Backend: Domain-Modell + Interface (ExecutionFeed.cs, IExecutionFeedService.cs)

Implementation steps

• 1.Inspect src/persistence/repository/task/execution_feed_repository.py to confirm how FeedFilter is defined (likely dataclass or Pydantic model), whether it already has any validation hooks, and whether repository logic depends on mutually combinable amount fields today.
• 2.Inspect src/agent_runtime/api/route/execution_feed.py end-to-end to verify how FeedFilter is instantiated, whether FastAPI exceptions are already raised manually anywhere in this route, and whether there is an existing helper pattern for 422 validation errors that should be reused.
• 3.Inspect tests/unit/agent_runtime/api/test_execution_feed.py for current conventions around asserting 422 responses and for any nearby amount-filter passthrough tests that should be extended rather than creating a new test module.
• 4.Add a narrow validation rule for amount filters: betrag_equal may not be combined with betrag_above and may not be combined with betrag_below. Preserve currently valid combinations such as betrag_above with betrag_below unless code inspection reveals an existing broader conflict rule.
• 5.Thread the validation through the shared FeedFilter layer so the invariant exists below the route boundary as requested by the work packet. Prefer the smallest native mechanism already used by FeedFilter (for example model validator, __post_init__, factory/helper, or explicit validate() method) rather than introducing a new abstraction.
• 6.Ensure ExecutionFeedService also enforces or invokes the shared FeedFilter validation before repository access, so the business rule is not only an HTTP concern. Reuse the same validation source rather than duplicating rule text in multiple places.
• 7.Map validation failures at the API route to HTTP 422. If FeedFilter/service validation raises a domain or value error, translate it in src/agent_runtime/api/route/execution_feed.py into FastAPI’s expected 422 behavior using the project’s existing error handling style. Avoid changing unrelated response formats unless tests show a standardized structure is required.
• 8.Keep repository-facing behavior unchanged for valid filters; the repository should continue to receive FeedFilter with amount fields intact when combinations are allowed, and it should never be called for rejected conflicting combinations when exercised through the route/service path.
• 9.Add focused API unit tests in tests/unit/agent_runtime/api/test_execution_feed.py covering at least: betrag_equal + betrag_above returns 422, betrag_equal + betrag_below returns 422, and a valid amount-filter request still succeeds and passes expected values through to the service.
• 10.If the codebase already has service-level unit tests for ExecutionFeedService or direct FeedFilter tests, add one small validation test there instead of broad new coverage. If none exist, keep the mandatory test investment in the API unit test file only to minimize surface area.