environmentd: add Prometheus metrics for MCP endpoints DEX-2#36535
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environmentd: add Prometheus metrics for MCP endpoints DEX-2#36535jubrad wants to merge 1 commit into
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Adds a `McpMetrics` struct tracking five time series at the JSON-RPC
protocol layer, complementing the existing HTTP-level `PrometheusLayer`
metrics:
- `mcp_requests_total{endpoint, method, status}` — per JSON-RPC method
(initialize / tools/list / tools/call) and outcome
- `mcp_tool_calls_total{endpoint, tool, status}` — per tool and outcome
- `mcp_tool_duration_seconds{endpoint, tool}` — tool execution latency
histogram
- `mcp_errors_total{endpoint, error_type}` — error breakdown by type
(ValidationError, ExecutionError, ResponseSizeExceeded, etc.)
- `mcp_timeouts_total{endpoint}` — requests that hit the 60 s timeout
The timeout arm now increments `requests_total` and `errors_total`
immediately (not delayed until the background task finishes) by
capturing the method name before the spawn.
Also replaces the inline `QueryExecutionFailed` string in
`format_rows_response` with a dedicated `ResponseSizeExceeded` error
variant so size-limit hits are distinguishable in `errors_total`.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
jubrad
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Summary
Adds a
McpMetricsstruct that tracks MCP traffic at the JSON-RPC protocol layer, complementing the existing HTTP-levelPrometheusLayermetrics (which already expose request counts/durations keyed on/api/mcp/agentand/api/mcp/developerpaths).Five new time series, all labelled by
endpoint(agentordeveloper):mcp_requests_totalendpoint,method,statusmcp_tool_calls_totalendpoint,tool,statusmcp_tool_duration_secondsendpoint,toolmcp_errors_totalendpoint,error_typemcp_timeouts_totalendpointTimeout counting — the timeout arm now increments
requests_totalanderrors_totalimmediately by capturingmethod_namebeforerequestis moved into the spawned task. Previously, those counters would only be updated when the background task eventually finished, which could lag by up to 60 s during timeout storms.ResponseSizeExceedederror variant — replaces the inlineQueryExecutionFailedstring informat_rows_responsewith a dedicated variant so size-limit hits appear aserror_type="ResponseSizeExceeded"inmcp_errors_totalrather than"ExecutionError".Tests
test_mcp_error_codesto assert thatResponseSizeExceededmaps toINTERNAL_ERRORerror code and"ResponseSizeExceeded"error type string.test_format_rows_response_errors_when_over_limitcontinues to pass unchanged (the error message text is preserved by the new variant's#[error]attribute).