feat: per-story model selection for Claude Code

[crywolfe]

Summary

• When using --tool claude, ralph.sh now reads an optional model field from the next incomplete story in prd.json
• Passes --model <value> to the Claude CLI, allowing per-story model control
• Stories without a model field use the default model (no behavior change)

This enables cost optimization across a run: use sonnet for straightforward stories and reserve opus for complex ones.

Changes

• ralph.sh: Before each iteration, reads the model field from the first passes: false story using jq. Passes --model flag to claude CLI if set.
• prd.json.example: Added model field to example story schema
• README.md: Documented per-story model selection feature

Example prd.json

{
  "id": "US-008",
  "title": "Complex table reconstruction",
  "model": "opus",
  "priority": 8,
  "passes": false
}

Valid model values: sonnet, opus, haiku, or full IDs like claude-opus-4-6.

Test plan

• Run ./ralph.sh --tool claude 2 with a prd.json containing stories with and without model field
• Verify story with "model": "opus" shows "Story US-XXX requests model: opus" in output
• Verify story without model field uses default (no --model flag passed)
• Verify --tool amp is unaffected (model field ignored for amp)

🤖 Generated with Claude Code