feat(openspec): add TDD schema for refactoring and fixes

openspec/schemas/tdd/schema.yaml

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+name: tdd-refactor
+version: 1
+description: Test-driven development for refactoring and fixes - proposal → design → tasks
+artifacts:
+    - id: proposal
+      generates: proposal.md
+      description: Problem statement and change overview
+      template: proposal.md
+      instruction: |
+          Create a focused proposal for the refactoring or fix.
+
+          For bugs:
+          - **Why**: What's broken? Observed vs. expected behavior
+          - **Root Cause**: Technical reason for the bug (if known)
+          - **What Changes**: What will be fixed? Which files/components?
+          - **Impact**: Who/what is affected? Is this breaking?
+
+          For refactoring:
+          - **Why**: What problem does current code have? Tech debt, maintainability, performance?
+          - **What Changes**: What will be restructured? Be specific about scope
+          - **Impact**: Affected code, APIs, or behavior changes (should be minimal for pure refactoring)
+
+          Keep it concise (1 page max). This is about fixing or improving existing code,
+          not adding new features. If you're adding features, use spec-driven instead.
+      requires: []
+
+    - id: design
+      generates: design.md
+      description: Test plan defining what needs to pass
+      template: design.md
+      instruction: |
+          Define the test cases that will verify the fix or refactoring.
+
+          For bugs:
+          - Reproduction test (currently failing)
+          - Edge cases related to the bug
+          - Regression tests for related functionality
+
+          For refactoring:
+          - Existing behavior preservation tests
+          - Tests for improved cases (if applicable)
+          - Performance/maintainability verification (if relevant)
+
+          Format:
+          ```
+          ## Test Cases
+
+          ### Category Name
+
+          - Test name - Description (unit/integration/e2e)
+            - **Given**: Setup/preconditions
+            - **When**: Action/trigger
+            - **Then**: Expected outcome
+          ```
+
+          Write tests that will FAIL initially (for bugs) or verify existing behavior (for refactoring).
+          Tests define the contract - implementation must make them pass without breaking anything.
+      requires:
+          - proposal
+
+    - id: tasks
+      generates: tasks.md
+      description: Implementation task breakdown
+      template: tasks.md
+      instruction: |
+          Break down the implementation into trackable TDD tasks.
+
+          **IMPORTANT: Follow the template below exactly.** Use checkbox format: `- [ ] X.Y Description`
+
+          Group tasks by phase:
+
+          ## 1. Test Setup
+          - [ ] 1.1 Write failing test for main issue
+          - [ ] 1.2 Add edge case tests
+
+          ## 2. Implementation
+          - [ ] 2.1 Fix core issue (make main test pass)
+          - [ ] 2.2 Handle edge cases (make edge tests pass)
+
+          ## 3. Refactoring
+          - [ ] 3.1 Clean up implementation while keeping tests green
+          - [ ] 3.2 Extract common logic/improve structure
+
+          ## 4. Verification
+          - [ ] 4.1 All tests passing
+          - [ ] 4.2 No regressions (run full test suite)
+
+          Order tasks by TDD cycle: Red (failing test) → Green (make it pass) → Refactor (clean up).
+          Each task should be completable in one session.
+      requires:
+          - design
+
+apply:
+    requires: [design, tasks]
+    tracks: tasks.md
+    instruction: |
+        Follow TDD workflow:
+        1. Review proposal.md - understand what's broken or needs refactoring
+        2. Review design.md - understand what tests need to pass
+        3. Work through tasks.md in order:
+           - Write failing tests first (Red)
+           - Implement minimal fix to pass tests (Green)
+           - Refactor while keeping tests green
+        4. Mark task checkboxes as you complete them
+
+        All tests must pass before marking complete. Pause if blocked or need clarification.

openspec/schemas/tdd/templates/design.md

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+## Test Cases
+
+<!-- For bugs: start with reproduction test. For refactoring: verify existing behavior preserved. -->
+
+### Reproduction Tests
+
+- Test name - Description (unit/integration/e2e)
+    - **Given**: Setup/preconditions
+    - **When**: Action/trigger
+    - **Then**: Expected outcome
+
+### Edge Cases
+
+- Test name - Description (unit/integration/e2e)
+    - **Given**: Setup/preconditions
+    - **When**: Action/trigger
+    - **Then**: Expected outcome
+
+### Regression Tests
+
+- Test name - Description (unit/integration/e2e)
+    - **Given**: Setup/preconditions
+    - **When**: Action/trigger
+    - **Then**: Expected outcome
+
+## Notes
+
+<!-- Track unexpected behaviors, additional edge cases found, test failures and resolutions. -->

openspec/schemas/tdd/templates/proposal.md

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+## Why
+
+<!-- For bugs: observed vs expected behavior. For refactoring: tech debt or maintainability issue. -->
+
+## Root Cause
+
+<!-- Technical reason for the bug or what makes current code problematic. -->
+
+## What Changes
+
+<!-- Which files/components affected? Mark breaking changes with **BREAKING**. -->
+
+## Impact
+
+<!-- Affected code, APIs, users. Breaking changes? Migration needed? -->

openspec/schemas/tdd/templates/tasks.md

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+## 1. Test Setup
+
+<!-- RED: Write failing tests first -->
+
+- [ ] 1.1 Write failing test for main issue
+- [ ] 1.2 Add edge case tests
+- [ ] 1.3 Add regression tests for related functionality
+
+## 2. Implementation
+
+<!-- GREEN: Make tests pass with minimal code -->
+
+- [ ] 2.1 Fix core issue (make main test pass)
+- [ ] 2.2 Handle edge cases (make edge tests pass)
+- [ ] 2.3 Verify no regressions
+
+## 3. Refactoring
+
+<!-- REFACTOR: Clean up while keeping tests green -->
+
+- [ ] 3.1 Clean up implementation
+- [ ] 3.2 Extract common logic/improve structure
+- [ ] 3.3 Remove duplication
+
+## 4. Verification
+
+- [ ] 4.1 All tests passing (including new tests)
+- [ ] 4.2 Full test suite passes (no regressions)
+- [ ] 4.3 Code review ready (clean, documented)
+
+## Notes
+
+<!-- Track test failures, refactoring decisions, blockers. -->