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tell a fresh writer from one replaying a snapshot a predecessor superseded.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/host/apiproxy/tests/api-proxy-config.spec.ts

@@ -257,6 +257,40 @@ describe('settings domain', () => {
       .toBe('settings-not-exposed')
   })
 
+  it('invalidates the model catalog when a provider namespace changes, and broadcasts a raw-only change', async () => {
+    // Editing `models` changes no route, so llm/adapters-updated never fires
+    // and an open model picker kept serving the old catalog. And storing an
+    // override equal to the resolved value emits nothing on settings/updated,
+    // so another tab never learned the field became overridden.
+    const ctx = await harness()
+    ctx.settings.register(NS, AdapterConfig, { base: { baseURL: 'https://base' } })
+    const api = createApiProxy(ctx, DEFAULTS)
+    const frames = await collectHost(api, ['host/settings-changed', 'host/models-changed'], 2, async () => {
+      await api.settings.update(request({ ns: 'llm-deepseek', patch: { baseURL: 'https://base' } }))
+    })
+    expect(frames).toEqual([
+      { type: 'host/settings-changed', ns: 'llm-deepseek' },
+      { type: 'host/models-changed' },
+    ])
+    // The resolved value never moved: base already said https://base.
+    expect(expectOk(await api.settings.describe(request({}))).namespaces[0]!.value)
+      .toEqual({ apiKeyEnv: 'DEEPSEEK_API_KEY', baseURL: 'https://base' })
+  })
+
+  it('maps a stale expectedRevision to settings-conflict carrying both revisions', async () => {
+    const ctx = await harness()
+    ctx.settings.register(NS, AdapterConfig)
+    const api = createApiProxy(ctx, DEFAULTS)
+    const opened = expectOk(await api.settings.describe(request({}))).namespaces[0]!.revision
+    expect(expectOk(await api.settings.update(request({ ns: 'llm-deepseek', patch: { baseURL: 'https://first' }, expectedRevision: opened })))
+      .revision).toBe(opened + 1)
+    const error = expectErr(await api.settings.update(request({ ns: 'llm-deepseek', patch: { baseURL: 'https://second' }, expectedRevision: opened })))
+    expect(error.code).toBe('settings-conflict')
+    expect(error.details).toEqual({ ns: 'llm-deepseek', expected: opened, actual: opened + 1 })
+    // The refused write changed nothing.
+    expect(expectOk(await api.settings.describe(request({}))).namespaces[0]!.user).toEqual({ baseURL: 'https://first' })
+  })
+
   it('updates the user layer, answers with the new redacted view, and broadcasts the frame', async () => {
     const ctx = await harness()
     ctx.settings.register(NS, AdapterConfig, { base: { baseURL: 'https://base' } })