Improve apply_diff tool description with examples

- Add explicit format documentation showing structure directly
- Include concrete examples (single and multiple edits)
- Simplify structure explanation (removed verbose 'then this, then that')
- Add critical warning about single '=======' separator
- Clarify start_line uses actual numbers in examples

This addresses agent confusion similar to read_file improvements.

src/core/prompts/tools/native-tools/apply_diff.ts

@@ -4,9 +4,13 @@ export const apply_diff_single_file = {
 	type: "function",
 	function: {
 		name: "apply_diff",
-		description: `
-Apply precise, targeted modifications to an existing file using one or more search/replace blocks. This tool is for surgical edits only; the 'SEARCH' block must exactly match the existing content, including whitespace and indentation. To make multiple targeted changes, provide multiple SEARCH/REPLACE blocks in the 'diff' parameter. Use the 'read_file' tool first if you are not confident in the exact content to search for.
-`,
+		description:
+			"Apply precise, targeted modifications to an existing file using one or more search/replace blocks. This tool is for surgical edits only; the 'SEARCH' block must exactly match the existing content, including whitespace and indentation. " +
+			"To make multiple targeted changes, provide multiple SEARCH/REPLACE blocks in the 'diff' parameter. Use the 'read_file' tool first if you are not confident in the exact content to search for. " +
+			"Structure: '<<<<<<< SEARCH\\n:start_line:N\\n-------\\nexact content\\n=======\\nreplacement\\n>>>>>>> REPLACE' where N is the actual line number. " +
+			"Example single change: { path: 'src/utils.ts', diff: '<<<<<<< SEARCH\\n:start_line:5\\n-------\\nfunction add(a, b) {\\n  return a + b;\\n}\\n=======\\nfunction add(a: number, b: number): number {\\n  return a + b;\\n}\\n>>>>>>> REPLACE' }. " +
+			"Example multiple changes: { path: 'src/app.ts', diff: '<<<<<<< SEARCH\\n:start_line:10\\n-------\\nold code here\\n=======\\nnew code here\\n>>>>>>> REPLACE\\n\\n<<<<<<< SEARCH\\n:start_line:25\\n-------\\nmore old code\\n=======\\nmore new code\\n>>>>>>> REPLACE' }. " +
+			"CRITICAL: Use exactly ONE line of '=======' between search and replace content - multiple '=======' lines will corrupt the file.",
 		parameters: {
 			type: "object",
 			properties: {
@@ -16,16 +20,12 @@ Apply precise, targeted modifications to an existing file using one or more sear
 				},
 				diff: {
 					type: "string",
-					description: `
-A string containing one or more search/replace blocks defining the changes. The ':start_line:' is required and indicates the starting line number of the original content.  You must not add a start line for the replacement content. Each block must follow this format:
-<<<<<<< SEARCH
-:start_line:[line_number]
--------
-[exact content to find]
-=======
-[new content to replace with]
->>>>>>> REPLACE
-`,
+					description:
+						"A string containing one or more search/replace blocks defining the changes. The ':start_line:' is required and indicates the starting line number of the original content. You must not add a start line for the replacement content. " +
+						"Format: '<<<<<<< SEARCH\\n:start_line:5\\n-------\\nexact content\\n=======\\nreplacement\\n>>>>>>> REPLACE'. " +
+						"Example: '<<<<<<< SEARCH\\n:start_line:10\\n-------\\nconst x = 1;\\n=======\\nconst x = 2;\\n>>>>>>> REPLACE'. " +
+						"For multiple edits: separate each block with a blank line and use different start_line values. " +
+						"IMPORTANT: The start_line must be the actual line number (e.g., :start_line:5, not :start_line:[5]).",
 				},
 			},
 			required: ["path", "diff"],