deepseek-harness/packages/pty/tool-bash-persistent/README.md

@deepseek-ai/dsh-tool-bash-persistent

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Model-facing bash(command) backed by one owner-scoped ctx.pty shell. The package owns the tool contract and shell reuse; deployments select the PTY backend and sandbox policy.

Config

Key	Default	Meaning
backendType	shell	Registered PTY backend used for each Agent shell.
timeoutMs	300000	Wall-clock limit for one command; timeout closes the shell.
maxOutputChars	16000	Maximum retained command-output characters; fixed diagnostics are added afterward.
description	Persistent-shell description	Model-facing environment contract.

Model Experience

Tool schema

What the model sees

The generated bash schema, including the configured description. The plugin contributes no standalone system-prompt section; the deployment owns persona and environment guidance.

Token effect

Fixed schema cost while bash is visible.

KV Cache effect

Prefix-stable while the configured description and schema remain unchanged.

Tool results

What the model sees

Commands share one shell per Agent, so cwd, exported variables, activated environments, functions, and background jobs persist across calls. Results exclude private completion markers and the shell prompt. A nonzero wrapped command appends [exit code: N]; a shell that exits before reporting that status instead appends [shell exited: code N], [shell killed by signal: SIG], or [shell exited] when the backend supplies neither, then resets and tells the model that the next call starts fresh. Long output keeps the earliest retained prefix plus a clipping notice. If the PTY has already dropped that prefix, the result says so explicitly instead of presenting a tail as complete output. Timeout returns bounded partial output, closes the uncertain shell, and reports the reset.

Token effect

Data-dependent. maxOutputChars bounds retained command output; fixed clipping, lost-prefix, status, timeout, and reset diagnostics can extend the result.

KV Cache effect

Append-only tool results follow the reusable request prefix.

Known Limitations and Deferred Work

• The tool requires an owning Agent and a real PTY backend.
• Explicit exit and timeout discard shell state. Cancellation also resets and discards the result, even when a complete status marker is already observable; the next call starts a fresh shell.
• Environment facts such as network access and package mirrors belong in the configured description, not this package's default.