feat(provider): Pi support

[danielmarbach]

What

Adds a pi provider so clawpatch can use the pi coding agent for review, fix, revalidate, and agent map workflows.

How it works

Shells out to pi -p --no-session in non-interactive print mode with all discovery flags disabled (--no-context-files --no-skills --no-extensions --no-prompt-templates --no-themes) to isolate the invocation from project/user config.

• Read-only (map, review, revalidate): passes --tools read to restrict pi to the read tool only
• Write (fix): uses the default tool set (read, bash, edit, write)
• Prompt delivery: written to temp file, passed via @<path> file reference
• Model: --model <pattern> forwarded from config (supports anthropic/claude-sonnet-4 and sonnet:high shorthands)
• Reasoning effort: --thinking <level> mapped from clawpatch reasoning effort
• Timeout: 180s default, configurable via CLAWPATCH_PI_TIMEOUT_MS or CLAWPATCH_PROVIDER_TIMEOUT_MS
• Output parsing: reuses shared extractJson() helper

Files changed

• src/provider.ts — piProvider + runPiJson, piPrompt, piFailureMessage, piTimeoutMs helpers
• src/provider.test.ts — providerByName("pi") assertion
• CHANGELOG.md — entry under 0.2.1
• docs/providers.md — pi section with usage, flags, and permission caveats

Checks

pnpm typecheck && pnpm lint && pnpm test && pnpm build

442 tests passing. Dogfooded against pi 0.74.1 with clawpatch doctor, clawpatch map --source agent, and clawpatch review.