Clarify search replace line matching

e2e-tests/snapshots/local_agent_advanced.spec.ts_local-agent---mcp-tool-search-1.txt

@@ -120,7 +120,7 @@
       },
       {
         "name": "search_replace",
-        "description": "Use this tool to propose a search and replace operation on an existing file.\n\nThe tool will replace ONE occurrence of old_string with new_string in the specified file.\n\nCRITICAL REQUIREMENTS FOR USING THIS TOOL:\n\n1. UNIQUENESS: The old_string MUST uniquely identify the specific instance you want to change. This means:\n   - Include AT LEAST 3-5 lines of context BEFORE the change point\n   - Include AT LEAST 3-5 lines of context AFTER the change point\n   - Include all whitespace, indentation, and surrounding code exactly as it appears in the file\n\n2. SINGLE INSTANCE: This tool can only change ONE instance at a time. If you need to change multiple instances:\n   - Make separate calls to this tool for each instance\n   - Each call must uniquely identify its specific instance using extensive context\n\n3. VERIFICATION: Before using this tool:\n   - If multiple instances exist, gather enough context to uniquely identify each one\n   - Plan separate tool calls for each instance\n",
+        "description": "Use this tool to propose a search and replace operation on an existing file.\n\nThe tool will replace ONE occurrence of old_string with new_string in the specified file. Matching is line-based: old_string must match whole file lines, not a partial fragment within a line. To edit part of a line, include the entire original line in old_string and the entire edited line in new_string.\n\nCRITICAL REQUIREMENTS FOR USING THIS TOOL:\n\n1. UNIQUENESS: The old_string MUST uniquely identify the specific instance you want to change. This means:\n   - Include AT LEAST 3-5 lines of context BEFORE the change point\n   - Include AT LEAST 3-5 lines of context AFTER the change point\n   - Include all whitespace, indentation, and surrounding code exactly as it appears in the file\n   - Do NOT use only a partial fragment of a line. Include the full line containing the change.\n\n2. SINGLE INSTANCE: This tool can only change ONE instance at a time. If you need to change multiple instances:\n   - Make separate calls to this tool for each instance\n   - Each call must uniquely identify its specific instance using extensive context\n\n3. VERIFICATION: Before using this tool:\n   - If multiple instances exist, gather enough context to uniquely identify each one\n   - Plan separate tool calls for each instance\n",
         "input_schema": {
           "$schema": "http://json-schema.org/draft-07/schema#",
           "type": "object",
@@ -131,7 +131,7 @@
             },
             "old_string": {
               "type": "string",
-              "description": "The text to replace (must be unique within the file, and must match the file contents exactly, including all whitespace and indentation)"
+              "description": "The text block to replace. Matching is line-based: each line in old_string must match a whole line in the file, not just a substring within a line. To edit part of a line, include the entire original line in old_string and the entire edited line in new_string. The block must be unique within the file."
             },
             "new_string": {
               "type": "string",

e2e-tests/snapshots/local_agent_advanced.spec.ts_local-agent---mention-apps-1.txt

@@ -57,7 +57,7 @@
       },
       {
         "name": "search_replace",
-        "description": "Use this tool to propose a search and replace operation on an existing file.\n\nThe tool will replace ONE occurrence of old_string with new_string in the specified file.\n\nCRITICAL REQUIREMENTS FOR USING THIS TOOL:\n\n1. UNIQUENESS: The old_string MUST uniquely identify the specific instance you want to change. This means:\n   - Include AT LEAST 3-5 lines of context BEFORE the change point\n   - Include AT LEAST 3-5 lines of context AFTER the change point\n   - Include all whitespace, indentation, and surrounding code exactly as it appears in the file\n\n2. SINGLE INSTANCE: This tool can only change ONE instance at a time. If you need to change multiple instances:\n   - Make separate calls to this tool for each instance\n   - Each call must uniquely identify its specific instance using extensive context\n\n3. VERIFICATION: Before using this tool:\n   - If multiple instances exist, gather enough context to uniquely identify each one\n   - Plan separate tool calls for each instance\n",
+        "description": "Use this tool to propose a search and replace operation on an existing file.\n\nThe tool will replace ONE occurrence of old_string with new_string in the specified file. Matching is line-based: old_string must match whole file lines, not a partial fragment within a line. To edit part of a line, include the entire original line in old_string and the entire edited line in new_string.\n\nCRITICAL REQUIREMENTS FOR USING THIS TOOL:\n\n1. UNIQUENESS: The old_string MUST uniquely identify the specific instance you want to change. This means:\n   - Include AT LEAST 3-5 lines of context BEFORE the change point\n   - Include AT LEAST 3-5 lines of context AFTER the change point\n   - Include all whitespace, indentation, and surrounding code exactly as it appears in the file\n   - Do NOT use only a partial fragment of a line. Include the full line containing the change.\n\n2. SINGLE INSTANCE: This tool can only change ONE instance at a time. If you need to change multiple instances:\n   - Make separate calls to this tool for each instance\n   - Each call must uniquely identify its specific instance using extensive context\n\n3. VERIFICATION: Before using this tool:\n   - If multiple instances exist, gather enough context to uniquely identify each one\n   - Plan separate tool calls for each instance\n",
         "input_schema": {
           "$schema": "http://json-schema.org/draft-07/schema#",
           "type": "object",
@@ -68,7 +68,7 @@
             },
             "old_string": {
               "type": "string",
-              "description": "The text to replace (must be unique within the file, and must match the file contents exactly, including all whitespace and indentation)"
+              "description": "The text block to replace. Matching is line-based: each line in old_string must match a whole line in the file, not just a substring within a line. To edit part of a line, include the entire original line in old_string and the entire edited line in new_string. The block must be unique within the file."
             },
             "new_string": {
               "type": "string",