fix: accept identical diffs as no-op instead of error

- Modified multi-search-replace.ts and multi-file-search-replace.ts to treat identical search/replace content as successful no-op operations
- Added comprehensive tests for the new behavior
- Fixes #7183 where Gemini and other AI providers sometimes generate identical diffs

src/core/diff/strategies/__tests__/identical-diff.spec.ts

@@ -0,0 +1,218 @@
+import { MultiSearchReplaceDiffStrategy } from "../multi-search-replace"
+import { MultiFileSearchReplaceDiffStrategy } from "../multi-file-search-replace"
+
+describe("Identical diff handling", () => {
+	describe("MultiSearchReplaceDiffStrategy", () => {
+		let strategy: MultiSearchReplaceDiffStrategy
+
+		beforeEach(() => {
+			strategy = new MultiSearchReplaceDiffStrategy()
+		})
+
+		it("should treat identical search and replace content as successful no-op", async () => {
+			const originalContent = `function test() {
+    console.log("hello");
+    return true;
+}`
+			const diffContent = `test.ts
+<<<<<<< SEARCH
+    console.log("hello");
+=======
+    console.log("hello");
+>>>>>>> REPLACE`
+
+			const result = await strategy.applyDiff(originalContent, diffContent)
+			expect(result.success).toBe(true)
+			if (result.success) {
+				// Content should remain unchanged
+				expect(result.content).toBe(originalContent)
+			}
+		})
+
+		it("should handle multiple diffs where some are identical (no-op)", async () => {
+			const originalContent = `function test() {
+    console.log("hello");
+    console.log("world");
+    return true;
+}`
+			const diffContent = `test.ts
+<<<<<<< SEARCH
+    console.log("hello");
+=======
+    console.log("hello");
+>>>>>>> REPLACE
+
+<<<<<<< SEARCH
+    console.log("world");
+=======
+    console.log("universe");
+>>>>>>> REPLACE`
+
+			const result = await strategy.applyDiff(originalContent, diffContent)
+			expect(result.success).toBe(true)
+			if (result.success) {
+				// First diff is no-op, second diff should apply
+				expect(result.content).toBe(`function test() {
+    console.log("hello");
+    console.log("universe");
+    return true;
+}`)
+			}
+		})
+
+		it("should handle all identical diffs as successful no-op", async () => {
+			const originalContent = `class Example {
+    constructor() {
+        this.value = 0;
+    }
+}`
+			const diffContent = `test.ts
+<<<<<<< SEARCH
+    constructor() {
+        this.value = 0;
+    }
+=======
+    constructor() {
+        this.value = 0;
+    }
+>>>>>>> REPLACE
+
+<<<<<<< SEARCH
+class Example {
+=======
+class Example {
+>>>>>>> REPLACE`
+
+			const result = await strategy.applyDiff(originalContent, diffContent)
+			expect(result.success).toBe(true)
+			if (result.success) {
+				// All diffs are no-op, content should remain unchanged
+				expect(result.content).toBe(originalContent)
+			}
+		})
+
+		it("should handle identical diffs with line numbers as no-op", async () => {
+			const originalContent = `function test() {
+    const x = 1;
+    return x;
+}`
+			const diffContent = `test.ts
+<<<<<<< SEARCH
+:start_line:2
+-------
+    const x = 1;
+=======
+    const x = 1;
+>>>>>>> REPLACE`
+
+			const result = await strategy.applyDiff(originalContent, diffContent)
+			expect(result.success).toBe(true)
+			if (result.success) {
+				// Content should remain unchanged
+				expect(result.content).toBe(originalContent)
+			}
+		})
+	})
+
+	describe("MultiFileSearchReplaceDiffStrategy", () => {
+		let strategy: MultiFileSearchReplaceDiffStrategy
+
+		beforeEach(() => {
+			strategy = new MultiFileSearchReplaceDiffStrategy()
+		})
+
+		it("should treat identical search and replace content as successful no-op", async () => {
+			const originalContent = `function test() {
+    console.log("hello");
+    return true;
+}`
+			const diffContent = `test.ts
+<<<<<<< SEARCH
+    console.log("hello");
+=======
+    console.log("hello");
+>>>>>>> REPLACE`
+
+			const result = await strategy.applyDiff(originalContent, diffContent)
+			expect(result.success).toBe(true)
+			if (result.success) {
+				// Content should remain unchanged
+				expect(result.content).toBe(originalContent)
+			}
+		})
+
+		it("should handle array of diffs with identical content as no-op", async () => {
+			const originalContent = `function test() {
+    console.log("hello");
+    console.log("world");
+    return true;
+}`
+			const diffItems = [
+				{
+					content: `<<<<<<< SEARCH
+    console.log("hello");
+=======
+    console.log("hello");
+>>>>>>> REPLACE`,
+					startLine: undefined,
+				},
+				{
+					content: `<<<<<<< SEARCH
+    console.log("world");
+=======
+    console.log("universe");
+>>>>>>> REPLACE`,
+					startLine: undefined,
+				},
+			]
+
+			const result = await strategy.applyDiff(originalContent, diffItems)
+			expect(result.success).toBe(true)
+			if (result.success) {
+				// First diff is no-op, second diff should apply
+				expect(result.content).toBe(`function test() {
+    console.log("hello");
+    console.log("universe");
+    return true;
+}`)
+			}
+		})
+
+		it("should handle all identical diffs in array as successful no-op", async () => {
+			const originalContent = `class Example {
+    constructor() {
+        this.value = 0;
+    }
+}`
+			const diffItems = [
+				{
+					content: `<<<<<<< SEARCH
+    constructor() {
+        this.value = 0;
+    }
+=======
+    constructor() {
+        this.value = 0;
+    }
+>>>>>>> REPLACE`,
+					startLine: undefined,
+				},
+				{
+					content: `<<<<<<< SEARCH
+class Example {
+=======
+class Example {
+>>>>>>> REPLACE`,
+					startLine: undefined,
+				},
+			]
+
+			const result = await strategy.applyDiff(originalContent, diffItems)
+			expect(result.success).toBe(true)
+			if (result.success) {
+				// All diffs are no-op, content should remain unchanged
+				expect(result.content).toBe(originalContent)
+			}
+		})
+	})
+})

src/core/diff/strategies/multi-file-search-replace.ts

@@ -510,16 +510,12 @@ Each file requires its own path, start_line, and diff elements.
 				replaceContent = stripLineNumbers(replaceContent)
 			}
 
-			// Validate that search and replace content are not identical
+			// If search and replace content are identical, treat as no-op (skip silently)
 			if (searchContent === replaceContent) {
-				diffResults.push({
-					success: false,
-					error:
-						`Search and replace content are identical - no changes would be made\n\n` +
-						`Debug Info:\n` +
-						`- Search and replace must be different to make changes\n` +
-						`- Use read_file to verify the content you want to change`,
-				})
+				// This is a no-op diff, skip it without error
+				// Some AI providers (like Gemini) sometimes generate identical diffs
+				// We treat these as successful no-ops rather than errors
+				appliedCount++ // Count it as applied since it's intentionally a no-op
 				continue
 			}
 

src/core/diff/strategies/multi-search-replace.ts

@@ -427,16 +427,12 @@ Only use a single line of '=======' between search and replacement content, beca
 				replaceContent = stripLineNumbers(replaceContent)
 			}
 
-			// Validate that search and replace content are not identical
+			// If search and replace content are identical, treat as no-op (skip silently)
 			if (searchContent === replaceContent) {
-				diffResults.push({
-					success: false,
-					error:
-						`Search and replace content are identical - no changes would be made\n\n` +
-						`Debug Info:\n` +
-						`- Search and replace must be different to make changes\n` +
-						`- Use read_file to verify the content you want to change`,
-				})
+				// This is a no-op diff, skip it without error
+				// Some AI providers (like Gemini) sometimes generate identical diffs
+				// We treat these as successful no-ops rather than errors
+				appliedCount++ // Count it as applied since it's intentionally a no-op
 				continue
 			}