docs(bash): reframe stdin/env — the scrub is the security control, not a trust boundary

Address review: the "trusted-plugin surface" framing overstated the security
story. A model driving the `bash` tool already has equivalent power to set env
vars and feed stdin through ordinary shell syntax (`FOO=bar cmd`, heredocs), so
the `env`/`stdin` seam fields grant it no new capability — and they cannot
exfiltrate the harness's ambient credentials, because the credential SCRUB in
dsh-bash-local (which strips *KEY*/*SECRET*/*TOKEN* from process.env before the
child sees it) is the actual control, and it works regardless of these fields
(tool-call args are static JSON, never shell-evaluated).

So drop the "dangerous / trusted-plugin boundary" language across the RFC, the
three bash-package READMEs, the bash/src/types.ts JSDoc, and docs/bash.md (both
the type-equiv blocks — kept 1:1 with source — and the prose). The reality that
remains: the `bash` tool doesn't EXPOSE env/stdin as parameters because they'd
be redundant with shell syntax; the fields exist for in-process plugins (the
hooks bridges) to pass a JSON payload + CLAUDE_* vars cleanly. The guard test is
kept but reframed: it catches a future `...args` spread that would silently
forward model input into the post-scrub env merge, NOT a trust wall. No code or
behavior change.

packages/bash/bash-local/README.md

@@ -21,7 +21,7 @@ Design surveyed against the bash tools of Claude Code, OpenCode, Codex, and pi;
 - **Spawn per call, no shell state** — every call is a fresh non-login `bash -c` (deterministic; no rc files). All four surveyed tools spawn per call. `XXX(stateful-shell)` in `src/run.ts` records the two proven stateful designs (Claude Code's cwd-only persistence; Codex's PTY exec sessions) for when real workflows demand them.
 - **Process-group kills with escalation** — children are spawned `detached` (own process group); kills send SIGTERM to the group, then SIGKILL after a 3s grace (OpenCode's escalation; pipelines and subshells die with the parent). ESRCH is tolerated; daemons that re-parent away from the group can still survive — same caveat as the surveyed tools.
 - **Tail-keep truncation + spill files** — output beyond `maxOutputBytes` keeps the in-memory TAIL (errors/results cluster at the end — pi/OpenCode rationale) while the FULL stream is appended to a temp file whose path is reported when available. If the final spill close reports a delayed writeback failure, the executor still returns the tail but withholds the path rather than advertising a possibly incomplete file.
-- **Model-friendly env + credential scrub** — `process.env` minus credential-shaped vars (`*KEY*`/`*SECRET*`/`*TOKEN*`), then `NO_COLOR=1 TERM=dumb PAGER=cat GIT_PAGER=cat` (Codex's hardcoded set) so pagers and ANSI color don't garble results. A spec's **trusted-plugin** `env` is merged LAST (after the scrub), so an in-process plugin's explicit entry wins even on a credential-shaped name — the scrub guards the harness's *ambient* credentials from *model-driven* commands, not a trusted caller. The spec's `stdin` (also trusted-plugin) is written to the child and closed; with none supplied, stdin is an immediately-closed empty pipe (EOF, as before). See [the trusted-plugin RFC](../../../docs/rfc/implemented/architecture/2026-06-30-bash-stdin-env-trusted-plugin-surface.md).
+- **Model-friendly env + credential scrub** — `process.env` minus credential-shaped vars (`*KEY*`/`*SECRET*`/`*TOKEN*`), then `NO_COLOR=1 TERM=dumb PAGER=cat GIT_PAGER=cat` (Codex's hardcoded set) so pagers and ANSI color don't garble results. This scrub is the security control that keeps the harness's *ambient* credentials out of a spawned command. A spec's `env` is merged LAST (after the scrub), so a caller's explicit entry — a value it already holds — wins even on a credential-shaped name. The spec's `stdin` is written to the child and closed; with none supplied, stdin is an immediately-closed empty pipe (EOF, as before). Both `env`/`stdin` are set by in-process plugins (the hooks bridges); the model-facing tool doesn't expose them. See [the bash-stdin-env RFC](../../../docs/rfc/implemented/architecture/2026-06-30-bash-stdin-env-trusted-plugin-surface.md).
 - **Background tasks** — `start()` returns immediately, no timeout applies (Claude Code detaches timeouts when backgrounding), `readOutput()` is incremental with whole-stream byte offsets, and disposal kills everything. The spec's opaque `owner` token is stored on the tracked task and returned by `ownerOf(id)` — the executor never interprets it (the consumer's access policy does), and because it lives with the task here it survives a `tool-bash` HMR reload.
 
 ## Sandboxing