core/cli: config open via VISUAL/EDITOR or system default

Prefer $VISUAL then $EDITOR (blocking). Without either, fall back to
xdg-open / open / startfile (non-blocking) for config paths only.
/edit stays blocking-only so the temp buffer can be re-read.

tests/test_cli/test_editor.py

@@ -15,10 +15,13 @@ from plyngent.cli.editor import (
 )
 
 
-def test_get_editor(monkeypatch: pytest.MonkeyPatch) -> None:
+def test_get_editor_prefers_visual(monkeypatch: pytest.MonkeyPatch) -> None:
     monkeypatch.delenv("EDITOR", raising=False)
+    monkeypatch.delenv("VISUAL", raising=False)
     assert get_editor() is None
-    monkeypatch.setenv("EDITOR", "  codium --wait  ")
+    monkeypatch.setenv("EDITOR", "  nano  ")
+    assert get_editor() == "nano"
+    monkeypatch.setenv("VISUAL", "  codium --wait  ")
     assert get_editor() == "codium --wait"
 
 
@@ -49,7 +52,8 @@ def test_open_in_editor_splits_args(tmp_path: Path, monkeypatch: pytest.MonkeyPa
         return Result()
 
     monkeypatch.setattr("plyngent.cli.editor.subprocess.run", fake_run)
-    open_in_editor(path, editor="codium --wait")
+    outcome = open_in_editor(path, editor="codium --wait")
+    assert outcome == "waited"
     assert len(calls) == 1
     assert calls[0][0] == "codium"
     assert calls[0][1] == "--wait"
@@ -57,10 +61,33 @@ def test_open_in_editor_splits_args(tmp_path: Path, monkeypatch: pytest.MonkeyPa
     assert path.is_file()
 
 
-def test_open_in_editor_missing_editor(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
+def test_open_in_editor_system_fallback(
+    tmp_path: Path,
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
     monkeypatch.delenv("EDITOR", raising=False)
-    with pytest.raises(Exception, match="EDITOR"):
-        open_in_editor(tmp_path / "x.toml", editor=None)
+    monkeypatch.delenv("VISUAL", raising=False)
+    path = tmp_path / "x.toml"
+    opened: list[str] = []
+
+    def fake_system(p: Path) -> None:
+        opened.append(str(p))
+
+    monkeypatch.setattr("plyngent.cli.editor._open_with_system_default", fake_system)
+    outcome = open_in_editor(path, editor=None, allow_system_open=True)
+    assert outcome == "system"
+    assert opened == [str(path)]
+    assert path.is_file()
+
+
+def test_open_in_editor_no_fallback_requires_editor(
+    tmp_path: Path,
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    monkeypatch.delenv("EDITOR", raising=False)
+    monkeypatch.delenv("VISUAL", raising=False)
+    with pytest.raises(Exception, match=r"VISUAL|EDITOR"):
+        open_in_editor(tmp_path / "x.toml", editor=None, allow_system_open=False)
 
 
 def test_edit_text_in_editor(monkeypatch: pytest.MonkeyPatch) -> None:
@@ -99,9 +126,13 @@ def test_edit_text_empty_cancels(monkeypatch: pytest.MonkeyPatch) -> None:
     assert edit_text_in_editor("") is None
 
 
-def test_prompt_edit_no_editor(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
+def test_edit_text_no_system_fallback(monkeypatch: pytest.MonkeyPatch) -> None:
+    from plyngent.cli.editor import edit_text_in_editor
+
     monkeypatch.delenv("EDITOR", raising=False)
-    assert prompt_edit_config(tmp_path / "p.toml") is False
+    monkeypatch.delenv("VISUAL", raising=False)
+    with pytest.raises(Exception, match=r"VISUAL|EDITOR"):
+        edit_text_in_editor("x")
 
 
 def test_prompt_edit_declined(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
@@ -111,7 +142,7 @@ def test_prompt_edit_declined(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -
         return False
 
     monkeypatch.setattr("click.confirm", _confirm)
-    assert prompt_edit_config(tmp_path / "p.toml", reason="empty") is False
+    assert prompt_edit_config(tmp_path / "p.toml", reason="empty") is None
 
 
 def test_prompt_edit_accepted(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
@@ -124,15 +155,40 @@ def test_prompt_edit_accepted(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -
     monkeypatch.setattr("click.confirm", _confirm)
     opened: list[Path] = []
 
-    def fake_open(p: Path, *, editor: str | None = None) -> None:
-        del editor
+    def fake_open(
+        p: Path,
+        *,
+        editor: str | None = None,
+        ensure_exists: bool = True,
+        allow_system_open: bool = True,
+    ) -> str:
+        del editor, ensure_exists, allow_system_open
         opened.append(p)
+        return "waited"
 
     monkeypatch.setattr("plyngent.cli.editor.open_in_editor", fake_open)
-    assert prompt_edit_config(path, reason="No providers.") is True
+    assert prompt_edit_config(path, reason="No providers.") == "waited"
     assert opened == [path]
 
 
+def test_prompt_edit_without_editor_can_system_open(
+    tmp_path: Path,
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    monkeypatch.delenv("EDITOR", raising=False)
+    monkeypatch.delenv("VISUAL", raising=False)
+
+    def _confirm(*_a: object, **_k: object) -> bool:
+        return True
+
+    monkeypatch.setattr("click.confirm", _confirm)
+    monkeypatch.setattr(
+        "plyngent.cli.editor.open_in_editor",
+        lambda *a, **k: "system",
+    )
+    assert prompt_edit_config(tmp_path / "p.toml") == "system"
+
+
 def test_config_path_command(tmp_path: Path) -> None:
     runner = CliRunner()
     result = runner.invoke(main, ["config", "path", "--config", str(tmp_path / "a.toml")])
@@ -159,3 +215,21 @@ def test_config_edit_command(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) ->
     result = runner.invoke(main, ["config", "edit", "--config", str(path)])
     assert result.exit_code == 0
     assert calls and calls[0][-1] == str(path)
+    assert "edited" in result.output
+
+
+def test_config_edit_system_fallback_message(
+    tmp_path: Path,
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    path = tmp_path / "edit.toml"
+    monkeypatch.delenv("EDITOR", raising=False)
+    monkeypatch.delenv("VISUAL", raising=False)
+    monkeypatch.setattr(
+        "plyngent.cli.editor._open_with_system_default",
+        lambda p: None,
+    )
+    runner = CliRunner()
+    result = runner.invoke(main, ["config", "edit", "--config", str(path)])
+    assert result.exit_code == 0
+    assert "system default" in result.output.lower() or "system default" in (result.stderr or "").lower()