feat(bash): resolve executor config through the bash settings namespace

The capability's namespace is owned by the seam because it names the
capability, not an implementation: a host composes exactly one provider of
ctx.bash, so both executor families register the same namespace with their
own schema and composition entry without ever colliding, and a settings
document carried between platforms keeps resolving on both.

Both executors read their config through a source thunk, so a stored change
reaches the next command. The constructor checks the schema cannot express
become the section validator, refusing a bad value at the write instead of
at the next command. pwsh re-resolves its executable only when the declared
path changed, so an unrelated settings change never re-probes the filesystem.

packages/bash/bash/README.md

@@ -27,6 +27,8 @@ The split is a standard capability seam ([capability-seams Agent Note](../../../
 
 Implementations subclass `BashExecutor` and implement the abstract methods. Disposal must kill every running process and await its exit.
 
+`BASH_SETTINGS_NAMESPACE` (`bash`) is exported here rather than by a provider because it names the capability, not an implementation. A host composes exactly one provider of `ctx.bash` — the win32 layer swaps the POSIX rows for the pwsh ones, and mounting both fails loud on a duplicate service registration — so every provider can register this one namespace with its own schema and composition entry without two of them ever colliding, and a `settings.yaml` carried between platforms keeps resolving on both.
+
 ## Vocabulary
 
 `BashExecRequest` (command, workdir?, timeoutMs?, stdoutMaxBytes?, signal?, stdin?, env?, dshEnv?, sandboxPolicy?) resolves to `BashExecSpec` (command, workdir, timeoutMs, stdoutMaxBytes, signal?, stdin?, env?, dshEnv?, sandboxPolicy) before execution. `stdoutMaxBytes` is a trusted foreground-run capture budget for consumers that must parse complete bounded stdout; the model-facing bash tool does not expose it. `sandboxPolicy` is optional on the request and required-but-nullable on the resolved spec: it carries the complete per-call mode and workspace root. The sandbox tool path resolves it from the calling session through `ctx.sandboxPolicy`; a direct sandbox-executor caller falls back to deployment policy, while a non-sandboxing executor carries the field and confines nothing.