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feat(acp): register client-provided MCP servers as agent tools

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ACP clients pass MCP server definitions in session/new, load_session,
resume_session, and fork_session. Previously these were accepted but
silently ignored — the agent never connected to them.

This wires the mcp_servers parameter into the existing MCP registration
pipeline (tools/mcp_tool.py) so client-provided servers are connected,
their tools discovered, and the agent's tool surface refreshed before
the first prompt.

Changes:

tools/mcp_tool.py:
- Extract sanitize_mcp_name_component() to replace all non-[A-Za-z0-9_]
  characters (fixes crash when server names contain / or other chars
  that violate provider tool-name validation rules)
- Use it in _convert_mcp_schema, _sync_mcp_toolsets, _build_utility_schemas
- Extract register_mcp_servers(servers: dict) as a public API that takes
  an explicit {name: config} map. discover_mcp_tools() becomes a thin
  wrapper that loads config.yaml and calls register_mcp_servers()

acp_adapter/server.py:
- Add _register_session_mcp_servers() which converts ACP McpServerStdio /
  McpServerHttp / McpServerSse objects to Hermes MCP config dicts,
  registers them via asyncio.to_thread (avoids blocking the ACP event
  loop), then rebuilds agent.tools, valid_tool_names, and invalidates
  the cached system prompt
- Call it from new_session, load_session, resume_session, fork_session

Tested with Eden (theproxycompany.com) as ACP client — 5 MCP servers
(HTTP + stdio) registered successfully, 110 tools available to the agent.
This commit is contained in:
Jack
2026-04-01 16:35:34 -04:00
committed by Teknium
parent 29c98e8f83
commit 9b2fb1cc2e
2 changed files with 171 additions and 59 deletions
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157
tools/mcp_tool.py
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@@ -1406,6 +1406,17 @@ def _normalize_mcp_input_schema(schema: dict | None) -> dict:
return schema
def sanitize_mcp_name_component(value: str) -> str:
"""Return an MCP name component safe for tool and prefix generation.
Preserves Hermes's historical behavior of converting hyphens to
underscores, and also replaces any other character outside
``[A-Za-z0-9_]`` with ``_`` so generated tool names are compatible with
provider validation rules.
"""
return re.sub(r"[^A-Za-z0-9_]", "_", str(value or ""))
def _convert_mcp_schema(server_name: str, mcp_tool) -> dict:
"""Convert an MCP tool listing to the Hermes registry schema format.
@@ -1417,9 +1428,8 @@ def _convert_mcp_schema(server_name: str, mcp_tool) -> dict:
Returns:
A dict suitable for ``registry.register(schema=...)``.
"""
# Sanitize: replace hyphens and dots with underscores for LLM API compatibility
safe_tool_name = mcp_tool.name.replace("-", "_").replace(".", "_")
safe_server_name = server_name.replace("-", "_").replace(".", "_")
safe_tool_name = sanitize_mcp_name_component(mcp_tool.name)
safe_server_name = sanitize_mcp_name_component(server_name)
prefixed_name = f"mcp_{safe_server_name}_{safe_tool_name}"
return {
"name": prefixed_name,
@@ -1449,7 +1459,7 @@ def _sync_mcp_toolsets(server_names: Optional[List[str]] = None) -> None:
all_mcp_tools: List[str] = []
for server_name in server_names:
safe_prefix = f"mcp_{server_name.replace('-', '_').replace('.', '_')}_"
safe_prefix = f"mcp_{sanitize_mcp_name_component(server_name)}_"
server_tools = sorted(
t for t in existing if t.startswith(safe_prefix)
)
@@ -1485,7 +1495,7 @@ def _build_utility_schemas(server_name: str) -> List[dict]:
Returns a list of (schema, handler_factory_name) tuples encoded as dicts
with keys: schema, handler_key.
"""
safe_name = server_name.replace("-", "_").replace(".", "_")
safe_name = sanitize_mcp_name_component(server_name)
return [
{
"schema": {
@@ -1772,6 +1782,72 @@ async def _discover_and_register_server(name: str, config: dict) -> List[str]:
# Public API
# ---------------------------------------------------------------------------
def register_mcp_servers(servers: Dict[str, dict]) -> List[str]:
"""Connect to explicit MCP servers and register their tools.
Idempotent for already-connected server names. Servers with
``enabled: false`` are skipped without disconnecting existing sessions.
Args:
servers: Mapping of ``{server_name: server_config}``.
Returns:
List of all currently registered MCP tool names.
"""
if not _MCP_AVAILABLE:
logger.debug("MCP SDK not available -- skipping explicit MCP registration")
return []
if not servers:
logger.debug("No explicit MCP servers provided")
return []
# Only attempt servers that aren't already connected and are enabled
# (enabled: false skips the server entirely without removing its config)
with _lock:
new_servers = {
k: v
for k, v in servers.items()
if k not in _servers and _parse_boolish(v.get("enabled", True), default=True)
}
if not new_servers:
_sync_mcp_toolsets(list(servers.keys()))
return _existing_tool_names()
# Start the background event loop for MCP connections
_ensure_mcp_loop()
async def _discover_one(name: str, cfg: dict) -> List[str]:
"""Connect to a single server and return its registered tool names."""
return await _discover_and_register_server(name, cfg)
async def _discover_all():
server_names = list(new_servers.keys())
# Connect to all servers in PARALLEL
results = await asyncio.gather(
*(_discover_one(name, cfg) for name, cfg in new_servers.items()),
return_exceptions=True,
)
for name, result in zip(server_names, results):
if isinstance(result, Exception):
command = new_servers.get(name, {}).get("command")
logger.warning(
"Failed to connect to MCP server '%s'%s: %s",
name,
f" (command={command})" if command else "",
_format_connect_error(result),
)
# Per-server timeouts are handled inside _discover_and_register_server.
# The outer timeout is generous: 120s total for parallel discovery.
_run_on_mcp_loop(_discover_all(), timeout=120)
_sync_mcp_toolsets(list(servers.keys()))
return _existing_tool_names()
def discover_mcp_tools() -> List[str]:
"""Entry point: load config, connect to MCP servers, register tools.
@@ -1793,69 +1869,32 @@ def discover_mcp_tools() -> List[str]:
logger.debug("No MCP servers configured")
return []
# Only attempt servers that aren't already connected and are enabled
# (enabled: false skips the server entirely without removing its config)
with _lock:
new_servers = {
k: v
for k, v in servers.items()
if k not in _servers and _parse_boolish(v.get("enabled", True), default=True)
}
new_server_names = [
name
for name, cfg in servers.items()
if name not in _servers and _parse_boolish(cfg.get("enabled", True), default=True)
]
if not new_servers:
_sync_mcp_toolsets(list(servers.keys()))
return _existing_tool_names()
tool_names = register_mcp_servers(servers)
if not new_server_names:
return tool_names
# Start the background event loop for MCP connections
_ensure_mcp_loop()
all_tools: List[str] = []
failed_count = 0
async def _discover_one(name: str, cfg: dict) -> List[str]:
"""Connect to a single server and return its registered tool names."""
return await _discover_and_register_server(name, cfg)
async def _discover_all():
nonlocal failed_count
server_names = list(new_servers.keys())
# Connect to all servers in PARALLEL
results = await asyncio.gather(
*(_discover_one(name, cfg) for name, cfg in new_servers.items()),
return_exceptions=True,
with _lock:
connected_server_names = [name for name in new_server_names if name in _servers]
new_tool_count = sum(
len(getattr(_servers[name], "_registered_tool_names", []))
for name in connected_server_names
)
for name, result in zip(server_names, results):
if isinstance(result, Exception):
failed_count += 1
command = new_servers.get(name, {}).get("command")
logger.warning(
"Failed to connect to MCP server '%s'%s: %s",
name,
f" (command={command})" if command else "",
_format_connect_error(result),
)
elif isinstance(result, list):
all_tools.extend(result)
else:
failed_count += 1
# Per-server timeouts are handled inside _discover_and_register_server.
# The outer timeout is generous: 120s total for parallel discovery.
_run_on_mcp_loop(_discover_all(), timeout=120)
_sync_mcp_toolsets(list(servers.keys()))
# Print summary
total_servers = len(new_servers)
ok_servers = total_servers - failed_count
if all_tools or failed_count:
summary = f" MCP: {len(all_tools)} tool(s) from {ok_servers} server(s)"
failed_count = len(new_server_names) - len(connected_server_names)
if new_tool_count or failed_count:
summary = f" MCP: {new_tool_count} tool(s) from {len(connected_server_names)} server(s)"
if failed_count:
summary += f" ({failed_count} failed)"
logger.info(summary)
# Return ALL registered tools (existing + newly discovered)
return _existing_tool_names()
return tool_names
def get_mcp_status() -> List[dict]: