feat(#172): Implement Herald status updates

Implements status broadcasting via bridge module to chat channels. The Herald
service subscribes to job events and broadcasts status updates to Discord threads
using PDA-friendly language.

Features:
- Herald module with HeraldService for status broadcasting
- Subscribe to job lifecycle, step lifecycle, and gate events
- Format messages with PDA-friendly language (no "FAILED", "URGENT", etc.)
- Visual indicators for quick scanning (🟢, 🔵, ✅, ⚠️, ⏸️)
- Channel selection logic via workspace settings
- Route to Discord threads based on job metadata
- Comprehensive unit tests (14 tests passing, 85%+ coverage)

Message format examples:
- Job created: 🟢 Job created for #42
- Job started: 🔵 Job started for #42
- Job completed: ✅ Job completed for #42 (120s)
- Job failed: ⚠️ Job encountered an issue for #42
- Gate passed: ✅ Gate passed: build
- Gate failed: ⚠️ Gate needs attention: test

Quality gates: ✅ typecheck, lint, test, build

PR comment support deferred - requires GitHub/Gitea API client implementation.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/scratchpads/172-herald-status.md

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+# Issue #172: Herald Status Updates
+
+## Objective
+
+Implement status reporting via the bridge module to chat channels and PR comments. The Herald service will broadcast job status updates to appropriate channels based on workspace configuration.
+
+## Approach
+
+1. Review existing code:
+   - JobEventsService (#169) for event types
+   - IChatProvider interface and Discord provider (#170)
+2. Create Herald module following TDD:
+   - RED: Write tests for status broadcasting
+   - GREEN: Implement Herald service
+   - REFACTOR: Clean up and optimize
+3. Implement channel selection logic (job type → channel mapping)
+4. Add PR comment support via GitHub/Gitea API
+5. Format messages using PDA-friendly language
+
+## Progress
+
+- [x] Create scratchpad
+- [x] Review JobEventsService and event types
+- [x] Review IChatProvider interface and Discord provider
+- [x] Write tests for Herald service (RED)
+- [x] Create Herald module structure
+- [x] Implement Herald service (GREEN)
+- [x] Add channel selection logic
+- [ ] Add PR comment support (deferred - GitHub API integration needed)
+- [x] Refactor and optimize (REFACTOR)
+- [x] Run quality gates (typecheck, lint, test, build)
+- [x] Commit changes
+
+## Key Findings
+
+### Event Types Available
+
+- Job lifecycle: `job.created`, `job.queued`, `job.started`, `job.completed`, `job.failed`, `job.cancelled`
+- Step lifecycle: `step.started`, `step.progress`, `step.output`, `step.completed`, `step.failed`
+- AI events: `ai.tool_called`, `ai.tokens_used`, `ai.artifact_created`
+- Gate events: `gate.started`, `gate.passed`, `gate.failed`
+
+### IChatProvider Interface
+
+- `sendMessage(channelId, content)` - Send message to channel
+- `createThread(options)` - Create thread for updates
+- `sendThreadMessage(options)` - Send message to thread
+- `isConnected()` - Check connection status
+
+### Workspace Settings
+
+- Workspace has `settings` JSON field for configuration
+- Can store channel mappings: `{ herald: { channelMappings: { "code-task": "channel-id" } } }`
+
+### Herald Responsibilities
+
+1. Subscribe to job events from JobEventsService
+2. Format status messages using PDA-friendly language
+3. Route to appropriate channels based on workspace config
+4. Support Discord (via bridge) and PR comments (via GitHub/Gitea API)
+5. Follow 10-second scannability rule
+
+## Testing
+
+- Unit tests for status broadcasting
+- Tests for channel selection logic
+- Tests for message formatting (PDA-friendly)
+- Tests for PR comment integration
+- Minimum 85% coverage required
+
+## Notes
+
+- Use PDA-friendly language (no "OVERDUE", "URGENT", etc.)
+- Follow 10-second scannability rule
+- Support multiple providers (Discord, GitHub PR comments)
+- Subscribe to job events via JobEventsService
+- Route to appropriate channels based on workspace config
+
+## Implementation Details
+
+### Architecture
+
+- Herald module created with HeraldService
+- Subscribes to job events (job lifecycle, step lifecycle, gate events)
+- Formats messages with PDA-friendly language and visual indicators
+- Routes to Discord threads via DiscordService
+
+### Message Formatting
+
+- Job created: 🟢 Job created for #42
+- Job started: 🔵 Job started for #42
+- Job completed: ✅ Job completed for #42 (120s)
+- Job failed: ⚠️ Job encountered an issue for #42
+- Job cancelled: ⏸️ Job paused for #42
+- Step completed: ✅ Step completed: Run tests
+- Gate passed: ✅ Gate passed: build
+- Gate failed: ⚠️ Gate needs attention: test
+
+### Channel Selection
+
+- Workspace settings store channel mappings: `{ herald: { channelMappings: { "code-task": "channel-id" } } }`
+- Falls back to default channel if job type not mapped
+- Returns null if no channel configured
+
+### Metadata Handling
+
+- Job metadata (including threadId) stored in first event payload (job.created)
+- Herald retrieves metadata from JobEvent table to determine where to send updates
+- This allows thread-based updates for each job
+
+## Deferred Features
+
+- PR comment support via GitHub/Gitea API (requires additional API client implementation)
+- This can be added in a future iteration when needed
+
+## Dependencies
+
+- #169 (JobEventsService) - ✅ COMPLETED
+- #170 (IChatProvider) - ✅ COMPLETED