fix(files): fail closed on remote symlinks, guard PUT for remote cases, bound ssh fan-out

Follow-up to #421 (remote-case file reads over ssh), addressing the review.

Symlink escape on a host without `readlink -f` (blocker). The probe's
portable fallback canonicalized only the directory chain and returned the
final component unresolved, so on macOS < 12.3 `ws/notes.txt -> ~/.ssh/id_rsa`
came back as `.../ws/notes.txt` (with the target's size), passed every
containment and blocklist check that runs on `realPath`, and `cat` followed
the link. The fallback now walks the directory chain with `cd -P`/`pwd -P`
and follows the LAST component with plain `readlink` for a bounded number of
hops, and anything it cannot fully resolve (a loop, a readlink failure, the
hop cap) is reported with an `x` marker that parses as null, i.e. 404. It
never returns the unresolved string. Measured on a real /bin/sh with
`readlink -f` shadowed: the pre-fix script reports `/ws/notes.txt`, the fixed
one `/secret/id_rsa`; both branches (native and fallback) now agree.

`PUT /api/sessions/:id/file-content` never had the remote guard the PR
described. It sits ahead of `validateSessionFilePath`, which resolves against
the LOCAL filesystem, because with a same-named directory on the Codeman host
(an sshfs mount of the remote tree, the documented stop-gap) the write landed
on the local twin while the viewer believed it edited the remote file.

ssh fan-out is bounded. `src/remote-ssh-limiter.ts` is a
document-conversion-limiter-shaped semaphore (default 4, env
`CODEMAN_MAX_REMOTE_FILE_SSH`) around every probe and buffered read; the
attachment-history list resolves its whole history in ONE batched probe
(`probeRemoteAttachmentHistory`, threaded into
`registerExternalAttachment({remoteProbes})` so the guards run unchanged)
instead of one handshake per entry; and probes chunk at 40 paths because the
whole script is one argv string. Terminal output in a remote session is
written on the remote host, so a prompt-injected agent printing hundreds of
`codeman://attach` links forked one ssh per link, each holding a 20 s
timeout, and a 100-entry history re-listed on every attachment:detected
tripped OpenSSH's default MaxStartups. Streams are deliberately not counted
(one per browser request, held for a whole playback, and gated behind a
counted probe anyway).

Smaller items from the same review: probe records are NUL-terminated and
index-keyed after a leading NUL (a newline in a filename can no longer shift
the alignment, and the banner is fenced off without last-N-lines guessing);
size comes from `stat -c %s || stat -f %z`; the three IO functions refuse
under VITEST instead of opening a connection; an unreachable host now reads
as unknown (missing: false) for detected AND external history entries, where
external used to fold its 502 into missing; a client that aborted during the
guard probe has its body's ssh child reaped (`reply.raw.destroyed` is checked
before the close listener is attached); `describeExecError` never returns
Node's `Command failed: <ssh line>` message, which carried the identity path
and the probe script into a 502 body; and the docs note that
`isSensitivePath`'s three home-anchored entries resolve against the Codeman
host's home, not the remote one.

Tests: the probe script runs on a real /bin/sh with a `readlink` shim that
rejects `-f` (the escape, a relative chain through a symlinked directory, a
loop, a newline filename, banner chatter that itself looks like a record),
the limiter's cap and FIFO order, and route tests for the PUT guard (local
twin untouched, no connection), the single batched history probe, the
unreachable-host alignment and the aborted-client reap. All four route tests
fail against the pre-fix file-routes.ts.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

CLAUDE.md

@@ -215,7 +215,7 @@ Codeman is a Claude Code session manager with web interface and autonomous Ralph
 
 **Cron (`CronJob`s)**: saved, named jobs on a recurring schedule (`once`/`interval`/`daily`/`weekly`) with per-job run history. ⚠️ **Distinct from the legacy `ScheduledRun`** (`/api/scheduled`, a run-now duration-bounded loop); the two never interact and keep separate `Scheduled*` / `Cron*` names. `CronService` **reuses the existing session layer** rather than rebuilding tmux logic. Next-run math is pure and unit-tested in `cron-time.ts` (server-local timezone). The schedule is advanced BEFORE launch so a slow launch cannot re-trigger. → [architecture-invariants#cron-jobs](docs/architecture-invariants.md#cron-jobs), `docs/cron-discovery.md`
 
-**Remote sessions + remote SSH cases**: a case can point at a remote host. The agent runs inside a durable remote `tmux -L codeman-remote` (session name `codeman-ssh-<id>`, deliberately failing the remote Codeman's `SAFE_MUX_NAME_PATTERN` so an instance on the target host never adopts it), fronted by a LOCAL tmux pane running `ssh`. Attached (`owned:false`) sessions **detach, never kill** on tab close; owned ones propagate `kill-session`. A bounded-backoff watcher auto-reconnects dropped sessions (`remoteAutoReconnect`, default ON). ⚠️ **It revives ONLY when the durable remote tmux session is verifiably still alive** (`remoteTmuxSessionAlive()`, a `has-session` probe over ssh, #355): a clean agent exit (Ctrl-C, Ctrl-D, `exit`) tears that session down, and `isPaneDead()` cannot tell it from a transport drop, so the watcher used to relaunch a FRESH agent after every clean exit (claude only looked fine because its `|| --resume` fallback masked it). An unreachable host answers `undefined`, which also means do not revive. ⚠️ `has-session` prints NOTHING on success, so the probe is classified by EXIT STATUS (`classifyRemoteAliveExit`: 0 alive, ssh's 255 or a timeout unknown, anything else gone); reading stdout classified every live session as gone and silently disabled transport-drop reconnects. The answer is cached per session and forgotten whenever the pane is seen alive again, or a stale `true` from one transport drop would revive the next clean exit. ⚠️ **File reads in a remote case are the second ssh surface** (#415, `src/remote-files.ts`): they go through `buildSshConnectionArgs()` as well, a browser-supplied path is only ever a `shellescape`d token, an unreachable host answers 502 (never 404), the size cap uses the REMOTE size, and no remote file is ever copied onto the server's disk — which is why writes, office previews and thumbnails are deliberately unsupported over ssh. The ATTACHMENT routes (a clicked path outside the case dir) go through the same layer, and which host a record is read from follows the SESSION, never the path string. ⚠️ **Command-injection surface: every ssh command line must flow through `buildSshConnectionArgs()`**, which `shellescape`s every user field. Never hand-build an ssh line elsewhere. ⚠️ Run flows must route remote cases through `POST /api/quick-start`, not `POST /api/sessions` (which stat-validates `workingDir` locally and has no `caseName`). → [architecture-invariants#remote-sessions-over-ssh](docs/architecture-invariants.md#remote-sessions-over-ssh), [#remote-ssh-cases](docs/architecture-invariants.md#remote-ssh-cases), `docs/remote-sessions.md`
+**Remote sessions + remote SSH cases**: a case can point at a remote host. The agent runs inside a durable remote `tmux -L codeman-remote` (session name `codeman-ssh-<id>`, deliberately failing the remote Codeman's `SAFE_MUX_NAME_PATTERN` so an instance on the target host never adopts it), fronted by a LOCAL tmux pane running `ssh`. Attached (`owned:false`) sessions **detach, never kill** on tab close; owned ones propagate `kill-session`. A bounded-backoff watcher auto-reconnects dropped sessions (`remoteAutoReconnect`, default ON). ⚠️ **It revives ONLY when the durable remote tmux session is verifiably still alive** (`remoteTmuxSessionAlive()`, a `has-session` probe over ssh, #355): a clean agent exit (Ctrl-C, Ctrl-D, `exit`) tears that session down, and `isPaneDead()` cannot tell it from a transport drop, so the watcher used to relaunch a FRESH agent after every clean exit (claude only looked fine because its `|| --resume` fallback masked it). An unreachable host answers `undefined`, which also means do not revive. ⚠️ `has-session` prints NOTHING on success, so the probe is classified by EXIT STATUS (`classifyRemoteAliveExit`: 0 alive, ssh's 255 or a timeout unknown, anything else gone); reading stdout classified every live session as gone and silently disabled transport-drop reconnects. The answer is cached per session and forgotten whenever the pane is seen alive again, or a stale `true` from one transport drop would revive the next clean exit. ⚠️ **File reads in a remote case are the second ssh surface** (#415, `src/remote-files.ts`): they go through `buildSshConnectionArgs()` as well, a browser-supplied path is only ever a `shellescape`d token, an unreachable host answers 502 (never 404), the size cap uses the REMOTE size, and no remote file is ever copied onto the server's disk — which is why writes, office previews and thumbnails are deliberately unsupported over ssh (the `PUT` guard sits BEFORE the local path validation, or a same-named local directory such as an sshfs mount takes the write). The probe's symlink resolution FAILS CLOSED (a path it cannot canonicalize is a 404, never its own unresolved string: the directory-only fallback let a `notes.txt -> ~/.ssh/id_rsa` link pass containment), and ssh children are BOUNDED by `src/remote-ssh-limiter.ts` plus one batched probe per attachment-history listing, because terminal output in a remote session is written on the remote host and a prompt-injected agent can print hundreds of `codeman://attach` links. The ATTACHMENT routes (a clicked path outside the case dir) go through the same layer, and which host a record is read from follows the SESSION, never the path string. ⚠️ **Command-injection surface: every ssh command line must flow through `buildSshConnectionArgs()`**, which `shellescape`s every user field. Never hand-build an ssh line elsewhere. ⚠️ Run flows must route remote cases through `POST /api/quick-start`, not `POST /api/sessions` (which stat-validates `workingDir` locally and has no `caseName`). → [architecture-invariants#remote-sessions-over-ssh](docs/architecture-invariants.md#remote-sessions-over-ssh), [#remote-ssh-cases](docs/architecture-invariants.md#remote-ssh-cases), `docs/remote-sessions.md`
 
 **Docker cases**: a case can point at a **container**, with any of the CLI run modes running inside it. Like remote-SSH this is a **LOCATION OVERLAY on cases, never a `SessionMode` of its own**. Exactly one long-lived container **per case**, shared by all its sessions, so killing a session kills only that session's in-container tmux and **never** `docker stop` while siblings remain. The workspace is a real host dir bind-mounted at the **same absolute path**, which is what keeps file-routes/watchers on real host bytes and makes the in-container transcript projHash match the host. Credentials are **seeded** (RO mount, copied into the container once) rather than shared RW, so in-container CLIs never write refreshed tokens back to the host, and bind mounts are excluded from `docker commit` so exports stay secret-free. **NEVER a create-time `-e` for secrets, NEVER `--privileged`, NEVER the docker socket.** Config drift is detected via a label hash and a drifted launch is REFUSED rather than silently launched with stale config. ⚠️ A case may instead **ADOPT** a container the user already runs (`DockerCase.owned === false`, mirror of remote-SSH's `owned:false`): Codeman only `exec`s into it and never creates, starts, stops, restarts or removes it, so a missing or stopped container FAILS CLOSED with an actionable message instead of being fixed. Absent = owned, so existing cases are byte-identical. The guarantee is enforced at four independent layers because it cannot be observed by using the feature: `buildDockerStopCommand`/`buildDockerRemoveCommand` throw during pure STRING CONSTRUCTION, `removeDockerContainer` refuses again, drift reports "none" (an adopted container carries no `codeman.confighash` label, so a real comparison would 409 the launch forever), and the boot reaper skips it. ⚠️ Two lifecycle touches the original design missed and that are easy to re-introduce: the full-image export `docker commit`s the container (refused for an adopted case) and the workspace export `docker pause`s it first (skipped — it freezes the owner's processes for the length of the tar). ⚠️ `owned` is applied AFTER `dockerConfigHash`, which takes an explicit field list, or every pre-existing case would trip the drift gate at once. ⚠️ Run modes for a container case come from the CONTAINER (`availableModes`, live-probed): gating the run menu on HOST CLIs (#201) is right for local sessions and wrong here, since a host with no `claude` may run a container that ships one. ⚠️ **A failed probe means opposite things per ownership** — for an ADOPTED case it is a fault worth reporting, for an OWNED one it is the NORMAL state before the first session (the launch chain creates the container), so treating it as a fault hid every agent mode on every freshly linked Docker case behind "start it yourself first". That is why `CaseInfo.docker.owned` is on the wire. ⚠️ Claude is launched WITHOUT `--dangerously-skip-permissions` when the container's exec user is root (Claude Code refuses the flag as root and the refusal is visible only inside the container); which flag to drop is a per-CLI fact, so it is the registry's `overlays.docker.rootCommand`, never a branch. ⚠️ Adoption is **admin-only in multi-user mode**, unlike `docker-link`: linking creates OUR container, whose one bind mount `isWorkingDirAllowed` has already confined, while an adopted container's mounts belong to its owner and one mounting `/` hands the adopter the host. The same reasoning admin-gates the container listing and the in-container directory browser; the preflight instead admits a non-admin for a container already linked to a case they own, because the run menu probes it for every docker case. ⚠️ On the loopback-only prod bind a container cannot reach 127.0.0.1, so in-container hooks need `CODEMAN_DOCKER_BRIDGE_HOOKS=1`; otherwise idle detection falls back to output-based. → [architecture-invariants#docker-cases](docs/architecture-invariants.md#docker-cases), `docs/docker-cases.md` (user guide), `docs/docker-cases-plan.md` (design)