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tell a fresh writer from one replaying a snapshot a predecessor superseded.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/src/client/ProviderEditor.tsx

@@ -127,6 +127,10 @@ export function ProviderEditor(props: ProviderEditorProps): ReactNode {
   const [keyState, setKeyState] = useState<CredentialView | undefined>(undefined)
   const [busy, setBusy] = useState(false)
   const [failure, setFailure] = useState<string | undefined>(undefined)
+  // The revision this card opened at. A write carrying it is refused if
+  // anything else — another tab, an external edit of settings.yaml — moved the
+  // namespace meanwhile, instead of silently overwriting that change.
+  const [openedAt] = useState(() => namespace.revision)
   const root = useMemo(() => rehydrateSchema(namespace.schema), [namespace.schema])
   const node = useMemo(() => nodeAtPath(root, settingsPath), [root, settingsPath])
   const fallback = getPath(namespace.value, settingsPath)
@@ -175,8 +179,12 @@ export function ProviderEditor(props: ProviderEditorProps): ReactNode {
     }
     const ops = pathOps(settingsPath, original, next)
     if (ops.length > 0) {
-      const response = await api.settings.mutate({ ns, ops })
-      if (!response.result.ok) return response.result.error.message
+      const response = await api.settings.mutate({ ns, ops, expectedRevision: openedAt })
+      if (!response.result.ok) {
+        return response.result.error.code === 'settings-conflict'
+          ? t('conflict')
+          : response.result.error.message
+      }
     }
     if (keyDraft.length > 0) {
       const stored = await api.credentials.set({ ref: keyRef, value: keyDraft })

packages/client/ui-models/src/client/locales.ts

@@ -16,6 +16,7 @@ export const en = {
   applying: 'Applying…',
   readOnly: 'The settings document is read-only in this deployment.',
   loadFailed: 'Loading the provider directory failed',
+  conflict: 'Someone else changed these settings while this card was open. Close it and reopen to edit the current values.',
   retry: 'Retry',
   keyInput: 'API key',
   keyPlaceholder: 'Enter your API key',
@@ -45,6 +46,7 @@ export const zh: typeof en = {
   applying: '保存中…',
   readOnly: '当前部署的设置文档为只读。',
   loadFailed: '加载提供方目录失败',
+  conflict: '这张卡片打开期间，这些设置已被其他地方改动。请关闭后重新打开，在当前值上编辑。',
   retry: '重试',
   keyInput: 'API 密钥',
   keyPlaceholder: '输入 API 密钥',