refactor(backend): drop noisy 80% storage warning + document write_file raises

The 80% warning fired on every write inside the band, producing repeated log
entries during a single CoPilot turn that writes multiple files. The frontend
storage bar already conveys usage to the user, and ops alerting belongs on a
metric, not a log line that scales with write rate.

Also document `VirusDetectedError` / `VirusScanError` in `WorkspaceManager.write_file`
so callers can decide between explicit handling and generic `Exception` catches.

autogpt_platform/backend/backend/util/workspace.py

@@ -192,7 +192,15 @@ class WorkspaceManager:
             Created WorkspaceFile instance
 
         Raises:
-            ValueError: If file exceeds size limit or path already exists
+            ValueError: If file exceeds size limit, exceeds the user's
+                tier-based storage quota, or path already exists.
+            VirusDetectedError: If the virus scanner flagged the content as
+                malicious. Callers that want a generic failure should still
+                catch ``Exception``, but a specific handler lets you log this
+                as a security event rather than a generic write failure.
+            VirusScanError: If the virus scanner is unreachable or otherwise
+                fails. Distinct from ``VirusDetectedError`` — typically maps
+                to a 5xx response (infrastructure issue, retry-able).
         """
         # Enforce file size limit
         max_file_size = Config().max_file_size_mb * 1024 * 1024
@@ -232,12 +240,6 @@ class WorkspaceManager:
                 f"{format_bytes(storage_limit)} quota. "
                 f"Delete some files or upgrade your plan for more storage."
             )
-        if storage_limit > 0 and projected_usage / storage_limit >= 0.8:
-            logger.warning(
-                f"User {self.user_id} workspace storage at "
-                f"{projected_usage / storage_limit * 100:.1f}% "
-                f"({projected_usage} / {storage_limit} bytes)"
-            )
 
         # Check if file exists at path (only error for non-overwrite case).
         # Done before virus scanning so a cheap duplicate-path check isn't

autogpt_platform/backend/backend/util/workspace_test.py

@@ -239,41 +239,6 @@ async def test_write_file_rejects_upload_when_usage_already_exceeds_downgraded_l
     mock_storage.store.assert_not_called()
 
 
-@pytest.mark.asyncio
-async def test_write_file_80pct_warning_logged(manager, mock_storage, mock_db, caplog):
-    """write_file logs a warning when workspace usage crosses 80%."""
-    created_file = _make_workspace_file()
-    mock_db.get_workspace_file_by_path.return_value = None
-    mock_db.create_workspace_file.return_value = created_file
-
-    limit_bytes = 100  # 100 bytes total limit
-    current_usage = 75  # 75 bytes used → 75% before write
-    content = b"123456"  # 6 bytes → 81% after write
-
-    with (
-        patch(
-            "backend.util.workspace.get_workspace_storage",
-            return_value=mock_storage,
-        ),
-        patch("backend.util.workspace.workspace_db", return_value=mock_db),
-        patch("backend.util.workspace.scan_content_safe", new_callable=AsyncMock),
-        patch(
-            "backend.util.workspace.get_workspace_storage_limit_bytes",
-            return_value=limit_bytes,
-        ),
-        patch(
-            "backend.util.workspace.get_workspace_total_size",
-            return_value=current_usage,
-        ),
-    ):
-        import logging
-
-        with caplog.at_level(logging.WARNING, logger="backend.util.workspace"):
-            await manager.write_file(filename="test.txt", content=content)
-
-    assert any("workspace storage at" in record.message for record in caplog.records)
-
-
 @pytest.mark.asyncio
 async def test_write_file_overwrite_not_double_counted(manager, mock_storage, mock_db):
     """Overwriting a file subtracts the old file size from usage check."""