feat(tools): wire guarded writes into the diff-view save paths (S4b, #1375)

src/core/task/Task.ts

@@ -103,6 +103,7 @@ import { ToolRepetitionDetector } from "../tools/ToolRepetitionDetector"
 import { restoreTodoListForTask } from "../tools/UpdateTodoListTool"
 import { FileContextTracker } from "../context-tracking/FileContextTracker"
 import { RooIgnoreController } from "../ignore/RooIgnoreController"
+import { ObservationRegistry } from "./observationRegistry"
 import { RooProtectedController } from "../protect/RooProtectedController"
 import { type AssistantMessageContent, presentAssistantMessage } from "../assistant-message"
 import { NativeToolCallParser } from "../assistant-message/NativeToolCallParser"
@@ -181,6 +182,7 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 	readonly parentTask: Task | undefined = undefined
 	readonly taskNumber: number
 	readonly workspacePath: string
+	readonly observationRegistry = new ObservationRegistry()
 
 	/**
 	 * The mode associated with this task. Persisted across sessions

src/core/task/__tests__/observationRegistry.spec.ts

@@ -0,0 +1,72 @@
+import { describe, it, expect, vi } from "vitest"
+
+import { ObservationRegistry } from "../observationRegistry"
+
+describe("ObservationRegistry", () => {
+	it("observe → get returns the recorded version and observedAt", () => {
+		const reg = new ObservationRegistry()
+		reg.observe("/a/b/c.ts", "1:2:300:4000000000:5000000000")
+
+		const obs = reg.get("/a/b/c.ts")
+		expect(obs).toBeDefined()
+		expect(obs!.version).toBe("1:2:300:4000000000:5000000000")
+		expect(typeof obs!.observedAt).toBe("number")
+	})
+
+	it("re-observe replaces the entry with a fresh observedAt", () => {
+		vi.useFakeTimers()
+		const reg = new ObservationRegistry()
+		reg.observe("/a/b/c.ts", "v1")
+		const first = reg.get("/a/b/c.ts")!
+		expect(first.version).toBe("v1")
+
+		vi.advanceTimersByTime(50)
+		reg.observe("/a/b/c.ts", "v2")
+		const second = reg.get("/a/b/c.ts")!
+		expect(second.version).toBe("v2")
+		expect(second.observedAt).toBeGreaterThan(first.observedAt)
+
+		vi.useRealTimers()
+	})
+
+	it("has returns true for observed paths, false otherwise", () => {
+		const reg = new ObservationRegistry()
+		reg.observe("/x.ts", "t1")
+		expect(reg.has("/x.ts")).toBe(true)
+		expect(reg.has("/y.ts")).toBe(false)
+	})
+
+	it("size reflects the number of observed entries", () => {
+		const reg = new ObservationRegistry()
+		expect(reg.size).toBe(0)
+		reg.observe("/a.ts", "t1")
+		reg.observe("/b.ts", "t2")
+		expect(reg.size).toBe(2)
+	})
+
+	it("clear removes all entries and resets size to 0", () => {
+		const reg = new ObservationRegistry()
+		reg.observe("/a.ts", "t1")
+		reg.observe("/b.ts", "t2")
+		reg.clear()
+		expect(reg.size).toBe(0)
+		expect(reg.get("/a.ts")).toBeUndefined()
+		expect(reg.has("/b.ts")).toBe(false)
+	})
+
+	it("get on empty registry returns undefined", () => {
+		const reg = new ObservationRegistry()
+		expect(reg.get("/any.ts")).toBeUndefined()
+	})
+
+	it("separate instances are independent — observing in one does not appear in the other", () => {
+		const regA = new ObservationRegistry()
+		const regB = new ObservationRegistry()
+		regA.observe("/shared.ts", "v1")
+		expect(regA.get("/shared.ts")).toBeDefined()
+		expect(regB.get("/shared.ts")).toBeUndefined()
+		regB.observe("/shared.ts", "v2")
+		expect(regA.get("/shared.ts")!.version).toBe("v1")
+		expect(regB.get("/shared.ts")!.version).toBe("v2")
+	})
+})

src/core/task/observationRegistry.ts

@@ -0,0 +1,47 @@
+/**
+ * Per-task file observation registry (upstream epic #1375, phase A2).
+ *
+ * Each Task owns its own instance so parent and subtask observations are
+ * independent. The S4 guarded-write will compare these versions against the
+ * token recomputed pre-write to detect stale reads or file replacement.
+ *
+ * Pure in-memory — zero I/O, no dependencies. No behavior change in this PR:
+ * observations are recorded but not consulted.
+ */
+
+export interface FileObservation {
+	/** Version token derived from on-disk fs.stat (bigint mode). */
+	version: string
+	/** Millisecond timestamp when the observation was recorded. */
+	observedAt: number
+}
+
+export class ObservationRegistry {
+	private readonly entries = new Map<string, FileObservation>()
+
+	/**
+	 * Record an observation for a file at its absolute path.
+	 *
+	 * Re-observing replaces the entry with a fresh observedAt timestamp and
+	 * the new version token.
+	 */
+	observe(absolutePath: string, version: string): void {
+		this.entries.set(absolutePath, { version, observedAt: Date.now() })
+	}
+
+	get(absolutePath: string): FileObservation | undefined {
+		return this.entries.get(absolutePath)
+	}
+
+	has(absolutePath: string): boolean {
+		return this.entries.has(absolutePath)
+	}
+
+	clear(): void {
+		this.entries.clear()
+	}
+
+	get size(): number {
+		return this.entries.size
+	}
+}

src/core/tools/ApplyDiffTool.ts

@@ -173,7 +173,8 @@ export class ApplyDiffTool extends BaseTool<"apply_diff"> {
 					return
 				}
 
-				// Save directly without showing diff view or opening the file
+				// Save directly without showing diff view or opening the file. The diff is
+				// applied to an existing file, so edit-guard semantics require a prior read.
 				task.diffViewProvider.editType = "modify"
 				task.diffViewProvider.originalContent = originalContent
 				await task.diffViewProvider.saveDirectly(
@@ -182,6 +183,7 @@ export class ApplyDiffTool extends BaseTool<"apply_diff"> {
 					false,
 					diagnosticsEnabled,
 					writeDelayMs,
+					"edit",
 				)
 			} else {
 				// Original behavior with diff view

src/core/tools/ApplyPatchTool.ts

@@ -11,6 +11,7 @@ import { RecordSource } from "../context-tracking/FileContextTrackerTypes"
 import { fileExistsAtPath } from "../../utils/fs"
 import { EXPERIMENT_IDS, experiments } from "../../shared/experiments"
 import { sanitizeUnifiedDiff, computeDiffStats } from "../diff/stats"
+import { versionTokenOfStat } from "../../utils/versionToken"
 import { BaseTool, ToolCallbacks } from "./BaseTool"
 import type { ToolUse } from "../../shared/tools"
 import { parsePatch, ParseError, processAllHunks } from "./apply-patch"
@@ -85,10 +86,25 @@ export class ApplyPatchTool extends BaseTool<"apply_patch"> {
 				return
 			}
 
-			// Process each hunk
+			// Process each hunk. The read doubles as the S2 observation for the
+			// guarded publish (ReadFileTool contract: stat before and after the
+			// read, observe only when the on-disk version is unchanged between the
+			// two stats). Without it, the in-place modify publish is an unobserved
+			// write and the composed chat-diff default rejects it ("File already
+			// exists ... and was not read before this write") even though this tool
+			// just read the exact content the patch was applied to.
 			const readFile = async (filePath: string): Promise<string> => {
 				const absolutePath = path.resolve(task.cwd, filePath)
-				return await fs.readFile(absolutePath, "utf8")
+				const preReadStats = await fs.stat(absolutePath, { bigint: true }).catch(() => undefined)
+				const content: string = await fs.readFile(absolutePath, "utf8")
+				const postReadStats = await fs.stat(absolutePath, { bigint: true }).catch(() => undefined)
+				if (preReadStats && postReadStats) {
+					const preReadToken = versionTokenOfStat(preReadStats)
+					if (preReadToken === versionTokenOfStat(postReadStats)) {
+						task.observationRegistry.observe(absolutePath, preReadToken)
+					}
+				}
+				return content
 			}
 
 			let changes: ApplyPatchFileChange[]
@@ -214,7 +230,16 @@ export class ApplyPatchTool extends BaseTool<"apply_patch"> {
 
 		// Save the changes
 		if (isPreventFocusDisruptionEnabled) {
-			await task.diffViewProvider.saveDirectly(relPath, newContent, true, diagnosticsEnabled, writeDelayMs)
+			// Guarded publish: the patch supplies the complete new content, so create-guard
+			// semantics apply (an unobserved existing target is rejected, not overwritten).
+			await task.diffViewProvider.saveDirectly(
+				relPath,
+				newContent,
+				true,
+				diagnosticsEnabled,
+				writeDelayMs,
+				"create",
+			)
 		} else {
 			await task.diffViewProvider.saveChanges(diagnosticsEnabled, writeDelayMs)
 		}
@@ -408,12 +433,14 @@ export class ApplyPatchTool extends BaseTool<"apply_patch"> {
 
 			// Save new content to the new path
 			if (isPreventFocusDisruptionEnabled) {
+				// The move destination is published with the complete new content.
 				await task.diffViewProvider.saveDirectly(
 					change.movePath,
 					newContent,
 					false,
 					diagnosticsEnabled,
 					writeDelayMs,
+					"create",
 				)
 			} else {
 				// Write to new path and delete old file
@@ -433,7 +460,16 @@ export class ApplyPatchTool extends BaseTool<"apply_patch"> {
 		} else {
 			// Save changes to the same file
 			if (isPreventFocusDisruptionEnabled) {
-				await task.diffViewProvider.saveDirectly(relPath, newContent, false, diagnosticsEnabled, writeDelayMs)
+				// Guarded publish: the patched file content is complete, so create-guard
+				// semantics apply (stale observed versions are rejected with a re-read hint).
+				await task.diffViewProvider.saveDirectly(
+					relPath,
+					newContent,
+					false,
+					diagnosticsEnabled,
+					writeDelayMs,
+					"create",
+				)
 			} else {
 				await task.diffViewProvider.saveChanges(diagnosticsEnabled, writeDelayMs)
 			}

src/core/tools/EditFileTool.ts

@@ -436,13 +436,16 @@ export class EditFileTool extends BaseTool<"edit_file"> {
 
 			// Save the changes
 			if (isPreventFocusDisruptionEnabled) {
-				// Direct file write without diff view or opening the file
+				// Direct file write without diff view or opening the file. In-place edits
+				// use edit-guard semantics (a prior read is required); new-file creation
+				// keeps create-guard semantics.
 				await task.diffViewProvider.saveDirectly(
 					relPath,
 					newContent,
 					isNewFile,
 					diagnosticsEnabled,
 					writeDelayMs,
+					isNewFile ? "create" : "edit",
 				)
 			} else {
 				// Call saveChanges to update the DiffViewProvider properties

src/core/tools/EditTool.ts

@@ -211,8 +211,16 @@ export class EditTool extends BaseTool<"edit"> {
 
 			// Save the changes
 			if (isPreventFocusDisruptionEnabled) {
-				// Direct file write without diff view or opening the file
-				await task.diffViewProvider.saveDirectly(relPath, newContent, false, diagnosticsEnabled, writeDelayMs)
+				// Direct file write without diff view or opening the file. This tool only
+				// edits existing files, so edit-guard semantics require a prior read.
+				await task.diffViewProvider.saveDirectly(
+					relPath,
+					newContent,
+					false,
+					diagnosticsEnabled,
+					writeDelayMs,
+					"edit",
+				)
 			} else {
 				// Call saveChanges to update the DiffViewProvider properties
 				await task.diffViewProvider.saveChanges(diagnosticsEnabled, writeDelayMs)

src/core/tools/ReadFileTool.ts

@@ -16,6 +16,7 @@ import type { ReadFileParams, ReadFileMode, ReadFileToolParams, FileEntry, LineR
 import { isLegacyReadFileParams, type ClineSayTool } from "@roo-code/types"
 
 import { Task } from "../task/Task"
+import { versionTokenOfStat } from "../../utils/versionToken"
 import { formatResponse } from "../prompts/responses"
 import { RecordSource } from "../context-tracking/FileContextTrackerTypes"
 import { isPathOutsideWorkspace } from "../../utils/pathUtils"
@@ -214,12 +215,29 @@ export class ReadFileTool extends BaseTool<"read_file"> {
 					// Read text file content with lossy UTF-8 conversion
 					// Reading as Buffer first allows graceful handling of non-UTF8 bytes
 					// (they become U+FFFD replacement characters instead of throwing)
+					// A2 (epic #1375): capture the on-disk token before the read so a mutation
+					// landing mid-read is detected by the post-read stat below.
+					const preReadStats = await fs.stat(fullPath, { bigint: true }).catch(() => undefined)
 					const buffer = await fs.readFile(fullPath)
 					const fileContent = buffer.toString("utf-8")
 					const result = this.processTextFile(fileContent, entry)
 
 					await task.fileContextTracker.trackFileContext(relPath, "read_tool" as RecordSource)
 
+					// A2 (plan #33 / epic #1375): record the observed on-disk version for the future write guard.
+					// The token is captured before AND after the read; the target is observed only
+					// when both match — a mutation between the two stats means the content the model
+					// received is not the on-disk state, and observing it would let a later write
+					// match a token the model never saw. A stat failure leaves the target
+					// unobserved and never fails the read.
+					const postReadStats = await fs.stat(fullPath, { bigint: true }).catch(() => undefined)
+					if (preReadStats && postReadStats) {
+						const preReadToken = versionTokenOfStat(preReadStats)
+						if (preReadToken === versionTokenOfStat(postReadStats)) {
+							task.observationRegistry.observe(fullPath, preReadToken)
+						}
+					}
+
 					updateFileResult(relPath, {
 						nativeContent: `File: ${relPath}\n${result}`,
 					})
@@ -768,6 +786,9 @@ export class ReadFileTool extends BaseTool<"read_file"> {
 				}
 
 				// Read text file
+				// A2 (epic #1375): capture the on-disk token before the read so a mutation
+				// landing mid-read is detected by the post-read stat below.
+				const preReadStats = await fs.stat(fullPath, { bigint: true }).catch(() => undefined)
 				const rawContent = await fs.readFile(fullPath, "utf8")
 
 				// Handle line ranges if specified
@@ -799,6 +820,19 @@ export class ReadFileTool extends BaseTool<"read_file"> {
 
 				// Track file in context
 				await task.fileContextTracker.trackFileContext(relPath, "read_tool")
+
+				// A2 (plan #33 / epic #1375): mirror the native path — record the observed
+				// on-disk version so legacy-format reads also feed the future write guard.
+				// Observe only when the pre-read and post-read tokens match (a mutation between
+				// them means the returned content is not the on-disk state). A stat failure
+				// leaves the target unobserved and never fails the read.
+				const postReadStats = await fs.stat(fullPath, { bigint: true }).catch(() => undefined)
+				if (preReadStats && postReadStats) {
+					const preReadToken = versionTokenOfStat(preReadStats)
+					if (preReadToken === versionTokenOfStat(postReadStats)) {
+						task.observationRegistry.observe(fullPath, preReadToken)
+					}
+				}
 			} catch (error) {
 				const errorMsg = error instanceof Error ? error.message : String(error)
 				results.push(`File: ${relPath}\nError: ${errorMsg}`)

src/core/tools/SearchReplaceTool.ts

@@ -207,8 +207,16 @@ export class SearchReplaceTool extends BaseTool<"search_replace"> {
 
 			// Save the changes
 			if (isPreventFocusDisruptionEnabled) {
-				// Direct file write without diff view or opening the file
-				await task.diffViewProvider.saveDirectly(relPath, newContent, false, diagnosticsEnabled, writeDelayMs)
+				// Direct file write without diff view or opening the file. This tool only
+				// edits existing files, so edit-guard semantics require a prior read.
+				await task.diffViewProvider.saveDirectly(
+					relPath,
+					newContent,
+					false,
+					diagnosticsEnabled,
+					writeDelayMs,
+					"edit",
+				)
 			} else {
 				// Call saveChanges to update the DiffViewProvider properties
 				await task.diffViewProvider.saveChanges(diagnosticsEnabled, writeDelayMs)

src/core/tools/WriteToFileTool.ts

@@ -133,7 +133,16 @@ export class WriteToFileTool extends BaseTool<"write_to_file"> {
 					return
 				}
 
-				await task.diffViewProvider.saveDirectly(relPath, newContent, false, diagnosticsEnabled, writeDelayMs)
+				// Guarded publish: this write carries the complete file content, so it uses
+				// create-guard semantics (unobserved targets may only be created when absent).
+				await task.diffViewProvider.saveDirectly(
+					relPath,
+					newContent,
+					false,
+					diagnosticsEnabled,
+					writeDelayMs,
+					"create",
+				)
 			} else {
 				if (!task.diffViewProvider.isEditing) {
 					const partialMessage = JSON.stringify(sharedMessageProps)