openchamber/packages/web/server/lib/terminal/DOCUMENTATION.md

Terminal Subsystem

Ownership

runtime.js owns terminal identity, PTY processes, launch mode, session purpose, ordered output, bounded scrollback, WebSocket attachments, and lifecycle routes. shells.js discovers executable shell families, resolves the persisted shell ID, and builds the per-shell argv for interactive versus command launches. Clients own tab arrangement. Interactive terminals use stable IDs; project actions keep a stable UI tab and allocate a fresh terminal ID for each command execution. Electron uses this same runtime in-process; VS Code returns an explicit unsupported error.

Protocol

/api/terminal/ws is the only terminal data transport. It uses v3 binary JSON control frames and is opened through openRuntimeWebSocket, preserving direct, Electron proxy, URL-token authentication, and private-relay routing.

• attach registers a connection for one terminal. One socket may attach to many terminals.
• Every attach and reconnect begins with an authoritative snapshot containing bounded history, the current sequence, and the PTY cols/rows the history was drawn for. The client replays the history at that size before fitting its viewport; replaying shell output at another width leaves stray fragments that the shell's own SIGWINCH redraw never clears.
• A current socket that closes or errors before its initial open invalidates its URL-scoped auth token before retrying, so retries mint a fresh token instead of backing off against a rejected upgrade. Hidden or offline clients wait 60 seconds and wake promptly on visibility/online recovery.
• output, exit, and restarted carry monotonically increasing per-terminal sequences. Output carries raw live bytes plus replay-safe bytes with terminal query exchanges removed.
• Attach registers before capturing the snapshot, buffers concurrent events, drops events represented by the snapshot sequence, then enters live delivery.
• write always includes the terminal ID; sockets never have mutable single-terminal binding state.
• detach removes only that attachment.
• Creation carries the active UI appearance. The PTY sets COLORFGBG and answers OSC 10, OSC 11, Mode 2031, and primary-device-attribute queries immediately, including queries emitted before a WebSocket attachment exists. The DA1 fallback prevents Fish from waiting ten seconds for a renderer that cannot observe or answer its startup query. Subscribed TUIs receive a Mode 2031 notification when the appearance changes.

HTTP remains the authenticated command plane for create, resize, appearance updates, restart, close, and force-kill. There is no SSE output or HTTP input compatibility path.

GET /api/terminal/sessions enumerates live sessions (optionally filtered by resolved cwd) so clients can adopt terminals their local tab projection does not know about — another device, a new browser tab, or cleared storage. Listings include the effective launch mode and the normalized purpose, but never the command text. POST /api/terminal/touch refreshes lastActivity for the listed session ids; open clients call it periodically so background tabs, which hold no WebSocket attachment, are not idle-reaped while a client still shows them.

PTY Lifecycle

• IDs are client-provided or generated with randomUUID().
• Create defaults to interactive mode. Command mode requires a non-empty trimmed command no longer than the terminal input limit and launches the shell so the PTY exits when that command exits. Each session also carries a normalized purpose. Omitted purpose means { type: 'terminal' }. Project actions use { type: 'project-action', actionId, executionId }, and the server validates both IDs as non-empty bounded strings. Create responses and attach snapshots echo the effective mode and purpose.
• Concurrent creates for one ID are single-flight only when working directory, shell preference, login mode, launch mode, and session purpose match. Command-mode creates must also match the command text, unless the purpose is a project action that is already running for the same resolved (cwd, actionId) pair. In that case the runtime returns the existing session and its existing execution identity, even when another client requested a different session ID. Existing IDs cannot be reused for another working directory or another purpose.
• Dimensions are bounded to 1-1000 columns and 1-500 rows; input is capped at 64 KiB.
• A client may create before its renderer has mounted. It derives an initial size from the container and font metrics (falling back to 80x24 when unavailable), then sends a resize once Ghostty reports its final dimensions. This allows shell startup and renderer initialization to overlap.
• PTY children never inherit NODE_CHANNEL_FD; daemon IPC descriptors are host-private and invalid after PTY descriptor cleanup, and an inherited value (even empty) makes Node CLIs such as opencode print Failed to parse IPC channel number on exit.
• PTY children also strip AppImage ARGV0 (and other host-private shell vars such as ELECTRON_RUN_AS_NODE, BASH_ENV, ENV, BASH_XTRACEFD). An exported ARGV0 makes zsh rewrite argv[0] for every external command, which breaks Python venv detection and other argv[0]/$0 consumers while leaving /proc/self/exe correct. On POSIX, PTY spawn is wrapped with env -u ARGV0 -u NODE_CHANNEL_FD (resolvePosixPtyLaunch) because bun-pty merges the native OS environ and would otherwise reintroduce both after a JS-only delete.
• GET /api/terminal/shells reports shell IDs available on the active server using the same augmented PATH provided to spawned PTYs, plus whether each executable has a supported login-mode argument. auto preserves environment/platform fallback order; an explicit unavailable shell fails creation instead of silently running a different shell. Login mode is opt-in and uses only built-in arguments for known shells. Interactive shells still launch as before. Command-mode launches reuse the same environment and login support, but switch argv by shell family: POSIX and Fish use interactive -c, Nushell uses -c, PowerShell uses -Command, and cmd uses /d /s /c. Preference changes affect new sessions and explicit restarts, not running PTYs.
• PTY data and exit callbacks enter one FIFO queue. The runtime wires those listeners in the same synchronous turn that receives the PTY object. node-pty and bun-pty both expose the PTY before dispatching registered callbacks. If a backend emitted exit before listener registration, this layer could not recover it, so the wiring stays adjacent to PTY creation.
• Scrollback is retained on the server and capped at 512 KiB with UTF-8-safe trimming. Device-status, device-attribute, cursor-position reply, and color-query exchanges are removed from replay history with incomplete control sequences carried across PTY chunks; live output remains byte-for-byte unchanged.
• Exited sessions remain attachable until explicit close, idle cleanup, or a successful replacement of the same project action. Creating a replacement retires only exited records for the same resolved directory and action, after the new PTY starts. Failed creation preserves the old record and output. These replaced records do not exhaust the terminal capacity limit.
• Deduplicated create responses may describe another client's execution. Cancellation cleanup closes only the terminal ID allocated for the cancelled request; it never closes an adopted peer execution.
• Create and restart validate the working directory with a real stat and answer HTTP 400 Invalid working directory when it is not a directory. When the path does not exist at all (ENOENT/ENOTDIR, a worktree deleted outside OpenChamber) the body also carries code: "TERMINAL_CWD_MISSING". The client shows the failure without moving the session. The runtime never substitutes a parent directory on its own.
• Restarts are serialized per terminal. Each restart spawns and wires the replacement before terminating the old process, retaining the terminal ID. Command-mode sessions reject restart with HTTP 400 instead of silently turning into interactive shells with stale action metadata.
• A delete that arrives while create is still pending leaves a cancellation tombstone. When the PTY arrives, the runtime terminates it immediately, never inserts the session into the live map, and returns a create error while the delete still succeeds.
• Close uses SIGTERM with bounded SIGKILL escalation. Force-kill, idle cleanup, and runtime shutdown terminate process groups immediately where supported. Removal explicitly sends a fatal scoped closure and evicts client projections even when a PTY backend fails to emit onExit; attached terminals are not considered idle.

Security And Relay

The WebSocket path must remain in both isUrlAuthWebSocketPath and relay ALLOWED_WS_PATHS. The client must use getRuntimeUrlResolver().websocket() and openRuntimeWebSocket; direct local URLs or raw browser WebSockets break relay and URL-token authentication.

Verification

Run:

bun test packages/web/server/lib/terminal/runtime.test.js packages/web/server/lib/terminal/terminal-ws-protocol.test.js
bun test packages/web/server/lib/ui-auth/ui-auth.test.js packages/web/server/lib/relay/cross-compat.test.js