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Harden cmux ssh for mixed-version remote sessions

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Lawrence Chen 2026-02-24 22:09:27 -08:00
parent 2b7928aa60
commit daa340fa87
8 changed files with 142 additions and 31 deletions
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docs/remote-daemon-spec.md
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@ -33,15 +33,17 @@ This is a **living implementation spec** (also called an **execution spec**): a
- `DONE` local app probes remote platform, builds/uploads `cmuxd-remote`, and runs `serve --stdio`.
- `DONE` daemon `hello` handshake is enforced.
- `DONE` bootstrap/probe failures surface actionable details.
- `DONE` bootstrap creates `~/.cmux/bin/cmux` symlink (also tries `/usr/local/bin/cmux`) so `cmux` is available in PATH on the remote.
- `DONE` bootstrap installs `~/.cmux/bin/cmux` wrapper (also tries `/usr/local/bin/cmux`) so `cmux` is available in PATH on the remote.
### 3.5 CLI Relay (Running cmux Commands From Remote)
- `DONE` `cmuxd-remote` includes a table-driven CLI relay (`cli` subcommand) that maps CLI args to v1 text or v2 JSON-RPC messages.
- `DONE` busybox-style argv[0] detection: when invoked as `cmux` via symlink, auto-dispatches to CLI relay.
- `DONE` busybox-style argv[0] detection: when invoked as `cmux` via wrapper/symlink, auto-dispatches to CLI relay.
- `DONE` background `ssh -N -R 127.0.0.1:PORT:/local/cmux.sock` process reverse-forwards a TCP port to the local cmux socket. Uses TCP instead of Unix socket forwarding because many servers have `AllowStreamLocalForwarding` disabled.
- `DONE` relay process uses `ControlPath=none` (avoids ControlMaster multiplexing and inherited `RemoteForward` directives) and `ExitOnForwardFailure=no` (inherited forwards from user ssh config failing should not kill the relay).
- `DONE` relay address written to `~/.cmux/socket_addr` on the remote with a 3s delay after the relay process starts, giving SSH time to establish the `-R` forward.
- `DONE` Go CLI re-reads `~/.cmux/socket_addr` on each TCP retry to pick up updated relay ports when multiple workspaces overwrite the file.
- `DONE` `cmux ssh` startup exports session-local `CMUX_SOCKET_PATH=127.0.0.1:<relay_port>` so parallel sessions pin to their own relay instead of racing on shared socket_addr.
- `DONE` relay startup writes `~/.cmux/relay/<relay_port>.daemon_path`; remote `cmux` wrapper uses this to select the right daemon binary per session, including mixed local cmux versions.
- `DONE` ephemeral port range (49152-65535) filtered from probe results to exclude relay ports from other workspaces.
- `DONE` multi-workspace port conflict detection uses TCP connect check (`isLoopbackPortReachable`) so ports already forwarded by another workspace are silently skipped instead of flagged as conflicts.
- `DONE` orphaned relay SSH processes from previous app sessions are cleaned up before starting a new relay.
@ -112,7 +114,7 @@ Recompute effective size on:
| M-002 | Remote bootstrap/upload/start + hello handshake | DONE | Current `cmuxd-remote` is minimal (`hello`, `ping`) |
| M-003 | Reconnect/disconnect UX + API + improved error surfacing | DONE | Includes retry count in surfaced errors |
| M-004 | Docker e2e for bootstrap/reconnect shell niceties | DONE | Existing docker tests currently validate mirroring-era path |
| M-004b | CLI relay: run cmux commands from within SSH sessions | DONE | Reverse TCP forward + Go CLI relay + bootstrap symlink (PR #374) |
| M-004b | CLI relay: run cmux commands from within SSH sessions | DONE | Reverse TCP forward + Go CLI relay + bootstrap wrapper (PR #374) |
| M-005 | Remove automatic remote port mirroring path | TODO | Delete probe/listen mirror loop from `WorkspaceRemoteSessionController` |
| M-006 | Transport-scoped local proxy broker (SOCKS5 + CONNECT) | TODO | Local component in app/daemon layer |
| M-007 | Remote proxy stream RPC in `cmuxd-remote` | TODO | Add `proxy.open/close` and multiplexed stream handling |