gemini gate: skip compiled tailwind.css when sizing the diff

ai/prreview/gate.go

@@ -253,6 +253,7 @@ func RunGate(ctx context.Context, cfg GateConfig) error {
 	if err != nil {
 		return fail("Gemini review failed: could not fetch diff", err)
 	}
+	diff = DropGeneratedFiles(diff)
 	if strings.TrimSpace(diff) == "" {
 		return fail("Gemini review inconclusive: empty diff", nil)
 	}

ai/prreview/prreview.go

@@ -230,6 +230,23 @@ func FetchFailingChecks(ctx context.Context, token, owner, repo, sha string) ([]
 	return failing, nil
 }
 
+// DropGeneratedFiles removes per-file sections for build output that is
+// regenerated from source (the compiled Tailwind stylesheets), so a one-line
+// minified file does not push a small change over the size limit.
+func DropGeneratedFiles(diff string) string {
+	var out strings.Builder
+	skip := false
+	for _, line := range strings.SplitAfter(diff, "\n") {
+		if strings.HasPrefix(line, "diff --git ") {
+			skip = strings.HasSuffix(strings.TrimSpace(line), "/tailwind.css")
+		}
+		if !skip {
+			out.WriteString(line)
+		}
+	}
+	return out.String()
+}
+
 // TruncateDiff caps diff at maxBytes so the Gemini request stays within the
 // model's input token budget. It reports whether truncation happened.
 func TruncateDiff(diff string, maxBytes int) (string, bool) {

ai/prreview/prreview_test.go

@@ -462,3 +462,12 @@ func TestPostCommentSuccess(t *testing.T) {
 		t.Fatalf("PostComment returned an unexpected error: %v", err)
 	}
 }
+
+func TestDropGeneratedFiles(t *testing.T) {
+	diff := "diff --git a/demo/tailwind.css b/demo/tailwind.css\n+minified\ndiff --git a/demo/index.html b/demo/index.html\n+<p>\n"
+	got := DropGeneratedFiles(diff)
+	want := "diff --git a/demo/index.html b/demo/index.html\n+<p>\n"
+	if got != want {
+		t.Fatalf("got %q, want %q", got, want)
+	}
+}