fix(core): secure argsPattern and revert WEB_FETCH_TOOL_NAME escalation (#22104)

Co-authored-by: Taylor Mullen <ntaylormullen@google.com>

packages/core/src/scheduler/policy.test.ts

@@ -660,7 +660,8 @@ describe('policy.ts', () => {
       expect(mockMessageBus.publish).toHaveBeenCalledWith(
         expect.objectContaining({
           toolName: 'write_file',
-          argsPattern: escapeRegex('"file_path":"src/foo.ts"'),
+          argsPattern:
+            '\\\\0' + escapeRegex('"file_path":"src/foo.ts"') + '\\\\0',
         }),
       );
     });