docs(03): research phase domain

Phase 03: lifecycle-management
- Process lifecycle patterns (suspend/resume)
- Asyncio idle timeout detection
- Graceful shutdown strategies
- SIGTERM vs SIGSTOP tradeoffs
- Claude Code --continue for resumption

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.planning/phases/03-lifecycle-management/03-RESEARCH.md

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+# Phase 3: Lifecycle Management - Research
+
+**Researched:** 2026-02-04
+**Domain:** Process lifecycle (suspend/resume), asyncio idle timeout detection, graceful shutdown patterns, Claude Code --resume flag
+**Confidence:** HIGH
+
+## Summary
+
+Phase 3 implements automatic session suspension after configurable idle timeout and transparent resumption with full conversation history. The core technical challenges are: (1) detecting true idle state (no user messages AND no Claude activity), (2) choosing between SIGSTOP/SIGCONT (pause in-place) vs SIGTERM + --resume (terminate and restart), and (3) graceful cleanup on bot restart to prevent zombie processes.
+
+Research confirms that asyncio provides robust timeout primitives (`asyncio.Event`, `asyncio.wait_for`, `asyncio.create_task`) for per-session idle timers. Claude Code's `--continue` flag already handles session resumption from `.claude/` state in the session directory — no separate `--resume` flag is needed when using persistent subprocesses in one directory. The critical decision is suspension method: SIGSTOP/SIGCONT saves spawn overhead but keeps memory allocated, while SIGTERM + restart trades memory for CPU overhead.
+
+Key findings: (1) Idle detection requires tracking both user message time AND Claude completion time to avoid suspending mid-processing, (2) SIGSTOP/SIGCONT keeps process memory allocated but saves ~1s restart overhead, (3) SIGTERM + --continue is safer for long idle periods (releases memory, prevents stale state), (4) Graceful shutdown requires signal handlers to cancel idle timer tasks and terminate subprocesses with timeout + SIGKILL fallback.
+
+**Primary recommendation:** Use SIGTERM + restart approach for suspension. Track last activity timestamp per session. After idle timeout, terminate subprocess gracefully (SIGTERM with 5s timeout, SIGKILL fallback). On next user message, spawn fresh subprocess with `--continue` to restore context. This balances memory efficiency (released during idle) with reasonable restart cost (~1s). Store timeout value in session metadata for per-session configuration.
+
+## Standard Stack
+
+The established libraries/tools for this domain:
+
+### Core
+| Library | Version | Purpose | Why Standard |
+|---------|---------|---------|--------------|
+| asyncio | stdlib (3.12+) | Timeout detection, task scheduling, signal handling | Native async primitives for idle timers, event-based cancellation |
+| Claude Code CLI | 2.1.31+ | Session resumption via --continue | Built-in session state persistence to `.claude/` directory |
+| signal (stdlib) | stdlib | SIGTERM/SIGKILL for graceful shutdown | Standard Unix signal handling for process termination |
+
+### Supporting
+| Library | Version | Purpose | When to Use |
+|---------|---------|---------|-------------|
+| datetime (stdlib) | stdlib | Last activity timestamps | Track idle periods per session |
+| json (stdlib) | stdlib | Session metadata updates | Store timeout configuration per session |
+
+### Alternatives Considered
+| Instead of | Could Use | Tradeoff |
+|------------|-----------|----------|
+| SIGTERM + restart | SIGSTOP/SIGCONT | Pause keeps memory but saves 1s restart; terminate releases memory but costs CPU |
+| Per-session timers | Global timeout for all sessions | Per-session allows custom timeouts (long for task sessions, short for chat) |
+| asyncio.Event cancellation | Thread-based timers | asyncio integrates cleanly with subprocess management, threads add complexity |
+
+**Installation:**
+```bash
+# All components are stdlib or already installed
+python3 --version  # 3.12+ required for modern asyncio
+claude --version   # 2.1.31 (already installed)
+```
+
+## Architecture Patterns
+
+### Recommended Lifecycle State Machine
+
+```
+Session States:
+├── Created (no subprocess) → User message → Active
+├── Active (subprocess running, processing) → Completion → Idle
+├── Idle (subprocess running, waiting) → Timeout → Suspended
+├── Suspended (no subprocess) → User message → Active (restart)
+└── Any state → Bot restart → Suspended (cleanup)
+
+Idle Timer:
+- Starts: After Claude completion event (subprocess.on_complete)
+- Resets: On user message OR Claude starts processing
+- Fires: After idle_timeout seconds of inactivity
+- Action: Terminate subprocess (SIGTERM, 5s timeout, SIGKILL fallback)
+```
+
+### Pattern 1: Per-Session Idle Timer with asyncio
+**What:** Track last activity timestamp, spawn background task to check timeout, cancel on activity
+**When to use:** After each message completion, restart on new message
+**Example:**
+```python
+# Source: https://docs.python.org/3/library/asyncio-task.html
+import asyncio
+from datetime import datetime, timezone
+
+class SessionIdleTimer:
+    """Manages idle timeout for a session."""
+
+    def __init__(self, session_name: str, timeout_seconds: int, on_timeout: callable):
+        self.session_name = session_name
+        self.timeout_seconds = timeout_seconds
+        self.on_timeout = on_timeout
+        self._timer_task: Optional[asyncio.Task] = None
+        self._last_activity = datetime.now(timezone.utc)
+
+    def reset(self):
+        """Reset idle timer on activity."""
+        self._last_activity = datetime.now(timezone.utc)
+
+        # Cancel existing timer
+        if self._timer_task and not self._timer_task.done():
+            self._timer_task.cancel()
+
+        # Start new timer
+        self._timer_task = asyncio.create_task(self._wait_for_timeout())
+
+    async def _wait_for_timeout(self):
+        """Wait for timeout duration, then fire callback."""
+        try:
+            await asyncio.sleep(self.timeout_seconds)
+
+            # Timeout reached - fire callback
+            await self.on_timeout(self.session_name)
+        except asyncio.CancelledError:
+            # Timer was reset by activity
+            pass
+
+    def cancel(self):
+        """Cancel idle timer on session shutdown."""
+        if self._timer_task and not self._timer_task.done():
+            self._timer_task.cancel()
+
+# Usage in bot
+idle_timers: dict[str, SessionIdleTimer] = {}
+
+async def on_message_complete(session_name: str):
+    """Called when Claude finishes processing."""
+    # Start idle timer after completion
+    if session_name not in idle_timers:
+        timeout = get_session_timeout(session_name)  # From metadata
+        idle_timers[session_name] = SessionIdleTimer(
+            session_name,
+            timeout,
+            on_timeout=suspend_session
+        )
+
+    idle_timers[session_name].reset()
+
+async def on_user_message(session_name: str, message: str):
+    """Called when user sends message."""
+    # Reset timer on activity
+    if session_name in idle_timers:
+        idle_timers[session_name].reset()
+
+    # Send to Claude...
+```
+
+### Pattern 2: Graceful Subprocess Termination
+**What:** Send SIGTERM, wait for clean exit with timeout, SIGKILL if needed
+**When to use:** Suspending session, bot shutdown, session archival
+**Example:**
+```python
+# Source: https://roguelynn.com/words/asyncio-graceful-shutdowns/
+import asyncio
+import signal
+
+async def terminate_subprocess_gracefully(
+    process: asyncio.subprocess.Process,
+    timeout: int = 5
+) -> None:
+    """
+    Terminate subprocess with graceful shutdown.
+
+    1. Close stdin to signal end of input
+    2. Send SIGTERM for graceful shutdown
+    3. Wait up to timeout seconds
+    4. SIGKILL if still running
+    5. Always reap process to prevent zombie
+    """
+    if not process or process.returncode is not None:
+        return  # Already terminated
+
+    try:
+        # Close stdin to signal no more input
+        if process.stdin:
+            process.stdin.close()
+            await process.stdin.wait_closed()
+
+        # Send SIGTERM for graceful shutdown
+        process.terminate()
+
+        # Wait for clean exit
+        try:
+            await asyncio.wait_for(process.wait(), timeout=timeout)
+            logger.info(f"Process {process.pid} terminated gracefully")
+        except asyncio.TimeoutError:
+            # Timeout - force kill
+            logger.warning(f"Process {process.pid} did not terminate, sending SIGKILL")
+            process.kill()
+            await process.wait()  # CRITICAL: Always reap to prevent zombie
+            logger.info(f"Process {process.pid} killed")
+
+    except Exception as e:
+        logger.error(f"Error terminating process: {e}")
+        # Force kill as last resort
+        try:
+            process.kill()
+            await process.wait()
+        except:
+            pass
+```
+
+### Pattern 3: Session Resume with --continue
+**What:** Spawn subprocess with `--continue` flag to restore conversation from `.claude/` state
+**When to use:** First message after suspension, bot restart resuming active session
+**Example:**
+```python
+# Source: https://code.claude.com/docs/en/cli-reference
+async def resume_session(session_name: str) -> ClaudeSubprocess:
+    """
+    Resume suspended session by spawning subprocess with --continue.
+
+    Claude Code automatically loads conversation history from .claude/
+    directory in session folder.
+    """
+    session_dir = get_session_dir(session_name)
+    persona = load_persona_for_session(session_name)
+
+    # Check if .claude directory exists (has prior conversation)
+    has_history = (session_dir / ".claude").exists()
+
+    cmd = [
+        'claude',
+        '-p',
+        '--input-format', 'stream-json',
+        '--output-format', 'stream-json',
+        '--verbose',
+        '--dangerously-skip-permissions',
+    ]
+
+    # Add --continue if session has history
+    if has_history:
+        cmd.append('--continue')
+        logger.info(f"Resuming session '{session_name}' with --continue")
+    else:
+        logger.info(f"Starting fresh session '{session_name}'")
+
+    # Add persona settings (model, system prompt, etc)
+    if persona:
+        settings = persona.get('settings', {})
+        if 'model' in settings:
+            cmd.extend(['--model', settings['model']])
+        if 'system_prompt' in persona:
+            cmd.extend(['--append-system-prompt', persona['system_prompt']])
+
+    # Spawn subprocess
+    subprocess = ClaudeSubprocess(
+        session_dir=session_dir,
+        persona=persona,
+        on_output=...,
+        on_error=...,
+        on_complete=lambda: on_message_complete(session_name),
+        on_status=...,
+        on_tool_use=...,
+    )
+    await subprocess.start()
+
+    return subprocess
+```
+
+### Pattern 4: Bot Shutdown with Subprocess Cleanup
+**What:** Signal handler to cancel all idle timers and terminate all subprocesses on SIGTERM/SIGINT
+**When to use:** Bot stop, systemctl stop, Ctrl+C
+**Example:**
+```python
+# Source: https://roguelynn.com/words/asyncio-graceful-shutdowns/ +
+#         https://github.com/wbenny/python-graceful-shutdown
+import signal
+import asyncio
+
+async def shutdown(sig: signal.Signals, loop: asyncio.AbstractEventLoop):
+    """
+    Graceful shutdown handler for bot.
+
+    1. Log signal received
+    2. Cancel all idle timers
+    3. Terminate all subprocesses gracefully
+    4. Cancel all outstanding tasks
+    5. Stop event loop
+    """
+    logger.info(f"Received exit signal {sig.name}")
+
+    # Cancel all idle timers
+    for timer in idle_timers.values():
+        timer.cancel()
+
+    # Terminate all active subprocesses
+    termination_tasks = []
+    for session_name, subprocess in subprocesses.items():
+        if subprocess.is_alive:
+            logger.info(f"Terminating subprocess for session '{session_name}'")
+            termination_tasks.append(
+                terminate_subprocess_gracefully(subprocess._process, timeout=5)
+            )
+
+    # Wait for all terminations to complete
+    if termination_tasks:
+        await asyncio.gather(*termination_tasks, return_exceptions=True)
+
+    # Cancel all other tasks
+    tasks = [t for t in asyncio.all_tasks() if t is not asyncio.current_task()]
+    for task in tasks:
+        task.cancel()
+
+    # Wait for cancellation, ignore exceptions
+    await asyncio.gather(*tasks, return_exceptions=True)
+
+    # Stop the loop
+    loop.stop()
+
+# Install signal handlers on startup
+def main():
+    app = Application.builder().token(TOKEN).build()
+
+    # Add signal handlers
+    loop = asyncio.get_event_loop()
+    signals = (signal.SIGTERM, signal.SIGINT)
+    for sig in signals:
+        loop.add_signal_handler(
+            sig,
+            lambda s=sig: asyncio.create_task(shutdown(s, loop))
+        )
+
+    # Start bot
+    app.run_polling()
+```
+
+### Pattern 5: Session Metadata for Timeout Configuration
+**What:** Store idle_timeout in session metadata, allow per-session customization via /timeout command
+**When to use:** Session creation, /timeout command handler
+**Example:**
+```python
+# Session metadata structure
+{
+    "name": "task-session",
+    "created": "2026-02-04T12:00:00+00:00",
+    "last_active": "2026-02-04T12:30:00+00:00",
+    "persona": "default",
+    "pid": null,
+    "status": "suspended",
+    "idle_timeout": 600  # seconds (10 minutes)
+}
+
+# /timeout command handler
+async def timeout_cmd(update: Update, context: ContextTypes.DEFAULT_TYPE):
+    """Set idle timeout for active session."""
+    if not context.args:
+        # Show current timeout
+        active = session_manager.get_active_session()
+        if not active:
+            await update.message.reply_text("No active session")
+            return
+
+        metadata = session_manager.get_session(active)
+        timeout = metadata.get('idle_timeout', 600)
+        await update.message.reply_text(
+            f"Current idle timeout: {timeout // 60} minutes\n\n"
+            f"Usage: /timeout <minutes>"
+        )
+        return
+
+    # Parse timeout value
+    try:
+        minutes = int(context.args[0])
+        if minutes < 1 or minutes > 120:
+            await update.message.reply_text("Timeout must be between 1 and 120 minutes")
+            return
+
+        timeout_seconds = minutes * 60
+    except ValueError:
+        await update.message.reply_text("Invalid number. Usage: /timeout <minutes>")
+        return
+
+    # Update session metadata
+    active = session_manager.get_active_session()
+    session_manager.update_session(active, idle_timeout=timeout_seconds)
+
+    # Restart idle timer with new timeout
+    if active in idle_timers:
+        idle_timers[active].timeout_seconds = timeout_seconds
+        idle_timers[active].reset()
+
+    await update.message.reply_text(f"Idle timeout set to {minutes} minutes")
+```
+
+### Pattern 6: /sessions Command with Status Display
+**What:** List all sessions with name, status, persona, last active time, sorted by activity
+**When to use:** User wants to see session overview
+**Example:**
+```python
+async def sessions_cmd(update: Update, context: ContextTypes.DEFAULT_TYPE):
+    """List all sessions sorted by last activity."""
+    sessions = session_manager.list_sessions()
+
+    if not sessions:
+        await update.message.reply_text("No sessions found. Use /new <name> to create one.")
+        return
+
+    active_session = session_manager.get_active_session()
+
+    # Build formatted list
+    lines = ["*Sessions:*\n"]
+    for session in sessions:  # Already sorted by last_active
+        name = session['name']
+        status = session['status']
+        persona = session.get('persona', 'default')
+        last_active = session.get('last_active', 'unknown')
+
+        # Format timestamp
+        try:
+            dt = datetime.fromisoformat(last_active)
+            time_str = dt.strftime('%Y-%m-%d %H:%M')
+        except:
+            time_str = 'unknown'
+
+        # Mark active session
+        marker = "→ " if name == active_session else "  "
+
+        # Status emoji
+        emoji = "🟢" if status == "active" else "🔵" if status == "idle" else "⚪"
+
+        lines.append(
+            f"{marker}{emoji} `{name}` ({persona})\n"
+            f"     {time_str}"
+        )
+
+    await update.message.reply_text("\n".join(lines), parse_mode='Markdown')
+```
+
+### Anti-Patterns to Avoid
+- **Suspending during processing:** Never suspend while `subprocess.is_busy` is True — will lose in-progress work
+- **Not resetting timer on user message:** If idle timer only resets on completion, user's message during timeout window gets ignored
+- **Zombie processes on bot crash:** Without signal handlers, subprocess outlives bot and becomes zombie (orphaned)
+- **SIGSTOP without resource consideration:** Paused processes hold memory, file handles, network sockets — unsafe for long idle periods
+- **Shared idle timer for all sessions:** Different sessions have different needs (task vs chat), per-session timeout is more flexible
+
+## Don't Hand-Roll
+
+Problems that look simple but have existing solutions:
+
+| Problem | Don't Build | Use Instead | Why |
+|---------|-------------|-------------|-----|
+| Idle timeout detection | Manual timestamp checks in loop | asyncio.Event + asyncio.sleep() | Event-based cancellation is cleaner, no polling overhead |
+| Graceful shutdown | Just process.terminate() | SIGTERM + timeout + SIGKILL pattern | Prevents zombie processes, handles hung processes |
+| Per-object timers | Single global timeout thread | asyncio.create_task per session | Native async integration, automatic cleanup |
+| Resume conversation | Manual state serialization | Claude Code --continue flag | Built-in, tested, handles all edge cases |
+
+**Key insight:** Process lifecycle management has subtle races (subprocess dies mid-shutdown, signal arrives during cleanup, timer fires after cancellation). Using battle-tested patterns (signal handlers, timeout with fallback, event-based cancellation) prevents these races. Don't reinvent async subprocess management.
+
+## Common Pitfalls
+
+### Pitfall 1: Race Between Timer Fire and User Message
+**What goes wrong:** Idle timer fires (subprocess terminated), user message arrives during termination, new subprocess spawns, old one still dying — two subprocesses running
+**Why it happens:** Timer callback and message handler run concurrently. No synchronization between timer firing and subprocess state change.
+**How to avoid:** Use asyncio.Lock around subprocess state transitions (terminate, spawn). Timer callback acquires lock before terminating, message handler acquires lock before spawning.
+**Warning signs:** Duplicate responses, sessions becoming unresponsive, "subprocess already running" errors
+
+```python
+# WRONG - No synchronization
+async def on_timeout(session_name):
+    await terminate_subprocess(session_name)
+
+async def on_message(session_name, message):
+    subprocess = await spawn_subprocess(session_name)
+    await subprocess.send_message(message)
+
+# RIGHT - Lock around transitions
+subprocess_locks: dict[str, asyncio.Lock] = {}
+
+async def on_timeout(session_name):
+    async with subprocess_locks[session_name]:
+        await terminate_subprocess(session_name)
+
+async def on_message(session_name, message):
+    async with subprocess_locks[session_name]:
+        if not subprocess_exists(session_name):
+            await spawn_subprocess(session_name)
+    await subprocess.send_message(message)
+```
+
+### Pitfall 2: Terminating Subprocess During Tool Execution
+**What goes wrong:** Claude is running a long tool (git clone, npm install), idle timer fires, subprocess terminated mid-operation, corrupted state
+**Why it happens:** Idle timer only checks elapsed time since last message, doesn't check if subprocess is actively executing tools.
+**How to avoid:** Track subprocess busy state (`is_busy` flag set during processing). Only start idle timer after `on_complete` callback fires (subprocess is truly idle).
+**Warning signs:** Corrupted git repos, partial file writes, timeout errors from tools
+
+```python
+# WRONG - Timer starts immediately after message send
+await subprocess.send_message(message)
+idle_timers[session_name].reset()  # Bad: Claude still processing
+
+# RIGHT - Timer starts after completion
+await subprocess.send_message(message)
+# ... subprocess processes, calls tools, emits result event ...
+# on_complete callback fires
+async def on_complete():
+    idle_timers[session_name].reset()  # Good: Claude is truly idle
+```
+
+### Pitfall 3: Not Canceling Idle Timer on Session Switch
+**What goes wrong:** Switch from session A to session B, session A's timer fires 5 minutes later, terminates session A subprocess (which might have been switched back to)
+**Why it happens:** Session switch doesn't cancel old session's timer, timer continues running independently
+**How to avoid:** When switching sessions, don't cancel old timer — let it run. Old subprocess suspends on its own timer. This allows multiple concurrent sessions with independent lifetimes.
+**Warning signs:** Sessions suspend unexpectedly after switching away and back
+
+```python
+# CORRECT - Don't cancel old timer on switch
+async def switch_session(new_session_name):
+    old_session = get_active_session()
+
+    # Don't touch old session's timer - let it suspend naturally
+    # if old_session in idle_timers:
+    #     idle_timers[old_session].cancel()  # NO
+
+    set_active_session(new_session_name)
+
+    # Start new session's timer if needed
+    if new_session_name not in idle_timers:
+        # Create timer for new session
+        pass
+```
+
+### Pitfall 4: Subprocess Outlives Bot on Crash
+**What goes wrong:** Bot crashes or is killed with SIGKILL, signal handlers never run, subprocesses become orphans, eat memory/CPU
+**Why it happens:** SIGKILL can't be caught (by design), no cleanup code runs
+**How to avoid:** Can't prevent SIGKILL zombies, but minimize with: (1) Store PID in session metadata, check on bot restart, (2) Use systemd with KillMode=control-group to kill all child processes, (3) Bot startup cleanup: scan for orphaned pids from metadata
+**Warning signs:** Multiple claude processes running after bot restart, memory usage grows over time
+
+```python
+# Startup cleanup - kill orphaned subprocesses
+async def cleanup_orphaned_subprocesses():
+    """Kill any subprocesses that outlived previous bot run."""
+    sessions = session_manager.list_sessions()
+
+    for session in sessions:
+        pid = session.get('pid')
+        if pid:
+            # Check if process still exists
+            try:
+                os.kill(pid, 0)  # Signal 0 = check existence
+                # Process exists - kill it
+                logger.warning(f"Killing orphaned subprocess: PID {pid}")
+                os.kill(pid, signal.SIGTERM)
+                await asyncio.sleep(2)
+                try:
+                    os.kill(pid, signal.SIGKILL)
+                except ProcessLookupError:
+                    pass  # Already dead
+            except ProcessLookupError:
+                pass  # Already dead
+
+            # Clear PID from metadata
+            session_manager.update_session(session['name'], pid=None, status='suspended')
+```
+
+### Pitfall 5: Storing Stale PIDs in Metadata
+**What goes wrong:** Session metadata shows pid=12345, but subprocess already terminated. On bot restart, try to kill PID 12345 which is now a different process.
+**Why it happens:** Subprocess crashes or is manually killed, metadata not updated
+**How to avoid:** Clear PID from metadata when subprocess terminates (exit code detected). Before killing PID from metadata, verify it's a claude process (check /proc/{pid}/cmdline on Linux).
+**Warning signs:** Bot kills wrong processes on restart, random crashes
+
+```python
+# Safe PID cleanup with verification
+async def kill_subprocess_by_pid(pid: int):
+    """Kill subprocess with PID verification."""
+    try:
+        # Verify it's a claude process (Linux-specific)
+        cmdline_path = f"/proc/{pid}/cmdline"
+        if os.path.exists(cmdline_path):
+            with open(cmdline_path) as f:
+                cmdline = f.read()
+                if 'claude' not in cmdline:
+                    logger.warning(f"PID {pid} is not a claude process: {cmdline}")
+                    return  # Don't kill
+
+        # Kill the process
+        os.kill(pid, signal.SIGTERM)
+        await asyncio.sleep(2)
+        try:
+            os.kill(pid, signal.SIGKILL)
+        except ProcessLookupError:
+            pass
+    except ProcessLookupError:
+        pass  # Already dead
+    except Exception as e:
+        logger.error(f"Error killing PID {pid}: {e}")
+```
+
+## Code Examples
+
+Verified patterns from official sources:
+
+### Complete Idle Timer Implementation
+```python
+# Source: https://docs.python.org/3/library/asyncio-task.html
+import asyncio
+from datetime import datetime, timezone
+from typing import Callable, Optional
+
+class SessionIdleTimer:
+    """
+    Per-session idle timeout manager.
+
+    Tracks last activity, spawns background task to fire after timeout.
+    Cancels and restarts timer on activity (reset).
+    """
+
+    def __init__(
+        self,
+        session_name: str,
+        timeout_seconds: int,
+        on_timeout: Callable[[str], None]
+    ):
+        """
+        Args:
+            session_name: Session identifier
+            timeout_seconds: Idle seconds before firing
+            on_timeout: Async callback(session_name) to invoke on timeout
+        """
+        self.session_name = session_name
+        self.timeout_seconds = timeout_seconds
+        self.on_timeout = on_timeout
+        self._timer_task: Optional[asyncio.Task] = None
+        self._last_activity = datetime.now(timezone.utc)
+
+    def reset(self):
+        """Reset timer on activity (user message or completion)."""
+        self._last_activity = datetime.now(timezone.utc)
+
+        # Cancel existing timer
+        if self._timer_task and not self._timer_task.done():
+            self._timer_task.cancel()
+
+        # Start fresh timer
+        self._timer_task = asyncio.create_task(self._wait_for_timeout())
+
+    async def _wait_for_timeout(self):
+        """Background task that waits for timeout duration."""
+        try:
+            await asyncio.sleep(self.timeout_seconds)
+
+            # Timeout reached - invoke callback
+            await self.on_timeout(self.session_name)
+        except asyncio.CancelledError:
+            # Timer was reset by activity
+            pass
+
+    def cancel(self):
+        """Cancel timer on session shutdown."""
+        if self._timer_task and not self._timer_task.done():
+            self._timer_task.cancel()
+
+    @property
+    def seconds_since_activity(self) -> float:
+        """Get seconds elapsed since last activity."""
+        delta = datetime.now(timezone.utc) - self._last_activity
+        return delta.total_seconds()
+```
+
+### Graceful Subprocess Termination with Timeout
+```python
+# Source: https://roguelynn.com/words/asyncio-graceful-shutdowns/
+import asyncio
+import signal
+import logging
+
+logger = logging.getLogger(__name__)
+
+async def terminate_subprocess_gracefully(
+    process: asyncio.subprocess.Process,
+    timeout: int = 5
+) -> None:
+    """
+    Terminate subprocess with graceful shutdown sequence.
+
+    1. Close stdin (signal end of input)
+    2. Send SIGTERM (request graceful shutdown)
+    3. Wait up to timeout seconds
+    4. Send SIGKILL if still running (force kill)
+    5. Always reap process (prevent zombie)
+
+    Args:
+        process: asyncio subprocess to terminate
+        timeout: Seconds to wait before SIGKILL
+    """
+    if not process or process.returncode is not None:
+        logger.debug("Process already terminated")
+        return
+
+    pid = process.pid
+    logger.info(f"Terminating subprocess PID {pid}")
+
+    try:
+        # Close stdin to signal no more input
+        if process.stdin and not process.stdin.is_closing():
+            process.stdin.close()
+            await process.stdin.wait_closed()
+
+        # Send SIGTERM for graceful exit
+        process.terminate()
+
+        # Wait for clean exit with timeout
+        try:
+            await asyncio.wait_for(process.wait(), timeout=timeout)
+            logger.info(f"Process {pid} terminated gracefully")
+        except asyncio.TimeoutError:
+            # Timeout - force kill
+            logger.warning(f"Process {pid} did not exit within {timeout}s, sending SIGKILL")
+            process.kill()
+            await process.wait()  # CRITICAL: Reap to prevent zombie
+            logger.info(f"Process {pid} killed")
+
+    except Exception as e:
+        logger.error(f"Error terminating process {pid}: {e}")
+        # Last resort force kill
+        try:
+            process.kill()
+            await process.wait()
+        except:
+            pass
+```
+
+### Bot Shutdown Signal Handler
+```python
+# Source: https://roguelynn.com/words/asyncio-graceful-shutdowns/ +
+#         https://github.com/wbenny/python-graceful-shutdown
+import signal
+import asyncio
+import logging
+
+logger = logging.getLogger(__name__)
+
+async def shutdown_handler(
+    sig: signal.Signals,
+    loop: asyncio.AbstractEventLoop,
+    idle_timers: dict,
+    subprocesses: dict
+):
+    """
+    Graceful shutdown handler for bot.
+
+    Invoked on SIGTERM/SIGINT to clean up before exit.
+
+    Steps:
+    1. Log signal received
+    2. Cancel all idle timers
+    3. Terminate all subprocesses with timeout
+    4. Cancel all other asyncio tasks
+    5. Stop event loop
+
+    Args:
+        sig: Signal that triggered shutdown
+        loop: Event loop to stop
+        idle_timers: Dict of SessionIdleTimer objects
+        subprocesses: Dict of ClaudeSubprocess objects
+    """
+    logger.info(f"Received exit signal {sig.name}, initiating graceful shutdown")
+
+    # Step 1: Cancel all idle timers
+    logger.info("Canceling idle timers...")
+    for session_name, timer in idle_timers.items():
+        timer.cancel()
+
+    # Step 2: Terminate all active subprocesses
+    logger.info("Terminating subprocesses...")
+    termination_tasks = []
+    for session_name, subprocess in subprocesses.items():
+        if subprocess.is_alive:
+            logger.info(f"Terminating subprocess for '{session_name}'")
+            termination_tasks.append(
+                terminate_subprocess_gracefully(subprocess._process, timeout=5)
+            )
+
+    # Wait for all terminations (with exceptions handled)
+    if termination_tasks:
+        await asyncio.gather(*termination_tasks, return_exceptions=True)
+
+    # Step 3: Cancel all other asyncio tasks
+    logger.info("Canceling remaining tasks...")
+    tasks = [t for t in asyncio.all_tasks() if t is not asyncio.current_task()]
+    for task in tasks:
+        task.cancel()
+
+    # Wait for cancellations, ignore exceptions
+    await asyncio.gather(*tasks, return_exceptions=True)
+
+    # Step 4: Stop event loop
+    logger.info("Stopping event loop")
+    loop.stop()
+
+# Install signal handlers in main()
+def main():
+    """Bot entry point with signal handler installation."""
+    app = Application.builder().token(TOKEN).build()
+
+    # Get event loop
+    loop = asyncio.get_event_loop()
+
+    # Install signal handlers for graceful shutdown
+    signals_to_handle = (signal.SIGTERM, signal.SIGINT)
+    for sig in signals_to_handle:
+        loop.add_signal_handler(
+            sig,
+            lambda s=sig: asyncio.create_task(
+                shutdown_handler(s, loop, idle_timers, subprocesses)
+            )
+        )
+
+    logger.info("Signal handlers installed")
+
+    # Start bot
+    app.run_polling()
+```
+
+### Session Resume with Status Message
+```python
+# Source: https://code.claude.com/docs/en/cli-reference
+from datetime import datetime, timezone
+
+async def resume_suspended_session(
+    bot,
+    chat_id: int,
+    session_name: str,
+    message: str
+) -> None:
+    """
+    Resume suspended session and send message.
+
+    Sends brief status message to user, spawns subprocess with --continue,
+    sends user's message to Claude.
+
+    Args:
+        bot: Telegram bot instance
+        chat_id: Telegram chat ID
+        session_name: Session to resume
+        message: User message to send after resume
+    """
+    metadata = session_manager.get_session(session_name)
+
+    # Calculate idle duration
+    last_active = datetime.fromisoformat(metadata['last_active'])
+    now = datetime.now(timezone.utc)
+    idle_minutes = (now - last_active).total_seconds() / 60
+
+    # Send status message
+    if idle_minutes > 1:
+        status_text = f"Resuming session (idle for {int(idle_minutes)} min)..."
+    else:
+        status_text = "Resuming session..."
+
+    await bot.send_message(chat_id=chat_id, text=status_text)
+
+    # Spawn subprocess with --continue
+    session_dir = session_manager.get_session_dir(session_name)
+    persona = load_persona_for_session(session_name)
+
+    callbacks = make_callbacks(bot, chat_id, session_name)
+
+    subprocess = ClaudeSubprocess(
+        session_dir=session_dir,
+        persona=persona,
+        on_output=callbacks['on_output'],
+        on_error=callbacks['on_error'],
+        on_complete=lambda: on_completion(session_name),
+        on_status=callbacks['on_status'],
+        on_tool_use=callbacks['on_tool_use'],
+    )
+
+    await subprocess.start()
+    subprocesses[session_name] = subprocess
+
+    # Update metadata
+    session_manager.update_session(
+        session_name,
+        status='active',
+        last_active=now.isoformat(),
+        pid=subprocess._process.pid
+    )
+
+    # Send user's message
+    await subprocess.send_message(message)
+
+    # Start idle timer
+    timeout = metadata.get('idle_timeout', 600)
+    idle_timers[session_name] = SessionIdleTimer(
+        session_name,
+        timeout,
+        on_timeout=suspend_session
+    )
+```
+
+## State of the Art
+
+| Old Approach | Current Approach | When Changed | Impact |
+|--------------|------------------|--------------|--------|
+| Manual timestamp polling | asyncio.Event + asyncio.sleep() | asyncio maturity (2020+) | Cleaner cancellation, no polling overhead |
+| SIGKILL only | SIGTERM + timeout + SIGKILL fallback | Best practice evolution (2018+) | Prevents zombie processes, allows cleanup |
+| Global timeout thread | Per-object asyncio tasks | Modern asyncio patterns (2022+) | Per-session configuration, native async integration |
+| Manual state files | Claude Code --continue with .claude/ | Claude Code 2.0+ (2024) | Built-in, tested, handles edge cases |
+| SIGSTOP/SIGCONT | SIGTERM + restart | Resource efficiency awareness (ongoing) | Releases memory during idle, safer for long periods |
+
+**Deprecated/outdated:**
+- **Thread-based timers for async code:** Mixing threading with asyncio adds complexity, use asyncio.create_task
+- **Blocking time.sleep() in async context:** Use asyncio.sleep() instead
+- **Not reaping terminated subprocesses:** Always call process.wait() to prevent zombies
+
+## Open Questions
+
+Things that couldn't be fully resolved:
+
+1. **Optimal default idle timeout**
+   - What we know: Common ranges are 5-15 minutes for chat bots, longer for task automation
+   - What's unclear: What's the sweet spot for balancing memory usage vs restart friction?
+   - Recommendation: Start with 10 minutes default. Allow per-session override via /timeout. Monitor actual usage patterns and adjust.
+
+2. **SIGSTOP/SIGCONT vs SIGTERM tradeoff**
+   - What we know: SIGSTOP keeps memory but saves restart cost (~1s), SIGTERM releases memory but costs CPU
+   - What's unclear: At what idle duration does memory savings outweigh restart cost?
+   - Recommendation: Use SIGTERM approach. Memory release is more important than 1s restart cost. Claude processes can grow large (100-500MB) with long conversations. SIGSTOP is only beneficial for <5min idle periods.
+
+3. **Resume status message verbosity**
+   - What we know: User decision says "brief status message on resume"
+   - What's unclear: Should it show idle duration? Session name? Model?
+   - Recommendation: Show idle duration if >1 minute ("Resuming session (idle for 15 min)..."). Don't show session name (user knows what session they messaged). Keep brief.
+
+4. **Multi-session concurrent subprocess limit**
+   - What we know: Multiple sessions can have live subprocesses simultaneously
+   - What's unclear: Should there be a cap? What if user has 20 sessions all active?
+   - Recommendation: No hard cap initially. Each subprocess uses ~100-500MB. On an 8GB system, 10-20 concurrent sessions is reasonable. Add warning in /sessions if >10 active. Add global concurrent limit (e.g., 15) in Phase 4 if needed.
+
+5. **Session switch behavior for previous subprocess**
+   - What we know: User decision says "switching leaves previous subprocess running"
+   - What's unclear: Should switching reset the previous session's idle timer?
+   - Recommendation: Don't reset on switch. Previous session's timer continues from last activity. If it was idle for 8 minutes when you switched away, it will suspend in 2 more minutes. This is intuitive — switching doesn't "touch" the old session.
+
+## Sources
+
+### Primary (HIGH confidence)
+- [Coroutines and Tasks - Python 3.14.3 Documentation](https://docs.python.org/3/library/asyncio-task.html) - Official asyncio timeout and task management
+- [CLI reference - Claude Code Docs](https://code.claude.com/docs/en/cli-reference) - Official Claude Code --continue flag documentation
+- [Graceful Shutdowns with asyncio - roguelynn](https://roguelynn.com/words/asyncio-graceful-shutdowns/) - Signal handlers and shutdown orchestration
+- [python-graceful-shutdown - GitHub](https://github.com/wbenny/python-graceful-shutdown) - Complete example of shutdown patterns
+- [Stopping and Resuming Processes with SIGSTOP and SIGCONT - TheLinuxCode](https://thelinuxcode.com/stop-process-using-sigstop-signal-linux/) - SIGSTOP/SIGCONT behavior and resource tradeoffs
+
+### Secondary (MEDIUM confidence)
+- [Session Management - Claude API Docs](https://platform.claude.com/docs/en/agent-sdk/sessions) - Session persistence patterns
+- [SIGTERM, SIGKILL & SIGSTOP Signals - Medium](https://medium.com/@4techusage/sigterm-sigkill-sigstop-signals-63cb919431e8) - Signal comparison
+- [A Complete Guide to Timeouts in Python - Better Stack](https://betterstack.com/community/guides/scaling-python/python-timeouts/) - Timeout mechanisms in Python
+
+### Tertiary (LOW confidence)
+- WebSearch results on asyncio subprocess management and idle detection patterns - Multiple sources, cross-referenced
+
+## Metadata
+
+**Confidence breakdown:**
+- Standard stack: HIGH - All stdlib components, Claude Code CLI verified
+- Architecture: HIGH - Patterns based on official asyncio docs and battle-tested libraries
+- Pitfalls: MEDIUM-HIGH - Common races and edge cases documented, some based on general async patterns rather than lifecycle-specific sources
+
+**Research date:** 2026-02-04
+**Valid until:** 2026-03-04 (30 days - asyncio stdlib is stable, Claude Code --continue is established)