feat(bash): shell tools reject a mismatched executor dialect at load

The seam gains ShellDialect ('bash' | 'powershell' - concrete shells, not
families: zsh or fish would be their own values, never 'bash'); bash-local
declares bash (bash-sandbox inherits), pwsh-local declares powershell, and
both tools throw at load when the mounted executor speaks another dialect -
previously tool-pwsh over bash-local handed PowerShell text to bash -c and
the deployment error surfaced as ordinary nonzero exits. Pinned by mismatch
tests on both tools; the parity note records the contract (both languages).

Also from the review round: the tool-bash README's managed-environment
section becomes a summary linking the owning dsh-bash-env contract (the
duplicated prose carried a stale owner in its example import), the
pwshOnly JSDoc drops the stale 'on PATH' phrasing, and the task-tools
contract comment in the two pwsh compositions is indented into its block.

packages/bash/tool-pwsh/tests/tools.spec.ts

@@ -23,7 +23,7 @@ import AgentRegistry from '@deepseek-ai/dsh-agent'
 import type { Agent } from '@deepseek-ai/dsh-agent'
 import { SessionId } from '@deepseek-ai/dsh-session'
 import { BashExecutor } from '@deepseek-ai/dsh-bash'
-import type { BashExecRequest, BashExecSpec, BashProcess, BashRunResult } from '@deepseek-ai/dsh-bash'
+import type { BashExecRequest, BashExecSpec, BashProcess, BashRunResult, ShellDialect } from '@deepseek-ai/dsh-bash'
 import * as ToolPwsh from '@deepseek-ai/dsh-tool-pwsh'
 import * as BashEnvPlugin from '@deepseek-ai/dsh-bash-env'
 import type { BashProcessRead } from '@deepseek-ai/dsh-bash'
@@ -38,6 +38,8 @@ const testToolSignal = new AbortController().signal
  * handle.
  */
 class FakeBash extends BashExecutor {
+  readonly dialect: ShellDialect = 'powershell'
+
   requests: BashExecRequest[] = []
   specs: BashExecSpec[] = []
   startCalls = 0
@@ -199,6 +201,19 @@ async function callUntilText(
 }
 
 describe('registration', () => {
+  it('rejects an executor speaking another shell dialect at load', async () => {
+    class BashDialectExecutor extends FakeBash {
+      override readonly dialect = 'bash' as const
+    }
+    const ctx = new Context()
+    await ctx.plugin(SystemPrompt)
+    await ctx.plugin(ToolRegistry)
+    await ctx.plugin(AgentRegistry)
+    await ctx.plugin(BashEnvPlugin)
+    await ctx.plugin(BashDialectExecutor)
+    await expect(ctx.plugin(ToolPwsh)).rejects.toThrow("the mounted executor speaks 'bash', not powershell")
+  })
+
   it('registers the pwsh tool with its prompt section and schema', async () => {
     const { ctx } = await setup()
     const schema = ctx.tools.schemas().find(s => s.name === 'pwsh')