fix: claude code startup error

[alpham8]

What / Why / How

It fixes a claude code startup error. I'm not sure, if it affects other platforms as well.

Affected platforms

• Claude Code
• Cursor
• VS Code Copilot (GitHub Copilot)
• Gemini CLI
• OpenCode
• KiloCode
• Codex CLI
• OpenClaw (Pi Agent)
• Kiro
• Antigravity
• Zed
• All platforms

Test plan

Nothing - just a one-liner.

Checklist

• Tests added/updated (TDD: red → green)
• npm test passes
• npm run typecheck passes
• Docs updated if needed (README, platform-support.md)
• No Windows path regressions (forward slashes only)
• Targets next branch (unless hotfix)

Cross-platform notes

On claude code on Ubuntu (installed via linuxbrew), I saw this error at startup:

  ⎿  SessionStart:startup hook error                                                                                 ⎿  Failed with non-blocking status code: No stderr output
  ⎿  SessionStart:startup hook error                                                                                 ⎿  Failed with non-blocking status code: No stderr output

[mksglu]

Fixed comprehensively on next ✅

Your bug report was spot-on — JSON.parse("") throws SyntaxError on empty stdin, silently disabling session continuity on affected installs.

Instead of patching just sessionstart.mjs, we fixed all 22 hook files across all 6 adapters with a central parseStdin() helper:

• 1 new helper: parseStdin(raw) in session-helpers.mjs — strips BOM, trims, returns {} on empty input
• 22 call sites fixed: Claude Code (5), Gemini CLI (4), VS Code Copilot (4), Cursor (4), Codex CLI (3), Kiro (2)
• 27 new tests: 6 unit tests for parseStdin + 21 empty-stdin resilience tests covering every hook file

All 70 integration tests pass on macOS. CI covers Ubuntu + Windows.

Thank you @alpham8 for catching this! 🙏

Commit: 3e65ee5