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tell a fresh writer from one replaying a snapshot a predecessor superseded.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/llm/llm-pi-ai/README.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/llm/llm-pi-ai/README.md
-README.md: 75442e2f1f6578ed458d05302b1cb6b063e26092
-README.zh.md: 3baed4e30bbce6ce21c52da79369ad096bbbb752
+README.md: e8c2682cbb72ca1ac6a5ad6b26bdf63f0695716b
+README.zh.md: 5fb19ee1343e905352609d96e7f540c1a411b4d8

packages/llm/llm-pi-ai/README.md

@@ -112,7 +112,7 @@ Recorded response content appends to the next request and does not invalidate it
 ## Known Limitations and Deferred Work
 
 - **Settings can add or override routes, not remove composition routes** — the user layer merges over the composition `base`, so deleting a `cordis.yml`-provided provider is a composition change; `replace` on the namespace only resets the user layer.
-- **`apiKey` is schema-tagged `role('secret')` but not yet masked anywhere** — the settings `describe()` envelope returns values verbatim; the wire/UI layer that must redact secret-role fields ships with the settings RPC surface.
+- **`headers` can carry a credential the redactor never sees** — the profile's `headers` dict is plain strings, so `Authorization` or `api-key` set there is returned verbatim by a redacted `describe()` and rendered by any configuration UI. Store credentials as `apiKeyEnv` references; making the dict write-only is deferred with the rest of the [wire-boundary work](../llm/README.md#known-limitations-and-deferred-work).
 - **Catalog membership is required** — custom model ids that are absent from the installed pi-ai catalog fail with `UNKNOWN_MODEL`, even when a provider profile supplies a custom endpoint.
 - **`GenerateOptions.stop` is unsupported** — pi-ai's common stream options cannot guarantee stop-sequence behavior across providers, so the adapter rejects the field.
 - **In-history `system` messages use pi-ai's common context conversion** — provider-specific placement follows pi-ai rather than a harness-owned wire override.

packages/llm/llm-pi-ai/README.zh.md

@@ -112,7 +112,7 @@ pi-ai 事件会变为 harness 推理、文本、工具调用、usage 与 finish
 ## 已知限制与暂缓事项
 
 - **settings 能新增或覆盖路由，但不能移除组合路由**：用户层合并在组合 `base` 之上，因此删除 `cordis.yml` 提供的提供方属于组合变更；对该 namespace 执行 `replace` 只会重置用户层。
-- **`apiKey` 已在 schema 中标注 `role('secret')`，但尚未在任何地方脱敏**：settings 的 `describe()` 信封原样返回值；负责对 secret 角色字段脱敏的 wire／UI 层将随 settings RPC 面一起交付。
+- **`headers` 可能承载一条脱敏器看不见的凭据**：profile 的 `headers` 是纯字符串字典，因此设在其中的 `Authorization` 或 `api-key` 会被脱敏后的 `describe()` 原样返回，并被任何配置 UI 渲染出来。请把凭据存为 `apiKeyEnv` 引用；把该字典整体改为只写与其余[协议边界工作](../llm/README.md#known-limitations-and-deferred-work)一并暂缓。
 - **必须属于 catalog**：已安装 pi-ai catalog 中不存在的自定义模型 id 会以 `UNKNOWN_MODEL` 失败，即使提供方 profile 配置了自定义端点。
 - **不支持 `GenerateOptions.stop`**：pi-ai 的通用流选项无法保证所有提供方都支持 stop sequence，因此适配器会拒绝该字段。
 - **历史中的 `system` 消息使用 pi-ai 通用上下文转换**：提供方特定位置由 pi-ai 决定，而非由 harness 拥有的协议覆盖决定。