@@ -258,6 +258,33 @@ Two consequences of that table are deliberate rather than incidental:
 
 **What the user sees.** The permission-mode selector and the model selector are hidden, not disabled and not accompanied by an error message (`webapp/lib/engine-capabilities.ts`, wired in `webapp/components/composer.tsx`). A toast would report a failure for something the user was never able to do, offer nothing to act on, and reappear on every click. The rule is fail-open: the controls are shown until the declaration positively says the engine cannot do it, so a failed or slow `/api/engine-capabilities` request never removes a working control.
 
+### M3-B10: the model and permission writes move behind the facade (no behaviour change)
+
+`POST /api/set-model` (#58) and `POST /api/permissions` (#59) are the second half of the model endpoint family; B4 moved its read, this batch moves the write. The reasoning leaves the route and lands in `packages/webui/server/engine/model-writes.js`, where it is named, exported and tested on its inputs.
+
+**Nothing a client can observe changed.** Every status, response field, field order, warning string and engine push — including which push happens first and what it is allowed to say when it fails — is the one these two endpoints produced before. The boundary is:
+
+| Concern | Home after B10 |
+| --- | --- |
+| webui id → engine wire value | `resolveEngineModelConfigValue` |
+| variant channel vs effort channel, and the push order each implies | `planModelSelectionPush` |
+| the `set_config_option` calls | `pushEngineModelSelection` / `pushEnginePermissionMode` |
+| permission mode → label / engine value | `resolvePermissionSelection` |
+| the rule for when the local `configOptions` snapshot may claim the engine's new effort | `applyThinkingEffortMirror` (the write stays in the route — `cs` is webui's own state) |
+| body parsing, the 400s, the `cs.model` / `cs.permissions` writes, `pushStateFor`, the response bodies | `packages/webui/server/routes/model.js` |
+
+Two forms the picker deals with are deliberately different and stay that way. What the **engine** receives is the wire form — `m:<provider>:<model>:u`, or `m:<provider>:<model>:v:<variant>` for a switchable builtin, plus a bare level for `thinkingEffort` and an engine vocabulary word for `permissionMode`. What **webui** records is the user-facing form — `cs.model.name` in `<providerKey>/<engineModelKey>`, `cs.model.thinking`, `cs.permissions` as a label. The map between them is what the suite pins, field by field, over one row per (engine option shape × request shape) in `packages/webui/test/lib/engine/model-writes.test.js`.
+
+**The variant channel (ticket 36) is unchanged and now covered by name.** A switchable builtin (`thinking_config.mode: switchable`, e.g. MiniMax-M3) has no engine effort vocabulary — the engine rejects every `thinkingEffort` value for it — and advertises it only as the wire pair `v:thinking` / `v:none-thinking`. Such a pick is therefore **one** `model` push carrying both the model and the on/off level, with no second push at all. Every other model keeps the two-push contract: `model` first, then `thinkingEffort`, because the engine rejects an effort set when no model is selected. A cleared level on the variant channel means the engine's **default** variant, not "off" — the normaliser only knows `on` and `off`.
+
+**The 4-second SSE race window is unchanged**, and now has both halves pinned. A pick stamps the fields the request actually carried, all with one timestamp, so `applyConfigOptionUpdate`'s ownership-aware mirror (`server/lib/mcode-acp.js`, ticket 08) defers the engine's wire-form echo for 4 seconds instead of letting it overwrite the chip a few milliseconds after the optimistic write. A field the request did *not* carry is not stamped, so a later cross-client change to that field still mirrors immediately.
+
+**`contextWindow` is still recorded and never pushed.** The engine's ACP surface has no channel for it, so the pick is a webui-side preference the picker reflects immediately.
+
+**These two endpoints are not gated, and that is an open decision rather than an oversight.** #59 writes `permissionMode` only, so gating it on `authCredentials.setPermissionMode` would be behaviourally inert today and safe against the shipped UI (the permission selector is already hidden under exactly that declaration) — it is one `assertEngineCapability` call. #58 also writes `thinkingEffort`, which is a *generic* config id: gating it the same way would make the thinking-effort control answer 501 for the same reason #68 does for an unrecognised id. Both branches are costed in the KNOWN DEBT section of `model-writes.js` — bridge `thinkingEffort` as a third bridged id, or accept the 501 and extend the frontend's degradation to a third control. Until that is decided, #58 keeps its pre-B10 behaviour.
+
+**The bridge is no longer an unverified exemption.** `selectModel` and `setPermissionMode` — the two sub-items `MODE_WRITE_BRIDGED_CONFIG_IDS` names — are now in the snapshot audit's `REQUIRED_METHODS`, so a real booted host is checked for both of them on the adapter *and* the CliService surface, and a declaration that stops listing one goes red. Neither surface carries a `setThinkingEffort` / `selectThinkingEffort`, which is the fact the gating decision above turns on.
+
 ### Migration state and constraints
 
 - **M1 done in this batch**: host construction (`createCatalogueHost`) moved verbatim into `server/engine/providers/local-runtime-v2.js`; `runtime-host.js` re-exports it, so every existing importer is untouched. No existing route's behaviour changed; `GET /api/engine-capabilities` is a new, additive endpoint.
 
@@ -258,6 +258,33 @@ GET  /api/engine-capabilities[?provider=<id>]
 
 **用户看到什么。** 权限模式选择器与模型选择器被**隐藏**，不是禁用，也不配任何错误提示（`webapp/lib/engine-capabilities.ts`，接线在 `webapp/components/composer.tsx`）。toast 会为一件用户从来就做不到的事报一次失败、无从处理、而且每点一次就再报一次。这条规则是 fail-open 的：控件会一直显示，直到声明明确说引擎做不到——因此一次失败或超时的 `/api/engine-capabilities` 请求绝不会拿掉一个本来能用的控件。
 
+### M3-B10：模型与权限写搬进引擎门面（行为零变更）
+
+`POST /api/set-model`（#58）与 `POST /api/permissions`（#59）是模型端点族的另一半：B4 搬了读，本批搬写。推理逻辑离开路由，落进 `packages/webui/server/engine/model-writes.js`，在那里被命名、导出，并按入参测试。
+
+**客户端能观察到的一切都没变。** 每个状态码、每个应答字段、字段顺序、警告文案与引擎推送——包括哪一次推送先发生、失败时它被允许说什么——都与本批之前逐字节一致。边界如下：
+
+| 关注点 | B10 之后的归属 |
+| --- | --- |
+| webui id → 引擎 wire 值 | `resolveEngineModelConfigValue` |
+| variant 通道 vs 强度通道，以及各自蕴含的推送顺序 | `planModelSelectionPush` |
+| `set_config_option` 调用 | `pushEngineModelSelection` / `pushEnginePermissionMode` |
+| 权限模式 → 标签 / 引擎值 | `resolvePermissionSelection` |
+| 本地 `configOptions` 快照何时可以宣称引擎的新强度 | `applyThinkingEffortMirror`（写仍留在路由——`cs` 是 webui 自己的状态） |
+| 请求体解析、400、`cs.model` / `cs.permissions` 写入、`pushStateFor`、应答体 | `packages/webui/server/routes/model.js` |
+
+选择器面对的两种形态本就不同，并且刻意保持不同。**引擎**收到的是 wire 形态——`m:<provider>:<model>:u`，可切换内置模型则是 `m:<provider>:<model>:v:<variant>`，另加 `thinkingEffort` 的裸档位与 `permissionMode` 的引擎词汇。**webui** 记录的是面向用户的形态——`<providerKey>/<engineModelKey>` 的 `cs.model.name`、`cs.model.thinking`、作为标签的 `cs.permissions`。两者之间的映射由测试逐字段钉住：`packages/webui/test/lib/engine/model-writes.test.js` 按（引擎选项形态 × 请求形态）每种组合一行。
+
+**variant 通道（ticket 36）语义不变，并且现在被具名覆盖。** 可切换内置模型（`thinking_config.mode: switchable`，如 MiniMax-M3）没有引擎强度词汇——引擎会拒绝它的一切 `thinkingEffort` 取值——只以 `v:thinking` / `v:none-thinking` 这一对 wire 形态公布。因此这样的选择是**一次** `model` 推送，同时带上模型与开/关档位，压根没有第二次推送。其余模型保持双推送契约：先 `model` 后 `thinkingEffort`，因为引擎在未选模型时会拒绝设置强度。在 variant 通道上「清空档位」意味着引擎的**默认** variant，而不是「off」——归一化器只认 `on` 与 `off`。
+
+**4 秒 SSE 竞态窗口不变**，且两个半边都被钉住。一次选择会为请求**实际携带**的字段打戳，全部共用同一个时间戳，于是 `applyConfigOptionUpdate` 的归属感知镜像（`server/lib/mcode-acp.js`，ticket 08）会把引擎的 wire 形态回声推迟 4 秒，而不是让它在乐观写入后几毫秒就覆盖芯片。请求**未**携带的字段不会被打戳，因此该字段后续的跨端变化仍会立即镜像。
+
+**`contextWindow` 依旧只记录、不推送。** 引擎 ACP 面没有它的通道，因此这项选择是 webui 侧的偏好，选择器立刻就能反映。
+
+**这两个端点没有挂门，而这是一个待人拍板的开口，不是疏漏。** #59 只写 `permissionMode`，所以把它挂到 `authCredentials.setPermissionMode` 上，今天在行为上是空转的，而且对已发布 UI 安全（权限选择器本来就按同一条声明被隐藏）——那只是一次 `assertEngineCapability` 调用。#58 还会写 `thinkingEffort`，而它是**通用** config id：照样挂门会让思考强度控件因为与 #68 遇到无法识别的 id 时完全相同的原因开始答 501。两个分支的成本都写在 `model-writes.js` 的 KNOWN DEBT 段——把 `thinkingEffort` 桥接成第三个 id，还是接受 501 并把前端降级扩到第三个控件。在拍板之前，#58 保持 B10 之前的行为。
+
+**桥接不再是未经核实的豁免。** `selectModel` 与 `setPermissionMode`——`MODE_WRITE_BRIDGED_CONFIG_IDS` 点名的两个子项——现已进入快照审计的 `REQUIRED_METHODS`，因此真实启动的 host 会在 adapter **与** CliService 两个面上被检查这两个方法，而停止列出其中之一的声明会变红。两个面都没有 `setThinkingEffort` / `selectThinkingEffort`，这正是上面那个挂门决策所依据的事实。
+
 ### 迁移状态与边界
 
 - **本批只做迁移第一步 M1**：host 构造（`createCatalogueHost`）原样移入 `engine/providers/local-runtime-v2.js`，`runtime-host.js` 转发导出，既有引用方零改动；没有任何现有路由行为变化，`GET /api/engine-capabilities` 是纯新增端点。
 
@@ -36,10 +36,37 @@ import {
 
 const MANIFEST_FILE = 'agent-name-conflicts.json';
 const EMPTY_REFERENCE_COUNTS = EMPTY_AGENT_NAME_CONFLICT_REFERENCE_COUNTS;
-// Synchronous backup/rewrite needs a long-lived dataDir lease.
-export const AGENT_NAME_CONFLICT_MIGRATION_LOCK_STALE_MS = 30 * 60_000;
-const AGENT_NAME_CONFLICT_MIGRATION_LOCK_RETRIES = {
-  retries: 120,
+// Synchronous backup/rewrite needs a dataDir lease, so the lease outlives the
+// critical section rather than the other way round.
+//
+// The window is 2 minutes, and it was 30. The reason is not "2 minutes is
+// enough to rewrite a database" — a live holder refreshes the lease every
+// `stale / 2` (proper-lockfile derives the heartbeat from the stale window), so
+// the ratio that actually matters — "two missed heartbeats before the lease is
+// called abandoned" — is unchanged. What changed is the cost of a lease that
+// is abandoned for real.
+//
+// This lease gates PROCESS STARTUP: `mcode acp` takes it during the V2 cutover
+// and cannot serve a prompt without it. The lease is a bare directory, so a
+// process killed between `mkdir` and `release` leaves it behind, and the only
+// evidence of a live holder is the directory's mtime. A 30-minute window
+// therefore made one killed process unstartable for half an hour — and the
+// retry budget (55s) was far too short to outlast it, so every launch during
+// that window burned 55s of backoff and then died with
+// `agent_name_conflict_migration_failed:lock`. That is the outage: repeated
+// sends producing no reply, no engine process, and no session.
+//
+// The migration itself is idempotent and re-inspects under the lease
+// (`ensureAgentNameConflictMigrationLocked`), so the worst a wrongly-considered
+// stale lease can cost is one extra inspection — not a double rewrite.
+export const AGENT_NAME_CONFLICT_MIGRATION_LOCK_STALE_MS = 2 * 60_000;
+// The wait must be able to OUTLAST the stale window, or a waiter gives up at
+// the moment the abandoned lease becomes reapable. At this backoff shape the
+// 120 retries summed to ~55s against a 30-minute window — a waiter could never
+// win, only die. 400 retries sum to ~195s, which rides out one full stale
+// expiry and then acquires.
+export const AGENT_NAME_CONFLICT_MIGRATION_LOCK_RETRIES = {
+  retries: 400,
   factor: 1.2,
   minTimeout: 25,
   maxTimeout: 500,
 
@@ -0,0 +1,121 @@
+import { mkdir, mkdtemp, rm, utimes } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { afterEach, describe, expect, it } from 'vitest';
+import lockfile from 'proper-lockfile';
+import {
+  AGENT_NAME_CONFLICT_MIGRATION_LOCK_RETRIES,
+  AGENT_NAME_CONFLICT_MIGRATION_LOCK_STALE_MS,
+  withAgentNameConflictMigrationLock,
+} from '../../src/persistence/migration/agent-name-conflict-migration.js';
+
+// The lease that gates `mcode acp` startup. `proper-lockfile` represents it as
+// a bare directory (`<dataDir>.lock`): mkdir acquires, rmdir releases, and a
+// live holder heartbeats the directory mtime every `stale / 2`. A process
+// killed between the two leaves the directory behind, and an abandoned lease is
+// indistinguishable from a live one except by that mtime.
+//
+// These tests pin the two properties the outage depended on. An abandoned lease
+// must become reapable on a timescale a process launch can wait out, AND a
+// lease that really is held must still be respected. Both halves matter: a fix
+// that only shortened the window would trade a startup outage for two
+// processes inside one critical section.
+
+const cleanups: Array<() => Promise<void | void>> = [];
+
+afterEach(async () => {
+  while (cleanups.length > 0) await cleanups.pop()!();
+});
+
+async function makeDataDir(): Promise<string> {
+  const dir = await mkdtemp(join(tmpdir(), 'agent-name-conflict-lock-'));
+  cleanups.push(async () => {
+    await rm(dir, { recursive: true, force: true });
+  });
+  cleanups.push(async () => {
+    await rm(`${dir}.lock`, { recursive: true, force: true });
+  });
+  return dir;
+}
+
+/** Create the lease directory and age its mtime to `ageMs` in the past. */
+async function plantAgedLease(dataDir: string, ageMs: number): Promise<void> {
+  const leaseDir = `${dataDir}.lock`;
+  await mkdir(leaseDir, { recursive: true });
+  const when = new Date(Date.now() - ageMs);
+  await utimes(leaseDir, when, when);
+}
+
+/**
+ * An abandoned lease of a fixed, real-world age.
+ *
+ * The age is ABSOLUTE and deliberately not derived from the stale constant.
+ * A fixture aged by `STALE + margin` is reaped instantly under any value of
+ * the constant, so it passes whatever the constant is — it cannot fail, and a
+ * test that cannot fail is decoration. Five minutes is the shape of the outage
+ * this pins: a lease orphaned 15+ minutes earlier by a killed process, still
+ * blocking every engine launch.
+ */
+const ABANDONED_LEASE_AGE_MS = 5 * 60_000;
+
+describe('agent name conflict migration lease', () => {
+  it('takes over an abandoned lease promptly instead of burning the whole retry budget', async () => {
+    const dataDir = await makeDataDir();
+    await plantAgedLease(dataDir, ABANDONED_LEASE_AGE_MS);
+
+    const startedAt = Date.now();
+    await expect(withAgentNameConflictMigrationLock(dataDir, () => 'reaped')).resolves.toBe(
+      'reaped',
+    );
+
+    // Fast, not merely eventually correct. Before the fix a 30-minute stale
+    // window made this wait out the whole ~55s retry budget and then throw,
+    // because the budget could not outlast the window — which is what killed
+    // every engine launch.
+    expect(Date.now() - startedAt).toBeLessThan(10_000);
+  });
+
+  it('still leaves a lease that is genuinely held alone', async () => {
+    const dataDir = await makeDataDir();
+    // A real holder, taken with the same library the migration uses, so the
+    // lease directory is a genuine one and its mtime is a live heartbeat —
+    // which is the ONLY thing that separates a held lease from an abandoned
+    // one. This is the half that guards against over-correcting: if the stale
+    // window were shortened to the point of reaping a beating lease, the
+    // takeover would trade a startup outage for two processes inside one
+    // critical section.
+    const release = await lockfile.lock(dataDir, {
+      stale: AGENT_NAME_CONFLICT_MIGRATION_LOCK_STALE_MS,
+    });
+
+    let entered = false;
+    const acquisition = withAgentNameConflictMigrationLock(dataDir, () => {
+      entered = true;
+    });
+    // Long enough to prove it is waiting rather than barging in.
+    await new Promise((resolve) => setTimeout(resolve, 3_000));
+    expect(entered).toBe(false);
+
+    // Once the holder releases, the waiter proceeds on its own.
+    await release();
+    await acquisition;
+    expect(entered).toBe(true);
+  });
+
+  it('keeps the retry budget long enough to outlast the stale window', async () => {
+    // The invariant behind both tests: a waiter must be able to survive one
+    // abandoned-lease expiry and then acquire, rather than dying at the moment
+    // the lease becomes reapable. With 120 retries at this backoff shape the
+    // wait was ~55s against a 30-minute window, so it could only ever lose.
+    const { retries, factor, minTimeout, maxTimeout } =
+      AGENT_NAME_CONFLICT_MIGRATION_LOCK_RETRIES;
+    let total = 0;
+    let delay = minTimeout;
+    for (let attempt = 0; attempt < retries; attempt += 1) {
+      total += delay;
+      delay = Math.min(delay * factor, maxTimeout);
+    }
+
+    expect(total).toBeGreaterThan(AGENT_NAME_CONFLICT_MIGRATION_LOCK_STALE_MS);
+  });
+});