feat(desktop): add daemon auto-restart and health check

[Kitenite]

Summary

• Add automatic daemon restart with exponential backoff when the terminal host daemon crashes or becomes unresponsive
• Add periodic health check (ping every 30s) to proactively detect stale daemons
• Add ping IPC command that returns daemon uptime and active session count
• Handle protocol version skew gracefully (older daemons without ping support)

Changes

Client (client.ts):

• Auto-restart on disconnect with exponential backoff (500ms → 30s, max 10 attempts)
• Periodic health check via ping, triggers restart on timeout
• New reconnected event emitted on successful auto-restart
• setAutoRestart() and setHealthCheck() methods for runtime control

Daemon (index.ts):

• Add ping handler with role check (control only)
• Defensive socket write handling (socket.writable checks)
• Extract removeStreamSocket() helper to reduce duplication

Types (types.ts):

• Add PingRequest / PingResponse types

Test plan

• Kill daemon manually (kill -9 <pid>) and verify auto-restart
• Verify health check detects frozen daemon
• Verify older daemon (without ping) disables health checks gracefully
• Verify reconnected event fires on successful restart

Summary by CodeRabbit

• New Features

  • Terminal daemon connections now auto-restart on disconnection using exponential backoff strategy
  • Health check mechanism monitors daemon responsiveness with automatic fallback for older systems
  • New reconnected event notifies when auto-restart succeeds

• Improvements

  • Enhanced server socket lifecycle and error handling robustness
  • Improved logging for unhandled exceptions and rejections

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

The changes add health check and auto-restart capabilities to the TerminalHostClient, implementing a ping-based health monitoring mechanism with exponential backoff auto-restart logic. New IPC types and daemon-side ping handler support this functionality with more robust socket management.

Changes

Cohort / File(s)	Summary
Client Health Check & Auto-Restart apps/desktop/src/main/lib/terminal-host/client.ts	Introduced exponential backoff auto-restart (500ms initial, 30s max, 2x factor, 10 max attempts) triggered on disconnect if previously connected. Added health check mechanism (30s interval, 5s per-check timeout) that disables gracefully for unsupported daemons. New public methods: ping() and setAutoRestart(), plus reconnected event. Internal state tracking for both subsystems with lifecycle management.
IPC Protocol Types apps/desktop/src/main/lib/terminal-host/types.ts	Added PingRequest and PingResponse types with fields for client timestamp, daemon uptime, and active session count. Registered ping entry in RequestTypeMap.
Daemon Ping Handler & Socket Robustness apps/desktop/src/main/terminal-host/index.ts	Implemented ping IPC handler with auth and control-role validation, responding with daemon uptime (computed from DAEMON_START_TIME) and active session count. Enhanced socket management with removeStreamSocket() helper and defensive checks before writes (skip destroyed/unwritable sockets, cleanup on failure). Wrapped response sending in try-catch. Updated error logging to indicate restart behavior.

Sequence Diagram

sequenceDiagram
    participant Client as TerminalHostClient
    participant Timer as Auto-Restart Timer
    participant Daemon as Terminal Host Daemon
    
    Note over Client,Daemon: Healthy State
    Client->>Daemon: ensureConnected()
    Daemon-->>Client: connected
    Client->>Client: resetAutoRestartState()
    Client->>Client: startHealthCheck()
    
    Note over Client,Daemon: Health Check Cycle
    Client->>Client: performHealthCheck()
    Client->>Daemon: ping(request)
    Daemon-->>Client: pong(uptime, sessions)
    Note over Client: Health OK, continue
    
    Note over Client,Daemon: Connection Lost
    Daemon--xClient: disconnect
    Client->>Client: Is autoRestartEnabled?
    alt Auto-Restart Enabled
        Client->>Timer: scheduleAutoRestart(initialDelay)
        Timer->>Client: timeout
        Client->>Client: attemptAutoRestart()
        alt Reconnection Success
            Client->>Daemon: ensureConnected()
            Daemon-->>Client: reconnected
            Client->>Client: resetAutoRestartState()
            Client->>Client: emit reconnected event
        else Retry with Backoff
            Client->>Timer: scheduleAutoRestart(delay × 2)
            Note over Client: Exponential backoff up to 10 attempts
        end
    else Auto-Restart Disabled
        Note over Client: Stay disconnected
    end

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~30 minutes

Possibly related PRs

• feat(desktop): terminal persistence via daemon process #619 — Foundational PR that introduces the terminal-host daemon and client infrastructure that these changes extend with health checks and auto-restart.

Suggested reviewers

• AviPeltz

Poem

🐰 Ping, ping! the client cries with glee,
Checking if the daemon's still free,
When connection fades, don't lose hope,
With exponential backoff we cope,
Hop, hop, reconnect—let's ski! 🚀✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 14.29% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main changes: adding daemon auto-restart and health check functionality to the desktop application.
Description check	✅ Passed	The PR description is well-structured, covering all key sections: summary of changes, detailed breakdown by file, new types, and a comprehensive test plan. It aligns with the required template structure.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

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