# PLAN: S3 — Hermes CLI Integration (call_hermes function)

## Goal
Encapsulate the inline `subprocess.run(["hermes", "chat", ...])` code in app.py into a standalone `call_hermes()` function.

## Current State
- Lines 1364-1386: inline hermes call in POST /api/conversations/<conv_id>/messages
- Uses subprocess.run (blocking), which is fine for now but S4 needs Popen for SSE
- Context building (history) already done above the call
- Error handling exists: TimeoutExpired, FileNotFoundError, generic Exception

## What to Change
1. Extract inline code into `call_hermes(user_input: str, timeout: int = 120) -> str`
2. Function takes user input string, runs `hermes chat -m`, returns stdout or error string
3. Update the route handler to call `call_hermes()` instead of inline code

## Files
- `app.py`: extract function + update caller
- `test_s3_hermes_call.py`: new test file

## Verification
- Test imports and runs without error
- Mock subprocess.run to verify function signature and behavior

## Risks
- None — purely refactoring, behavior unchanged