Codeman/docs/remote-sessions.md

Remote Sessions (SSH)

Codeman can run a session's agent on a remote host over SSH instead of the local machine. The agent (Claude, OpenCode, Codex, Antigravity, Gemini, Pi, Grok, or a plain shell) runs inside a tmux server on the remote host, so it survives the SSH connection dropping; Codeman attaches to it the same way it attaches to a local managed session.

This document covers the data model, the shell-safe SSH command construction (COD-107), the durable-launch design (COD-104), and the operational caveats. For the local session/mux machinery this builds on, see the Mux and Session entries in CLAUDE.md → Architecture.

Why it exists

A developer box (AA-DESKTOP) often needs to drive an agent on another machine — a NAS, a build server, a host reachable only through a jump box or a cloudflared SOCKS5 proxy. Rather than wrap ssh by hand per host, Codeman stores reusable remote hosts + remote cases and reproduces the exact connection the operator already uses (ssh-aa-desktop-style configs: custom port, identity file, -J jump host, -o ProxyCommand).

Data model

Types live in src/types/session.ts; persistence in src/remote-hosts.ts.

Type	Role
RemoteSshOptions	The HOW-to-reach fields, shared by host + session: identityFile, socksProxy (host:port), jumpHost ([user@]host[:port]), extraSshOptions (KEY=VALUE[]). Every field optional — all-absent reproduces port-22, default-identity, directly-SSH-able behavior.
RemoteHost (extends RemoteSshOptions)	A saved host: id, label, host, username, port?, commands? (per-mode launch command override).
RemoteCase	A working directory on a host: name, type: 'remote', hostId, remotePath.
SessionRemote (extends RemoteSshOptions)	The resolved bundle stamped onto a live session: host coordinates + remotePath + commands, plus owned? and remoteSessionName? (COD-105 — see Ownership). Built by toSessionRemote(host, case) (sets owned: true) for the launch path, or toAttachedSessionRemote(host, name, path) (sets owned: false) for the attach path. Both copy the advanced SSH options through so every connection is identical.
RemoteCommandMode	Extract<SessionMode, 'shell' | 'claude' | 'opencode' | 'codex' | 'gemini' | 'antigravity' | 'pi' | 'grok' | 'deepseek' | 'omp'> — the modes that can run remotely.
RemoteSessionInfo (COD-105)	One discovered remote tmux session: name (always codeman-*), attached (a client is connected), created (epoch s), windows. Returned by listRemoteCodemanSessions().

Persistence is two flat JSON arrays in the instance data dir:

• ~/.codeman/remote-hosts.json — readRemoteHosts() / writeRemoteHosts()
• ~/.codeman/remote-cases.json — readRemoteCases() / writeRemoteCases()

(Paths via remoteHostsPath() / remoteCasesPath(); both honor CODEMAN_INSTANCE because the config dir is the instance data dir.)

On the live Session, the remote rides as _remote?: SessionRemote. When attaching, resolveMuxAttachCwd() forces the cwd to /tmp for remote sessions — the local working directory is meaningless on the remote box.

SSH command construction (COD-107 — the injection surface)

All SSH command lines flow through one function so user-controlled fields are escaped once and the launch + prereq probe can never drift apart:

// src/remote-hosts.ts
buildSshConnectionArgs(remote: RemoteSshOptions & Pick<RemoteHost, 'port'>): string[]

It returns the ordered leading tokens of an ssh command line (no -t, no target, no remote command):

ssh -o BatchMode=yes
    [-p <port>]
    [-i <abs-identity>]            # ~ / $HOME expanded, then shellescaped
    [-J <jumpHost>]                # shellescaped, single token
    [-o ProxyCommand=nc -X 5 -x <socks> %h %p]   # ONE shellescaped -o token
    [-o <KEY=VALUE>] …             # each extra option, shellescaped

Rules that keep this safe — do not bypass them by hand-building an ssh line elsewhere:

• Every user-controlled value (-i, -J, -o, ProxyCommand) is POSIX single-quote shellescaped ('…' with embedded '\''). The helper mirrors the one in tmux-manager.ts.
• ~/$HOME in identityFile is expanded at build time (expandIdentityPath), before escaping — ssh does not expand ~ inside -i, and the escaped value never reaches a shell that would.
• The ProxyCommand is one shellescaped -o KEY=VALUE token, so its spaces and the %h/%p placeholders reach ssh as a single argument. %h %p survive verbatim — ssh expands them to the real host/port, not the shell.
• Empty options ⇒ ['ssh', '-o BatchMode=yes'] (+ -p only when set) — byte-identical to the historical behavior.

Token construction is unit-tested independently of any live connection (see test/ for buildSshConnectionArgs / buildRemoteTmuxCheckCommand cases).

Durable launch (COD-104)

buildRemoteLaunchCommand({ mode, remote, sessionId }) in tmux-manager.ts builds the command that launches (or reattaches to) the remote session:

ssh -o BatchMode=yes -t <connection-args> user@host \
  'tmux -L codeman-remote new-session -A -s codeman-ssh-<id8> -c <remotePath> "cd <remotePath> && exec <cli>" \; \
     set -t codeman-ssh-<id8> status off \; set -t codeman-ssh-<id8> mouse off \; \
     set -t codeman-ssh-<id8> prefix C-q \; set -s escape-time 0 \; \
     set -t codeman-ssh-<id8> window-size latest'

Key points:

• new-session -A -s codeman-ssh-<id8> = attach-if-exists-else-create, so a reconnect (same deterministic remoteTmuxSessionName(sessionId) — codeman-ssh- + the first 8 chars of the session id) lands back in the same remote session rather than spawning a duplicate. This is what makes the remote agent survive an SSH drop. The name deliberately fails SAFE_MUX_NAME_PATTERN so a Codeman running ON the remote host never adopts it.
• -L codeman-remote = a DEDICATED socket for sessions launched by remote Codemans, NOT the canonical -L codeman socket the remote host's own Codeman uses. Options are set per-session (set -t), never -g, so a shared remote tmux server's other sessions are untouched (#145 hardening). Note the asymmetry: discovery/attach (COD-105) target the canonical -L codeman socket — they join sessions the remote's own Codeman manages, while owned durable launches live on -L codeman-remote.
• exec <cli> replaces the pane shell with the agent, so the pane PID is the agent. The per-mode command comes from remote.commands?.[mode] or defaultRemoteCommandForMode(mode) (exec claude / exec opencode / exec codex / exec gemini / exec agy / exec bash -l). ⚠️ claude and omp no longer take that path: both have their own arm in buildRemoteLaunchCommand so a respawn can continue the same conversation (see Respawn / reattach continuation), and because the claude arm is an a || b pair under -c, its pane PID is the login shell, not the agent.
• The whole tmux invocation is a single shell-quoted ssh argument, and the pane command is independently quoted, so a remotePath with spaces is safe.
• Connection options come from the same buildSshConnectionArgs(remote) as the prereq probe; -t is inserted right after ssh -o BatchMode=yes, preserving historical token order.

tmux prerequisite probe

Because durable remote sessions require tmux on the remote host, checkRemoteTmuxAvailable(host) runs command -v tmux over SSH before creating a remote case/session and returns a structured, never-throwing result:

• empty stdout / non-zero exit → "remote host <host> needs tmux installed for durable remote sessions"
• stderr present → "could not verify tmux on remote host <host>: <stderr>" (a real connection failure, surfaced to the operator)
• success → { ok: true, tmuxPath }

It connects with the identical options as the launch (buildRemoteTmuxCheckCommand reuses buildSshConnectionArgs and inserts -o ConnectTimeout=10), so a proxied/custom-port/identity host that the launch can reach also passes the probe (and vice-versa).

Test-mode short-circuit: under VITEST the probe returns { ok: true, tmuxPath: '(test-mode)' } without opening a socket — mirroring TmuxManager's no-op-shell-under-VITEST (IS_TEST_MODE). Without it, remote-case create-path tests would hit a real ~10s ssh timeout. Only the live probe is skipped; command construction is still asserted by unit tests.

Ownership: launched vs. discovered-and-attached (COD-105)

COD-104 (above) was Phase 1 — Codeman launches a remote session and owns it. COD-105 is Phase 2 — Codeman can also discover codeman-* tmux sessions already running on a remote host (created by the remote's own Codeman or another instance) and attach to one it didn't launch. Ownership decides what happens when the tab closes.

SessionRemote.owned carries this:

• owned: true (or absent — legacy/COD-104 sessions persisted before this field) — we launched it via buildRemoteLaunchCommand and may explicitly kill it.
• owned: false — discovered + attached; another Codeman owns the remote session. remoteSessionName holds its existing tmux name. Closing the tab detaches, never kills.

Discovery

listRemoteCodemanSessions(host) lists the remote's codeman-* sessions:

• buildRemoteListSessionsCommand() runs tmux -L codeman list-sessions -F "…" over SSH (connection args from the shared buildSshConnectionArgs, so discovery connects identically to launch/probe). 2>/dev/null swallows tmux's "no server running" stderr.
• parseRemoteSessionList() is a pure, unit-tested parser. ⚠️ Quirk: the remote tmux's -F "…\t…" format emits the literal two-character \t, not a real tab (verified on tmux next-3.7), so the parser splits on /\\t|\t/ (literal backslash-t or a real tab, for builds that do expand it). It keeps only codeman-* names, coerces types, and skips malformed lines.
• listRemoteCodemanSessions() never throws — unreachable host / no tmux / no sessions all map to []. Like the prereq probe, it no-ops to [] under VITEST so a request path never opens a real ssh connection.

Discovery is explicit — the UI has a "Discover existing sessions" button per host; Codeman never auto-discovers on host select.

Attach vs. launch selection

buildRemoteSessionCommand(mode, remote, sessionId) in tmux-manager.ts picks the remote command line by ownership:

• owned === false → buildRemoteAttachCommand(remote, name) — emits ssh … -t … 'tmux -L codeman attach -t <remoteSessionName>'. It uses attach, NOT new-session -A, so it only joins an existing session and never creates one.
• owned (default) → buildRemoteLaunchCommand (the COD-104 path above).

Detach-not-kill

TmuxManager.killSession() has an early return for non-owned remote sessions: it tears down only the LOCAL pane holding the ssh client (tmux -L codeman kill-session on this host's socket). Killing the local ssh sends SIGHUP to the remote tmux attach, which detaches — the durable remote session survives. The early return is a structural guarantee that no code path can ever issue a remote kill-session for a session we don't own — the only kill-session run is on the local socket, which never reaches the remote socket.

Respawn / reattach continuation

A dropped connection or a dead pane must reconnect to the same conversation, not launch a fresh one — the whole point of a durable remote session.

• Claude: the launch command is idempotent — claude --session-id <id> || claude --resume <id> (see buildRemoteLaunchCommand's claude branch). The first run creates the conversation under the deterministic session id; every later reattach/respawn re-runs the same line, --session-id fails ("already in use"), and the || fallback resumes it.
• OMP: omp has no equivalent idempotent single-line form, so Session._pinOmpRespawnId() resolves and pins an explicit --resume <id> before a respawn (mirroring the local/docker builders, rendered through the same buildSpawnCommandFromRegistry engine — not a hand-rolled command and not appendResumeFlag(), which is docker-only and cannot work here: appending a flag after the quoted -c 'omp' hands the id to the login shell as $0 instead of to omp). ⚠️ The resolver only ever reads THIS host's local ~/.omp/agent/sessions/, which is meaningless for a remote session — the conversation and its session file live on the remote host, under the remote user's home. For a remote session, _pinOmpRespawnId() therefore skips local resolution entirely and falls back to omp's own ambiguous --continue (ompConfig.continueSession), which the remote pane command already renders. This is a known, accepted degradation versus the local/docker paths' exact --resume pin — safe in practice because each remote respawn talks to exactly one remote pane's own omp history, so "most recent" is normally correct, but it can drift the same way --continue always could if two remote sessions ever share one remote directory.

Auto-reconnect vs. a clean agent exit

remoteAutoReconnect (default ON) watches for a dropped SSH connection and reconnects with bounded backoff. It must never revive a session whose agent exited cleanly (Ctrl-C, Ctrl-D, exit) — that tears down the durable remote tmux session itself, and a transport-level isPaneDead() cannot tell that apart from a plain network drop. remoteTmuxSessionAlive() (#355) resolves this by probing the remote host directly: tmux -L codeman-remote has-session -t codeman-ssh-<id8> over the same buildSshConnectionArgs as launch, classified by exit status alone (classifyRemoteAliveExit: 0 = alive, ssh's 255 or a timeout = unknown, anything else = gone) — has-session prints nothing on success, so reading stdout would misclassify every live session as gone. An unreachable host answers "unknown", which also means do not revive. The answer is cached per session and cleared whenever the pane is next seen alive, so a stale true from one transport drop can never revive the NEXT clean exit.

File access over SSH

A remote case's workingDir is an absolute path on the remote host (Session.workingDir = RemoteCase.remotePath), so the file routes cannot use local fs: a local realpathSync on a remote-only path fails by construction, which is why previewing a file used to answer 404 File not found for a case that was working perfectly (#415). src/remote-files.ts is the one module that reads remote bytes, and it follows the same rule as the launch path: every ssh command line comes from buildSshConnectionArgs() — never a hand-built ssh line.

Request	What happens
GET /api/sessions/:id/file-raw	Streamed over ssh (cat, or tail -c +N | head -c L for a Range); the same 200/206/416 contract as a local file, so <video>/<audio> seeking works
GET /api/sessions/:id/file-content	cat into memory, capped by the existing text limit; edit=1 answers 400 (see below) and editable is always false
GET /api/sessions/:id/file-preview	Non-office files redirect to file-raw (which works remotely); docx/pptx answer 400
GET /api/sessions/:id/file-thumbnail	400 for remote files
POST /api/sessions/:id/attachments	Registers an absolute path that lives on the remote host (a clicked link pointing outside the case directory) by probing it there
GET /api/sessions/:id/attachments/:attachmentId/raw	Streams the registered remote file over ssh, same 200/206/416 contract; preview (office) and thumbnail answer 400
GET /api/sessions/:id/attachments/:attachmentId, GET …/attachments (history)	Size/mtime/existence resolved over ssh, so a remote entry is not reported missing

⚠️ The attachment route is the one a clicked path takes when it is outside the case directory (a remote /tmp scratchpad capture, a screenshot elsewhere in the home dir): the frontend's _isExternalPreviewPath() sends every absolute path that is not under workingDir there, so fixing only file-raw would leave exactly that half broken.

Guard order is deliberately the same as locally, and the checks are not weakened by the transport:

1. Ownership (findSessionOrFail / the scope helper) — unchanged.
2. Lexical containment of workingDir + path — a ../ escape is refused before any connection is opened.
3. ONE ssh round trip that returns realpath and stat for the path and the workspace root (remoteProbePaths). Resolving the root remotely is what keeps the boundary honest for a symlinked remotePath; the probe uses readlink -f when available and a POSIX cd/pwd -P fallback otherwise.
4. Containment of the remote realpath against the remote root. The sensitive-path blocklist then applies on whichever routes already apply it locally (/api/download, attachment registration, edit mode — where resolving symlinks first is what makes it meaningful); the remote branch neither drops a guard the local path has nor invents a stricter one.
5. Size cap (CODEMAN_MAX_DOWNLOAD_BYTES) applied to the remote size, before the body is requested.

The path arrives from the browser (?path=) and is interpolated as a single shellescape-quoted token, in a command that is itself shellescaped into the ssh line; BatchMode=yes means a host needing a passphrase fails fast instead of hanging. A failed connection is reported as 502 with the remote reason — never a 404, which used to make an unreachable host look like a typo in the agent's output.

⚠️ There is deliberately NO local fallback. A remote case reads the remote bytes or fails, even when a file with the same absolute name exists on the Codeman host — which is the ordinary case for the documented stop-gap workaround, an sshfs mount of the remote tree at the identical path. Serving the local twin instead would silently hand back a DIFFERENT filesystem's bytes under a name the user believes is the remote file (a stale mount, a different checkout, a leftover file), and the failure would be invisible. An existing mount therefore stops being load-bearing for previews and downloads but is harmless, and a missing remote file stays a 404 even if the mount still has it.

Not available over ssh (by choice, not by accident): editing a file (writes would need SFTP; docs/file-viewer-edit-plan.md §6), office-document previews and generated thumbnails (both need the bytes on the server's disk — no remote file is ever spilled onto the server), the file-tree/picker listings, and tail-file. Those routes are still local-only, so with an sshfs mount in place they read the mounted copy — the two views can only disagree when that mount is stale. Docker cases are unaffected: their workspace is bind-mounted at the same absolute path, so local fs reads real bytes.

⚠️ A remote record stores the remote path, and the same absolute path STRING means a different file on each host. What decides which host to read is therefore never the path but the SESSION (session.remote): a remote session never falls back to local fs, and a local session never opens an ssh connection — including for attachment records, which are keyed to the session that registered them.

API

Routes are registered in src/web/routes/case-routes.ts:

Method	Path	Purpose
GET	/api/remote-hosts	List saved hosts
POST	/api/remote-hosts	Create a host
PUT	/api/remote-hosts/:id	Update a host
DELETE	/api/remote-hosts/:id	Delete a host
GET	/api/remote-hosts/:hostId/sessions	Discover codeman-* sessions on the host (COD-105; listRemoteCodemanSessions, never errors)
POST	/api/cases/remote-link	Link a case to a remote host (creates the RemoteCase)

Attaching to a discovered session is a session-create path, not a host route: POST /api/sessions accepts attachRemoteSession: { hostId, remoteSessionName } (schema in schemas.ts; remoteSessionName must match ^codeman-[a-zA-Z0-9._-]+$), which session-routes.ts turns into a non-owned (owned: false) session.

Frontend touchpoints: the remote-host management UI is in session-ui.js / panels-ui.js; a remote session is created by picking a remote host/case in the session-create flow, or via the per-host "Discover existing sessions" button → Attach action (creates an owned: false session).

Security notes

• identityFile is a path only — never key bytes. Codeman stores the path and passes it to ssh -i; the key never enters Codeman's state or the wire.
• The injection surface is the SSH option fields. The single-source buildSshConnectionArgs + shellescape discipline (COD-107) is the control — audit any new code path that constructs an ssh command to route through it rather than concatenating options inline.
• BatchMode=yes means no interactive password/passphrase prompts — remote hosts must be reachable with key-based or agent auth (or an unencrypted key the agent has loaded). A host needing a passphrase will fail the probe with an ssh diagnostic rather than hang.

Related

• CLAUDE.md → Architecture → Remote row, and the Remote sessions (SSH) Key Pattern.
• docs/security-architecture.md — overall network/auth model.
• COD-104 (tmux prereq + durable launch), COD-105 (discover + attach, detach-not-kill ownership), COD-107 (shell-safe connection args).