cli: start MCP servers around chat and add /mcp slash command

src/plyngent/cli/app.py

@@ -26,7 +26,7 @@ from plyngent.cli.state import ReplState
 from plyngent.config.models import DatabaseConfig
 from plyngent.memory import MemoryStore
 from plyngent.prompting import NonInteractiveBackend, configure_prompting
-from plyngent.runtime import ProviderNotSupportedError, create_client
+from plyngent.runtime import McpManager, ProviderNotSupportedError, create_client
 
 if TYPE_CHECKING:
     from collections.abc import Mapping
@@ -134,6 +134,24 @@ def _setup_hooks(*, interactive: bool) -> None:
         PtyManager.set_limit_continue_hook(None)
 
 
+async def _start_mcp_manager(store: ConfigStore) -> McpManager | None:
+    """Start configured MCP servers before the REPL state is built.
+
+    Returns ``None`` when nothing is enabled. Failures degrade to a warning
+    per server (the rest of the session, including LLM traffic, continues).
+    """
+    manager = McpManager(store.mcp_config)
+    if not manager.enabled_servers():
+        return None
+    await manager.ensure_started()
+    for name, status, count in manager.statuses():
+        if status.startswith("error"):
+            click.secho(f"warning: mcp server {name!r} failed: {status}", fg="yellow", err=True)
+        else:
+            click.secho(f"mcp: {name} ({status}, tools={count})", fg="bright_black", err=True)
+    return manager
+
+
 async def _bind_session(
     state: ReplState,
     *,
@@ -285,6 +303,7 @@ async def _run_chat(  # noqa: C901, PLR0912, PLR0915 — chat orchestration
         except ProviderNotSupportedError as exc:
             raise click.ClickException(str(exc)) from exc
 
+        mcp_manager = await _start_mcp_manager(store)
         state = ReplState(
             config=store,
             memory=memory,
@@ -297,6 +316,7 @@ async def _run_chat(  # noqa: C901, PLR0912, PLR0915 — chat orchestration
             stream_enabled=stream,
             interactive_limits=interactive,
             yolo=yolo,
+            mcp_manager=mcp_manager,
         )
         # Path denylist and policy confirm live on instance.workspace (no process bag).
         state.instance_state.workspace.path_denylist = tuple(store.agent_config.path_denylist or ())
@@ -353,6 +373,8 @@ async def _run_chat(  # noqa: C901, PLR0912, PLR0915 — chat orchestration
             set_fetch_policy_confirm_hook(None, instance=state_obj.instance_state)
             clear_private_grants(instance=state_obj.instance_state)
             clear_ssrf_assume_public_cidrs()
+            if state_obj.mcp_manager is not None:
+                await state_obj.mcp_manager.aclose()
             await state_obj.instance_state.shutdown()
         else:
             # No ReplState: only PTY class cleanup (temps require instance allowlist).

src/plyngent/cli/slash.py

@@ -1147,6 +1147,53 @@ def plugins_slash_cmd(state: ReplState, action: str | None, name: str | None) ->
         raise click.UsageError(str(exc)) from exc
 
 
+def _print_mcp_status(state: ReplState) -> None:
+    manager = state.mcp_manager
+    if manager is None:
+        click.echo("mcp: no servers configured (or none enabled)")
+        return
+    rows = manager.statuses()
+    if not rows:
+        click.echo("mcp: no servers configured (or none enabled)")
+        return
+    for name, status, count in rows:
+        click.echo(f"  {name}\t{status}\ttools={count}")
+        connection = next(
+            (conn for conn in manager.connections() if conn.name == name),
+            None,
+        )
+        if connection is not None and connection.error is not None:
+            for line in connection.stderr_tail()[-3:]:
+                click.secho(f"    {line}", fg="bright_black")
+
+
+@slash.command("mcp")
+@click.argument("action", required=False, type=click.Choice(["list", "reconnect"]))
+@click.pass_obj
+def mcp_slash_cmd(state: ReplState, action: str | None) -> None:
+    """List MCP server statuses, or reconnect after config edits.
+
+    ``/mcp`` or ``/mcp list`` — per-server connection status and tool count.
+    ``/mcp reconnect`` — re-read the config file, restart every enabled
+    server, and rebuild the tool registry (adopts newly added servers too).
+    """
+    act = (action or "list").lower()
+    if act == "list":
+        _print_mcp_status(state)
+        return
+    from plyngent.runtime import McpManager
+
+    state.config.reload()
+    if state.mcp_manager is None:
+        state.mcp_manager = McpManager(state.config.mcp_config)
+    else:
+        _await(state.mcp_manager.restart(state.config.mcp_config))
+    _await(state.mcp_manager.ensure_started())
+    _slash_rebuild_tools_if_on(state)
+    click.echo(f"mcp reconnected; tools={'on' if state.tools_enabled else 'off'}")
+    _print_mcp_status(state)
+
+
 @slash.command("yolo")
 @click.argument("mode", required=False, type=YOLO_MODE, metavar="[on|off|once]")
 @click.pass_obj

src/plyngent/cli/state.py

@@ -32,6 +32,7 @@ if TYPE_CHECKING:
     from plyngent.config.store import ConfigStore
     from plyngent.memory import MemoryStore
     from plyngent.memory.database.schema import Session as SessionRow
+    from plyngent.runtime.mcp_client import McpManager
 
 type YoloMode = Literal["off", "on", "once"]
 
@@ -65,6 +66,8 @@ class ReplState:
     todo_stack: TodoStack = field(default_factory=TodoStack)
     instance_state: InstanceState = field(default_factory=InstanceState)
     session_state: SessionState = field(default_factory=SessionState)
+    # MCP connections started by the host app before this state was built.
+    mcp_manager: McpManager | None = None
     _todo_persist_tasks: set[object] = field(default_factory=set, init=False, repr=False)
     # Session ids for Tab complete (updated when listing/creating/resuming).
     _session_id_cache: list[int] = field(default_factory=list, init=False, repr=False)
@@ -215,6 +218,11 @@ class ReplState:
             plugins_cfg.enable,
             disable=plugins_cfg.disable,
         )
+        if self.mcp_manager is not None:
+            from plyngent.tools.mcp import register_mcp_tools
+
+            # Connections were started by the host; registration is sync-only.
+            _ = register_mcp_tools(self.mcp_manager, self.config.mcp_config)
         # Local surface: builtins + allowlisted plugins (import registers into catalog).
         tools = catalog.select(surface="local")
         yolo = self.effective_yolo() != "off"

tests/test_cli/test_mcp_cmd.py

@@ -0,0 +1,122 @@
+"""CLI slash ``/mcp`` command and MCP wiring in ``ReplState``."""
+
+from __future__ import annotations
+
+import json
+import sys
+from pathlib import Path
+from typing import TYPE_CHECKING
+
+import pytest
+import tomlkit
+
+from plyngent.cli.slash import handle_slash
+from plyngent.cli.state import ReplState
+from plyngent.config.models import DatabaseConfig, McpConfig, McpServerConfig, OpenAIProvider
+from plyngent.config.store import ConfigStore
+from plyngent.memory import MemoryStore
+from plyngent.runtime.mcp_client import McpManager
+
+if TYPE_CHECKING:
+    from collections.abc import AsyncIterator
+
+_FAKE_SERVER = Path(__file__).parent.parent / "test_runtime" / "mcp_fake_server.py"
+
+
+def _server_config(**overrides: object) -> McpServerConfig:
+    base: dict[str, object] = {
+        "command": sys.executable,
+        "args": [str(_FAKE_SERVER)],
+        "timeout": 5.0,
+    }
+    return McpServerConfig(**{**base, **overrides})  # type: ignore[arg-type]
+
+
+@pytest.fixture
+async def state(tmp_path: Path) -> AsyncIterator[ReplState]:
+    memory = await MemoryStore.open(DatabaseConfig())
+    provider = OpenAIProvider(access_key_or_token="sk-test")
+    config = ConfigStore(path=tmp_path / "plyngent.toml", document=tomlkit.document())
+    config.providers = {"local": provider}
+    st = ReplState(
+        config=config,
+        memory=memory,
+        workspace=tmp_path,
+        provider_name="local",
+        provider=provider,
+        model="gpt-test",
+        tools_enabled=False,
+    )
+    await st.new_session("t")
+    yield st
+    await memory.close()
+
+
+async def test_slash_mcp_list_without_manager(state: ReplState, capsys: pytest.CaptureFixture[str]) -> None:
+    assert await handle_slash(state, "/mcp") is True
+    assert "no servers configured" in capsys.readouterr().out
+    assert await handle_slash(state, "/mcp list") is True
+    assert "no servers configured" in capsys.readouterr().out
+
+
+async def test_slash_mcp_list_statuses(state: ReplState, capsys: pytest.CaptureFixture[str]) -> None:
+    manager = McpManager(McpConfig(servers={"fake": _server_config()}, disable=[]))
+    await manager.ensure_started()
+    state.mcp_manager = manager
+    try:
+        assert await handle_slash(state, "/mcp list") is True
+        out = capsys.readouterr().out
+        assert "fake" in out
+        assert "connected" in out
+        assert "tools=3" in out
+    finally:
+        await manager.aclose()
+
+
+async def test_slash_mcp_reconnect_connects_new_config(
+    state: ReplState,
+    capsys: pytest.CaptureFixture[str],
+    tmp_path: Path,
+) -> None:
+    # The fixture's config file does not exist yet; write one with an MCP server.
+    payload = (
+        "[mcp.servers.fake]\n"
+        f"command = {json.dumps(sys.executable)}\n"
+        f"args = [{json.dumps(str(_FAKE_SERVER))}]\n"
+        "timeout = 5.0\n"
+    )
+    _ = (tmp_path / "plyngent.toml").write_text(payload, encoding="utf-8")
+    assert await handle_slash(state, "/mcp reconnect") is True
+    try:
+        assert state.mcp_manager is not None
+        statuses = state.mcp_manager.statuses()
+        assert [name for name, _, _ in statuses] == ["fake"]
+        assert statuses[0][1] == "connected"
+        assert statuses[0][2] == 3
+        out = capsys.readouterr().out
+        assert "tools=off" in out
+        assert "fake" in out
+    finally:
+        if state.mcp_manager is not None:
+            await state.mcp_manager.aclose()
+
+
+async def test_mcp_tools_registered_on_tools_rebuild(state: ReplState) -> None:
+    manager = McpManager(McpConfig(servers={"fake": _server_config()}, disable=[]))
+    await manager.ensure_started()
+    state.mcp_manager = manager
+    try:
+        from plyngent.tools.catalog import catalog_scope
+
+        state.tools_enabled = True
+        with catalog_scope(empty=True):
+            state.rebuild_client()
+        registry = state.agent.tools
+        assert registry is not None
+        assert registry.get("mcp__fake__echo") is not None
+        assert registry.get("mcp__fake__fail") is not None
+        # Handler proxies to the live server subprocess.
+        out = await registry.execute("mcp__fake__echo", '{"text": "hi"}')
+        assert out == "echo: hi"
+    finally:
+        await manager.aclose()