fix(cli): exit non-zero when feedback submission is rejected (#1766)

## Bug

`mcpproxy feedback` exits 0 when the submission was not accepted.
`SubmitFeedback` returns `Success: false` without an error in two cases:
the backend answers 2xx with `{"success": false, "error": "..."}`, or it
answers a non-JSON 3xx. `runFeedback` prints "Feedback submission
failed: ..." (in text mode) and then returns `nil`. In `-o json` mode it
prints the JSON and also returns `nil`. Scripts and CI wrappers
therefore treat a rejected submission as sent.

## Trigger

With the telemetry endpoint returning `200
{"success":false,"error":"rejected by backend"}`:

```
$ mcpproxy feedback "the search results could be more relevant" --category bug
Feedback submission failed: rejected by backend
$ echo $?
0
```

## Fix

After rendering the output, return `feedback submission failed: <error>`
when `resp.Success` is false, so the exit code is non-zero in both text
and JSON modes. The text branch no longer prints its own failure line,
because cobra prints the returned error. The success path is unchanged.

## Test

`TestRunFeedback_RejectedSubmissionReturnsError` points the telemetry
endpoint at an `httptest` server that returns `{"success":false}`, and
asserts that `runFeedback` returns an error.

## Commands run

- `go vet ./cmd/mcpproxy`: clean
- `go test -count=1 ./cmd/mcpproxy`: ok (needs cgo; run with `SDKROOT`
set to the macOS 26.5 SDK locally)
- Without the fix, the new test fails with `runFeedback returned nil for
a submission the backend rejected`.
- `gofmt -l` on the edited files: no output

Author: rudycelekli

cmd/mcpproxy/feedback_cmd.go

@@ -91,11 +91,12 @@ func runFeedback(cmd *cobra.Command, args []string) error {
 			if resp.IssueURL != "" {
 				fmt.Printf("Track your feedback: %s\n", resp.IssueURL)
 			}
-		} else {
-			fmt.Printf("Feedback submission failed: %s\n", resp.Error)
 		}
 	}
 
+	if !resp.Success {
+		return fmt.Errorf("feedback submission failed: %s", resp.Error)
+	}
 	return nil
 }
 

cmd/mcpproxy/feedback_cmd_failure_test.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// A backend that answers 2xx with {"success":false} rejected the feedback;
+// the command must exit non-zero so scripts don't treat it as submitted.
+func TestRunFeedback_RejectedSubmissionReturnsError(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"success":false,"error":"rejected by backend"}`))
+	}))
+	defer srv.Close()
+
+	dir := t.TempDir()
+	cfgPath := filepath.Join(dir, "mcp_config.json")
+	cfgJSON := fmt.Sprintf(`{"data_dir": %q, "telemetry": {"endpoint": %q}}`, dir, srv.URL)
+	if err := os.WriteFile(cfgPath, []byte(cfgJSON), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	origConfig, origCategory := configFile, feedbackCategory
+	t.Cleanup(func() { configFile, feedbackCategory = origConfig, origCategory })
+	configFile, feedbackCategory = cfgPath, "bug"
+
+	if err := runFeedback(nil, []string{"the search results could be more relevant"}); err == nil {
+		t.Fatal("runFeedback returned nil for a submission the backend rejected")
+	}
+}