Emits structured `mcp.turn` log events on every Anthropic-path chat turn,
capturing whether MCP was wired in (mcp_available), whether the model
actually invoked an MCP tool (mcp_invoked), which tool names fired,
and whether the silent retry-without-MCP fallback was triggered.
Adds a separate `mcp.fallback` event with error type/message for
fallback occurrences.
Establishes baseline data for deciding whether MCP investment is earning
its keep before Phase 2+ expands the product footprint. Scope: the one
MCP-using code path (`_call_anthropic_cached`) — not a general
instrumentation layer.
No new dependencies, no schema changes, no behavior change. Standard
library `logging` is the sink; PostHog is not wired on the backend.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Michael Chihlas
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