feat(settings): detect stale writers with a revision, and announce raw changes

The remaining P1 from the #939 review, plus the P2 it shares a mechanism with.

Nothing carried a version, so two tabs editing one namespace silently
overwrote each other — reproduced as tab B's `reasoning` lost to tab A's
older draft. The seam's per-namespace write queue orders writes; it cannot
tell a fresh writer from one replaying a snapshot a predecessor superseded.

Each namespace now carries a monotonic `revision` over its RAW section. A
write may send `expectedRevision`, checked at the FRONT of the queue (not at
call time, which would race the very predecessor it guards against); a
mismatch rejects with `SettingsConflictError` → `settings-conflict` on the
wire, carrying both revisions. The editor captures the revision it opened at
and, on conflict, asks the user to reopen rather than replaying its snapshot.

The same counter fixes the missing broadcast. `settings/updated` is gated on
the resolved value — correct for consumers, wrong for configuration surfaces:
storing an override equal to the composition base leaves the resolved value
alone while changing what the document says (the field is now overridden, not
inherited) and moving every open editor's revision. `settings/document-updated
(ns, revision)` fires on any raw-section change, in-process or external, and
`host/settings-changed` now rides it.

That event also closes the stale model picker: editing a provider's `models`
changes no route, so `llm/adapters-updated` never fired and an open picker
kept serving the old catalog. A change to an exposed provider namespace now
emits `host/models-changed` too — that namespace holds the catalog.

Docs: both sides of the five touched README pairs, a type-equiv block for
`SettingsPathOp`, and an Agent Note recording what the plane exposes and who
may overwrite what. The deferred wire-redaction gaps (secrets behind
union/intersection/transform, `.default(...)` in the served envelope, schema
text in rejection messages, `new Function` rehydration, pi-ai's `headers`) are
recorded as TODO(settings-wire-redaction) and in Known Limitations rather than
half-fixed.

packages/client/ui-models/README.md

@@ -6,7 +6,7 @@ Models settings section plugin: the provider configuration page. It joins three
 
 Rows are the *configured* providers (their profile resolves in the owning namespace); a whole-section provider whose key is not configured anywhere (the first-run DeepSeek posture) renders as its open setup card instead of a row, and the add flow is a card carrying the dormant-directory provider select — a bare-mounted `llm-pi-ai` offers its whole installed catalog before any route exists. The editor is a hand-written card per adapter family: the primary field is a single **API key** input — the page never asks for an environment-variable name; a typed key stores **write-only** through `credentials.set` under the profile's reference, deriving `<ROUTE>_API_KEY` when the profile has none, and the pi-ai profile records that derivation as `apiKeyEnv`, so `settings.yaml` never carries a key value. The collapsed 自定义设置 fold carries the curated extras — `baseURL` for both families (the deepseek placeholder shows the public endpoint), plus `reasoningEffort` (deepseek) or `reasoning` (pi-ai); every other profile field stays owned by `settings.yaml`. A row is deletable only when the user layer alone carries it (removal restores the composition base).
 
-Apply semantics mirror the settings seam: an edit without removals lands as a minimal `settings.update` merge patch, while clearing a fold field back to inherited or deleting a row lands through `settings.replace` of the whole user section so removals actually take effect — safe wholesale, because the section stores key references, never key values. The page refetches on the pushed invalidations (`settings/changed`, `credentials/changed`, `models/changed`, and `connection/reset`) once it has loaded, so an external `settings.yaml` edit, a second tab, or a settings-born route converges without polling.
+Every edit lands as `settings.mutate` path ops against the stored section — a set per changed field, an unset per cleared one, and a single unset for a deleted row. The page only ever holds the REDACTED descriptor, so it names the fields it can see rather than rebuilding a section: a stored literal secret it never received is mentioned by no op and survives. Each write carries the `revision` the card opened at, so a concurrent write from another tab or an external `settings.yaml` edit is refused as `settings-conflict` and the card asks the user to reopen instead of replaying its stale snapshot. The page refetches on the pushed invalidations (`settings/changed`, `credentials/changed`, `models/changed`, and `connection/reset`) once it has loaded, so an external `settings.yaml` edit, a second tab, or a settings-born route converges without polling.
 
 ## Model Experience
 
@@ -18,8 +18,7 @@ None; this package neither assembles nor sends a provider request.
 
 ## Known Limitations and Deferred Work
 
-- **A reset can drop a stored literal secret in the same subtree** — a replace-carried removal cannot re-supply secrets the wire never returned; store keys behind `credentials.*` references (the product default) and the case cannot arise.
 - **Only the API key and the curated fold fields are editable on the card** — the hand-written editor traded schema-generic field coverage for the mockup layout ([Agent Note](../../../.agents/notes/implemented/architecture/2026-07-30-web-config-plane.md)); advanced fields (`models`, retry policy, timeouts…) are edited in `settings.yaml`, which the fold points at. A profile schema without the conventional fields renders the hint alone, and the two curated layouts key on the `llm-deepseek`/`llm-pi-ai` namespaces by name.
-- **Deleting a row leaves its stored key in `.env`** — removal replaces the settings profile but deliberately does not unset the derived credential; re-adding the provider finds the key already configured. An explicit key-removal control is deferred.
+- **Deleting a row leaves its stored key in `.env`** — removal unsets the settings profile but deliberately does not unset the derived credential; re-adding the provider finds the key already configured. An explicit key-removal control is deferred.
 - **No per-provider model listing on the page** — the picker surfaces models; this page shows route state only. A models preview per row is deferred until a consumer needs it.
 - **Undeclared live routes render nowhere** — a route registered without a configurable-provider declaration has no settings address; it stays visible in pickers but not on this page's rows.