Kyle Carberry
e388a88592
## Summary
Adds a new `coderd/chatd/mcpclient` package that connects to
admin-configured MCP servers and wraps their tools as
`fantasy.AgentTool` values that the chat loop can invoke.
## What changed
### New: `coderd/chatd/mcpclient/mcpclient.go`
The core package with a single entry point:
```go
func ConnectAll(
ctx context.Context,
logger slog.Logger,
configs []database.MCPServerConfig,
tokens []database.MCPServerUserToken,
) (tools []fantasy.AgentTool, cleanup func(), err error)
```
This:
1. Connects to each enabled MCP server using `mark3labs/mcp-go`
(streamable HTTP or SSE transport)
2. Discovers tools via the MCP `tools/list` method
3. Wraps each tool as a `fantasy.AgentTool` with namespaced name
(`serverslug__toolname`)
4. Applies tool allow/deny list filtering from the server config
5. Handles auth: OAuth2 bearer tokens, API keys, and custom headers
6. Skips broken servers with a warning (10s connect timeout per server)
7. Returns a cleanup function to close all MCP connections
### Modified: `coderd/chatd/chatd.go`
In `runChat()`, after loading the model/messages but before assembling
the tool list:
- Reads `chat.MCPServerIDs` from the chat record
- Loads the MCP server configs from the database
- Resolves the user's auth tokens
- Calls `mcpclient.ConnectAll()` to connect and discover tools
- Appends the MCP tools to the chat's tool set
- Defers cleanup to close connections when the chat turn ends
The chat loop (`chatloop.Run`) already handles tools generically —
MCP-backed tools are invoked identically to built-in workspace tools. No
changes needed in `chatloop/`.
### New: `coderd/chatd/mcpclient/mcpclient_test.go`
10 tests covering:
- Tool discovery and namespacing
- Tool call forwarding and result conversion
- Allow/deny list filtering
- Connection failure handling (graceful skip)
- Multi-server support with correct prefixes
- OAuth2 auth header injection
- Disabled server skipping
- Invalid input handling
- Tool info parameter propagation
## Design decisions
- **Tool namespacing**: `slug__toolname` with double underscore
separator. Avoids collisions with tools containing single underscores.
Stripped when forwarding to `tools/call`.
- **Connection lifecycle**: Fresh connections per chat turn, closed via
`defer`. Matches the `turnWorkspaceContext` pattern.
- **Failure isolation**: Each server connects independently. A broken
server doesn't fail the chat — its tools are simply unavailable.
- **No chatloop changes**: The existing `[]fantasy.AgentTool` interface
is already fully generic.
## What's NOT in this PR (follow-ups)
- Frontend MCP server picker UI (selecting servers for a chat)
- System prompt additions describing available MCP tools
- Token refresh on expiry mid-chat
- The deprecated `aibridged` MCP proxy cleanup
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