fix(security): neutralize file paths in mutation-verifier footer (#35584) (#35684)

The per-turn file-mutation verifier footer rendered failed-write paths as
bare absolute paths in the user-facing response. The gateway's
extract_local_files() scans response text for bare paths ending in a
deliverable extension (.yaml/.json/etc.), validates os.path.isfile(), and
auto-attaches matches as native uploads — so a denied write to
~/.hermes/config.yaml surfaced the path in the footer and got the
credential file silently uploaded to the messaging channel.

The gateway denylist (validate_media_delivery_path) already blocks the
config.yaml case after #35634. This is defense-in-depth at the source:
backtick-wrap every path the footer emits — both the bullet path and any
path echoed inside the tool's error preview (the protected-file denial
message embeds the path in single quotes, which do NOT block the
extractor regex). extract_local_files skips paths inside inline-code
spans, so wrapping defeats auto-attachment for ANY protected file while
keeping the path human-readable.

- run_agent.py: _format_file_mutation_failure_footer wraps bullet paths;
  new _neutralize_footer_paths backticks any remaining bare path (covers
  the preview echo). staticmethod -> classmethod (caller unaffected).
- tests: backtick-wrap assertion + end-to-end extract_local_files leak test.

run_agent.py

@@ -2106,13 +2106,48 @@ class AIAgent:
             pass
         return True  # safe default: verifier on
 
-    @staticmethod
+    # Bare absolute / home / Windows-drive file paths in a footer line.
-    def _format_file_mutation_failure_footer(failed: Dict[str, Dict[str, Any]]) -> str:
+    # Anchors mirror the gateway's ``extract_local_files`` bare-path
+    # detector so that anything the gateway WOULD auto-attach is wrapped
+    # in inline-code backticks here first (the extractor skips paths inside
+    # `code` spans).  Defense-in-depth: even if a future error message
+    # echoes a credential path (config.yaml, .env, auth.json) into the
+    # user-facing footer, it can never be matched as a deliverable bare
+    # path and silently uploaded to a messaging channel (#35584).
+    _FOOTER_PATH_RE = re.compile(
+        r"(?<![/:\w.`])(?:~/|/|[A-Za-z]:[/\\])(?:[\w.\-]+[/\\])*[\w.\-]+\.[\w]+",
+    )
+
+    @classmethod
+    def _neutralize_footer_paths(cls, text: str) -> str:
+        """Wrap bare file paths in backticks so they aren't auto-delivered.
+
+        The gateway's ``extract_local_files`` scans response text for bare
+        absolute/home paths ending in a deliverable extension and uploads
+        any that exist on disk as native attachments — but it explicitly
+        skips paths inside inline-code (`` `...` ``) spans.  Backticking
+        every path the footer renders defeats that auto-detection while
+        keeping the path fully human-readable.  Paths already wrapped in a
+        backtick (the negative lookbehind excludes a preceding `` ` ``) are
+        left untouched so we never double-wrap.
+        """
+        if not text:
+            return text
+        return cls._FOOTER_PATH_RE.sub(lambda m: f"`{m.group(0)}`", text)
+
+    @classmethod
+    def _format_file_mutation_failure_footer(cls, failed: Dict[str, Dict[str, Any]]) -> str:
         """Render the per-turn failed-mutation dict as a user-facing footer.
 
         Displays up to 10 paths with their first error preview, then a
         count of any additional failures.  Returns an empty string when
         the dict is empty so callers can concatenate unconditionally.
+
+        Every file path that reaches the user-facing text — both the bullet
+        path and any path echoed inside the tool's error preview — is
+        backtick-wrapped via ``_neutralize_footer_paths`` so the gateway's
+        bare-path media extractor can never auto-attach a protected file
+        (e.g. ``~/.hermes/config.yaml``) to a messaging channel (#35584).
         """
         if not failed:
             return ""
@@ -2129,14 +2164,17 @@ class AIAgent:
             preview = (info.get("error_preview") or "").strip()
             tool = info.get("tool") or "patch"
             if preview:
-                lines.append(f"  • {path} — [{tool}] {preview}")
+                lines.append(f"  • `{path}` — [{tool}] {preview}")
             else:
-                lines.append(f"  • {path} — [{tool}] failed")
+                lines.append(f"  • `{path}` — [{tool}] failed")
             shown += 1
         remaining = len(failed) - shown
         if remaining > 0:
             lines.append(f"  • … and {remaining} more")
-        return "\n".join(lines)
+        # Neutralize any path the preview text echoed (the bullet path is
+        # already backticked above; the lookbehind keeps it from being
+        # double-wrapped).
+        return cls._neutralize_footer_paths("\n".join(lines))
 
     def _turn_completion_explainer_enabled(self) -> bool:
         """Check whether the end-of-turn completion explainer footer is on.

tests/run_agent/test_file_mutation_verifier.py

@@ -300,6 +300,57 @@ class TestFormatFooter:
         bullet_lines = [ln for ln in lines if ln.lstrip().startswith("•")]
         assert len(bullet_lines) == 11  # 10 shown + 1 summary
 
+    def test_paths_are_backtick_wrapped(self):
+        """Footer paths must be inline-code wrapped so the gateway's bare-path
+        media extractor can't auto-attach them (#35584 defense-in-depth)."""
+        out = AIAgent._format_file_mutation_failure_footer(
+            {"/home/u/.hermes/config.yaml": {
+                "tool": "patch",
+                "error_preview": (
+                    "Write denied: '/home/u/.hermes/config.yaml' is a "
+                    "protected system/credential file."
+                ),
+            }},
+        )
+        # Path still human-readable.
+        assert "/home/u/.hermes/config.yaml" in out
+        # Bullet path is backticked.
+        assert "`/home/u/.hermes/config.yaml`" in out
+        # The path echoed inside the preview is ALSO backticked (the real
+        # file_operations.py denial message embeds it in single quotes, which
+        # do NOT block the gateway extractor's regex).
+        assert "'`/home/u/.hermes/config.yaml`'" in out
+        # No double-backticking anywhere.
+        assert "``" not in out
+
+    def test_footer_path_not_extracted_by_gateway(self):
+        """End-to-end: the gateway's extract_local_files must NOT pull a
+        config.yaml path out of the rendered footer (#35584)."""
+        import os
+        import tempfile
+        from gateway.platforms.base import BasePlatformAdapter
+
+        tmp = tempfile.mkdtemp(prefix="hermes_footer_")
+        try:
+            cfg = os.path.join(tmp, "config.yaml")
+            with open(cfg, "w") as fh:
+                fh.write("openrouter_api_key: sk-LEAK\n")
+            footer = AIAgent._format_file_mutation_failure_footer(
+                {cfg: {
+                    "tool": "patch",
+                    "error_preview": (
+                        f"Write denied: '{cfg}' is a protected "
+                        "system/credential file."
+                    ),
+                }},
+            )
+            response = "I updated your config.\n\n" + footer
+            paths, _ = BasePlatformAdapter.extract_local_files(response)
+            assert paths == [], f"footer leaked deliverable path(s): {paths}"
+        finally:
+            import shutil
+            shutil.rmtree(tmp, ignore_errors=True)
+
 
 # ---------------------------------------------------------------------------
 # _file_mutation_verifier_enabled — env + config precedence