fix(code): route explicit --stdin + --skill to headless path (#4611)

`dcode --skill ... --stdin` with piped input now runs headless instead
of launching the interactive TUI.

---

When a user explicitly passes `--stdin` together with `--skill`, `dcode`
previously routed the piped text into the interactive TUI seed
(`initial_prompt`), which hangs/fails on non-TTY environments.
`apply_stdin_pipe` now skips the skill→interactive convenience when
`--stdin` is explicit, falling through to the headless
`non_interactive_message` path (which already supports `--skill`).
Auto-detected pipes (no `--stdin`) keep the interactive seeding
behavior.

Made by [Open
SWE](https://openswe.vercel.app/agents/057272c4-7946-e220-f7b8-ea929d2fe9ce)

---------

Co-authored-by: open-swe[bot] <open-swe@users.noreply.github.com>

libs/code/deepagents_code/main.py

@@ -2305,15 +2305,25 @@ def apply_stdin_pipe(args: argparse.Namespace) -> None:
         # initial_prompt = "{contents of error.log}\n\nexplain this"
         ```
 
-    - If `initial_skill` is already set (`--skill`, but not `-n`), stores the
-        piped text in `initial_prompt` so the skill receives it as the
-        startup request:
+    - If `initial_skill` is already set (`--skill`, but not `-n`/`-m`) and the
+        pipe was auto-detected (no explicit `--stdin`), stores the piped text in
+        `initial_prompt` so the skill receives it as the seed for the
+        interactive TUI:
 
         ```bash
         cat diff.txt | dcode --skill code-review
         # initial_prompt = "{contents of diff.txt}"
         ```
 
+        When `--stdin` is passed explicitly, this convenience is skipped: the
+        piped text falls through to `non_interactive_message` so the skill runs
+        headless (see below):
+
+        ```bash
+        cat diff.txt | dcode --skill code-review --stdin
+        # non_interactive_message = "{contents of diff.txt}"
+        ```
+
     - Otherwise, sets `non_interactive_message` to the piped text, causing
         the CLI to run non-interactively with it as the prompt:
 
@@ -2389,12 +2399,20 @@ def apply_stdin_pipe(args: argparse.Namespace) -> None:
     if not stdin_text:
         return
 
-    # Priority: -n message > -m prompt > --skill (no -m) > fallback to -n.
+    # Priority: -n message > -m prompt > --skill (no -m, no explicit --stdin)
+    # > fallback to -n.
     # The initial_prompt branch uses `is not None` (not truthiness) so that
     # `-m ""` is distinguished from "no -m at all", allowing stdin to land
     # in initial_prompt even when the explicit value is empty.  The --skill
     # branch only fires when -m was NOT provided; when both -m and --skill
     # are set, stdin merges with the -m value (previous branch).
+    #
+    # The --skill -> interactive `initial_prompt` routing applies only to
+    # auto-detected pipes (no explicit `--stdin`), where seeding an interactive
+    # TUI is a deliberate convenience.  When the user passes `--stdin`
+    # explicitly, that signals non-interactive intent, so we skip this branch
+    # and fall through to `non_interactive_message` (headless), which also
+    # supports `--skill`.
     if args.non_interactive_message:
         args.non_interactive_message = f"{stdin_text}\n\n{args.non_interactive_message}"
     elif args.initial_prompt is not None:
@@ -2402,7 +2420,7 @@ def apply_stdin_pipe(args: argparse.Namespace) -> None:
             args.initial_prompt = f"{stdin_text}\n\n{args.initial_prompt}"
         else:
             args.initial_prompt = stdin_text
-    elif getattr(args, "initial_skill", None):
+    elif getattr(args, "initial_skill", None) and not explicit_stdin:
         args.initial_prompt = stdin_text
     else:
         args.non_interactive_message = stdin_text

libs/code/tests/unit_tests/test_main_args.py

@@ -612,6 +612,46 @@ class TestSkillFlagValidation:
             cli_main()
         assert exc_info.value.code == 2
 
+    def test_skill_with_explicit_stdin_and_quiet_runs_headless(self) -> None:
+        """`--skill --stdin -q` clears the guard and forwards the skill headless.
+
+        Explicit `--stdin` routes the piped text to `non_interactive_message`
+        (not the interactive `-m` seed), which satisfies the `--skill` +
+        `--quiet` guard and reaches `run_non_interactive` with both the piped
+        message and `initial_skill`.
+        """
+        from deepagents_code.main import cli_main
+
+        mock_stdin = MagicMock()
+        mock_stdin.isatty.return_value = False
+        mock_stdin.read.return_value = "review this repo"
+        with (
+            patch.object(
+                sys,
+                "argv",
+                ["deepagents", "--skill", "code-review", "--stdin", "-q"],
+            ),
+            patch.object(sys, "stdin", mock_stdin),
+            patch("deepagents_code.main.check_optional_tools", return_value=[]),
+            patch(
+                "deepagents_code.main._should_ensure_managed_ripgrep",
+                return_value=False,
+            ),
+            # Skip the /dev/tty dance — os.open would fail in test sandboxes
+            # and the real code path already tolerates that failure.
+            patch("os.open", side_effect=OSError("No tty in test sandbox")),
+            patch(
+                "deepagents_code.client.non_interactive.run_non_interactive",
+                new_callable=AsyncMock,
+                return_value=0,
+            ) as mock_run,
+            pytest.raises(SystemExit) as exc_info,
+        ):
+            cli_main()
+        assert exc_info.value.code == 0
+        assert mock_run.await_args.kwargs["initial_skill"] == "code-review"  # ty: ignore
+        assert mock_run.await_args.kwargs["message"] == "review this repo"  # ty: ignore
+
 
 class TestMaxTurnsArgument:
     """Tests for --max-turns argument parsing and validation."""
@@ -1183,6 +1223,46 @@ class TestApplyStdinPipe:
         assert args.initial_prompt == "diff contents\n\nreview this"
         assert args.non_interactive_message is None
 
+    def test_explicit_stdin_with_skill_runs_headless(self) -> None:
+        """Explicit `--stdin` + `--skill` runs headless, not the seeded TUI."""
+        args = _make_args(initial_skill="code-review", stdin=True)
+        fake_stdin = io.StringIO("review this repo")
+        fake_stdin.isatty = lambda: False  # ty: ignore
+        with patch.object(sys, "stdin", fake_stdin):
+            apply_stdin_pipe(args)
+        assert args.non_interactive_message == "review this repo"
+        assert args.initial_prompt is None
+
+    def test_explicit_stdin_without_skill_sets_non_interactive(self) -> None:
+        """Explicit `--stdin` with no skill/`-n`/`-m` sets non_interactive_message."""
+        args = _make_args(stdin=True)
+        fake_stdin = io.StringIO("my prompt")
+        fake_stdin.isatty = lambda: False  # ty: ignore
+        with patch.object(sys, "stdin", fake_stdin):
+            apply_stdin_pipe(args)
+        assert args.non_interactive_message == "my prompt"
+        assert args.initial_prompt is None
+
+    def test_explicit_stdin_prepends_to_non_interactive(self) -> None:
+        """Explicit `--stdin` still prepends to an existing -n message."""
+        args = _make_args(non_interactive_message="do something", stdin=True)
+        fake_stdin = io.StringIO("context from pipe")
+        fake_stdin.isatty = lambda: False  # ty: ignore
+        with patch.object(sys, "stdin", fake_stdin):
+            apply_stdin_pipe(args)
+        assert args.non_interactive_message == "context from pipe\n\ndo something"
+        assert args.initial_prompt is None
+
+    def test_explicit_stdin_prepends_to_initial_prompt(self) -> None:
+        """Explicit `--stdin` still merges into an existing -m message."""
+        args = _make_args(initial_prompt="explain this", stdin=True)
+        fake_stdin = io.StringIO("error log contents")
+        fake_stdin.isatty = lambda: False  # ty: ignore
+        with patch.object(sys, "stdin", fake_stdin):
+            apply_stdin_pipe(args)
+        assert args.initial_prompt == "error log contents\n\nexplain this"
+        assert args.non_interactive_message is None
+
     def test_non_interactive_takes_priority_over_initial_prompt(self) -> None:
         """When both -n and -m are set, stdin is prepended to -n."""
         args = _make_args(non_interactive_message="task", initial_prompt="ignored")