feat: add verification and debugging workflow skills

.config/opencode/skills/test-driven-development/SKILL.md

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+---
+name: test-driven-development
+description: Enforce test-first development for features and bug fixes — no production
+  code before a failing test
+permalink: opencode-config/skills/test-driven-development/skill
+---
+
+# Test-Driven Development (TDD)
+
+## When to Use
+
+Use this skill when implementing behavior changes:
+- New features
+- Bug fixes
+- Refactors that alter behavior
+
+If the work introduces or changes production behavior, TDD applies.
+
+## Core Rule
+
+```
+NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST
+```
+
+If production code was written first, delete or revert it and restart from a failing test.
+
+## Red → Green → Refactor Loop
+
+### 1) RED: Write one failing test
+- Write one small test that expresses the next expected behavior.
+- Prefer clear test names describing observable behavior.
+- Use real behavior paths where practical; mock only when isolation is required.
+
+### 2) Verify RED (mandatory)
+Run the new test and confirm:
+- It fails (not just errors)
+- It fails for the expected reason
+- It fails because behavior is missing, not because the test is broken
+
+If it passes immediately, the test is not proving the new behavior. Fix the test first.
+
+### 3) GREEN: Add minimal production code
+- Implement only enough code to make the failing test pass.
+- Do not add extra features, abstractions, or speculative options.
+
+### 4) Verify GREEN (mandatory)
+Run the test suite scope needed for confidence:
+- New test passes
+- Related tests still pass
+
+If failures appear, fix production code first unless requirements changed.
+
+### 5) REFACTOR
+- Improve names, remove duplication, and simplify structure.
+- Keep behavior unchanged.
+- Keep tests green throughout.
+
+Repeat for the next behavior.
+
+## Quality Checks Before Completion
+
+- [ ] Each behavior change has a test that failed before implementation
+- [ ] New tests failed for the expected reason first
+- [ ] Production code was added only after RED was observed
+- [ ] Tests now pass cleanly
+- [ ] Edge cases for changed behavior are covered
+
+## Practical Guardrails
+
+- "I'll write tests after" is not TDD.
+- Manual verification does not replace automated failing-then-passing tests.
+- If a test is hard to write, treat it as design feedback and simplify interfaces.
+- Keep test intent focused on behavior, not internals.
+
+## Related Reference
+
+For common mistakes around mocks and test design, see [testing-anti-patterns](./testing-anti-patterns.md).