feat(adoption): one owner for config/layout identity and the adoption sequence

`src/config-adoption.ts` owns config/layout with revision and fingerprint;
the host keeps `_serverCfg`/`_cfgRev`/`_layout`/`_layoutRev` as delegates.
All seven authoritative adoptions go through `adoptAuthoritativeGated`
(backdrop readiness → continuity → adopt → profile tail); the post-write
paths (space/delete ×2, optimize_undo, import/apply) gain the gate and take
revisions from the re-read bodies. `rollbackOptimistic` moves to the owner;
plan-optimize, space copy and the vacuum writers stop assigning identity.

Issue: #500
User-Visible: no

src/plan-optimize-write.ts

@@ -1,6 +1,6 @@
+import type { ConfigAdoption } from './config-adoption';
 import type { DeviceLayout } from './device-position-history';
 import type { ServerConfig } from './types';
-import { contentFingerprint } from './visual-continuity';
 
 interface Clearable { clear(): void }
 interface Flushable { pending(): boolean; flush(): void }
@@ -9,11 +9,10 @@ export interface PlanOptimizeWriteHost {
   hass: { callWS(message: Record<string, unknown>): Promise<Record<string, unknown>> };
   _saveConfigDebounced: Flushable;
   _writeChain: Promise<void>;
-  _cfgRev: number;
-  _cfgContentFingerprint: string;
-  _layoutRev: number;
-  _serverCfg: ServerConfig | null;
-  _layout: DeviceLayout;
+  readonly _cfgRev: number;
+  readonly _layoutRev: number;
+  /** #500: identity owner — bodies and revisions of the pair land through it. */
+  readonly _adoption: ConfigAdoption;
   _geometryHistory: Clearable;
   _devicePositionHistory: Clearable;
   _cancelDeviceDrag(): boolean;
@@ -30,9 +29,6 @@ export interface PlanOptimizeWriteHost {
   requestUpdate(): void;
 }
 
-const finiteRevision = (value: unknown, fallback: number): number =>
-  typeof value === 'number' && Number.isFinite(value) ? value : fallback;
-
 /** The one adoption path shared by the Optimize dialog and Copy space. */
 export async function commitPlanOptimization(
   host: PlanOptimizeWriteHost,
@@ -48,14 +44,11 @@ export async function commitPlanOptimization(
     expected_config_rev: host._cfgRev,
     expected_layout_rev: host._layoutRev,
   });
-  host._serverCfg = config;
-  host._cfgContentFingerprint = contentFingerprint(config);
-  host._layout = layout;
+  // Both bodies with both revisions from the reply that accepted them (#500 I2).
+  host._adoption.acceptPairWrite(config, layout, response);
   host._geometryHistory.clear();
   host._cancelDeviceDrag();
   host._devicePositionHistory.clear();
-  host._cfgRev = finiteRevision(response.config_rev, host._cfgRev + 1);
-  host._layoutRev = finiteRevision(response.layout_rev, host._layoutRev + 1);
   host._canOptimizeUndo = response.can_undo === true;
   host._undoKind = response.can_undo === true ? 'optimize' : null;
   host._dirtyPos.clear();