fix: prevent exception diagnostics from leaking in API problem responses (#1405)

* Potential fix for code scanning alert no. 11: Information exposure through an exception

traceback should not be in client side code

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

* fix: keep unexpected API error details private and test problem responses

---------

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

tests/test_rest_error.py

@@ -0,0 +1,95 @@
+"""Problem responses keep server diagnostics private and preserve public errors."""
+
+import pytest
+from fastapi import FastAPI, HTTPException
+from fastapi.testclient import TestClient
+from loguru import logger
+
+from akkudoktoreos.server.rest.error import EOSProblem, register_problem_handlers
+
+
+@pytest.mark.parametrize("api_level", ["TRACE", "DEBUG", "INFO", "WARNING", "ERROR"])
+@pytest.mark.parametrize("unexpected", [False, True])
+def test_problem_responses_keep_diagnostics_in_logs(config_eos, api_level, unexpected):
+    config_eos.logging.api_level = api_level
+    app = FastAPI()
+    register_problem_handlers(app)
+    private_detail = "Database failed at /private/server.db with password=secret"
+
+    @app.get("/failure")
+    def failure():
+        try:
+            raise RuntimeError(private_detail)
+        except RuntimeError as exc:
+            if unexpected:
+                raise
+            raise EOSProblem(
+                status=503,
+                title="Service Unavailable",
+                detail="The service is temporarily unavailable.",
+                type="/problems/service-unavailable",
+                cause=exc,
+            ) from exc
+
+    logs: list[str] = []
+    sink_id = logger.add(logs.append, level="ERROR", backtrace=False, diagnose=False)
+    try:
+        with TestClient(app, raise_server_exceptions=False) as client:
+            response = client.get("/failure?token=private-query-token")
+    finally:
+        logger.remove(sink_id)
+
+    status = 500 if unexpected else 503
+    assert response.status_code == status
+    assert response.headers["content-type"] == "application/problem+json"
+    assert response.json() == {
+        "type": "/problems/internal-server-error" if unexpected else "/problems/service-unavailable",
+        "title": "Internal Server Error" if unexpected else "Service Unavailable",
+        "status": status,
+        "detail": (
+            "An unexpected error occurred."
+            if unexpected
+            else "The service is temporarily unavailable."
+        ),
+        "instance": "/failure",
+    }
+    assert private_detail not in response.text
+    assert "private-query-token" not in response.text
+    assert any(private_detail in message and "Traceback" in message for message in logs)
+
+
+def test_http_and_validation_errors_preserve_public_details():
+    app = FastAPI()
+    register_problem_handlers(app)
+
+    @app.get("/missing")
+    def missing():
+        raise HTTPException(status_code=404, detail="The requested item does not exist.")
+
+    @app.get("/validate")
+    def validate(value: int):
+        return {"value": value}
+
+    with TestClient(app) as client:
+        missing_response = client.get("/missing")
+        validation_response = client.get("/validate?value=private-invalid-input")
+
+    assert missing_response.status_code == 404
+    assert missing_response.headers["content-type"] == "application/problem+json"
+    assert missing_response.json() == {
+        "type": "about:blank",
+        "title": "HTTP Error",
+        "status": 404,
+        "detail": "The requested item does not exist.",
+        "instance": "/missing",
+    }
+    assert validation_response.status_code == 422
+    assert validation_response.headers["content-type"] == "application/problem+json"
+    assert validation_response.json() == {
+        "type": "/problems/validation",
+        "title": "Validation Error",
+        "status": 422,
+        "detail": "Request validation failed.",
+        "instance": "/validate",
+    }
+    assert "private-invalid-input" not in validation_response.text