Add batch editing capabilities to Edit Tool (#648)

Co-authored-by: N. Taylor Mullen <[email protected]>

4 files changed, 835 insertions, 8 deletions

diff --git a/packages/core/src/utils/editCorrector.test.ts b/packages/core/src/utils/editCorrector.test.ts
index 7d6f5a53..53872253 100644
--- a/packages/core/src/utils/editCorrector.test.ts
+++ b/packages/core/src/utils/editCorrector.test.ts
@@ -214,6 +214,9 @@ describe('editCorrector', () => {
         const currentContent = 'This is a test string to find me.';
         const originalParams = {
           file_path: '/test/file.txt',
+          edits: [
+            { old_string: 'find me', new_string: 'replace with \\"this\\"' },
+          ],
           old_string: 'find me',
           new_string: 'replace with \\"this\\"',
         };
@@ -235,6 +238,7 @@ describe('editCorrector', () => {
         const currentContent = 'This is a test string to find me.';
         const originalParams = {
           file_path: '/test/file.txt',
+          edits: [{ old_string: 'find me', new_string: 'replace with this' }],
           old_string: 'find me',
           new_string: 'replace with this',
         };
@@ -253,6 +257,9 @@ describe('editCorrector', () => {
         const currentContent = 'This is a test string to find\\me.';
         const originalParams = {
           file_path: '/test/file.txt',
+          edits: [
+            { old_string: 'find\\me', new_string: 'replace with \\"this\\"' },
+          ],
           old_string: 'find\\me',
           new_string: 'replace with \\"this\\"',
         };
@@ -274,6 +281,7 @@ describe('editCorrector', () => {
         const currentContent = 'This is a test string to find\\me.';
         const originalParams = {
           file_path: '/test/file.txt',
+          edits: [{ old_string: 'find\\me', new_string: 'replace with this' }],
           old_string: 'find\\me',
           new_string: 'replace with this',
         };
@@ -295,6 +303,12 @@ describe('editCorrector', () => {
         const currentContent = 'This is a test string to find "me".';
         const originalParams = {
           file_path: '/test/file.txt',
+          edits: [
+            {
+              old_string: 'find \\"me\\"',
+              new_string: 'replace with \\"this\\"',
+            },
+          ],
           old_string: 'find \\"me\\"',
           new_string: 'replace with \\"this\\"',
         };
@@ -314,6 +328,9 @@ describe('editCorrector', () => {
         const currentContent = 'This is a test string to find "me".';
         const originalParams = {
           file_path: '/test/file.txt',
+          edits: [
+            { old_string: 'find \\"me\\"', new_string: 'replace with this' },
+          ],
           old_string: 'find \\"me\\"',
           new_string: 'replace with this',
         };
@@ -332,6 +349,9 @@ describe('editCorrector', () => {
         const currentContent = 'This is a test string to find \\me.';
         const originalParams = {
           file_path: '/test/file.txt',
+          edits: [
+            { old_string: 'find \\\\me', new_string: 'replace with foobar' },
+          ],
           old_string: 'find \\\\me',
           new_string: 'replace with foobar',
         };
@@ -356,6 +376,12 @@ describe('editCorrector', () => {
         const currentContent = 'This is a test string to corrected find me.';
         const originalParams = {
           file_path: '/test/file.txt',
+          edits: [
+            {
+              old_string: 'find me',
+              new_string: 'replace with \\\\"this\\\\"',
+            },
+          ],
           old_string: 'find me',
           new_string: 'replace with \\\\"this\\\\"',
         };
@@ -376,6 +402,12 @@ describe('editCorrector', () => {
         const currentContent = 'This is a test string to corrected find me.';
         const originalParams = {
           file_path: '/test/file.txt',
+          edits: [
+            {
+              old_string: 'find\\me',
+              new_string: 'replace with \\\\"this\\\\"',
+            },
+          ],
           old_string: 'find\\me',
           new_string: 'replace with \\\\"this\\\\"',
         };
@@ -398,6 +430,9 @@ describe('editCorrector', () => {
         const currentContent = 'This is a test string to be corrected.';
         const originalParams = {
           file_path: '/test/file.txt',
+          edits: [
+            { old_string: 'fiiind me', new_string: 'replace with "this"' },
+          ],
           old_string: 'fiiind me',
           new_string: 'replace with "this"',
         };
@@ -418,6 +453,12 @@ describe('editCorrector', () => {
         const currentContent = 'This is a test string to corrected find me.';
         const originalParams = {
           file_path: '/test/file.txt',
+          edits: [
+            {
+              old_string: 'find me',
+              new_string: 'replace with \\\\"this\\\\"',
+            },
+          ],
           old_string: 'find me',
           new_string: 'replace with \\\\"this\\\\"',
         };
@@ -442,6 +483,9 @@ describe('editCorrector', () => {
         const currentContent = 'This content has nothing to find.';
         const originalParams = {
           file_path: '/test/file.txt',
+          edits: [
+            { old_string: 'nonexistent string', new_string: 'some new string' },
+          ],
           old_string: 'nonexistent string',
           new_string: 'some new string',
         };
@@ -453,7 +497,11 @@ describe('editCorrector', () => {
           abortSignal,
         );
         expect(mockGenerateJson).toHaveBeenCalledTimes(1);
-        expect(result.params).toEqual(originalParams);
+        expect(result.params).toEqual({
+          file_path: originalParams.file_path,
+          old_string: originalParams.old_string,
+          new_string: originalParams.new_string,
+        });
         expect(result.occurrences).toBe(0);
       });
       it('Test 4.2: unescapedOldStringAttempt results in >1 occurrences -> returns original params, count occurrences', async () => {
@@ -461,6 +509,7 @@ describe('editCorrector', () => {
           'This content has find "me" and also find "me" again.';
         const originalParams = {
           file_path: '/test/file.txt',
+          edits: [{ old_string: 'find "me"', new_string: 'some new string' }],
           old_string: 'find "me"',
           new_string: 'some new string',
         };
@@ -471,7 +520,11 @@ describe('editCorrector', () => {
           abortSignal,
         );
         expect(mockGenerateJson).toHaveBeenCalledTimes(0);
-        expect(result.params).toEqual(originalParams);
+        expect(result.params).toEqual({
+          file_path: originalParams.file_path,
+          old_string: originalParams.old_string,
+          new_string: originalParams.new_string,
+        });
         expect(result.occurrences).toBe(2);
       });
     });
@@ -481,6 +534,12 @@ describe('editCorrector', () => {
         const currentContent = 'const x = "a\\nbc\\\\"def\\\\"';
         const originalParams = {
           file_path: '/test/file.txt',
+          edits: [
+            {
+              old_string: 'const x = \\\\"a\\\\nbc\\\\\\\\"def\\\\\\\\"',
+              new_string: 'const y = \\\\"new\\\\nval\\\\\\\\"content\\\\\\\\"',
+            },
+          ],
           old_string: 'const x = \\\\"a\\\\nbc\\\\\\\\"def\\\\\\\\"',
           new_string: 'const y = \\\\"new\\\\nval\\\\\\\\"content\\\\\\\\"',
         };
diff --git a/packages/core/src/utils/editCorrector.test.ts.backup b/packages/core/src/utils/editCorrector.test.ts.backup
new file mode 100644
index 00000000..7d6f5a53
--- /dev/null
+++ b/packages/core/src/utils/editCorrector.test.ts.backup
@@ -0,0 +1,503 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/* eslint-disable @typescript-eslint/no-explicit-any */
+import { vi, describe, it, expect, beforeEach, type Mocked } from 'vitest';
+
+// MOCKS
+let callCount = 0;
+const mockResponses: any[] = [];
+
+let mockGenerateJson: any;
+let mockStartChat: any;
+let mockSendMessageStream: any;
+
+vi.mock('../core/client.js', () => ({
+  GeminiClient: vi.fn().mockImplementation(function (
+    this: any,
+    _config: Config,
+  ) {
+    this.generateJson = (...params: any[]) => mockGenerateJson(...params); // Corrected: use mockGenerateJson
+    this.startChat = (...params: any[]) => mockStartChat(...params); // Corrected: use mockStartChat
+    this.sendMessageStream = (...params: any[]) =>
+      mockSendMessageStream(...params); // Corrected: use mockSendMessageStream
+    return this;
+  }),
+}));
+// END MOCKS
+
+import {
+  countOccurrences,
+  ensureCorrectEdit,
+  unescapeStringForGeminiBug,
+  resetEditCorrectorCaches_TEST_ONLY,
+} from './editCorrector.js';
+import { GeminiClient } from '../core/client.js';
+import type { Config } from '../config/config.js';
+import { ToolRegistry } from '../tools/tool-registry.js';
+
+vi.mock('../tools/tool-registry.js');
+
+describe('editCorrector', () => {
+  describe('countOccurrences', () => {
+    it('should return 0 for empty string', () => {
+      expect(countOccurrences('', 'a')).toBe(0);
+    });
+    it('should return 0 for empty substring', () => {
+      expect(countOccurrences('abc', '')).toBe(0);
+    });
+    it('should return 0 if substring is not found', () => {
+      expect(countOccurrences('abc', 'd')).toBe(0);
+    });
+    it('should return 1 if substring is found once', () => {
+      expect(countOccurrences('abc', 'b')).toBe(1);
+    });
+    it('should return correct count for multiple occurrences', () => {
+      expect(countOccurrences('ababa', 'a')).toBe(3);
+      expect(countOccurrences('ababab', 'ab')).toBe(3);
+    });
+    it('should count non-overlapping occurrences', () => {
+      expect(countOccurrences('aaaaa', 'aa')).toBe(2);
+      expect(countOccurrences('ababab', 'aba')).toBe(1);
+    });
+    it('should correctly count occurrences when substring is longer', () => {
+      expect(countOccurrences('abc', 'abcdef')).toBe(0);
+    });
+    it('should be case sensitive', () => {
+      expect(countOccurrences('abcABC', 'a')).toBe(1);
+      expect(countOccurrences('abcABC', 'A')).toBe(1);
+    });
+  });
+
+  describe('unescapeStringForGeminiBug', () => {
+    it('should unescape common sequences', () => {
+      expect(unescapeStringForGeminiBug('\\n')).toBe('\n');
+      expect(unescapeStringForGeminiBug('\\t')).toBe('\t');
+      expect(unescapeStringForGeminiBug("\\'")).toBe("'");
+      expect(unescapeStringForGeminiBug('\\"')).toBe('"');
+      expect(unescapeStringForGeminiBug('\\`')).toBe('`');
+    });
+    it('should handle multiple escaped sequences', () => {
+      expect(unescapeStringForGeminiBug('Hello\\nWorld\\tTest')).toBe(
+        'Hello\nWorld\tTest',
+      );
+    });
+    it('should not alter already correct sequences', () => {
+      expect(unescapeStringForGeminiBug('\n')).toBe('\n');
+      expect(unescapeStringForGeminiBug('Correct string')).toBe(
+        'Correct string',
+      );
+    });
+    it('should handle mixed correct and incorrect sequences', () => {
+      expect(unescapeStringForGeminiBug('\\nCorrect\t\\`')).toBe(
+        '\nCorrect\t`',
+      );
+    });
+    it('should handle backslash followed by actual newline character', () => {
+      expect(unescapeStringForGeminiBug('\\\n')).toBe('\n');
+      expect(unescapeStringForGeminiBug('First line\\\nSecond line')).toBe(
+        'First line\nSecond line',
+      );
+    });
+    it('should handle multiple backslashes before an escapable character', () => {
+      expect(unescapeStringForGeminiBug('\\\\n')).toBe('\n');
+      expect(unescapeStringForGeminiBug('\\\\\\t')).toBe('\t');
+      expect(unescapeStringForGeminiBug('\\\\\\\\`')).toBe('`');
+    });
+    it('should return empty string for empty input', () => {
+      expect(unescapeStringForGeminiBug('')).toBe('');
+    });
+    it('should not alter strings with no targeted escape sequences', () => {
+      expect(unescapeStringForGeminiBug('abc def')).toBe('abc def');
+      expect(unescapeStringForGeminiBug('C:\\Folder\\File')).toBe(
+        'C:\\Folder\\File',
+      );
+    });
+    it('should correctly process strings with some targeted escapes', () => {
+      expect(unescapeStringForGeminiBug('C:\\Users\\name')).toBe(
+        'C:\\Users\name',
+      );
+    });
+    it('should handle complex cases with mixed slashes and characters', () => {
+      expect(
+        unescapeStringForGeminiBug('\\\\\\\nLine1\\\nLine2\\tTab\\\\`Tick\\"'),
+      ).toBe('\nLine1\nLine2\tTab`Tick"');
+    });
+  });
+
+  describe('ensureCorrectEdit', () => {
+    let mockGeminiClientInstance: Mocked<GeminiClient>;
+    let mockToolRegistry: Mocked<ToolRegistry>;
+    let mockConfigInstance: Config;
+    const abortSignal = new AbortController().signal;
+
+    beforeEach(() => {
+      mockToolRegistry = new ToolRegistry({} as Config) as Mocked<ToolRegistry>;
+      const configParams = {
+        apiKey: 'test-api-key',
+        model: 'test-model',
+        sandbox: false as boolean | string,
+        targetDir: '/test',
+        debugMode: false,
+        question: undefined as string | undefined,
+        fullContext: false,
+        coreTools: undefined as string[] | undefined,
+        toolDiscoveryCommand: undefined as string | undefined,
+        toolCallCommand: undefined as string | undefined,
+        mcpServerCommand: undefined as string | undefined,
+        mcpServers: undefined as Record<string, any> | undefined,
+        userAgent: 'test-agent',
+        userMemory: '',
+        geminiMdFileCount: 0,
+        alwaysSkipModificationConfirmation: false,
+      };
+      mockConfigInstance = {
+        ...configParams,
+        getApiKey: vi.fn(() => configParams.apiKey),
+        getModel: vi.fn(() => configParams.model),
+        getSandbox: vi.fn(() => configParams.sandbox),
+        getTargetDir: vi.fn(() => configParams.targetDir),
+        getToolRegistry: vi.fn(() => mockToolRegistry),
+        getDebugMode: vi.fn(() => configParams.debugMode),
+        getQuestion: vi.fn(() => configParams.question),
+        getFullContext: vi.fn(() => configParams.fullContext),
+        getCoreTools: vi.fn(() => configParams.coreTools),
+        getToolDiscoveryCommand: vi.fn(() => configParams.toolDiscoveryCommand),
+        getToolCallCommand: vi.fn(() => configParams.toolCallCommand),
+        getMcpServerCommand: vi.fn(() => configParams.mcpServerCommand),
+        getMcpServers: vi.fn(() => configParams.mcpServers),
+        getUserAgent: vi.fn(() => configParams.userAgent),
+        getUserMemory: vi.fn(() => configParams.userMemory),
+        setUserMemory: vi.fn((mem: string) => {
+          configParams.userMemory = mem;
+        }),
+        getGeminiMdFileCount: vi.fn(() => configParams.geminiMdFileCount),
+        setGeminiMdFileCount: vi.fn((count: number) => {
+          configParams.geminiMdFileCount = count;
+        }),
+        getAlwaysSkipModificationConfirmation: vi.fn(
+          () => configParams.alwaysSkipModificationConfirmation,
+        ),
+        setAlwaysSkipModificationConfirmation: vi.fn((skip: boolean) => {
+          configParams.alwaysSkipModificationConfirmation = skip;
+        }),
+      } as unknown as Config;
+
+      callCount = 0;
+      mockResponses.length = 0;
+      mockGenerateJson = vi
+        .fn()
+        .mockImplementation((_contents, _schema, signal) => {
+          // Check if the signal is aborted. If so, throw an error or return a specific response.
+          if (signal && signal.aborted) {
+            return Promise.reject(new Error('Aborted')); // Or some other specific error/response
+          }
+          const response = mockResponses[callCount];
+          callCount++;
+          if (response === undefined) return Promise.resolve({});
+          return Promise.resolve(response);
+        });
+      mockStartChat = vi.fn();
+      mockSendMessageStream = vi.fn();
+
+      mockGeminiClientInstance = new GeminiClient(
+        mockConfigInstance,
+      ) as Mocked<GeminiClient>;
+      resetEditCorrectorCaches_TEST_ONLY();
+    });
+
+    describe('Scenario Group 1: originalParams.old_string matches currentContent directly', () => {
+      it('Test 1.1: old_string (no literal \\), new_string (escaped by Gemini) -> new_string unescaped', async () => {
+        const currentContent = 'This is a test string to find me.';
+        const originalParams = {
+          file_path: '/test/file.txt',
+          old_string: 'find me',
+          new_string: 'replace with \\"this\\"',
+        };
+        mockResponses.push({
+          corrected_new_string_escaping: 'replace with "this"',
+        });
+        const result = await ensureCorrectEdit(
+          currentContent,
+          originalParams,
+          mockGeminiClientInstance,
+          abortSignal,
+        );
+        expect(mockGenerateJson).toHaveBeenCalledTimes(1);
+        expect(result.params.new_string).toBe('replace with "this"');
+        expect(result.params.old_string).toBe('find me');
+        expect(result.occurrences).toBe(1);
+      });
+      it('Test 1.2: old_string (no literal \\), new_string (correctly formatted) -> new_string unchanged', async () => {
+        const currentContent = 'This is a test string to find me.';
+        const originalParams = {
+          file_path: '/test/file.txt',
+          old_string: 'find me',
+          new_string: 'replace with this',
+        };
+        const result = await ensureCorrectEdit(
+          currentContent,
+          originalParams,
+          mockGeminiClientInstance,
+          abortSignal,
+        );
+        expect(mockGenerateJson).toHaveBeenCalledTimes(0);
+        expect(result.params.new_string).toBe('replace with this');
+        expect(result.params.old_string).toBe('find me');
+        expect(result.occurrences).toBe(1);
+      });
+      it('Test 1.3: old_string (with literal \\), new_string (escaped by Gemini) -> new_string unchanged (still escaped)', async () => {
+        const currentContent = 'This is a test string to find\\me.';
+        const originalParams = {
+          file_path: '/test/file.txt',
+          old_string: 'find\\me',
+          new_string: 'replace with \\"this\\"',
+        };
+        mockResponses.push({
+          corrected_new_string_escaping: 'replace with "this"',
+        });
+        const result = await ensureCorrectEdit(
+          currentContent,
+          originalParams,
+          mockGeminiClientInstance,
+          abortSignal,
+        );
+        expect(mockGenerateJson).toHaveBeenCalledTimes(1);
+        expect(result.params.new_string).toBe('replace with "this"');
+        expect(result.params.old_string).toBe('find\\me');
+        expect(result.occurrences).toBe(1);
+      });
+      it('Test 1.4: old_string (with literal \\), new_string (correctly formatted) -> new_string unchanged', async () => {
+        const currentContent = 'This is a test string to find\\me.';
+        const originalParams = {
+          file_path: '/test/file.txt',
+          old_string: 'find\\me',
+          new_string: 'replace with this',
+        };
+        const result = await ensureCorrectEdit(
+          currentContent,
+          originalParams,
+          mockGeminiClientInstance,
+          abortSignal,
+        );
+        expect(mockGenerateJson).toHaveBeenCalledTimes(0);
+        expect(result.params.new_string).toBe('replace with this');
+        expect(result.params.old_string).toBe('find\\me');
+        expect(result.occurrences).toBe(1);
+      });
+    });
+
+    describe('Scenario Group 2: originalParams.old_string does NOT match, but unescapeStringForGeminiBug(originalParams.old_string) DOES match', () => {
+      it('Test 2.1: old_string (over-escaped, no intended literal \\), new_string (escaped by Gemini) -> new_string unescaped', async () => {
+        const currentContent = 'This is a test string to find "me".';
+        const originalParams = {
+          file_path: '/test/file.txt',
+          old_string: 'find \\"me\\"',
+          new_string: 'replace with \\"this\\"',
+        };
+        mockResponses.push({ corrected_new_string: 'replace with "this"' });
+        const result = await ensureCorrectEdit(
+          currentContent,
+          originalParams,
+          mockGeminiClientInstance,
+          abortSignal,
+        );
+        expect(mockGenerateJson).toHaveBeenCalledTimes(1);
+        expect(result.params.new_string).toBe('replace with "this"');
+        expect(result.params.old_string).toBe('find "me"');
+        expect(result.occurrences).toBe(1);
+      });
+      it('Test 2.2: old_string (over-escaped, no intended literal \\), new_string (correctly formatted) -> new_string unescaped (harmlessly)', async () => {
+        const currentContent = 'This is a test string to find "me".';
+        const originalParams = {
+          file_path: '/test/file.txt',
+          old_string: 'find \\"me\\"',
+          new_string: 'replace with this',
+        };
+        const result = await ensureCorrectEdit(
+          currentContent,
+          originalParams,
+          mockGeminiClientInstance,
+          abortSignal,
+        );
+        expect(mockGenerateJson).toHaveBeenCalledTimes(0);
+        expect(result.params.new_string).toBe('replace with this');
+        expect(result.params.old_string).toBe('find "me"');
+        expect(result.occurrences).toBe(1);
+      });
+      it('Test 2.3: old_string (over-escaped, with intended literal \\), new_string (simple) -> new_string corrected', async () => {
+        const currentContent = 'This is a test string to find \\me.';
+        const originalParams = {
+          file_path: '/test/file.txt',
+          old_string: 'find \\\\me',
+          new_string: 'replace with foobar',
+        };
+        mockResponses.push({
+          corrected_target_snippet: 'find \\me',
+        });
+        const result = await ensureCorrectEdit(
+          currentContent,
+          originalParams,
+          mockGeminiClientInstance,
+          abortSignal,
+        );
+        expect(mockGenerateJson).toHaveBeenCalledTimes(1);
+        expect(result.params.new_string).toBe('replace with foobar');
+        expect(result.params.old_string).toBe('find \\me');
+        expect(result.occurrences).toBe(1);
+      });
+    });
+
+    describe('Scenario Group 3: LLM Correction Path', () => {
+      it('Test 3.1: old_string (no literal \\), new_string (escaped by Gemini), LLM re-escapes new_string -> final new_string is double unescaped', async () => {
+        const currentContent = 'This is a test string to corrected find me.';
+        const originalParams = {
+          file_path: '/test/file.txt',
+          old_string: 'find me',
+          new_string: 'replace with \\\\"this\\\\"',
+        };
+        const llmNewString = 'LLM says replace with "that"';
+        mockResponses.push({ corrected_new_string_escaping: llmNewString });
+        const result = await ensureCorrectEdit(
+          currentContent,
+          originalParams,
+          mockGeminiClientInstance,
+          abortSignal,
+        );
+        expect(mockGenerateJson).toHaveBeenCalledTimes(1);
+        expect(result.params.new_string).toBe(llmNewString);
+        expect(result.params.old_string).toBe('find me');
+        expect(result.occurrences).toBe(1);
+      });
+      it('Test 3.2: old_string (with literal \\), new_string (escaped by Gemini), LLM re-escapes new_string -> final new_string is unescaped once', async () => {
+        const currentContent = 'This is a test string to corrected find me.';
+        const originalParams = {
+          file_path: '/test/file.txt',
+          old_string: 'find\\me',
+          new_string: 'replace with \\\\"this\\\\"',
+        };
+        const llmCorrectedOldString = 'corrected find me';
+        const llmNewString = 'LLM says replace with "that"';
+        mockResponses.push({ corrected_target_snippet: llmCorrectedOldString });
+        mockResponses.push({ corrected_new_string: llmNewString });
+        const result = await ensureCorrectEdit(
+          currentContent,
+          originalParams,
+          mockGeminiClientInstance,
+          abortSignal,
+        );
+        expect(mockGenerateJson).toHaveBeenCalledTimes(2);
+        expect(result.params.new_string).toBe(llmNewString);
+        expect(result.params.old_string).toBe(llmCorrectedOldString);
+        expect(result.occurrences).toBe(1);
+      });
+      it('Test 3.3: old_string needs LLM, new_string is fine -> old_string corrected, new_string original', async () => {
+        const currentContent = 'This is a test string to be corrected.';
+        const originalParams = {
+          file_path: '/test/file.txt',
+          old_string: 'fiiind me',
+          new_string: 'replace with "this"',
+        };
+        const llmCorrectedOldString = 'to be corrected';
+        mockResponses.push({ corrected_target_snippet: llmCorrectedOldString });
+        const result = await ensureCorrectEdit(
+          currentContent,
+          originalParams,
+          mockGeminiClientInstance,
+          abortSignal,
+        );
+        expect(mockGenerateJson).toHaveBeenCalledTimes(1);
+        expect(result.params.new_string).toBe('replace with "this"');
+        expect(result.params.old_string).toBe(llmCorrectedOldString);
+        expect(result.occurrences).toBe(1);
+      });
+      it('Test 3.4: LLM correction path, correctNewString returns the originalNewString it was passed (which was unescaped) -> final new_string is unescaped', async () => {
+        const currentContent = 'This is a test string to corrected find me.';
+        const originalParams = {
+          file_path: '/test/file.txt',
+          old_string: 'find me',
+          new_string: 'replace with \\\\"this\\\\"',
+        };
+        const newStringForLLMAndReturnedByLLM = 'replace with "this"';
+        mockResponses.push({
+          corrected_new_string_escaping: newStringForLLMAndReturnedByLLM,
+        });
+        const result = await ensureCorrectEdit(
+          currentContent,
+          originalParams,
+          mockGeminiClientInstance,
+          abortSignal,
+        );
+        expect(mockGenerateJson).toHaveBeenCalledTimes(1);
+        expect(result.params.new_string).toBe(newStringForLLMAndReturnedByLLM);
+        expect(result.occurrences).toBe(1);
+      });
+    });
+
+    describe('Scenario Group 4: No Match Found / Multiple Matches', () => {
+      it('Test 4.1: No version of old_string (original, unescaped, LLM-corrected) matches -> returns original params, 0 occurrences', async () => {
+        const currentContent = 'This content has nothing to find.';
+        const originalParams = {
+          file_path: '/test/file.txt',
+          old_string: 'nonexistent string',
+          new_string: 'some new string',
+        };
+        mockResponses.push({ corrected_target_snippet: 'still nonexistent' });
+        const result = await ensureCorrectEdit(
+          currentContent,
+          originalParams,
+          mockGeminiClientInstance,
+          abortSignal,
+        );
+        expect(mockGenerateJson).toHaveBeenCalledTimes(1);
+        expect(result.params).toEqual(originalParams);
+        expect(result.occurrences).toBe(0);
+      });
+      it('Test 4.2: unescapedOldStringAttempt results in >1 occurrences -> returns original params, count occurrences', async () => {
+        const currentContent =
+          'This content has find "me" and also find "me" again.';
+        const originalParams = {
+          file_path: '/test/file.txt',
+          old_string: 'find "me"',
+          new_string: 'some new string',
+        };
+        const result = await ensureCorrectEdit(
+          currentContent,
+          originalParams,
+          mockGeminiClientInstance,
+          abortSignal,
+        );
+        expect(mockGenerateJson).toHaveBeenCalledTimes(0);
+        expect(result.params).toEqual(originalParams);
+        expect(result.occurrences).toBe(2);
+      });
+    });
+
+    describe('Scenario Group 5: Specific unescapeStringForGeminiBug checks (integrated into ensureCorrectEdit)', () => {
+      it('Test 5.1: old_string needs LLM to become currentContent, new_string also needs correction', async () => {
+        const currentContent = 'const x = "a\\nbc\\\\"def\\\\"';
+        const originalParams = {
+          file_path: '/test/file.txt',
+          old_string: 'const x = \\\\"a\\\\nbc\\\\\\\\"def\\\\\\\\"',
+          new_string: 'const y = \\\\"new\\\\nval\\\\\\\\"content\\\\\\\\"',
+        };
+        const expectedFinalNewString = 'const y = "new\\nval\\\\"content\\\\"';
+        mockResponses.push({ corrected_target_snippet: currentContent });
+        mockResponses.push({ corrected_new_string: expectedFinalNewString });
+        const result = await ensureCorrectEdit(
+          currentContent,
+          originalParams,
+          mockGeminiClientInstance,
+          abortSignal,
+        );
+        expect(mockGenerateJson).toHaveBeenCalledTimes(2);
+        expect(result.params.old_string).toBe(currentContent);
+        expect(result.params.new_string).toBe(expectedFinalNewString);
+        expect(result.occurrences).toBe(1);
+      });
+    });
+  });
+});
diff --git a/packages/core/src/utils/editCorrector.ts b/packages/core/src/utils/editCorrector.ts
index 67d23cde..c1d7be77 100644
--- a/packages/core/src/utils/editCorrector.ts
+++ b/packages/core/src/utils/editCorrector.ts
@@ -61,10 +61,16 @@ export interface CorrectedEditResult {
  */
 export async function ensureCorrectEdit(
   currentContent: string,
-  originalParams: EditToolParams, // This is the EditToolParams from edit.ts, without \'corrected\'
+  originalParams: EditToolParams & { old_string: string; new_string: string },
   client: GeminiClient,
   abortSignal: AbortSignal,
 ): Promise<CorrectedEditResult> {
+  // Ensure we have required old_string and new_string
+  if (!originalParams.old_string || !originalParams.new_string) {
+    throw new Error(
+      'old_string and new_string are required for edit correction',
+    );
+  }
   const cacheKey = `${currentContent}---${originalParams.old_string}---${originalParams.new_string}`;
   const cachedResult = editCorrectionCache.get(cacheKey);
   if (cachedResult) {
@@ -96,7 +102,11 @@ export async function ensureCorrectEdit(
     // If user expects multiple replacements, return as-is
     if (occurrences === expectedReplacements) {
       const result: CorrectedEditResult = {
-        params: { ...originalParams },
+        params: {
+          file_path: originalParams.file_path,
+          old_string: originalParams.old_string!,
+          new_string: originalParams.new_string!,
+        },
         occurrences,
       };
       editCorrectionCache.set(cacheKey, result);
@@ -106,7 +116,11 @@ export async function ensureCorrectEdit(
     // If user expects 1 but found multiple, try to correct (existing behavior)
     if (expectedReplacements === 1) {
       const result: CorrectedEditResult = {
-        params: { ...originalParams },
+        params: {
+          file_path: originalParams.file_path,
+          old_string: originalParams.old_string!,
+          new_string: originalParams.new_string!,
+        },
         occurrences,
       };
       editCorrectionCache.set(cacheKey, result);
@@ -115,7 +129,11 @@ export async function ensureCorrectEdit(
 
     // If occurrences don't match expected, return as-is (will fail validation later)
     const result: CorrectedEditResult = {
-      params: { ...originalParams },
+      params: {
+        file_path: originalParams.file_path,
+        old_string: finalOldString,
+        new_string: finalNewString,
+      },
       occurrences,
     };
     editCorrectionCache.set(cacheKey, result);
@@ -169,7 +187,11 @@ export async function ensureCorrectEdit(
       } else {
         // LLM correction also failed for old_string
         const result: CorrectedEditResult = {
-          params: { ...originalParams },
+          params: {
+            file_path: originalParams.file_path,
+            old_string: finalOldString,
+            new_string: finalNewString,
+          },
           occurrences: 0, // Explicitly 0 as LLM failed
         };
         editCorrectionCache.set(cacheKey, result);
@@ -178,7 +200,11 @@ export async function ensureCorrectEdit(
     } else {
       // Unescaping old_string resulted in > 1 occurrences
       const result: CorrectedEditResult = {
-        params: { ...originalParams },
+        params: {
+          file_path: originalParams.file_path,
+          old_string: finalOldString,
+          new_string: finalNewString,
+        },
         occurrences, // This will be > 1
       };
       editCorrectionCache.set(cacheKey, result);
diff --git a/packages/core/src/utils/positionBasedEditProcessor.ts b/packages/core/src/utils/positionBasedEditProcessor.ts
new file mode 100644
index 00000000..977d6859
--- /dev/null
+++ b/packages/core/src/utils/positionBasedEditProcessor.ts
@@ -0,0 +1,239 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * Single edit operation with position information
+ */
+export interface PositionedEdit {
+  /**
+   * Original edit operation
+   */
+  original: EditOperation;
+
+  /**
+   * Index in the original edits array
+   */
+  index: number;
+
+  /**
+   * Start position in the file content
+   */
+  startPos: number;
+
+  /**
+   * End position in the file content
+   */
+  endPos: number;
+
+  /**
+   * The replacement text
+   */
+  newString: string;
+}
+
+/**
+ * Result of failed edit with reason
+ */
+export interface FailedEdit {
+  index: number;
+  edit: EditOperation;
+  reason: 'not_found' | 'multiple_matches' | 'empty_old_string';
+}
+
+/**
+ * Result of position-based edit processing
+ */
+export interface PositionBasedEditResult {
+  finalContent: string;
+  appliedEdits: PositionedEdit[];
+  failedEdits: FailedEdit[];
+}
+
+/**
+ * Edit operation interface (matches existing EditOperation)
+ */
+export interface EditOperation {
+  old_string: string;
+  new_string: string;
+}
+
+/**
+ * Efficient position-based edit processor that minimizes memory usage
+ * and applies edits in optimal order to prevent position conflicts.
+ */
+export class PositionBasedEditProcessor {
+  /**
+   * Process edits with minimal memory usage and optimal ordering
+   */
+  processEdits(
+    content: string,
+    edits: EditOperation[],
+  ): PositionBasedEditResult {
+    // Phase 1: Find positions for all edits
+    const { validEdits, failedEdits } = this.analyzeEdits(content, edits);
+
+    // Phase 2: Sort by position (highest first) to prevent position drift
+    const sortedEdits = validEdits.sort((a, b) => b.startPos - a.startPos);
+
+    // Phase 3: Build final content in single pass
+    const finalContent = this.buildFinalContent(content, sortedEdits);
+
+    return {
+      finalContent,
+      appliedEdits: sortedEdits,
+      failedEdits,
+    };
+  }
+
+  /**
+   * Analyze all edits and categorize into valid/failed
+   */
+  private analyzeEdits(
+    content: string,
+    edits: EditOperation[],
+  ): {
+    validEdits: PositionedEdit[];
+    failedEdits: FailedEdit[];
+  } {
+    const validEdits: PositionedEdit[] = [];
+    const failedEdits: FailedEdit[] = [];
+
+    for (let i = 0; i < edits.length; i++) {
+      const edit = edits[i];
+
+      // Handle empty old_string (file creation case)
+      if (edit.old_string === '') {
+        failedEdits.push({
+          index: i,
+          edit,
+          reason: 'empty_old_string',
+        });
+        continue;
+      }
+
+      // Find all positions of old_string
+      const positions = this.findAllPositions(content, edit.old_string);
+
+      if (positions.length === 0) {
+        failedEdits.push({
+          index: i,
+          edit,
+          reason: 'not_found',
+        });
+      } else if (positions.length > 1) {
+        failedEdits.push({
+          index: i,
+          edit,
+          reason: 'multiple_matches',
+        });
+      } else {
+        // Exactly one match - valid edit
+        const startPos = positions[0];
+        validEdits.push({
+          original: edit,
+          index: i,
+          startPos,
+          endPos: startPos + edit.old_string.length,
+          newString: edit.new_string,
+        });
+      }
+    }
+
+    return { validEdits, failedEdits };
+  }
+
+  /**
+   * Find all positions where searchString occurs in content
+   */
+  private findAllPositions(content: string, searchString: string): number[] {
+    const positions: number[] = [];
+    let index = content.indexOf(searchString);
+
+    while (index !== -1) {
+      positions.push(index);
+      index = content.indexOf(searchString, index + 1);
+    }
+
+    return positions;
+  }
+
+  /**
+   * Build final content in single pass with minimal memory allocation
+   */
+  private buildFinalContent(original: string, edits: PositionedEdit[]): string {
+    if (edits.length === 0) {
+      return original;
+    }
+
+    // Check for overlapping edits (should not happen with our validation, but safety check)
+    if (this.hasOverlappingEdits(edits)) {
+      throw new Error('Overlapping edits detected - this should not happen');
+    }
+
+    // Build segments array working backwards through the string
+    const segments: string[] = [];
+    let currentPos = original.length;
+
+    // Process edits from end to beginning (edits are already sorted by startPos desc)
+    for (const edit of edits) {
+      // Add text after this edit position
+      if (currentPos > edit.endPos) {
+        segments.unshift(original.slice(edit.endPos, currentPos));
+      }
+
+      // Add the replacement text
+      segments.unshift(edit.newString);
+
+      // Update current position
+      currentPos = edit.startPos;
+    }
+
+    // Add remaining text from beginning
+    if (currentPos > 0) {
+      segments.unshift(original.slice(0, currentPos));
+    }
+
+    // Single join operation creates final string
+    return segments.join('');
+  }
+
+  /**
+   * Check if any edits overlap (safety validation)
+   */
+  private hasOverlappingEdits(edits: PositionedEdit[]): boolean {
+    for (let i = 0; i < edits.length - 1; i++) {
+      for (let j = i + 1; j < edits.length; j++) {
+        const edit1 = edits[i];
+        const edit2 = edits[j];
+
+        // Check if ranges overlap
+        if (
+          !(edit1.endPos <= edit2.startPos || edit2.endPos <= edit1.startPos)
+        ) {
+          return true;
+        }
+      }
+    }
+
+    return false;
+  }
+
+  /**
+   * Get human-readable error message for failed edit reason
+   */
+  static getErrorMessage(reason: FailedEdit['reason']): string {
+    switch (reason) {
+      case 'not_found':
+        return 'Old string not found in current content';
+      case 'multiple_matches':
+        return 'Old string found multiple times - please be more specific';
+      case 'empty_old_string':
+        return 'Cannot use empty old_string on existing file';
+      default:
+        return 'Unknown error';
+    }
+  }
+}