fix(docker): read attached binary files in backend (#76577)

agent/context_references.py

@@ -555,6 +555,30 @@ def _rg_files(path: Path, cwd: Path, limit: int) -> list[Path] | None:
     return files[:limit]
 
 
+def _agent_visible_path(path: Path) -> str:
+    """Map a host path to the path the agent's tools can read in the active backend.
+
+    Under a container backend (docker) the gateway host path dangles inside the
+    sandbox — the container has its own filesystem and the host path is not
+    mounted. Files staged into an auto-mounted cache dir (``images/``,
+    ``attachments/``, ...) are translated to their in-container path via the
+    existing ``tools.credential_files`` machinery (#76577). Falls back to the
+    host path when the backend is local or translation is unavailable.
+    """
+    try:
+        # Desktop/in-process gateways may not have bridged ``terminal.*``
+        # config into ``TERMINAL_ENV`` at startup; run the idempotent bridge so
+        # the credential_files translation gate sees the active backend.
+        from tools.terminal_tool import _ensure_terminal_env_bridged
+
+        _ensure_terminal_env_bridged()
+        from tools.credential_files import to_agent_visible_cache_path
+
+        return to_agent_visible_cache_path(str(path))
+    except Exception:
+        return str(path)
+
+
 def _binary_reference_block(ref: ContextReference, path: Path) -> str:
     mime, _ = mimetypes.guess_type(path.name)
     mime = mime or "application/octet-stream"
@@ -564,7 +588,7 @@ def _binary_reference_block(ref: ContextReference, path: Path) -> str:
         size = "unknown size"
     return (
         f"📎 {ref.raw} ({mime}, {size}) — binary file, not inlined as text. "
-        f"It is available on disk at `{path}`. Use your tools to work with it "
+        f"It is available on disk at `{_agent_visible_path(path)}`. Use your tools to work with it "
         f"(read or convert it, extract its text, or view/render it as needed); "
         f"do not tell the user the file type is unsupported."
     )