fix: strip CLAUDECODE env var from spawned sessions to prevent crashes

[wisdommen]

Summary

• Strip CLAUDECODE and CLAUDE_CODE_ENTRYPOINT environment variables from all session spawn paths (SDK query, daemon regular spawn, daemon tmux spawn) to prevent Claude Code nested-session detection from crashing remote sessions
• Fix Error object serialization in the logger — JSON.stringify(new Error(...)) produces {}, now uses err.stack or err.message for meaningful log output

Problem

When happy daemon start is run from within a Claude Code session (e.g., VS Code terminal), the daemon inherits CLAUDECODE=1. This propagates to all spawned session processes. Claude Code detects this and refuses to start with "cannot be launched inside another Claude Code session", causing every mobile/remote session to immediately crash with "Process exited unexpectedly".

The error was nearly impossible to debug because JSON.stringify(new Error("...")) produces {} (Error objects have no enumerable properties), so logs only showed [remote]: launch error {}.

Changes

1. packages/happy-cli/src/claude/sdk/utils.ts — Delete CLAUDECODE and CLAUDE_CODE_ENTRYPOINT in getCleanEnv(), which is used when spawning Claude Code via the SDK
2. packages/happy-cli/src/daemon/run.ts — Delete these vars in both the regular process spawn path and the tmux spawn path
3. packages/happy-cli/src/ui/logger.ts — Handle Error instances in logToFile() by using err.stack || err.message instead of JSON.stringify(err)

Test plan

• Start daemon from within a Claude Code session (e.g., VS Code terminal) and verify remote sessions launch successfully from the mobile app
• Start daemon from a clean shell and verify existing behavior is unchanged
• Trigger a session spawn error and verify the log output now shows the actual error message/stack instead of {}

Fixes #682

🤖 Generated with Claude Code