feat: implement Monitor tool for streaming shell output (#649)

* feat: implement Monitor tool for streaming shell output

Add the Monitor tool that executes shell commands in the background and
streams stdout line-by-line as notifications to the model. This enables
real-time monitoring of logs, builds, and long-running processes.

Implementation:
- MonitorTool (src/tools/MonitorTool/) — spawns LocalShellTask with
  kind='monitor', returns immediately with task ID
- MonitorMcpTask (src/tasks/MonitorMcpTask/) — task lifecycle management
  and agent cleanup via killMonitorMcpTasksForAgent()
- MonitorPermissionRequest — permission dialog component

The codebase already had all integration points wired (tools.ts, tasks.ts,
PermissionRequest.tsx, LocalShellTask kind='monitor', BashTool prompt).
This PR provides the missing implementations.

* fix: command-specific permission rule + architecture docs

- MonitorPermissionRequest: "don't ask again" now creates a
  command-prefix rule (like BashTool) instead of a blanket
  tool-name-only rule that would auto-allow all Monitor commands
- MonitorMcpTask: clarify architecture comments explaining why
  monitor_mcp type exists as a registry stub while actual tasks
  are local_bash with kind='monitor'

* fix: address Copilot review feedback

- Fix permission rule field: expression → ruleContent (Copilot #1)
- Handle empty command prefix: skip rule creation (Copilot #2)
- Remove unused useTheme() import (Copilot #3)
- Save permission rules under 'Bash' toolName so bashToolHasPermission
  can match them — Monitor delegates to Bash permission system (Copilot #4)
- Remove unused logError import from MonitorMcpTask (Copilot #6)
- Copilot #5 (getAppState throws): same pattern as BashTool:915, not a bug

src/tools/MonitorTool/MonitorTool.ts

@@ -0,0 +1,195 @@
+import type { ToolResultBlockParam } from '@anthropic-ai/sdk/resources/index.mjs'
+import React from 'react'
+import { z } from 'zod/v4'
+import { buildTool, type ToolDef } from '../../Tool.js'
+import { spawnShellTask } from '../../tasks/LocalShellTask/LocalShellTask.js'
+import { lazySchema } from '../../utils/lazySchema.js'
+import { exec } from '../../utils/Shell.js'
+import { getTaskOutputPath } from '../../utils/task/diskOutput.js'
+import {
+  bashToolHasPermission,
+  matchWildcardPattern,
+  permissionRuleExtractPrefix,
+} from '../BashTool/bashPermissions.js'
+import { parseForSecurity } from '../../utils/bash/ast.js'
+
+export const MONITOR_TOOL_NAME = 'Monitor'
+
+const MONITOR_TIMEOUT_MS = 30 * 60 * 1000 // 30 minutes
+
+const inputSchema = lazySchema(() =>
+  z.strictObject({
+    command: z
+      .string()
+      .describe('The shell command to run and monitor'),
+    description: z
+      .string()
+      .describe(
+        'Clear, concise description of what this command does in active voice.',
+      ),
+  }),
+)
+type InputSchema = ReturnType<typeof inputSchema>
+
+const outputSchema = lazySchema(() =>
+  z.object({
+    taskId: z
+      .string()
+      .describe('The ID of the background monitor task'),
+    outputFile: z
+      .string()
+      .describe('Path to the file where output is being written'),
+  }),
+)
+type OutputSchema = ReturnType<typeof outputSchema>
+
+type Output = z.infer<OutputSchema>
+
+export const MonitorTool = buildTool({
+  name: MONITOR_TOOL_NAME,
+  searchHint: 'stream shell output as notifications',
+  maxResultSizeChars: 10_000,
+  strict: true,
+
+  isConcurrencySafe() {
+    return true
+  },
+
+  toAutoClassifierInput(input) {
+    return input.command
+  },
+
+  async preparePermissionMatcher({ command }) {
+    const parsed = await parseForSecurity(command)
+    if (parsed.kind !== 'simple') {
+      return () => true
+    }
+    const subcommands = parsed.commands.map(c => c.argv.join(' '))
+    return (pattern: string) => {
+      const prefix = permissionRuleExtractPrefix(pattern)
+      return subcommands.some(cmd => {
+        if (prefix !== null) {
+          return cmd === prefix || cmd.startsWith(`${prefix} `)
+        }
+        return matchWildcardPattern(pattern, cmd)
+      })
+    }
+  },
+
+  async checkPermissions(input, context) {
+    // Delegate to the bash permission system — Monitor runs shell commands
+    // just like Bash does, so the same permission rules apply.
+    return bashToolHasPermission({ command: input.command }, context)
+  },
+
+  async description(input) {
+    return input.description || 'Monitor shell command'
+  },
+
+  async prompt() {
+    return `Execute a shell command in the background and stream its stdout line-by-line as notifications. Each polling interval (~1s), new output lines are delivered to you. Use this for monitoring logs, watching build output, or observing long-running processes. For one-shot "wait until done" commands, prefer Bash with run_in_background instead.`
+  },
+
+  get inputSchema(): InputSchema {
+    return inputSchema()
+  },
+
+  get outputSchema(): OutputSchema {
+    return outputSchema()
+  },
+
+  userFacingName() {
+    return 'Monitor'
+  },
+
+  getToolUseSummary(input) {
+    if (!input?.description) {
+      return input?.command ?? null
+    }
+    return input.description
+  },
+
+  getActivityDescription(input) {
+    if (!input?.description) {
+      return 'Starting monitor'
+    }
+    return `Monitoring ${input.description}`
+  },
+
+  renderToolUseMessage(
+    input: Partial<z.infer<InputSchema>>,
+  ): React.ReactNode {
+    const cmd = input.command ?? ''
+    const desc = input.description ?? ''
+    if (desc && cmd) {
+      return `${desc}: ${cmd}`
+    }
+    return cmd || desc || ''
+  },
+
+  renderToolResultMessage(
+    output: Output,
+  ): React.ReactNode {
+    return `Monitor started (task ${output.taskId})`
+  },
+
+  mapToolResultToToolResultBlockParam(
+    output: Output,
+    toolUseID: string,
+  ): ToolResultBlockParam {
+    const outputPath = output.outputFile
+    return {
+      tool_use_id: toolUseID,
+      type: 'tool_result',
+      content: `Monitor task started with ID: ${output.taskId}. Output is being streamed to: ${outputPath}. You will receive notifications as new output lines appear (~1s polling). Use TaskStop to end monitoring when done.`,
+    }
+  },
+
+  async call(input, toolUseContext) {
+    const { command, description } = input
+    const { abortController, setAppState } = toolUseContext
+
+    // Create the shell command — uses the same Shell.exec() as BashTool.
+    // This is intentionally a shell execution (not execFile) because
+    // MonitorTool needs full shell features (pipes, redirects, etc.)
+    // just like BashTool does.
+    const shellCommand = await exec(
+      command,
+      abortController.signal,
+      'bash',
+      { timeout: MONITOR_TIMEOUT_MS },
+    )
+
+    // Spawn as a background task with kind='monitor' — identical to
+    // BashTool's run_in_background path but always monitor-flavored.
+    const handle = await spawnShellTask(
+      {
+        command,
+        description: description || command,
+        shellCommand,
+        toolUseId: toolUseContext.toolUseId,
+        agentId: toolUseContext.agentId,
+        kind: 'monitor',
+      },
+      {
+        abortController,
+        getAppState: () => {
+          throw new Error(
+            'getAppState not available in MonitorTool spawn context',
+          )
+        },
+        setAppState: toolUseContext.setAppStateForTasks ?? setAppState,
+      },
+    )
+
+    const taskId = handle.taskId
+    const outputFile = getTaskOutputPath(taskId)
+
+    return {
+      data: {
+        taskId,
+        outputFile,
+      },
+    }
+  },
+} satisfies ToolDef<InputSchema, Output>)