fix(settings): harden seam and provider per review findings

Confirmed and fixed, each with a regression test that failed first:

- Concurrent update() lost patches (merge over one stale snapshot):
  per-namespace serialized write queues; a failed write cannot poison
  the queue for later writers.
- Fixed-name .tmp write followed planted symlinks and kept stale modes:
  random-suffix sibling, exclusive-create (wx), 0600, cleanup on
  failure, then rename.
- A throwing settings/updated listener escaped commit and permanently
  wedged the provider reload chain (rejected refreshTask): commit now
  contains listener failures (INVARIANT-coded errors still propagate),
  async watcher rejections are adopted and contained
  (watch callbacks are officially void | Promise<void>), and the
  provider chains refreshes on a settled tail with an error log.
- No way to remove a user override: scope/service replace(section)
  sets the user section wholesale; replace({}) re-inherits base and
  schema defaults.
- The three-primitive provider contract did not hold (base never
  called load()): the base Service.init loads and publishes once;
  settings-local delegates via yield* super[Service.init]().
- Dispose did not quiesce: teardown flags closed, closes the watcher,
  then awaits queued/in-flight reloads; closed is re-checked across
  await points.
- Invariant now checks the authoritative relation with the seam's own
  deepEqualJson: emitted next must equal settings.get(ns), and
  next/prev must differ structurally (cosmokit dependency dropped).
- New docs/core-data-structures/settings.{md,zh.md} with type-equiv
  blocks + manifest entries; catalog types moved from exemptions to
  LINK_MAP; website page registered.

Both packages stay at per-file 100% coverage.

packages/settings/settings/README.md

@@ -9,12 +9,13 @@ Abstract user-settings seam (`ctx.settings`). One provider holds a raw document
 - `register(ns, schema, { base?, applies? })` — returns the owner `SettingsScope` (`get`/`watch`/`update`). The registration is an effect on the calling plugin's fiber: disposing that fiber removes the namespace and its observers. A stored section the schema rejects fails the registration itself; a duplicate namespace fails loud.
 - `describe()` — one descriptor per namespace (`schema.toJSON()` envelope, resolved value, `applies`) for configuration surfaces.
 - `get(ns)` — resolved value, `undefined` while unregistered.
-- `update(ns, patch)` — deep-merges the plain-object patch into the user section only (never the `base`), validates the resolved candidate, persists through the provider, then commits. Validation failure rejects before anything is persisted; a read-only provider (`writable: false`) rejects every update.
-- Resolved values are deep-frozen snapshots; watchers receive `(next, prev)` after each commit, and watcher failures are contained.
+- `update(ns, patch)` — deep-merges the plain-object patch into the user section only (never the `base`), validates the resolved candidate, persists through the provider, then commits. Validation failure rejects before anything is persisted; a read-only provider (`writable: false`) rejects every write. Writes to one namespace are serialized in call order.
+- `replace(ns, section)` — sets the user section wholesale: the removal/reset path a merge cannot express (`replace({})` re-inherits `base` and schema defaults).
+- Resolved values are deep-frozen snapshots; watchers receive `(next, prev)` after each commit, and watcher failures — sync throws and async rejections alike — are contained.
 
 ## Provider contract
 
-Subclasses implement `writable`, `load()`, and `persist(ns, section)`, and push externally observed documents through the protected `publish(doc)`. At publish, each registered namespace re-resolves independently: an invalid section keeps that namespace's last good value and warns — a live reload never takes the process down — while boot-time and registration-time validation fail loud.
+Subclasses implement `writable`, `load()`, and `persist(ns, section)`, and push externally observed documents through the protected `publish(doc)`. The base service init loads and publishes the document once before the service becomes injectable; a provider with its own init (watcher, connection) delegates first via `yield* super[Service.init]()`. At publish, each registered namespace re-resolves independently: an invalid section keeps that namespace's last good value and warns — a live reload never takes the process down — while boot-time and registration-time validation fail loud.
 
 ## Events
 
@@ -31,5 +32,5 @@ No direct invalidation; a consumer that folds a settings value into the request
 ## Known Limitations and Deferred Work
 
 - **Single user layer** — resolution knows schema defaults, one composition `base`, and one user document; there is no project/managed layering or per-value provenance yet.
-- **Cross-process concurrency is provider-defined** — the seam serializes nothing across processes; concurrent writers converge by provider behavior (the local file provider is last-write-wins).
+- **Cross-process concurrency is provider-defined** — the seam serializes writes per namespace in-process only; concurrent processes converge by provider behavior (the local file provider is last-write-wins).
 - **No secret-field redaction** — `describe()` returns resolved values verbatim; a wire surface (RPC/UI) must redact `role('secret')` fields before exposure.