fix: EPIPE crash on stdin.write and add lenient JSON parsing for Claude output

[madhavikodale]

Thinking Path

• Paperclip orchestrates AI agents for zero-human companies
• The claude-local adapter spawns child processes and communicates via stdin/stdout
• When a child process exits quickly (e.g. auth errors, transient failures), its stdin stream may close before the parent writes to it
• Node.js emits EPIPE as an asynchronous 'error' event on writable streams, not as a thrown exception
• The previous try/catch around stdin.write() could not catch this, causing the entire Paperclip server to crash with an unhandled EPIPE
• Additionally, Claude occasionally outputs JSON wrapped in markdown code blocks or mixed with progress text, which the strict line-by-line parser rejects
• This PR fixes the EPIPE crash by adding an error listener on stdin and using callback-style write, and adds lenient JSON parsing to handle non-standard Claude output
• The benefit is a more stable server that survives child-process edge cases and correctly interprets Claude responses

What Changed

• Added parseJsonLenient() utility in adapter-utils/src/server-utils.ts that attempts direct parse, then code-block extraction, then progressive substring parsing
• Added extractResultFromMixedOutput() in claude-local/src/server/parse.ts to find JSON objects with "type": "result" inside mixed text
• Updated parseClaudeStreamJson() to use lenient parsing as fallback when line-by-line parsing finds no result
• Fixed EPIPE crash in runChildProcess(): replaced try/catch with stdin.on("error", ...) listener and callback-style stdin.write(chunk, cb)
• Updated claude-local execute logic to treat exit-code-0 + parse failure as inferred success rather than error
• Added comprehensive tests for parseJsonLenient() (9 cases), parseClaudeStreamJson() (8 cases), and EPIPE handling (2 cases)
• Updated CHANGELOGs for both adapter-utils and claude-local
• References: Fix agent runtime parsing failures and restore automatic workflow execution #16

Verification

pnpm -r typecheck  # passes
pnpm exec vitest run packages/adapter-utils/src/server-utils.test.ts packages/adapters/claude-local/src/server/parse.test.ts  # 61/61 tests pass

Manual verification:

1. Start server with pnpm dev
2. Trigger a claude-local run that exits quickly (e.g. auth error or empty prompt)
3. Confirm server does not crash with EPIPE
4. Verify Claude output with markdown-wrapped JSON is correctly parsed

Risks

• Low risk for EPIPE fix: only changes error handling path, normal operation unchanged
• Lenient parsing could theoretically accept malformed JSON in edge cases, but it only activates when strict parsing fails
• The inferredSuccess flag may mask genuine failures if Claude exits 0 with garbage output; monitored via resultJson.inferredSuccess

Model Used

• Kimi K2.5 (Moonshot AI, 256k context, tool use enabled)
• Assisted with debugging EPIPE behavior and implementing lenient parsing strategies

Checklist

• I have included a thinking path that traces from project context to this change
• I have specified the model used (with version and capability details)
• I have checked ROADMAP.md and confirmed this PR does not duplicate planned core work
• I have run tests locally and they pass
• I have added or updated tests where applicable
• If this change affects the UI, I have included before/after screenshots (N/A — no UI changes)
• I have updated relevant documentation to reflect my changes
• I have considered and documented any risks above
• I will address all Greptile and reviewer comments before requesting merge