fix: improve error handling and prevent race conditions

[la14-1]

Code health improvements.

Changes

1. OAuth session cleanup race condition fix (shared/common.sh:755-767)

   • Added kill -0 check before killing OAuth server process
   • Prevents accidentally terminating unrelated processes if PID gets reused
   • Impact: Eliminates potential for killing user processes in high-load scenarios

2. Float arithmetic error handling (shared/common.sh:703-717)

   • Check for python3 availability before attempting float math
   • Explicit fallback to integer seconds with comment about early timeout risk
   • Impact: More predictable behavior on minimal systems without Python

3. Exit code documentation (.claude/skills/setup-agent-team/refactor.sh:46-67)

   • Added clarifying comments about exit code capture timing
   • No functional change, improves maintainability

Testing

• Syntax validated with bash -n on all modified files
• Changes preserve existing behavior while adding safety guards
• No breaking changes to public APIs

-- refactor/code-health

[louisgv]

Security Review

Verdict: APPROVED

Findings

No security issues found. All changes improve code robustness and error handling:

• refactor.sh:52-68 - Exit code preservation in cleanup: Correctly captures exit code before cleanup operations. No issues.
• shared/common.sh:713-718 - Python3 availability check: Safely checks for python3 before use, falls back to integer arithmetic. No command injection risk.
• shared/common.sh:765-769 - PID validation before kill: Prevents race conditions by verifying PID exists with kill -0 before sending signals. Defensive programming improvement.

Tests

• ✅ bash -n: PASS (refactor.sh, shared/common.sh)
• ✅ bun test: PASS (all tests passing after dependency installation)
• ✅ curl|bash: OK (no changes to source/eval patterns)
• ✅ macOS compat: OK (no bash 3.x incompatibilities introduced)

Code Quality

The changes demonstrate good defensive programming:

1. Exit code preservation prevents masking errors in cleanup
2. Python3 availability check improves portability across systems
3. PID validation prevents race conditions in process cleanup

All changes align with the codebase's safety and error-handling standards.

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-- security/pr-reviewer-1349