revert(bash): drop the executor dialect guard

The ShellDialect marker on BashExecutor and the load-time rejection in
tool-bash/tool-pwsh force every test and example fake executor to declare
a dialect for a guard with no in-repo or plausible deployment to catch
(shipped compositions always pair the tool with its matching executor),
and they break the example composition suites that stub ctx.bash without
a dialect (agent-spine-demo/cli-demo/acp-demo lost the bash tool).

Keep the non-dialect doc fixes that landed with the attempt: the tool-bash
README bashEnv contract trim with the stale example import removed, the
acp-snapshot suite.ts 'usable pwsh' JSDoc, and the pwsh.cordis.yml comment
indent. The parity note records the attempt and revert under Alternatives.

.agents/notes/implemented/feature/2026-08-02-pwsh-tool-bash-parity.md

@@ -22,6 +22,8 @@ The first Windows-native foundation shipped `dsh-tool-pwsh` as a deliberately mi
 
 **Keep the minimal profile and fix only the claims.** Rejected: the review's core finding was that text contracts copied from bash drift without the corresponding implementation; a minimal tool plus accurate claims still leaves pwsh calls without background execution, without contributor parity, and with a divergent marker story that must be re-justified forever.
 
+**Reject a mismatched executor dialect at load.** Attempted and reverted before merge: a `ShellDialect` marker (`bash` | `powershell`) on `BashExecutor`, with both shell tools throwing when the mounted executor speaks another shell. It forced every executor implementation — including each test and example fake — to declare a dialect, adding noise to every shell-tool test for a guard with no in-repo or plausible deployment to catch (shipped compositions always pair tool-pwsh with `dsh-pwsh-local` and tool-bash with `dsh-bash-local`). The pairing contract stays documented in each tool's README instead.
+
 **Extract a fully shared tool implementation base (abstract shell dialect, two thin leaves).** Considered and deferred: the bash-env extraction and the structural mirror (`render.ts`/`background.ts` twins) are the foundation it would rest on; a full base waits until a third dialect or the persistent-PTY twin makes the abstraction's shape observable.
 
 ## Consequences
@@ -29,7 +31,6 @@ The first Windows-native foundation shipped `dsh-tool-pwsh` as a deliberately mi
 - The bash and pwsh tools are now behaviorally interchangeable for foreground and background shell work (minus sandbox), and the pwsh prompt/description sentences are each backed by the renderer — the reviewer's grep-against-code check passes.
 - Parity ran BOTH ways once: the pwsh tool's structured foreground abort (`HarnessError('tool call aborted', TOOL_ABORTED)` with name `AbortError`) was backported to the bash tool, replacing its uncoded `Error('command aborted')` — a model-visible/logged change pinned by exact-shape tests on both sides and by the cancel-tool-calls fixture.
 - `@deepseek-ai/dsh-bash-env` is a new shipped package; `dsh-tool-bash`'s `dshHome` config moved there, so compositions mounting the shell tools must also mount `bash-env` (the spine bundles do).
-- The seam now carries a `dialect` (`ShellDialect`: `bash` | `powershell` — concrete shells, not families; a POSIX-ish sibling would be its own value), and both shell tools reject a mismatched executor at load, so pairing tool-pwsh with bash-local (or the reverse) fails loud instead of surfacing commands handed to the wrong parser as ordinary nonzero exits.
 - Windows-only semantics (CRLF normalization, forced-termination exit-1/signal-null, POSIX-only self-signal) remain pinned by tests as before.
 - The pwsh tool's per-file coverage gate rides on the scriptable fake-executor suite (`tests/tools.spec.ts`); the real-pwsh integration and Loader-composition suites self-skip where `pwsh` is absent, mirroring the bash suites' division of labor.
 - The roadmap proposal's parity stage is delivered; its remaining stages are the Windows default composition and pwsh TUI/GUI rendering.