Add background process management with process tool, wait, PTY, and stdin support

New process registry and tool for managing long-running background processes
across all terminal backends (local, Docker, Singularity, Modal, SSH).

Process Registry (tools/process_registry.py):
- ProcessSession tracking with rolling 200KB output buffer
- spawn_local() with optional PTY via ptyprocess for interactive CLIs
- spawn_via_env() for non-local backends (runs inside sandbox, never on host)
- Background reader threads per process (Popen stdout or PTY)
- wait() with timeout clamping, interrupt support, and transparent limit reporting
- JSON checkpoint to ~/.hermes/processes.json for gateway crash recovery
- Module-level singleton shared across agent loop, gateway, and RL

Process Tool (model_tools.py):
- 7 actions: list, poll, log, wait, kill, write, submit
- Paired with terminal in all toolsets (CLI, messaging, RL)
- Timeout clamping with transparent notes in response

Terminal Tool Updates (tools/terminal_tool.py):
- Replaced nohup background mode with registry spawn (returns session_id)
- Added workdir parameter for per-command working directory
- Added check_interval parameter for gateway auto-check watchers
- Added pty parameter for interactive CLI tools (Codex, Claude Code)
- Updated TERMINAL_TOOL_DESCRIPTION with full background workflow docs
- Cleanup thread now respects active background processes (won't reap sandbox)

Gateway Integration (gateway/run.py, session.py, config.py):
- Session reset protection: sessions with active processes exempt from reset
- Default idle timeout increased from 2 hours to 24 hours
- from_dict fallback aligned to match (was 120, now 1440)
- session_key env var propagated to process registry for session mapping
- Crash recovery on gateway startup via checkpoint probe
- check_interval watcher: asyncio task polls process, delivers updates to platform

RL Safety (environments/):
- tool_context.py cleanup() kills background processes on episode end
- hermes_base_env.py warns when enabled_toolsets is None (loads all tools)
- Process tool safe in RL via wait() blocking the agent loop

Also:
- Added ptyprocess as optional dependency (in pyproject.toml [pty] extra + [all])
- Fixed pre-existing bug: rl_test_inference missing from TOOL_TO_TOOLSET_MAP
- Updated AGENTS.md with process management docs and project structure
- Updated README.md terminal section with process management overview

AGENTS.md

@@ -25,6 +25,7 @@ hermes-agent/
 │   ├── uninstall.py      # Uninstaller
 │   └── cron.py           # Cron job management
 ├── tools/                # Tool implementations
+│   ├── process_registry.py     # Background process management (spawn, poll, wait, kill)
 │   ├── transcription_tools.py  # Speech-to-text (Whisper API)
 ├── gateway/              # Messaging platform adapters
 │   ├── pairing.py        # DM pairing code system
@@ -412,6 +413,37 @@ The terminal tool includes safety checks for potentially destructive commands (e
 
 ---
 
+## Background Process Management
+
+The `process` tool works alongside `terminal` for managing long-running background processes:
+
+**Starting a background process:**
+```python
+terminal(command="pytest -v tests/", background=true)
+# Returns: {"session_id": "proc_abc123", "pid": 12345, ...}
+```
+
+**Managing it with the process tool:**
+- `process(action="list")` -- show all running/recent processes
+- `process(action="poll", session_id="proc_abc123")` -- check status + new output
+- `process(action="log", session_id="proc_abc123")` -- full output with pagination
+- `process(action="wait", session_id="proc_abc123", timeout=600)` -- block until done
+- `process(action="kill", session_id="proc_abc123")` -- terminate
+- `process(action="write", session_id="proc_abc123", data="y")` -- send stdin
+- `process(action="submit", session_id="proc_abc123", data="yes")` -- send + Enter
+
+**Key behaviors:**
+- Background processes execute through the configured terminal backend (local/Docker/Modal/SSH/Singularity) -- never directly on the host unless `TERMINAL_ENV=local`
+- The `wait` action blocks the tool call until the process finishes, times out, or is interrupted by a new user message
+- PTY mode (`pty=true` on terminal) enables interactive CLI tools (Codex, Claude Code)
+- In RL training, background processes are auto-killed when the episode ends (`tool_context.cleanup()`)
+- In the gateway, sessions with active background processes are exempt from idle reset
+- The process registry checkpoints to `~/.hermes/processes.json` for crash recovery
+
+Files: `tools/process_registry.py` (registry), `model_tools.py` (tool definition + handler), `tools/terminal_tool.py` (spawn integration)
+
+---
+
 ## Adding New Tools
 
 Follow this strict order to maintain consistency: