feat: implement tdd workflow (#1309)

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

.taskmaster/docs/tdd-workflow-phase-0-spike.md

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+# Phase 0: Spike - Autonomous TDD Workflow ✅ COMPLETE
+
+## Objective
+Validate feasibility and build foundational understanding before full implementation.
+
+## Status
+**COMPLETED** - All deliverables implemented and validated.
+
+See `apps/cli/src/commands/autopilot.command.ts` for implementation.
+
+## Scope
+- Implement CLI skeleton `tm autopilot` with dry-run mode
+- Show planned steps from a real task with subtasks
+- Detect test runner from package.json
+- Detect git state and render preflight report
+
+## Deliverables
+
+### 1. CLI Command Skeleton
+- Create `apps/cli/src/commands/autopilot.command.ts`
+- Support `tm autopilot <taskId>` command
+- Implement `--dry-run` flag
+- Basic help text and usage information
+
+### 2. Preflight Detection System
+- Detect test runner from package.json (npm test, pnpm test, etc.)
+- Check git working tree state (clean/dirty)
+- Validate required tools are available (git, gh, node/npm)
+- Detect default branch
+
+### 3. Dry-Run Execution Plan Display
+Display planned execution for a task including:
+- Preflight checks status
+- Branch name that would be created
+- Tag that would be set
+- List of subtasks in execution order
+- For each subtask:
+  - RED phase: test file that would be created
+  - GREEN phase: implementation files that would be modified
+  - COMMIT: commit message that would be used
+- Finalization steps: test suite run, coverage check, push, PR creation
+
+### 4. Task Loading & Validation
+- Load task from TaskMaster state
+- Validate task exists and has subtasks
+- If no subtasks, show message about needing to expand first
+- Show dependency order for subtasks
+
+## Example Output
+
+```bash
+$ tm autopilot 42 --dry-run
+
+Autopilot Plan for Task #42 [analytics]: User metrics tracking
+─────────────────────────────────────────────────────────────
+
+Preflight Checks:
+  ✓ Working tree is clean
+  ✓ Test command detected: npm test
+  ✓ Tools available: git, gh, node, npm
+  ✓ Current branch: main (will create new branch)
+  ✓ Task has 3 subtasks ready to execute
+
+Branch & Tag:
+  → Will create branch: analytics/task-42-user-metrics
+  → Will set active tag: analytics
+
+Execution Plan (3 subtasks):
+
+  1. Subtask 42.1: Add metrics schema
+     RED:    Generate tests → src/__tests__/schema.test.js
+     GREEN:  Implement code → src/schema.js
+     COMMIT: "feat(metrics): add metrics schema (task 42.1)"
+
+  2. Subtask 42.2: Add collection endpoint [depends on 42.1]
+     RED:    Generate tests → src/api/__tests__/metrics.test.js
+     GREEN:  Implement code → src/api/metrics.js
+     COMMIT: "feat(metrics): add collection endpoint (task 42.2)"
+
+  3. Subtask 42.3: Add dashboard widget [depends on 42.2]
+     RED:    Generate tests → src/components/__tests__/MetricsWidget.test.jsx
+     GREEN:  Implement code → src/components/MetricsWidget.jsx
+     COMMIT: "feat(metrics): add dashboard widget (task 42.3)"
+
+Finalization:
+  → Run full test suite with coverage (threshold: 80%)
+  → Push branch to origin (will confirm)
+  → Create PR targeting main
+
+Estimated commits: 3
+Estimated duration: ~20-30 minutes (depends on implementation complexity)
+
+Run without --dry-run to execute.
+```
+
+## Success Criteria
+- Dry-run output is clear and matches expected workflow
+- Preflight detection works correctly on the project repo
+- Task loading integrates with existing TaskMaster state
+- No actual git operations or file modifications occur in dry-run mode
+
+## Out of Scope
+- Actual test generation
+- Actual code implementation
+- Git operations (branch creation, commits, push)
+- PR creation
+- Test execution
+
+## Implementation Notes
+- Reuse existing `TaskService` from `packages/tm-core`
+- Use existing git utilities from `scripts/modules/utils/git-utils.js`
+- Load task/subtask data from `.taskmaster/tasks/tasks.json`
+- Detect test command via package.json → scripts.test field
+
+## Dependencies
+- Existing TaskMaster CLI structure
+- Existing task storage format
+- Git utilities
+
+## Estimated Effort
+2-3 days
+
+## Validation
+Test dry-run mode with:
+- Task with 1 subtask
+- Task with multiple subtasks
+- Task with dependencies between subtasks
+- Task without subtasks (should show warning)
+- Dirty git working tree (should warn)
+- Missing tools (should error with helpful message)