Splits the standalone molecule-mcp wrapper into three single-concern
modules per the OSS-shape refactor program:
* mcp_heartbeat.py — register POST + heartbeat loop + auth-failure
escalation + inbound-secret persistence
* mcp_workspace_resolver.py — single + multi-workspace env validation
+ on-disk token-file read + operator-help printer
* mcp_inbox_pollers.py — activate inbox singleton + spawn one daemon
poller per workspace
mcp_cli.py becomes a 193-LOC orchestrator: validates env, calls each
module's helpers, hands off to a2a_mcp_server.cli_main. The console-
script entry molecule-mcp = molecule_runtime.mcp_cli:main is preserved.
Back-compat aliases (mcp_cli._build_agent_card, _heartbeat_loop,
_resolve_workspaces, etc.) re-export the new modules' authoritative
functions so existing tests + wheel_smoke.py + any downstream caller
keeps working unchanged. A new test file pins each alias as the
exact same callable (drift gate via `is`).
Tests:
* 62 existing test_mcp_cli.py + test_mcp_cli_multi_workspace.py
pass against the split.
* Two heartbeat-loop persist tests + the auth-escalation caplog
setup updated to target mcp_heartbeat (the module where the loop
body now lives) instead of mcp_cli (still works through aliases
for direct calls, but Python's name resolution inside the loop
body uses the new module's namespace).
* test_mcp_cli_split.py adds 11 new tests: alias drift gate +
inbox-poller single + multi-workspace branches + degraded
inbox-import logging path (none of those existed before).
Refs RFC #2873.
