fix: pass non-unified-diff input through to stdout (closes #115)

cmd/input.go

@@ -0,0 +1,15 @@
+package cmd
+
+import "strings"
+
+// isUnifiedDiff reports whether the input looks like a git unified-diff stream
+// (the format the TUI is built to render).
+//
+// `git diff` and `git show` produce unified diffs that always contain at least
+// one `diff --git ` header line, regardless of which dialect of the diff
+// command was invoked. Summary forms (`--stat`, `--shortstat`, `--name-only`,
+// `--name-status`) and metadata-only commands (`git log` with no patch) emit
+// other shapes that the renderer cannot consume.
+func isUnifiedDiff(input string) bool {
+	return strings.Contains(input, "diff --git ")
+}

cmd/input_test.go

@@ -0,0 +1,82 @@
+package cmd
+
+import "testing"
+
+func TestIsUnifiedDiff(t *testing.T) {
+	cases := []struct {
+		name  string
+		input string
+		want  bool
+	}{
+		{
+			name: "git diff (unified)",
+			input: "diff --git a/foo.go b/foo.go\n" +
+				"index 1234567..89abcde 100644\n" +
+				"--- a/foo.go\n" +
+				"+++ b/foo.go\n" +
+				"@@ -1,3 +1,4 @@\n" +
+				" package foo\n" +
+				"+\n" +
+				" func A() {}\n",
+			want: true,
+		},
+		{
+			name: "git show (preamble + unified)",
+			input: "commit abc1234567890\n" +
+				"Author: Someone <s@example.com>\n" +
+				"Date:   Mon Jan 1 00:00:00 2026 +0000\n" +
+				"\n" +
+				"    subject\n" +
+				"\n" +
+				"diff --git a/foo.go b/foo.go\n" +
+				"@@ -1 +1,2 @@\n" +
+				" a\n+b\n",
+			want: true,
+		},
+		{
+			name: "git diff --stat",
+			input: " main.go | 5 ++---\n" +
+				" foo.go  | 1 +\n" +
+				" 2 files changed, 3 insertions(+), 3 deletions(-)\n",
+			want: false,
+		},
+		{
+			name:  "git diff --shortstat",
+			input: " 2 files changed, 3 insertions(+), 3 deletions(-)\n",
+			want:  false,
+		},
+		{
+			name:  "git diff --name-only",
+			input: "main.go\nfoo.go\n",
+			want:  false,
+		},
+		{
+			name:  "git diff --name-status",
+			input: "M\tmain.go\nA\tfoo.go\n",
+			want:  false,
+		},
+		{
+			name: "git log (no patch)",
+			input: "commit abc1234567890\n" +
+				"Author: Someone <s@example.com>\n" +
+				"Date:   Mon Jan 1 00:00:00 2026 +0000\n" +
+				"\n" +
+				"    subject\n",
+			want: false,
+		},
+		{
+			name:  "empty",
+			input: "",
+			want:  false,
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			got := isUnifiedDiff(tc.input)
+			if got != tc.want {
+				t.Fatalf("isUnifiedDiff(%q) = %v, want %v", tc.name, got, tc.want)
+			}
+		})
+	}
+}

cmd/root.go

@@ -202,6 +202,14 @@ func init() {
 				fmt.Println("No input provided, exiting")
 				os.Exit(0)
 			}
+
+			if !isUnifiedDiff(input) {
+				fmt.Print(input)
+				if !strings.HasSuffix(input, "\n") {
+					fmt.Println()
+				}
+				os.Exit(0)
+			}
 		}
 
 		cfg := config.Load()