fix(task): declare the observation registry on Task in this unit

The read tools record the observed on-disk version through task.observationRegistry, but the field
was only declared in a later unit, so at this head the call dereferences undefined and the mocked
e2e run fails on the read_file smoke tests. The registry is introduced by this unit, so the field
belongs here.

tsc clean on this unit, 11 observationRegistry tests pass, ESLint --max-warnings=0 clean.

Author: easonLiangWorldedtech

src/core/task/Task.ts

@@ -111,6 +111,7 @@ import { buildNativeToolsArrayWithRestrictions } from "./build-tools"
 import { ToolRepetitionDetector } from "../tools/ToolRepetitionDetector"
 import { restoreTodoListForTask } from "../tools/UpdateTodoListTool"
 import { FileContextTracker } from "../context-tracking/FileContextTracker"
+import { ObservationRegistry } from "./observationRegistry"
 import { RooIgnoreController } from "../ignore/RooIgnoreController"
 import { RooProtectedController } from "../protect/RooProtectedController"
 import { type AssistantMessageContent, presentAssistantMessage } from "../assistant-message"
@@ -286,6 +287,10 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 	readonly instanceId: string
 	readonly metadata: TaskMetadata
 
+	// The observed on-disk version of each file this task has read. Declared here so the
+	// read tools can record it; a write guard later compares a token against this registry.
+	readonly observationRegistry = new ObservationRegistry()
+
 	todoList?: TodoItem[]
 
 	readonly rootTask: Task | undefined = undefined