freeloader: fix 404 tool_unsupported detection and FIFO-drain recovery

- backend: add HTTP 404 and "no endpoints found" to isToolUnsupported
  so OpenRouter 404s are correctly classified as tool_unsupported
- core: drain FIFO on error return from executeTurn so freeloader's
  resubmitted prompt (queued via fifo.in while running) is picked up

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pkg/agent/core.go

@@ -987,6 +987,10 @@ func (s *agent) executeTurn(ctx context.Context, input string, handler EventHand
 			s.session.messages = snapMessages
 		}
 		handler(Event{Role: "error", Content: err.Error()})
+		// Drain one FIFO item — the turnError hook may have queued a recovery prompt.
+		if next, ok := s.fifo.Pop(); ok {
+			return next
+		}
 		return ""
 	}
 

pkg/backend/backend.go

@@ -159,7 +159,7 @@ func streamRequest(client *http.Client, req *http.Request, label string, parseFn
 		if resp.StatusCode == http.StatusBadRequest && isContextOverflow(msg) {
 			return nil, &ContextOverflowError{Message: fmt.Sprintf("%s HTTP %d: %s", label, resp.StatusCode, msg)}
 		}
-		if (resp.StatusCode == http.StatusBadRequest || resp.StatusCode == http.StatusUnprocessableEntity) && isToolUnsupported(msg) {
+		if (resp.StatusCode == http.StatusBadRequest || resp.StatusCode == http.StatusUnprocessableEntity || resp.StatusCode == http.StatusNotFound) && isToolUnsupported(msg) {
 			return nil, &ToolUnsupportedError{Message: fmt.Sprintf("%s HTTP %d: %s", label, resp.StatusCode, msg)}
 		}
 		return nil, fmt.Errorf("%s HTTP %d: %s", label, resp.StatusCode, msg)
@@ -184,6 +184,7 @@ func isToolUnsupported(body string) bool {
 		"does not support function",
 		"tool_use is not enabled",
 		"not support tool",
+		"no endpoints found that support tool",
 	}
 	lower := strings.ToLower(body)
 	for _, m := range markers {