feat(#171): Implement chat command parsing

Add command parsing layer for chat integration (Discord, Mattermost, Slack).

Features:
- Parse @mosaic commands with action dispatch
- Support 3 issue reference formats: #42, owner/repo#42, full URL
- Handle 7 actions: fix, status, cancel, retry, verbose, quiet, help
- Comprehensive error handling with helpful messages
- Case-insensitive parsing
- Platform-agnostic design

Implementation:
- CommandParserService with tokenizer and action dispatcher
- Regex-based issue reference parsing
- Type-safe command structures
- 24 unit tests with 100% coverage

TDD approach:
- RED: Wrote comprehensive tests first
- GREEN: Implemented parser to pass all tests
- REFACTOR: Fixed TypeScript strict mode and linting issues

Quality gates passed:
- ✓ Typecheck
- ✓ Lint
- ✓ Build
- ✓ Tests (24/24 passing)

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

docs/scratchpads/171-command-parser.md

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+# Issue #171: Chat Command Parsing
+
+## Objective
+
+Implement command parsing layer for chat integration that is shared across Discord, Mattermost, and Slack bridges.
+
+## Approach
+
+1. Create command interface types
+2. Write comprehensive tests for all command formats (TDD RED phase)
+3. Implement tokenizer for parsing @mosaic commands
+4. Implement action dispatch logic
+5. Add error handling with helpful messages
+6. Verify all tests pass (TDD GREEN phase)
+7. Refactor if needed (TDD REFACTOR phase)
+
+## Command Grammar
+
+- Pattern: `@mosaic <action> [args...]`
+- Actions: fix, status, cancel, retry, verbose, quiet, help
+- Issue reference formats:
+  - `#42` - Current repo issue
+  - `owner/repo#42` - Cross-repo issue
+  - `https://git.example.com/owner/repo/issues/42` - Full URL
+
+## Progress
+
+- [x] Create command interface types
+- [x] Write unit tests (RED phase)
+- [x] Implement command parser service
+- [x] Implement tokenizer
+- [x] Implement action dispatch
+- [x] Handle error responses
+- [x] Verify all tests pass (GREEN phase) - 24/24 tests passing
+- [x] Run quality gates (typecheck, lint, build, test) - All passing
+- [x] Commit changes
+
+## Testing
+
+- Test all command formats
+- Test issue reference parsing (all 3 formats)
+- Test error cases (invalid commands, missing args)
+- Test edge cases (extra whitespace, case sensitivity)
+
+## Notes
+
+- Parser must be platform-agnostic (works with Discord, Mattermost, Slack)
+- Error messages should be helpful and guide users
+- Follow strict TDD: tests before implementation
+
+## Implementation Details
+
+- Used regex patterns for issue reference parsing (current repo, cross-repo, full URL)
+- Tokenizer splits on whitespace after normalizing input
+- Action dispatch uses switch statement for type safety
+- Helpful error messages with examples provided for invalid input
+- Case-insensitive command parsing (@Mosaic, @mosaic both work)
+- Handles edge cases: extra whitespace, leading zeros in issue numbers
+
+## Files Created
+
+- `/home/jwoltje/src/mosaic-stack/apps/api/src/bridge/parser/command.interface.ts` - Type definitions
+- `/home/jwoltje/src/mosaic-stack/apps/api/src/bridge/parser/command-parser.service.ts` - Parser service
+- `/home/jwoltje/src/mosaic-stack/apps/api/src/bridge/parser/command-parser.spec.ts` - Unit tests
+
+## Test Results
+
+- 24/24 tests passing
+- All quality gates passed (typecheck, lint, build)