/add-modernizer-skill

Guides creation of a new pipeline phase. Follows strict priority order — each step must be complete before the next begins.

Required Input

Ask the user for:

• Phase name: e.g. migrate-ddl, validate-schema, cost-estimate
• Purpose: What this phase does in one sentence
• Needs LLM?: Whether this phase requires LLM judgment (yes/no)
• Input: What artifacts from previous phases it reads
• Output: What it produces

Phase 1: Contract (MUST complete first)

1. Create src/contracts/{phase_name}_output.py

2. Define the output Pydantic model with:

   • Clear field descriptions
   • Appropriate types and constraints
   • Validators where needed

3. If LLM is needed, define the LLM output model separately (keep it minimal — only what requires judgment)

4. Verify:

   uv run python -c "from src.contracts.{phase_name}_output import *; print('OK')"
   

STOP: Do not proceed until the contract compiles and the user approves the field design.

Phase 2: Deterministic Logic

1. Create src/agents/{phase_name}/handler.py

2. Implement run_{phase_name}_deterministic(input) -> contract

3. If LLM is needed, implement:

   • prepare_{phase_name}_llm_input(contract, input) -> dict
   • apply_{phase_name}_llm_output(contract, llm_typed) -> updated_contract

4. Write tests in tests/agents/test_{phase_name}.py

5. Verify:

   uv run pytest tests/agents/test_{phase_name}.py -v
   

STOP: Do not proceed until tests pass.

Phase 3: Script

1. Create scripts/run_{phase_name}.py

2. Must support: --job-id, --db, --llm-mode (none/external/bedrock), --finalize, --artifact-root

3. In external mode, inject output_schema:

   llm_request["output_schema"] = LlmModel.model_json_schema()
   

4. In finalize mode, deserialize through Pydantic:

   llm_typed = LlmModel.model_validate(llm_response)
   updated = apply_llm_output(contract, llm_typed)
   

5. Output JSON to stdout: {"status": "complete"} or {"status": "awaiting_llm", "llm_request": "..."} or {"status": "validation_failed", "errors": [...]}

6. Verify deterministic mode works:

   uv run python scripts/run_{phase_name}.py --job-id test --db test --llm-mode none
   

STOP: Do not proceed until the script runs successfully.

Phase 4: Domain Expertise (if LLM phase exists)

1. Create src/skills/{phase_name}-expertise.md
2. Write the domain knowledge the LLM needs to make good decisions
3. Keep it focused — principles and anti-patterns, not implementation details

Phase 5: Command

1. Create .claude/commands/{phase_name}.md
2. No frontmatter. Follow this exact template, matching the other shipped commands:

# /{phase_name}

{Brief description.}

## Prerequisites

- {What must be true}

## Steps

1. **Run phase**

   ```bash
   uv run python scripts/run_{phase_name}.py --job-id {job_id} --db {database_name} --llm-mode external

2. If status is awaiting_llm: a. Read: artifacts/{database_name}/{job_id}/llm_requests/{phase_name}.json

   • Contains context data and output_schema b. Read: src/skills/{phase_name}-expertise.md c. Produce JSON conforming to output_schema d. Write to: artifacts/{database_name}/{job_id}/llm_responses/{phase_name}.json e. Finalize:

   uv run python scripts/run_{phase_name}.py --job-id {job_id} --db {database_name} --finalize
   

   If validation fails, fix errors and retry up to 3 times.

3. Update state Set phase_status.{phase_name} = "complete"

3. Validate:

   ```bash
   uv run python scripts/validate_skills.py

Phase 6: Integration

1. Add the new phase to the /modernize orchestrator skill if it belongs in the main pipeline

2. Update .claude/commands/modernize.md with the new step in the correct position

3. Run the pre-commit hook to verify everything links up:

   uv run python scripts/validate_skills.py
   

Rules

• NEVER skip a phase. Each phase depends on the previous.
• NEVER put contract details in the skill. The script injects output_schema.
• NEVER reference Python source files from skills.
• Keep LLM output contracts minimal. If logic can be deterministic, it MUST be.
• The script is the source of truth for validation — the skill just runs it.