🤖 Implement SSH connection pooling

[ammar-agent]

Problem

SSHRuntime generated random controlPaths for each instance, preventing SSH ControlMaster from multiplexing connections. This meant every workspace operation opened a new TCP connection to the remote host, even when targeting the same server.

Solution

Replaced random controlPath generation with deterministic hashing based on connection config (host, port, srcBaseDir, identityFile). Identical configs now produce identical controlPaths, enabling SSH ControlMaster to automatically multiplex connections.

Key changes:

• New sshConnectionPool module with pure function for deterministic controlPath generation (~53 lines)
• SSHRuntime constructor uses getControlPath(config) instead of random IDs
• Added ControlMaster options to buildSSHArgs() so git bundle transfers also multiplex
• Simplified dispose() to no-op since ControlPersist=60 handles cleanup automatically

Design approach:

• Pure functions only - no state management, no reference counting, no cleanup timers
• Filesystem is the state (socket files in /tmp managed by SSH)
• Pool is private implementation detail of SSHRuntime (perfect SoC)

Impact

Performance:

• 10× fewer SSH connections for bulk operations (e.g., 10 workspaces = 1 connection vs 10)
• Saves 50-200ms per operation (eliminates SSH handshake overhead)
• Prevents exhausting SSH MaxSessions or rate limits

Example:

// Before: Each runtime gets random controlPath
const r1 = new SSHRuntime({host: "dev.com", srcBaseDir: "/work"});
// controlPath: /tmp/cmux-ssh-a1b2c3d4 (random)

const r2 = new SSHRuntime({host: "dev.com", srcBaseDir: "/work"});
// controlPath: /tmp/cmux-ssh-e5f6g7h8 (different random!)
// Result: 2 separate TCP connections

// After: Same config produces same controlPath
const r1 = new SSHRuntime({host: "dev.com", srcBaseDir: "/work"});
// controlPath: /tmp/cmux-ssh-abc123def456 (deterministic hash)

const r2 = new SSHRuntime({host: "dev.com", srcBaseDir: "/work"});
// controlPath: /tmp/cmux-ssh-abc123def456 (same hash!)
// Result: 1 shared TCP connection, auto-cleanup after 60s idle

Testing

• Added 8 unit tests for connection pool (all passing)
• All 806 existing tests still pass
• Verified SSHRuntime instances with same config share controlPath
• Verified buildSSHArgs includes ControlMaster options

Generated with cmux

[chatgpt-codex-connector]

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