Local `node-pty` backend for `ctx.pty`. It starts an interactive shell under the shared `ctx.sandboxPolicy`, strips credential-shaped ambient environment variables, retains bounded line-oriented output, detects readiness, and tears down the captured process tree rooted at the `node-pty` child.
The plugin injects `agents`, `pty`, `sandbox`, and `sandboxPolicy`, then registers the configured backend type (`shell`). `danger-full-access` starts the shell directly; confined modes wrap the exact shell argv through `ctx.sandbox`. The effective session mode is resolved at spawn. A change to a different effective mode is rejected before its `sandbox/mode` event commits while that owner has an open PTY or a spawn in progress; wait for creation to settle and close the sessions before changing modes, so a terminal opened with wider access cannot survive a downgrade.
Linux readiness combines a foreground-verified private bash prompt marker, foreground-process-group syscall inspection, silence fallback, and absolute timeout. macOS uses the verified prompt marker plus silence/timeout because it has no `/proc` syscall surface. A marker is not ready until printable prompt text arrives, including when the OSC marker and `PS1` are split across data callbacks. Unrecognized or unreadable process state is never a positive exact-idle signal. During unpublished startup, a fallback requires observed output; zero-output silence cannot publish an empty session, and timeout rejects the spawn. Incomplete terminal-control sequences are bounded by `maxReadBytes` and discarded through their terminator after crossing that limit; a trailing carriage return is carried across callbacks so split CRLF becomes one newline.
Send cancellation resolves the current foreground process group and delivers a real `SIGINT`; it never emulates interruption by writing `\x03`, so raw-mode programs remain cancellable. Close sends `SIGTERM` to descendants, waits, rescans and sends `SIGKILL` to the remaining tree, verifies that descendants left the process table while the shell can still reap them, and only then stops the shell. A survivor failure does not cache a permanently rejected close; a later close retries the teardown.
Nothing directly. Through `@deepseek-ai/dsh-tool-pty`, the model may receive bounded MOTD, send deltas, scrollback pages, readiness reasons, and cleanup errors.
#### Token effect
None until a consumer returns bounded backend output. Retained PTY scrollback is not placed in model history by this package.
#### KV Cache effect
No direct invalidation; the consumer owns prompts, schemas, and appended results.
## Known Limitations and Deferred Work
- Line-oriented output is normalized; full-screen alternate-buffer interaction is unsupported.
- Linux exact probes support x64 and arm64 UAPI tables; other architectures use prompt-marker and silence/timeout readiness.
- A descendant that daemonizes and reparents before teardown leaves the captured tree; cleanup never broadens to the launcher PID's POSIX session because that can include unrelated processes.
