# RFC: Extract a generic long-running tool runtime
Status: proposed
## Problem
The bash capability seam supports both foreground commands and long-running background tasks. Background support is large: the abstract executor exposes `start`, `get`, `ownerOf`, `list`, `readOutput`, `kill`, and `onTaskDone`; the local executor tracks tasks, incremental reads, owner tokens, process cleanup, and completion listeners; the model sees three tools (`bash`, `bash_output`, `bash_kill`); the tool plugin injects completion notices back into the owning agent's session. The local executor fences task access behind owner tokens because predictable global task ids are a cross-session read/kill hazard.
The [tool cookbook](../../../cookbook/adding-a-tool.md) already points at the real design smell: background bash is really generic long-running-tool infrastructure living inside one tool. If future tools need background execution, polling, kill, ownership, and completion notices, those semantics should not be hidden in `dsh-bash`.
Move long-running task semantics above bash into a tool-agnostic runtime. Bash remains able to run background commands, but it stops owning the general concepts of task ids, ownership tokens, polling, cancellation, completion notifications, and model-facing "read/kill this task" commands.
The runtime should own:
- Stable task ids and owner tokens keyed to the calling session/agent.
- Registration of a long-running task with a producer for incremental output and a completion promise.
- Generic read/cancel/list operations with the same cross-session authorization rule for every tool.
- Completion notification injection into the owning session.
- Presentation hooks for pending/running/completed task state, with bash supplying only command-specific labels and output formatting.
`dsh-bash` then keeps the bash-specific execution contract: resolve a request into a command spec, run a foreground command, or start a process and hand its streams/process handle to the generic runtime. `dsh-tool-bash` keeps the model-facing command tool, but the follow-up operations become generic long-running-tool operations or a shared utility that bash registers with, rather than bespoke `bash_output`/`bash_kill` plumbing.
Current consumers split cleanly: `dsh-tool-bash` uses the full foreground/background seam, while hook bridges use only foreground `resolve` and `run` with trusted `stdin` and `env`. `get` and `list` are test-only; `BashTask.done` is implementation-only for disposal, while production completion uses `onTaskDone`. An extracted runtime should expose one public completion mechanism, preserve the simple foreground path for hooks, and decide whether background `timeoutMs` belongs on `start`. If it owns process spawning, it should also centralize the duplicated credential scrub.
- The bash-specific packages no longer define the generic task registry, owner-token authorization, polling, cancellation, or completion-notification machinery.
- A shared long-running-task service or tool layer owns those semantics and is documented as the path for any future background-capable tool.
- Bash background behavior remains available through the shared layer, with tests proving cross-session isolation still holds.
- ACP and snapshot fixtures render background bash through the shared task vocabulary, not through bash-only lifecycle semantics.
- The [tool cookbook](../../../cookbook/adding-a-tool.md) points long-running tools at the shared runtime instead of telling each tool to invent its own task protocol.
The bash package loses local ownership of an already-working background-task implementation, and the implementing PR may temporarily churn model-facing tool names or transcript presentation. That churn is worthwhile if it leaves one background-task contract instead of making every future long-running tool clone bash's private protocol.
