core/cli: open config in $EDITOR with optional prompt

shlex-split EDITOR (e.g. codium --wait); prompt when no providers;
add config path/edit commands.

src/plyngent/cli/app.py

@@ -7,7 +7,11 @@ from typing import TYPE_CHECKING
 import click
 import msgspec
 
-from plyngent import config as config_mod
+from plyngent.cli.editor import (
+    load_config_with_optional_edit,
+    open_in_editor,
+    resolve_config_path,
+)
 from plyngent.cli.repl import run_repl
 from plyngent.cli.selection import select_model, select_provider
 from plyngent.cli.state import ReplState
@@ -21,7 +25,7 @@ if TYPE_CHECKING:
 
 
 def _load_config(config_path: Path | None) -> ConfigStore:
-    return config_mod.load(config_path)
+    return load_config_with_optional_edit(config_path)
 
 
 def _database_config(store: ConfigStore) -> DatabaseConfig:
@@ -137,5 +141,38 @@ def providers_cmd(config_path: Path | None) -> None:
         click.secho(f"bad: {', '.join(sorted(store.bad_providers.keys()))}", fg="yellow")
 
 
+@main.group("config")
+def config_group() -> None:
+    """Manage plyngent configuration."""
+
+
+@config_group.command("path")
+@click.option(
+    "--config",
+    "config_path",
+    type=click.Path(path_type=Path, dir_okay=False),
+    default=None,
+    help="Override config path (prints the path that would be used).",
+)
+def config_path_cmd(config_path: Path | None) -> None:
+    """Print the resolved config file path."""
+    click.echo(str(resolve_config_path(config_path)))
+
+
+@config_group.command("edit")
+@click.option(
+    "--config",
+    "config_path",
+    type=click.Path(path_type=Path, dir_okay=False),
+    default=None,
+    help="Path to plyngent.toml (default: platform config dir).",
+)
+def config_edit_cmd(config_path: Path | None) -> None:
+    """Open the config file in $EDITOR (supports e.g. ``codium --wait``)."""
+    path = resolve_config_path(config_path)
+    open_in_editor(path)
+    click.echo(f"edited {path}")
+
+
 if __name__ == "__main__":
     main()

src/plyngent/cli/editor.py

@@ -0,0 +1,107 @@
+from __future__ import annotations
+
+import os
+import shlex
+import subprocess
+from pathlib import Path
+from typing import TYPE_CHECKING
+
+import click
+
+from plyngent import config as config_mod
+
+if TYPE_CHECKING:
+    from plyngent.config.store import ConfigStore
+
+_MINIMAL_CONFIG = """\
+# plyngent configuration
+# edit providers below
+
+[database]
+implementation = "sqlite"
+url = ":memory:"
+
+# [providers.example]
+# preset = "openai-compatible"
+# url = "https://api.openai.com/v1"
+# access_key_or_token = "sk-..."
+#
+# [providers.example.models]
+# "gpt-4o-mini" = { text = true }
+"""
+
+
+def get_editor() -> str | None:
+    """Return the ``EDITOR`` environment value, or ``None`` if unset/empty."""
+    value = os.environ.get("EDITOR", "").strip()
+    return value or None
+
+
+def resolve_config_path(config_path: Path | None) -> Path:
+    """Resolve CLI ``--config`` or the platform default path."""
+    if config_path is not None:
+        return config_path
+    return Path(config_mod.default_config_source)
+
+
+def ensure_config_file(path: Path) -> None:
+    """Create parent dirs and a minimal template if the file does not exist."""
+    path.parent.mkdir(parents=True, exist_ok=True)
+    if not path.exists():
+        _ = path.write_text(_MINIMAL_CONFIG, encoding="utf-8")
+
+
+def open_in_editor(path: Path, *, editor: str | None = None) -> None:
+    """Open ``path`` with ``EDITOR`` (supports values like ``codium --wait``)."""
+    editor_cmd = editor if editor is not None else get_editor()
+    if editor_cmd is None:
+        msg = "EDITOR is not set"
+        raise click.ClickException(msg)
+
+    ensure_config_file(path)
+    try:
+        argv = [*shlex.split(editor_cmd, posix=os.name != "nt"), str(path)]
+    except ValueError as exc:
+        msg = f"invalid EDITOR value {editor_cmd!r}: {exc}"
+        raise click.ClickException(msg) from exc
+    if not argv:
+        msg = "EDITOR is empty after parsing"
+        raise click.ClickException(msg)
+
+    try:
+        completed = subprocess.run(argv, check=False)
+    except FileNotFoundError as exc:
+        msg = f"editor executable not found: {argv[0]}"
+        raise click.ClickException(msg) from exc
+    except OSError as exc:
+        msg = f"failed to run editor: {exc}"
+        raise click.ClickException(msg) from exc
+
+    if completed.returncode != 0:
+        msg = f"editor exited with status {completed.returncode}"
+        raise click.ClickException(msg)
+
+
+def prompt_edit_config(path: Path, *, reason: str | None = None) -> bool:
+    """If ``EDITOR`` is set, ask whether to edit ``path``. Returns True if opened."""
+    if get_editor() is None:
+        return False
+    message = f"{reason} Edit config file {path}?" if reason else f"Edit config file {path}?"
+    if not click.confirm(message, default=False):
+        return False
+    open_in_editor(path)
+    return True
+
+
+def load_config_with_optional_edit(config_path: Path | None) -> ConfigStore:
+    """Load config; if there are no providers and EDITOR is set, offer to edit and reload."""
+    path = resolve_config_path(config_path)
+    store = config_mod.load(path)
+    if store.providers:
+        return store
+    reason = "No providers configured."
+    if not path.exists():
+        reason = f"Config file not found ({path})."
+    if prompt_edit_config(path, reason=reason):
+        store = config_mod.load(path)
+    return store