63ef3b128c
Follow-up to commit 0a87dec5 (PR #2461, merged before live verification).
Two corrections to the docstring on `_build_initialize_result()`:
1. The original "mirrors molecule-mcp-claude-channel server.ts:374"
claim is wrong on two axes. Line 374 is unrelated poll-init code
(a comment inside `registerAsPoll`). The actual capability site
is server.ts:475, where the bun bridge declares only
`{ capabilities: { tools: {} } }` — *no* `experimental.claude/channel`.
The bun bridge is reported to deliver `notifications/claude/channel`
successfully in Claude Code despite this, which is direct counter-
evidence that adding the capability was the bug fix.
2. The `@modelcontextprotocol/sdk` server's `assertNotificationCapability`
does not include `notifications/claude/channel` in any of its switch
cases, meaning custom (non-spec) notification methods are sent
regardless of declared capabilities. Server-side, the declaration
is almost certainly a no-op.
This commit doesn't remove the capability — additive, not destructive,
and the new tests pin its presence — but downgrades the docstring's
certainty so the next person debugging "channel notification didn't
fire" doesn't trust a stale claim and pursues the more likely root
causes:
- writer.drain() swallowing exceptions on a closed pipe
- inbox-thread → asyncio.run_coroutine_threadsafe race during init
- MCP transport not yet attached when the first inbox event fires
Live verification per #2444 §2 (fresh Claude Code session on this wheel
with a peer A2A message, observe whether the interrupt fires) remains
the open hard-gate.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
343 lines
12 KiB
Python
343 lines
12 KiB
Python
#!/usr/bin/env python3
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"""A2A MCP Server — runs inside each workspace container.
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Exposes A2A delegation, peer discovery, and workspace info as MCP tools
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so CLI-based runtimes (Claude Code, Codex) can communicate with other workspaces.
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Launched automatically by main.py for CLI runtimes. Runs on stdio transport
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and is configured as a local MCP server for the claude --print invocation.
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Environment variables (set by the workspace container):
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WORKSPACE_ID — this workspace's ID
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PLATFORM_URL — platform API base URL (e.g. http://platform:8080)
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"""
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import asyncio
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import json
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import logging
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import sys
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# Top-level (not inside main()) so the wheel rewriter expands this to
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# `import molecule_runtime.inbox as inbox`. A local `import inbox as _x`
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# would expand to `import molecule_runtime.inbox as inbox as _x`,
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# which is invalid — see scripts/build_runtime_package.py:rewrite_imports.
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import inbox
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from a2a_tools import (
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tool_check_task_status,
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tool_commit_memory,
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tool_delegate_task,
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tool_delegate_task_async,
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tool_get_workspace_info,
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tool_inbox_peek,
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tool_inbox_pop,
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tool_list_peers,
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tool_recall_memory,
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tool_send_message_to_user,
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tool_wait_for_message,
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)
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from platform_tools.registry import TOOLS as _PLATFORM_TOOL_SPECS
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logger = logging.getLogger(__name__)
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# Re-export constants and client functions so existing imports
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# (e.g. tests that do `import a2a_mcp_server`) still work.
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from a2a_client import ( # noqa: F401, E402
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PLATFORM_URL,
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WORKSPACE_ID,
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_A2A_ERROR_PREFIX,
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_peer_names,
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discover_peer,
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get_peers,
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get_workspace_info,
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send_a2a_message,
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)
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from a2a_tools import report_activity # noqa: F401, E402
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# --- Tool definitions (schemas) ---
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#
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# Built once at import time from the platform_tools registry. The MCP
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# `description` field is the spec's `short` line — that's the unified
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# tool description used by both the MCP tool listing AND the bullet
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# rendering in the agent-facing system-prompt section. The deeper
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# `when_to_use` guidance is appended to the system prompt only (it's
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# too long to live in MCP `description` without bloating every
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# tool-list response the model sees).
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TOOLS = [
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{
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"name": _spec.name,
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"description": _spec.short,
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"inputSchema": _spec.input_schema,
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}
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for _spec in _PLATFORM_TOOL_SPECS
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]
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# --- Tool dispatch ---
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async def handle_tool_call(name: str, arguments: dict) -> str:
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"""Handle a tool call and return the result as text."""
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if name == "delegate_task":
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return await tool_delegate_task(
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arguments.get("workspace_id", ""),
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arguments.get("task", ""),
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)
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elif name == "delegate_task_async":
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return await tool_delegate_task_async(
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arguments.get("workspace_id", ""),
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arguments.get("task", ""),
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)
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elif name == "check_task_status":
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return await tool_check_task_status(
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arguments.get("workspace_id", ""),
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arguments.get("task_id", ""),
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)
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elif name == "send_message_to_user":
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raw_attachments = arguments.get("attachments")
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attachments: list[str] | None = None
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if isinstance(raw_attachments, list):
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# Defensive: filter to strings only — claude-code SDK occasionally
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# emits dicts here when the model misreads the schema. Drop the
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# bad entries rather than 500 the whole call.
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attachments = [p for p in raw_attachments if isinstance(p, str) and p]
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return await tool_send_message_to_user(
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arguments.get("message", ""),
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attachments=attachments,
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)
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elif name == "list_peers":
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return await tool_list_peers()
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elif name == "get_workspace_info":
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return await tool_get_workspace_info()
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elif name == "commit_memory":
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return await tool_commit_memory(
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arguments.get("content", ""),
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arguments.get("scope", "LOCAL"),
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)
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elif name == "recall_memory":
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return await tool_recall_memory(
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arguments.get("query", ""),
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arguments.get("scope", ""),
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)
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elif name == "wait_for_message":
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return await tool_wait_for_message(
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arguments.get("timeout_secs", 60.0),
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)
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elif name == "inbox_peek":
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return await tool_inbox_peek(
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arguments.get("limit", 10),
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)
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elif name == "inbox_pop":
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return await tool_inbox_pop(
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arguments.get("activity_id", ""),
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)
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return f"Unknown tool: {name}"
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# --- MCP Notification bridge ---
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# `notifications/claude/channel` matches the contract used by the
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# molecule-mcp-claude-channel bun bridge (server.ts:509). Claude Code's
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# MCP runtime treats this method as a conversation interrupt — `content`
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# becomes the agent turn, `meta` is structured metadata. Notification-
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# capable hosts (Claude Code today; any compliant client tomorrow)
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# get push UX automatically; pollers (`wait_for_message` / `inbox_peek`)
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# still work unchanged. See task #46 + the deprecation path documented
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# in workspace/inbox.py:set_notification_callback.
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_CHANNEL_NOTIFICATION_METHOD = "notifications/claude/channel"
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def _build_initialize_result() -> dict:
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"""MCP initialize handshake result.
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Declares ``experimental.claude/channel`` as a *hypothesized*
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contract for routing ``notifications/claude/channel`` emissions
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into Claude Code as conversation interrupts (push UX). The
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failure mode from molecule-core#2444 §2 — "notification arrives
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over the wire but is silently dropped instead of becoming a
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``<channel>`` tag" — motivated this declaration.
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UNVERIFIED: end-to-end push delivery has not been confirmed since
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this capability was added. Counter-evidence: the
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molecule-mcp-claude-channel bun bridge declares only
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``{ capabilities: { tools: {} } }`` (server.ts:475 — NOT line 374
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as the original commit message claimed; line 374 is unrelated
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poll-init code) and is reported to deliver
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``notifications/claude/channel`` successfully in Claude Code.
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The MCP SDK's ``assertNotificationCapability`` also does not gate
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custom (non-spec) notification methods on a declared capability,
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so server-side this declaration is likely a no-op. If push UX is
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still missing after this ships, the real fault probably lives
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in writer.drain swallowing on closed pipes, the inbox-thread →
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asyncio loop bridge, or initialize-ordering between the inbox
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callback and the MCP transport — not in this handshake. Treat
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this as belt-and-braces until verified.
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"""
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return {
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"protocolVersion": "2024-11-05",
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"capabilities": {
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"tools": {"listChanged": False},
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"experimental": {"claude/channel": {}},
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},
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"serverInfo": {"name": "a2a-delegation", "version": "1.0.0"},
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}
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def _build_channel_notification(msg: dict) -> dict:
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"""Transform an ``InboxMessage.to_dict()`` into the MCP notification
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envelope expected by Claude Code's channel-bridge contract.
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Pure function so the wire shape is unit-testable without spinning
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up an asyncio loop. The wire-up in ``main()`` just composes this
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with ``asyncio.run_coroutine_threadsafe``.
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"""
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return {
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"jsonrpc": "2.0",
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"method": _CHANNEL_NOTIFICATION_METHOD,
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"params": {
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"content": msg.get("text", ""),
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"meta": {
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"source": "molecule",
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"kind": msg.get("kind", ""),
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"peer_id": msg.get("peer_id", ""),
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"method": msg.get("method", ""),
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"activity_id": msg.get("activity_id", ""),
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"ts": msg.get("created_at", ""),
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},
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},
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}
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# --- MCP Server (JSON-RPC over stdio) ---
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async def main(): # pragma: no cover
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"""Run MCP server on stdio — reads JSON-RPC requests, writes responses."""
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reader = asyncio.StreamReader()
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protocol = asyncio.StreamReaderProtocol(reader)
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await asyncio.get_event_loop().connect_read_pipe(lambda: protocol, sys.stdin)
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writer_transport, writer_protocol = await asyncio.get_event_loop().connect_write_pipe(
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asyncio.streams.FlowControlMixin, sys.stdout
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)
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writer = asyncio.StreamWriter(writer_transport, writer_protocol, None, asyncio.get_event_loop())
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async def write_response(response: dict):
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data = json.dumps(response) + "\n"
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writer.write(data.encode())
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await writer.drain()
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# Wire the inbox → MCP notification bridge. Inbox poller (daemon
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# thread) calls into here when a new activity row lands; we
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# schedule the notification onto the asyncio loop and best-effort
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# fire it on the same stdout the responses go to.
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loop = asyncio.get_running_loop()
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async def _emit_notification(payload: dict) -> None:
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data = json.dumps(payload) + "\n"
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writer.write(data.encode())
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try:
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await writer.drain()
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except Exception: # noqa: BLE001
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# Closed pipe (host disconnected) shouldn't crash the
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# inbox poller; let it sit until the host reconnects.
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pass
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def _on_inbox_message(msg: dict) -> None:
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try:
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asyncio.run_coroutine_threadsafe(
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_emit_notification(_build_channel_notification(msg)),
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loop,
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)
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except RuntimeError:
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# Loop closed during shutdown — best-effort, swallow.
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pass
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inbox.set_notification_callback(_on_inbox_message)
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buffer = ""
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while True:
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try:
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chunk = await reader.read(65536)
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if not chunk:
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break
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buffer += chunk.decode(errors="replace")
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while "\n" in buffer:
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line, buffer = buffer.split("\n", 1)
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line = line.strip()
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if not line:
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continue
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try:
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request = json.loads(line)
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except json.JSONDecodeError:
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continue
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req_id = request.get("id")
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method = request.get("method", "")
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if method == "initialize":
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await write_response({
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"jsonrpc": "2.0",
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"id": req_id,
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"result": _build_initialize_result(),
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})
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elif method == "notifications/initialized":
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pass # No response needed
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elif method == "tools/list":
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await write_response({
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"jsonrpc": "2.0",
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"id": req_id,
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"result": {"tools": TOOLS},
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})
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elif method == "tools/call":
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params = request.get("params", {})
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tool_name = params.get("name", "")
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tool_args = params.get("arguments", {})
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result_text = await handle_tool_call(tool_name, tool_args)
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await write_response({
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"jsonrpc": "2.0",
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"id": req_id,
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"result": {
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"content": [{"type": "text", "text": result_text}],
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},
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})
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else:
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await write_response({
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"jsonrpc": "2.0",
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"id": req_id,
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"error": {"code": -32601, "message": f"Method not found: {method}"},
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})
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except Exception as e:
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logger.error(f"MCP server error: {e}")
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break
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def cli_main() -> None: # pragma: no cover
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"""Synchronous wrapper around the async MCP stdio loop.
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Called by ``mcp_cli.main`` (the ``molecule-mcp`` console-script
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entry point in scripts/build_runtime_package.py) AFTER env
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validation and the standalone register + heartbeat thread setup.
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Direct callers (in-container code that already validated env and
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runs heartbeat.py separately) can also invoke this — it's the
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smallest possible "run the MCP stdio JSON-RPC loop" surface.
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Wheel-smoke gates in scripts/wheel_smoke.py pin the importability
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of this name (alongside ``mcp_cli.main``) so a silent rename can't
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break every external-runtime operator's MCP install — the 0.1.16
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``main_sync`` rename incident is the cautionary precedent.
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"""
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asyncio.run(main())
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if __name__ == "__main__": # pragma: no cover
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cli_main()
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