diff --git a/src/services/tools/fileCommon.test.ts b/src/services/tools/fileCommon.test.ts
index 34fea621ed..983e48ed9a 100644
--- a/src/services/tools/fileCommon.test.ts
+++ b/src/services/tools/fileCommon.test.ts
@@ -1,75 +1,8 @@
 import { describe, it, expect } from "bun:test";
 import type * as fs from "fs";
-import { leaseFromContent, validatePathInCwd, validateFileSize, MAX_FILE_SIZE } from "./fileCommon";
+import { validatePathInCwd, validateFileSize, MAX_FILE_SIZE } from "./fileCommon";
 
 describe("fileCommon", () => {
-  describe("leaseFromContent", () => {
-    it("should return a 6-character hexadecimal string", () => {
-      const content = "Hello, world!";
-      const lease = leaseFromContent(content);
-
-      expect(lease).toMatch(/^[0-9a-f]{6}$/);
-      expect(lease.length).toBe(6);
-    });
-
-    it("should be deterministic for same content", () => {
-      const content = "Hello, world!";
-      const lease1 = leaseFromContent(content);
-      const lease2 = leaseFromContent(content);
-
-      expect(lease1).toBe(lease2);
-    });
-
-    it("should produce different leases for different content", () => {
-      const content1 = "Hello, world!";
-      const content2 = "Hello, world!!";
-
-      const lease1 = leaseFromContent(content1);
-      const lease2 = leaseFromContent(content2);
-
-      expect(lease1).not.toBe(lease2);
-    });
-
-    it("should work with Buffer input", () => {
-      const buffer = Buffer.from("Hello, world!", "utf-8");
-      const lease = leaseFromContent(buffer);
-
-      expect(lease).toMatch(/^[0-9a-f]{6}$/);
-      expect(lease.length).toBe(6);
-    });
-
-    it("should produce same lease for string and equivalent Buffer", () => {
-      const content = "Hello, world!";
-      const buffer = Buffer.from(content, "utf-8");
-
-      const lease1 = leaseFromContent(content);
-      const lease2 = leaseFromContent(buffer);
-
-      expect(lease1).toBe(lease2);
-    });
-
-    it("should produce different leases for empty vs non-empty content", () => {
-      const lease1 = leaseFromContent("");
-      const lease2 = leaseFromContent("a");
-
-      expect(lease1).not.toBe(lease2);
-    });
-
-    it("should produce identical lease for same content regardless of external factors", () => {
-      // This test verifies that content-based leases are immune to mtime changes
-      // that could be triggered by external processes (e.g., IDE, git, filesystem tools)
-      const content = "const x = 42;\n";
-      const lease1 = leaseFromContent(content);
-
-      // Simulate same content but different metadata (like mtime)
-      // In the old mtime-based system, this would produce a different lease
-      // With content-based leases, it produces the same lease
-      const lease2 = leaseFromContent(content);
-
-      expect(lease1).toBe(lease2);
-    });
-  });
-
   describe("validateFileSize", () => {
     it("should return null for files within size limit", () => {
       const stats = {
diff --git a/src/services/tools/file_edit_insert.test.ts b/src/services/tools/file_edit_insert.test.ts
index 857956338a..85d6c969f0 100644
--- a/src/services/tools/file_edit_insert.test.ts
+++ b/src/services/tools/file_edit_insert.test.ts
@@ -3,7 +3,6 @@ import * as fs from "fs/promises";
 import * as path from "path";
 import * as os from "os";
 import { createFileEditInsertTool } from "./file_edit_insert";
-import { leaseFromContent } from "./fileCommon";
 import type { FileEditInsertToolArgs, FileEditInsertToolResult } from "@/types/tools";
 import type { ToolCallOptions } from "ai";
 
@@ -33,15 +32,11 @@ describe("file_edit_insert tool", () => {
     const initialContent = "line1\nline2\nline3";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditInsertTool({ cwd: testDir });
     const args: FileEditInsertToolArgs = {
       file_path: testFilePath,
       line_offset: 0,
       content: "INSERTED",
-      lease,
     };
 
     // Execute
@@ -49,10 +44,6 @@ describe("file_edit_insert tool", () => {
 
     // Assert
     expect(result.success).toBe(true);
-    if (result.success) {
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
-      expect(result.lease).not.toBe(lease); // New lease should be different
-    }
 
     const updatedContent = await fs.readFile(testFilePath, "utf-8");
     expect(updatedContent).toBe("INSERTED\nline1\nline2\nline3");
@@ -63,15 +54,11 @@ describe("file_edit_insert tool", () => {
     const initialContent = "line1\nline2\nline3";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditInsertTool({ cwd: testDir });
     const args: FileEditInsertToolArgs = {
       file_path: testFilePath,
       line_offset: 1,
       content: "INSERTED",
-      lease,
     };
 
     // Execute
@@ -79,9 +66,6 @@ describe("file_edit_insert tool", () => {
 
     // Assert
     expect(result.success).toBe(true);
-    if (result.success) {
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
-    }
 
     const updatedContent = await fs.readFile(testFilePath, "utf-8");
     expect(updatedContent).toBe("line1\nINSERTED\nline2\nline3");
@@ -92,15 +76,11 @@ describe("file_edit_insert tool", () => {
     const initialContent = "line1\nline2\nline3";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditInsertTool({ cwd: testDir });
     const args: FileEditInsertToolArgs = {
       file_path: testFilePath,
       line_offset: 2,
       content: "INSERTED",
-      lease,
     };
 
     // Execute
@@ -108,9 +88,6 @@ describe("file_edit_insert tool", () => {
 
     // Assert
     expect(result.success).toBe(true);
-    if (result.success) {
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
-    }
 
     const updatedContent = await fs.readFile(testFilePath, "utf-8");
     expect(updatedContent).toBe("line1\nline2\nINSERTED\nline3");
@@ -121,15 +98,11 @@ describe("file_edit_insert tool", () => {
     const initialContent = "line1\nline2\nline3";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditInsertTool({ cwd: testDir });
     const args: FileEditInsertToolArgs = {
       file_path: testFilePath,
       line_offset: 3,
       content: "INSERTED",
-      lease,
     };
 
     // Execute
@@ -137,9 +110,6 @@ describe("file_edit_insert tool", () => {
 
     // Assert
     expect(result.success).toBe(true);
-    if (result.success) {
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
-    }
 
     const updatedContent = await fs.readFile(testFilePath, "utf-8");
     expect(updatedContent).toBe("line1\nline2\nline3\nINSERTED");
@@ -150,15 +120,11 @@ describe("file_edit_insert tool", () => {
     const initialContent = "line1\nline2";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditInsertTool({ cwd: testDir });
     const args: FileEditInsertToolArgs = {
       file_path: testFilePath,
       line_offset: 1,
       content: "INSERTED1\nINSERTED2",
-      lease,
     };
 
     // Execute
@@ -166,9 +132,6 @@ describe("file_edit_insert tool", () => {
 
     // Assert
     expect(result.success).toBe(true);
-    if (result.success) {
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
-    }
 
     const updatedContent = await fs.readFile(testFilePath, "utf-8");
     expect(updatedContent).toBe("line1\nINSERTED1\nINSERTED2\nline2");
@@ -178,15 +141,11 @@ describe("file_edit_insert tool", () => {
     // Setup
     await fs.writeFile(testFilePath, "");
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditInsertTool({ cwd: testDir });
     const args: FileEditInsertToolArgs = {
       file_path: testFilePath,
       line_offset: 0,
       content: "INSERTED",
-      lease,
     };
 
     // Execute
@@ -194,9 +153,6 @@ describe("file_edit_insert tool", () => {
 
     // Assert
     expect(result.success).toBe(true);
-    if (result.success) {
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
-    }
 
     const updatedContent = await fs.readFile(testFilePath, "utf-8");
     expect(updatedContent).toBe("INSERTED\n");
@@ -211,7 +167,6 @@ describe("file_edit_insert tool", () => {
       file_path: nonExistentPath,
       line_offset: 0,
       content: "INSERTED",
-      lease: "000000", // Doesn't matter, file doesn't exist
     };
 
     // Execute
@@ -229,15 +184,11 @@ describe("file_edit_insert tool", () => {
     const initialContent = "line1\nline2";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditInsertTool({ cwd: testDir });
     const args: FileEditInsertToolArgs = {
       file_path: testFilePath,
       line_offset: -1,
       content: "INSERTED",
-      lease,
     };
 
     // Execute
@@ -255,15 +206,11 @@ describe("file_edit_insert tool", () => {
     const initialContent = "line1\nline2";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditInsertTool({ cwd: testDir });
     const args: FileEditInsertToolArgs = {
       file_path: testFilePath,
       line_offset: 10, // File only has 2 lines
       content: "INSERTED",
-      lease,
     };
 
     // Execute
@@ -275,62 +222,4 @@ describe("file_edit_insert tool", () => {
       expect(result.error).toContain("beyond file length");
     }
   });
-
-  it("should reject edit with incorrect lease", async () => {
-    // Setup
-    const initialContent = "line1\nline2";
-    await fs.writeFile(testFilePath, initialContent);
-
-    const tool = createFileEditInsertTool({ cwd: testDir });
-    const args: FileEditInsertToolArgs = {
-      file_path: testFilePath,
-      line_offset: 1,
-      content: "INSERTED",
-      lease: "ffffff", // Incorrect lease
-    };
-
-    // Execute
-    const result = (await tool.execute!(args, mockToolCallOptions)) as FileEditInsertToolResult;
-
-    // Assert
-    expect(result.success).toBe(false);
-    if (!result.success) {
-      expect(result.error).toContain("lease mismatch");
-      expect(result.error).toContain("obtain a new lease from tool");
-    }
-
-    // File should remain unchanged
-    const content = await fs.readFile(testFilePath, "utf-8");
-    expect(content).toBe(initialContent);
-  });
-
-  it("should detect file modified between read and insert", async () => {
-    // Setup - create initial file
-    const initialContent = "line1\nline2";
-    await fs.writeFile(testFilePath, initialContent);
-
-    // Get initial lease
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
-    // Modify file to simulate concurrent edit
-    await fs.writeFile(testFilePath, "Modified content");
-
-    const tool = createFileEditInsertTool({ cwd: testDir });
-    const args: FileEditInsertToolArgs = {
-      file_path: testFilePath,
-      line_offset: 1,
-      content: "INSERTED",
-      lease, // This lease is now stale
-    };
-
-    // Execute
-    const result = (await tool.execute!(args, mockToolCallOptions)) as FileEditInsertToolResult;
-
-    // Assert
-    expect(result.success).toBe(false);
-    if (!result.success) {
-      expect(result.error).toContain("lease mismatch");
-    }
-  });
 });
diff --git a/src/services/tools/file_edit_insert.ts b/src/services/tools/file_edit_insert.ts
index 019ae33a0f..e8d84d4897 100644
--- a/src/services/tools/file_edit_insert.ts
+++ b/src/services/tools/file_edit_insert.ts
@@ -5,7 +5,7 @@ import writeFileAtomic from "write-file-atomic";
 import type { FileEditInsertToolResult } from "@/types/tools";
 import type { ToolConfiguration, ToolFactory } from "@/utils/tools/tools";
 import { TOOL_DEFINITIONS } from "@/utils/tools/toolDefinitions";
-import { leaseFromContent, generateDiff, validatePathInCwd, validateFileSize } from "./fileCommon";
+import { generateDiff, validatePathInCwd, validateFileSize } from "./fileCommon";
 
 /**
  * File edit insert tool factory for AI assistant
@@ -16,12 +16,7 @@ export const createFileEditInsertTool: ToolFactory = (config: ToolConfiguration)
   return tool({
     description: TOOL_DEFINITIONS.file_edit_insert.description,
     inputSchema: TOOL_DEFINITIONS.file_edit_insert.schema,
-    execute: async ({
-      file_path,
-      line_offset,
-      content,
-      lease,
-    }): Promise<FileEditInsertToolResult> => {
+    execute: async ({ file_path, line_offset, content }): Promise<FileEditInsertToolResult> => {
       try {
         // Validate that the path is within the working directory
         const pathValidation = validatePathInCwd(file_path, config.cwd);
@@ -57,16 +52,6 @@ export const createFileEditInsertTool: ToolFactory = (config: ToolConfiguration)
 
         // Read file content
         const originalContent = await fs.readFile(resolvedPath, { encoding: "utf-8" });
-
-        // Validate lease to prevent editing stale file state
-        // Use content-based lease to avoid mtime issues with external processes
-        const currentLease = leaseFromContent(originalContent);
-        if (currentLease !== lease) {
-          return {
-            success: false,
-            error: `WRITE DENIED: File lease mismatch. The file has been modified since it was read. Please obtain a new lease from tool \`file_read\`.`,
-          };
-        }
         const lines = originalContent.split("\n");
 
         // Validate line_offset
@@ -93,15 +78,11 @@ export const createFileEditInsertTool: ToolFactory = (config: ToolConfiguration)
         // Write the modified content back to file atomically
         await writeFileAtomic(resolvedPath, newContent, { encoding: "utf-8" });
 
-        // Compute new lease from modified content
-        const newLease = leaseFromContent(newContent);
-
         // Generate diff
         const diff = generateDiff(resolvedPath, originalContent, newContent);
 
         return {
           success: true,
-          lease: newLease,
           diff,
         };
       } catch (error) {
diff --git a/src/services/tools/file_edit_replace.test.ts b/src/services/tools/file_edit_replace.test.ts
index de8c68e842..3ab3cb19be 100644
--- a/src/services/tools/file_edit_replace.test.ts
+++ b/src/services/tools/file_edit_replace.test.ts
@@ -3,7 +3,6 @@ import * as fs from "fs/promises";
 import * as path from "path";
 import * as os from "os";
 import { createFileEditReplaceTool } from "./file_edit_replace";
-import { leaseFromContent } from "./fileCommon";
 import type { FileEditReplaceToolArgs, FileEditReplaceToolResult } from "@/types/tools";
 import type { ToolCallOptions } from "ai";
 
@@ -14,9 +13,8 @@ const mockToolCallOptions: ToolCallOptions = {
 };
 
 // Test helpers
-const setupFile = async (filePath: string, content: string): Promise<string> => {
+const setupFile = async (filePath: string, content: string): Promise<void> => {
   await fs.writeFile(filePath, content);
-  return leaseFromContent(content);
 };
 
 const readFile = async (filePath: string): Promise<string> => {
@@ -26,10 +24,9 @@ const readFile = async (filePath: string): Promise<string> => {
 const executeReplace = async (
   tool: ReturnType<typeof createFileEditReplaceTool>,
   filePath: string,
-  edits: FileEditReplaceToolArgs["edits"],
-  lease: string
+  edits: FileEditReplaceToolArgs["edits"]
 ): Promise<FileEditReplaceToolResult> => {
-  const args: FileEditReplaceToolArgs = { file_path: filePath, edits, lease };
+  const args: FileEditReplaceToolArgs = { file_path: filePath, edits };
   return (await tool.execute!(args, mockToolCallOptions)) as FileEditReplaceToolResult;
 };
 
@@ -49,45 +46,34 @@ describe("file_edit_replace tool", () => {
   });
 
   it("should apply a single edit successfully", async () => {
-    const lease = await setupFile(testFilePath, "Hello world\nThis is a test\nGoodbye world");
+    await setupFile(testFilePath, "Hello world\nThis is a test\nGoodbye world");
     const tool = createFileEditReplaceTool({ cwd: testDir });
 
-    const result = await executeReplace(
-      tool,
-      testFilePath,
-      [{ old_string: "Hello world", new_string: "Hello universe" }],
-      lease
-    );
+    const result = await executeReplace(tool, testFilePath, [
+      { old_string: "Hello world", new_string: "Hello universe" },
+    ]);
 
     expect(result.success).toBe(true);
     if (result.success) {
       expect(result.edits_applied).toBe(1);
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
-      expect(result.lease).not.toBe(lease);
     }
 
     expect(await readFile(testFilePath)).toBe("Hello universe\nThis is a test\nGoodbye world");
   });
 
   it("should apply multiple edits sequentially", async () => {
-    const lease = await setupFile(testFilePath, "foo bar baz");
+    await setupFile(testFilePath, "foo bar baz");
     const tool = createFileEditReplaceTool({ cwd: testDir });
 
-    const result = await executeReplace(
-      tool,
-      testFilePath,
-      [
-        { old_string: "foo", new_string: "FOO" },
-        { old_string: "bar", new_string: "BAR" },
-        { old_string: "baz", new_string: "BAZ" },
-      ],
-      lease
-    );
+    const result = await executeReplace(tool, testFilePath, [
+      { old_string: "foo", new_string: "FOO" },
+      { old_string: "bar", new_string: "BAR" },
+      { old_string: "baz", new_string: "BAZ" },
+    ]);
 
     expect(result.success).toBe(true);
     if (result.success) {
       expect(result.edits_applied).toBe(3);
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
     }
 
     expect(await readFile(testFilePath)).toBe("FOO BAR BAZ");
@@ -100,9 +86,6 @@ describe("file_edit_replace tool", () => {
     const initialContent = "foo bar baz";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditReplaceTool({ cwd: testDir });
     const args: FileEditReplaceToolArgs = {
       file_path: testFilePath,
@@ -118,7 +101,6 @@ describe("file_edit_replace tool", () => {
           new_string: "qux",
         },
       ],
-      lease,
     };
 
     // Execute
@@ -143,9 +125,6 @@ describe("file_edit_replace tool", () => {
     const initialContent = "cat dog cat bird cat";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditReplaceTool({ cwd: testDir });
     const args: FileEditReplaceToolArgs = {
       file_path: testFilePath,
@@ -156,7 +135,6 @@ describe("file_edit_replace tool", () => {
           replace_count: -1,
         },
       ],
-      lease,
     };
 
     // Execute
@@ -166,7 +144,6 @@ describe("file_edit_replace tool", () => {
     expect(result.success).toBe(true);
     if (result.success) {
       expect(result.edits_applied).toBe(3);
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
     }
 
     const updatedContent = await fs.readFile(testFilePath, "utf-8");
@@ -178,9 +155,6 @@ describe("file_edit_replace tool", () => {
     const initialContent = "cat dog bird";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditReplaceTool({ cwd: testDir });
     const args: FileEditReplaceToolArgs = {
       file_path: testFilePath,
@@ -191,7 +165,6 @@ describe("file_edit_replace tool", () => {
           // replace_count omitted, defaults to 1
         },
       ],
-      lease,
     };
 
     // Execute
@@ -201,7 +174,6 @@ describe("file_edit_replace tool", () => {
     expect(result.success).toBe(true);
     if (result.success) {
       expect(result.edits_applied).toBe(1);
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
     }
 
     const updatedContent = await fs.readFile(testFilePath, "utf-8");
@@ -213,9 +185,6 @@ describe("file_edit_replace tool", () => {
     const initialContent = "Hello world";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditReplaceTool({ cwd: testDir });
     const args: FileEditReplaceToolArgs = {
       file_path: testFilePath,
@@ -225,7 +194,6 @@ describe("file_edit_replace tool", () => {
           new_string: "replacement",
         },
       ],
-      lease,
     };
 
     // Execute
@@ -247,9 +215,6 @@ describe("file_edit_replace tool", () => {
     const initialContent = "cat dog cat bird cat";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditReplaceTool({ cwd: testDir });
     const args: FileEditReplaceToolArgs = {
       file_path: testFilePath,
@@ -260,7 +225,6 @@ describe("file_edit_replace tool", () => {
           replace_count: 1, // Explicitly set to 1
         },
       ],
-      lease,
     };
 
     // Execute
@@ -284,9 +248,6 @@ describe("file_edit_replace tool", () => {
     const initialContent = "cat dog cat bird cat";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditReplaceTool({ cwd: testDir });
     const args: FileEditReplaceToolArgs = {
       file_path: testFilePath,
@@ -297,7 +258,6 @@ describe("file_edit_replace tool", () => {
           replace_count: 2, // Replace first 2 occurrences
         },
       ],
-      lease,
     };
 
     // Execute
@@ -307,7 +267,6 @@ describe("file_edit_replace tool", () => {
     expect(result.success).toBe(true);
     if (result.success) {
       expect(result.edits_applied).toBe(2);
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
     }
 
     const updatedContent = await fs.readFile(testFilePath, "utf-8");
@@ -319,9 +278,6 @@ describe("file_edit_replace tool", () => {
     const initialContent = "cat dog bird";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditReplaceTool({ cwd: testDir });
     const args: FileEditReplaceToolArgs = {
       file_path: testFilePath,
@@ -332,7 +288,6 @@ describe("file_edit_replace tool", () => {
           replace_count: 5, // Only 1 occurrence exists
         },
       ],
-      lease,
     };
 
     // Execute
@@ -363,7 +318,6 @@ describe("file_edit_replace tool", () => {
           new_string: "bar",
         },
       ],
-      lease: "000000", // Doesn't matter, file doesn't exist
     };
 
     // Execute
@@ -381,9 +335,6 @@ describe("file_edit_replace tool", () => {
     const initialContent = "line1\nline2\nline3\nline4";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditReplaceTool({ cwd: testDir });
     const args: FileEditReplaceToolArgs = {
       file_path: testFilePath,
@@ -393,7 +344,6 @@ describe("file_edit_replace tool", () => {
           new_string: "REPLACED",
         },
       ],
-      lease,
     };
 
     // Execute
@@ -403,7 +353,6 @@ describe("file_edit_replace tool", () => {
     expect(result.success).toBe(true);
     if (result.success) {
       expect(result.edits_applied).toBe(1);
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
     }
 
     const updatedContent = await fs.readFile(testFilePath, "utf-8");
@@ -415,9 +364,6 @@ describe("file_edit_replace tool", () => {
     const initialContent = "Hello [DELETE_ME] world";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditReplaceTool({ cwd: testDir });
     const args: FileEditReplaceToolArgs = {
       file_path: testFilePath,
@@ -427,7 +373,6 @@ describe("file_edit_replace tool", () => {
           new_string: "",
         },
       ],
-      lease,
     };
 
     // Execute
@@ -437,7 +382,6 @@ describe("file_edit_replace tool", () => {
     expect(result.success).toBe(true);
     if (result.success) {
       expect(result.edits_applied).toBe(1);
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
     }
 
     const updatedContent = await fs.readFile(testFilePath, "utf-8");
@@ -449,9 +393,6 @@ describe("file_edit_replace tool", () => {
     const initialContent = "step1";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditReplaceTool({ cwd: testDir });
     const args: FileEditReplaceToolArgs = {
       file_path: testFilePath,
@@ -465,7 +406,6 @@ describe("file_edit_replace tool", () => {
           new_string: "step3",
         },
       ],
-      lease,
     };
 
     // Execute
@@ -475,87 +415,17 @@ describe("file_edit_replace tool", () => {
     expect(result.success).toBe(true);
     if (result.success) {
       expect(result.edits_applied).toBe(2);
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
     }
 
     const updatedContent = await fs.readFile(testFilePath, "utf-8");
     expect(updatedContent).toBe("step3");
   });
 
-  it("should reject edit with incorrect lease", async () => {
-    // Setup
-    const initialContent = "Hello world";
-    await fs.writeFile(testFilePath, initialContent);
-
-    const tool = createFileEditReplaceTool({ cwd: testDir });
-    const args: FileEditReplaceToolArgs = {
-      file_path: testFilePath,
-      edits: [
-        {
-          old_string: "world",
-          new_string: "universe",
-        },
-      ],
-      lease: "ffffff", // Incorrect lease
-    };
-
-    // Execute
-    const result = (await tool.execute!(args, mockToolCallOptions)) as FileEditReplaceToolResult;
-
-    // Assert
-    expect(result.success).toBe(false);
-    if (!result.success) {
-      expect(result.error).toContain("lease mismatch");
-      expect(result.error).toContain("obtain a new lease from tool");
-    }
-
-    // File should remain unchanged
-    const unchangedContent = await fs.readFile(testFilePath, "utf-8");
-    expect(unchangedContent).toBe(initialContent);
-  });
-
-  it("should detect file modified between read and edit", async () => {
-    // Setup - create initial file
-    const initialContent = "Hello world";
-    await fs.writeFile(testFilePath, initialContent);
-
-    // Get initial lease
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
-    // Modify file to simulate concurrent edit
-    await fs.writeFile(testFilePath, "Modified content");
-
-    const tool = createFileEditReplaceTool({ cwd: testDir });
-    const args: FileEditReplaceToolArgs = {
-      file_path: testFilePath,
-      edits: [
-        {
-          old_string: "world",
-          new_string: "universe",
-        },
-      ],
-      lease, // This lease is now stale
-    };
-
-    // Execute
-    const result = (await tool.execute!(args, mockToolCallOptions)) as FileEditReplaceToolResult;
-
-    // Assert
-    expect(result.success).toBe(false);
-    if (!result.success) {
-      expect(result.error).toContain("lease mismatch");
-    }
-  });
-
   it("should return unified diff with context of 3", async () => {
     // Setup - create a file with multiple lines
     const initialContent = "line1\nline2\nline3\nline4\nline5\nline6\nline7\nline8\nline9";
     await fs.writeFile(testFilePath, initialContent);
 
-    const content = await fs.readFile(testFilePath, "utf-8");
-    const lease = leaseFromContent(content);
-
     const tool = createFileEditReplaceTool({ cwd: testDir });
     const args: FileEditReplaceToolArgs = {
       file_path: testFilePath,
@@ -565,7 +435,6 @@ describe("file_edit_replace tool", () => {
           new_string: "LINE5_MODIFIED",
         },
       ],
-      lease,
     };
 
     // Execute
diff --git a/src/services/tools/file_edit_replace.ts b/src/services/tools/file_edit_replace.ts
index 7c161077f7..f0face101e 100644
--- a/src/services/tools/file_edit_replace.ts
+++ b/src/services/tools/file_edit_replace.ts
@@ -5,7 +5,7 @@ import writeFileAtomic from "write-file-atomic";
 import type { FileEditReplaceToolResult } from "@/types/tools";
 import type { ToolConfiguration, ToolFactory } from "@/utils/tools/tools";
 import { TOOL_DEFINITIONS } from "@/utils/tools/toolDefinitions";
-import { leaseFromContent, generateDiff, validatePathInCwd, validateFileSize } from "./fileCommon";
+import { generateDiff, validatePathInCwd, validateFileSize } from "./fileCommon";
 
 /**
  * File edit replace tool factory for AI assistant
@@ -17,7 +17,7 @@ export const createFileEditReplaceTool: ToolFactory = (config: ToolConfiguration
     description: TOOL_DEFINITIONS.file_edit_replace.description,
     inputSchema: TOOL_DEFINITIONS.file_edit_replace.schema,
     execute: async (
-      { file_path, edits, lease },
+      { file_path, edits },
       { abortSignal: _abortSignal }
     ): Promise<FileEditReplaceToolResult> => {
       // Note: abortSignal available but not used - file operations are fast and complete quickly
@@ -56,16 +56,6 @@ export const createFileEditReplaceTool: ToolFactory = (config: ToolConfiguration
 
         // Read file content
         const originalContent = await fs.readFile(resolvedPath, { encoding: "utf-8" });
-
-        // Validate lease to prevent editing stale file state
-        // Use content-based lease to avoid mtime issues with external processes
-        const currentLease = leaseFromContent(originalContent);
-        if (currentLease !== lease) {
-          return {
-            success: false,
-            error: `WRITE DENIED: File lease mismatch. The file has been modified since it was read. Please obtain a new lease from tool \`file_read\`.`,
-          };
-        }
         let content = originalContent;
 
         // Apply each edit sequentially
@@ -143,16 +133,12 @@ export const createFileEditReplaceTool: ToolFactory = (config: ToolConfiguration
         // Write the modified content back to file atomically
         await writeFileAtomic(resolvedPath, content, { encoding: "utf-8" });
 
-        // Compute new lease from modified content
-        const newLease = leaseFromContent(content);
-
         // Generate diff
         const diff = generateDiff(resolvedPath, originalContent, content);
 
         return {
           success: true,
           edits_applied: editsApplied,
-          lease: newLease,
           diff,
         };
       } catch (error) {
diff --git a/src/services/tools/file_read.test.ts b/src/services/tools/file_read.test.ts
index a92f9c0907..03ba0a7256 100644
--- a/src/services/tools/file_read.test.ts
+++ b/src/services/tools/file_read.test.ts
@@ -46,7 +46,6 @@ describe("file_read tool", () => {
       expect(result.lines_read).toBe(3);
       expect(result.content).toBe("1\tline one\n2\tline two\n3\tline three");
       expect(result.file_size).toBeGreaterThan(0);
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
     }
   });
 
@@ -69,7 +68,6 @@ describe("file_read tool", () => {
     if (result.success) {
       expect(result.lines_read).toBe(3);
       expect(result.content).toBe("3\tline3\n4\tline4\n5\tline5");
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
     }
   });
 
@@ -92,7 +90,6 @@ describe("file_read tool", () => {
     if (result.success) {
       expect(result.lines_read).toBe(2);
       expect(result.content).toBe("1\tline1\n2\tline2");
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
     }
   });
 
@@ -116,7 +113,6 @@ describe("file_read tool", () => {
     if (result.success) {
       expect(result.lines_read).toBe(2);
       expect(result.content).toBe("2\tline2\n3\tline3");
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
     }
   });
 
@@ -138,7 +134,6 @@ describe("file_read tool", () => {
     if (result.success) {
       expect(result.lines_read).toBe(1);
       expect(result.content).toBe("1\tsingle line");
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
     }
   });
 
@@ -159,7 +154,6 @@ describe("file_read tool", () => {
     if (result.success) {
       expect(result.lines_read).toBe(0);
       expect(result.content).toBe("");
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
     }
   });
 
@@ -226,7 +220,6 @@ describe("file_read tool", () => {
       expect(lines[1]).toContain("... [truncated]");
       expect(Buffer.byteLength(lines[1], "utf-8")).toBeLessThan(1100); // Should be around 1024 + prefix + truncation marker
       expect(lines[2]).toBe("3\tanother short line");
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
     }
   });
 
@@ -294,7 +287,6 @@ describe("file_read tool", () => {
     expect(result.success).toBe(true);
     if (result.success) {
       expect(result.lines_read).toBe(500);
-      expect(result.lease).toMatch(/^[0-9a-f]{6}$/);
     }
   });
 
diff --git a/src/services/tools/file_read.ts b/src/services/tools/file_read.ts
index d17bed5417..3c1227da63 100644
--- a/src/services/tools/file_read.ts
+++ b/src/services/tools/file_read.ts
@@ -4,7 +4,7 @@ import * as path from "path";
 import type { FileReadToolResult } from "@/types/tools";
 import type { ToolConfiguration, ToolFactory } from "@/utils/tools/tools";
 import { TOOL_DEFINITIONS } from "@/utils/tools/toolDefinitions";
-import { leaseFromContent, validatePathInCwd, validateFileSize } from "./fileCommon";
+import { validatePathInCwd, validateFileSize } from "./fileCommon";
 
 /**
  * File read tool factory for AI assistant
@@ -53,10 +53,8 @@ export const createFileReadTool: ToolFactory = (config: ToolConfiguration) => {
           };
         }
 
-        // Read full file content once for both display and lease computation
-        // This ensures lease matches the exact content snapshot being returned
+        // Read full file content
         const fullContent = await fs.readFile(resolvedPath, { encoding: "utf-8" });
-        const lease = leaseFromContent(fullContent);
 
         const startLineNumber = offset ?? 1;
 
@@ -133,15 +131,12 @@ export const createFileReadTool: ToolFactory = (config: ToolConfiguration) => {
         const content = numberedLines.join("\n");
 
         // Return file info and content
-        // IMPORTANT: lease must be last in the return object so it remains fresh in the LLM's context
-        // when it's reading this tool result. The LLM needs the lease value to perform subsequent edits.
         return {
           success: true,
           file_size: stats.size,
           modifiedTime: stats.mtime.toISOString(),
           lines_read: numberedLines.length,
           content,
-          lease, // Must be last - see comment above
         };
       } catch (error) {
         // Handle specific errors
diff --git a/src/types/tools.ts b/src/types/tools.ts
index 7d52e4a02a..2bab15c9c7 100644
--- a/src/types/tools.ts
+++ b/src/types/tools.ts
@@ -44,7 +44,6 @@ export type FileReadToolResult =
       modifiedTime: string;
       lines_read: number;
       content: string;
-      lease: string;
     }
   | {
       success: false;
@@ -61,14 +60,12 @@ export interface FileEditReplaceEdit {
 export interface FileEditReplaceToolArgs {
   file_path: string;
   edits: FileEditReplaceEdit[];
-  lease: string;
 }
 
 export type FileEditReplaceToolResult =
   | {
       success: true;
       edits_applied: number;
-      lease: string;
       diff: string;
     }
   | {
@@ -81,13 +78,11 @@ export interface FileEditInsertToolArgs {
   file_path: string;
   line_offset: number; // 1-indexed line position (0 = insert at top, N = insert after line N)
   content: string;
-  lease: string;
 }
 
 export type FileEditInsertToolResult =
   | {
       success: true;
-      lease: string;
       diff: string;
     }
   | {
diff --git a/src/utils/tools/toolDefinitions.ts b/src/utils/tools/toolDefinitions.ts
index 14cd4094e7..b9434346f0 100644
--- a/src/utils/tools/toolDefinitions.ts
+++ b/src/utils/tools/toolDefinitions.ts
@@ -25,13 +25,6 @@ interface ToolSchema {
   };
 }
 
-/**
- * Shared schema definitions
- */
-const leaseSchema = z
-  .string()
-  .describe("The lease from the file_read result. Used to prevent edits on stale file state.");
-
 /**
  * Tool definitions: single source of truth
  * Key = tool name, Value = { description, schema }
@@ -112,7 +105,6 @@ export const TOOL_DEFINITIONS = {
         )
         .min(1)
         .describe("Array of edits to apply sequentially"),
-      lease: leaseSchema,
     }),
   },
   file_edit_insert: {
@@ -126,7 +118,6 @@ export const TOOL_DEFINITIONS = {
         .min(0)
         .describe("1-indexed line position (0 = insert at top, N = insert after line N)"),
       content: z.string().describe("The content to insert"),
-      lease: leaseSchema,
     }),
   },
   propose_plan: {