diff --git a/packages/core/src/utils/paths.test.ts b/packages/core/src/utils/paths.test.ts
index 09b58d41870..ebeb0a7ff64 100644
--- a/packages/core/src/utils/paths.test.ts
+++ b/packages/core/src/utils/paths.test.ts
@@ -561,6 +561,36 @@ describe('resolveToRealPath', () => {
     expect(resolveToRealPath(input)).toBe(expected);
   });
 
+  it('should return input path even if fs.realpathSync fails with ENAMETOOLONG', () => {
+    // Regression test for #26010: pasting long strings that the at-mention
+    // regex misinterprets as a path must not throw an unhandled ENAMETOOLONG
+    // up to the caller.
+    vi.spyOn(fs, 'realpathSync').mockImplementationOnce(() => {
+      const err = new Error('name too long') as NodeJS.ErrnoException;
+      err.code = 'ENAMETOOLONG';
+      throw err;
+    });
+
+    const longInput = path.resolve('/tmp', 'a'.repeat(4096));
+
+    expect(resolveToRealPath(longInput)).toBe(longInput);
+  });
+
+  it('should return input path even if fs.realpathSync fails with ENOTDIR', () => {
+    // Regression test for #26010: an intermediate path component being a
+    // regular file (e.g. @path/to/file.json/extra) surfaces ENOTDIR from
+    // realpathSync — handle it the same way as a non-existent path.
+    vi.spyOn(fs, 'realpathSync').mockImplementationOnce(() => {
+      const err = new Error('not a directory') as NodeJS.ErrnoException;
+      err.code = 'ENOTDIR';
+      throw err;
+    });
+
+    const input = path.resolve('/tmp', 'file.json', 'extra');
+
+    expect(resolveToRealPath(input)).toBe(input);
+  });
+
   it('should recursively resolve symlinks for non-existent child paths', () => {
     const parentPath = path.resolve('/some/parent/path');
     const resolvedParentPath = path.resolve('/resolved/parent/path');
diff --git a/packages/core/src/utils/paths.ts b/packages/core/src/utils/paths.ts
index fee8b8d8556..12163ea482d 100644
--- a/packages/core/src/utils/paths.ts
+++ b/packages/core/src/utils/paths.ts
@@ -412,6 +412,14 @@ export function resolveToRealPath(pathStr: string): string {
   return robustRealpath(path.resolve(resolvedPath));
 }
 
+function hasErrorCode(e: unknown, codes: readonly string[]): boolean {
+  if (!e || typeof e !== 'object' || !('code' in e)) {
+    return false;
+  }
+  const code = e.code;
+  return typeof code === 'string' && codes.includes(code);
+}
+
 function robustRealpath(p: string, visited = new Set<string>()): string {
   const key = process.platform === 'win32' ? p.toLowerCase() : p;
   if (visited.has(key)) {
@@ -421,12 +429,7 @@ function robustRealpath(p: string, visited = new Set<string>()): string {
   try {
     return fs.realpathSync(p);
   } catch (e: unknown) {
-    if (
-      e &&
-      typeof e === 'object' &&
-      'code' in e &&
-      (e.code === 'ENOENT' || e.code === 'EISDIR')
-    ) {
+    if (hasErrorCode(e, ['ENOENT', 'EISDIR'])) {
       try {
         const stat = fs.lstatSync(p);
         if (stat.isSymbolicLink()) {
@@ -437,14 +440,7 @@ function robustRealpath(p: string, visited = new Set<string>()): string {
       } catch (lstatError: unknown) {
         // Not a symlink, or lstat failed. Re-throw if it's not an expected
         // ENOENT (e.g., a permissions error), otherwise resolve parent.
-        if (
-          !(
-            lstatError &&
-            typeof lstatError === 'object' &&
-            'code' in lstatError &&
-            (lstatError.code === 'ENOENT' || lstatError.code === 'EISDIR')
-          )
-        ) {
+        if (!hasErrorCode(lstatError, ['ENOENT', 'EISDIR'])) {
           throw lstatError;
         }
       }
@@ -452,6 +448,14 @@ function robustRealpath(p: string, visited = new Set<string>()): string {
       if (parent === p) return p;
       return path.join(robustRealpath(parent, visited), path.basename(p));
     }
+    if (hasErrorCode(e, ['ENAMETOOLONG', 'ENOTDIR'])) {
+      // The input is not a resolvable real path — for example a caller
+      // is probing whether a pasted string is a file reference (see the
+      // @-mention path parsing in atCommandProcessor). Returning the
+      // input unchanged lets downstream fileExists / fs.stat calls
+      // reject it normally instead of surfacing an unhandled rejection.
+      return p;
+    }
     throw e;
   }
 }