ✅
6. getAppState throwing stub — kept for consistency with BashTool pattern ✅

✅ Task cleanup

killMonitorMcpTasksForAgent provides belt-and-suspenders cleanup: kills both monitor_mcp-typed tasks AND local_bash tasks with kind='monitor'. The existing killShellTasksForAgent already handles the latter, but being explicit guards against ordering issues. dequeueAllMatching purges queued notifications for the dead agent.

✅ Monitor-specific behavior in LocalShellTask

• Stall watchdog disabled for kind: 'monitor' — correct, monitor tasks are expected to run indefinitely
• Distinct notification summaries: "Monitor X stream ended" vs "background command completed" — prevents confusion
• 30-minute timeout is reasonable for monitor tasks

🟡 Non-blocking observation: test coverage

The PR has no test files. The tool is mostly wiring (delegating to existing infrastructure), so the blast radius of bugs is limited. The permission logic and task cleanup paths are the most testable. This is acceptable for a tool that fills a pre-wired slot, but a follow-up adding tests for MonitorPermissionRequest's rule creation and killMonitorMcpTasksForAgent's cleanup would be valuable.

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Verdict: Approve-ready ✅

Clean implementation, addresses all Copilot review feedback, follows established patterns, security properties correct. Kevin already approved. No blockers.