feat(coding-agent): wire the filesystem tools into the demo

Load dsh-fs-local + dsh-fs-policy + dsh-tool-fs after tool-todo (mirroring the
acp-agent wiring), and steer the system prompt to prefer read/write/edit for
file ops with bash for shell/tests/search. Update the welcome line and the
FIXME(config-comments) bash note.

Doc sweep now that both demos ship the fs tools and the seam resolves per-session
cwd: architecture.md and the event-gate RFC no longer say the demos do file ops
through bash / that no config wires the tools; the coding-agent + examples
READMEs and the AGENTS.md layout blurb list the fs tools; the acp-agent README
drops the launch-dir caveat (per-session cwd now works, so the server can launch
anywhere).

(stdio-agent is single-session, so fs-local's cwd = process.cwd() is the
workspace. Keyless boot smoke is blocked locally by an unrelated inotify
watcher-limit ENOSPC that also hits demo:echo; the config parses and the same fs
stack boots green in the acp-agent snapshot tier.)

docs/architecture.md

@@ -78,7 +78,7 @@ Swappable capabilities are split into **three packages** so each part evolves in
 
 The LLM seam has the same topology folded differently: `dsh-llm` carries the interface (`LlmAdapter`) AND the consumer surface (`ctx.llm.stream()`), with adapters as implementation packages — there the consumer is the loop itself, not a swappable schema surface. Use the full three-package split when the consumer is independently replaceable; keep interface + consumer together when they are one concern. Don't split preemptively: a capability with one conceivable implementation and one consumer stays one package until proven otherwise.
 
-The filesystem capability follows the bash topology with a fourth layer, but the policy is contributed through an **event gate**, not a method service: `dsh-fs` owns the abstract `ctx.fs` provider seam (text IO + atomic mutation primitives whose version guard is optional) and the `fs/*` policy event vocabulary, `dsh-fs-local` provides the local backend, `dsh-tool-fs` is the model-facing `read`/`write`/`edit` tools AND the executor (it reads/writes/edits through `ctx.fs` directly, owns read windowing, dispatches the `fs/*` events), and `dsh-fs-policy` is a policy PLUGIN (no service) that decides the `fs/write-intent`/`fs/edit-intent` waterfalls and records on `fs/observed` to add observed-state + read-before-edit + version-guarded write/edit. Because the tool is not method-coupled to the policy, dropping `dsh-fs-policy` gracefully loses the policy and leaves the unconstrained bare provider rather than breaking the tool at a service-injection boundary. The fs tools are not wired into any default/example config yet (the demo agents do file ops through bash); a deployment that loads `dsh-tool-fs` is expected to also load `dsh-fs-policy` so the default behavior is read-before-write/edit. See [the fs-policy event-gate RFC](rfc/implemented/architecture/2026-06-26-file-context-as-event-gate.md).
+The filesystem capability follows the bash topology with a fourth layer, but the policy is contributed through an **event gate**, not a method service: `dsh-fs` owns the abstract `ctx.fs` provider seam (text IO + atomic mutation primitives whose version guard is optional) and the `fs/*` policy event vocabulary, `dsh-fs-local` provides the local backend, `dsh-tool-fs` is the model-facing `read`/`write`/`edit` tools AND the executor (it reads/writes/edits through `ctx.fs` directly, owns read windowing, dispatches the `fs/*` events), and `dsh-fs-policy` is a policy PLUGIN (no service) that decides the `fs/write-intent`/`fs/edit-intent` waterfalls and records on `fs/observed` to add observed-state + read-before-edit + version-guarded write/edit. Because the tool is not method-coupled to the policy, dropping `dsh-fs-policy` gracefully loses the policy and leaves the unconstrained bare provider rather than breaking the tool at a service-injection boundary. The demo agents (`coding-agent`, `acp-agent`) wire the full stack — `dsh-fs-local` + `dsh-fs-policy` + `dsh-tool-fs` — so `read`/`write`/`edit` are the default file surface (bash stays for shell/tests/search); the tools resolve a relative path against the caller's session cwd, matching bash ([the per-session cwd RFC](rfc/implemented/architecture/2026-07-02-fs-per-session-cwd.md)). See [the fs-policy event-gate RFC](rfc/implemented/architecture/2026-06-26-file-context-as-event-gate.md).
 
 > **"Capability" — two unrelated meanings.** (1) The *seam pattern* above ("one plugin provides a capability, another needs it") is realized by plain Cordis **services + `inject`**: a provider registers a service (`ctx.bash`, declared in `interface Context`); a consumer declares `inject: ['bash']` and its fiber stays pending until the service exists, tearing down via HMR if it later vanishes. No extra library is needed. (2) `@cordisjs/plugin-capability` is a different axis entirely — a **permission/capability-security** service (named permissions with inheritance/dependency, tested against a session via `ctx.capability.test`). It is a candidate for the deferred permissions/sandbox work (the `tools/execute` veto seam), NOT a mechanism for swapping implementations.