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[bot] Anthropic MCP connector tool calls (mcp_tool_use/mcp_tool_result) produce broken, input-less child spans

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Valutazione

Difficoltà
2/5
Tempo stimato
1-3 ore
Idoneità per principianti
82/100
Tipo di issue
Bug
Chiarezza
Specificata chiaramente
Stato di attività
Attiva
Stack tecnologico
java
Ambito
observability

Direzione di ricerca

Inizia in InstrumentationSemConv.addAnthropicServerSideChildSpans in braintrust-sdk/src/main/java/dev/braintrust/instrumentation/InstrumentationSemConv.java, dove i blocchi vengono dispatchati tramite type; leggi anche ANTHROPIC_SERVER_TOOL_USE_TYPE, isAnthropicToolResultType e i fallback call == null. Registra mcp_tool_use come tipo di chiamata in modo che la corrispondenza dei risultati basata sul suffisso esistente lo abbini a mcp_tool_result. Rispecchia la copertura esistente di server_tool_use in BraintrustAnthropicServerSideSpansTest.java ed esegui quella classe di test; fatto significa che lo span figlio MCP porta il nome reale dello strumento e input_json.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

bug java

Summary

InstrumentationSemConv.addAnthropicServerSideChildSpans dispatches Anthropic Messages response content blocks by checking each block's "type" against the literal string "server_tool_use" (see ANTHROPIC_SERVER_TOOL_USE_TYPE and the dispatch check). Anthropic's MCP connector feature emits a different, distinct pair of block types for server-executed MCP tool calls: "mcp_tool_use" (the call) and "mcp_tool_result" (the result). "mcp_tool_use" does not match the "server_tool_use" check, so it is never registered in the call-tracking map used to pair calls with results.

Meanwhile "mcp_tool_result" does match the result-type check, which is a suffix check (type.endsWith("_tool_result") && !type.equals("tool_result")). So the result proceeds through the pairing logic, never finds its matching call, and is emitted alone with call == null.

Consequence for every MCP connector tool invocation:

  • The child span is named generically "mcp_tool" (derived by stripping "_tool_result" off the result's type) instead of the real tool name, because the fallback naming path only runs when call == null.
  • input_json is never set on the span, because the input-extraction path also returns null when call == null. The tool's name, server_name, and input arguments — which live only in the dropped mcp_tool_use block — are permanently lost from the structured child span.

The raw response body is still present in the parent LLM span's full JSON passthrough, so the data isn't gone from Braintrust entirely, but the per-tool-call child span that Braintrust's UI specifically surfaces for tool calls is broken for every MCP connector invocation — call name and input are unrecoverable from that span.

Braintrust docs status: supported

Braintrust's docs at https://www.braintrust.dev/docs/integrations/ai-providers/anthropic describe this capability for the Python SDK: tool calls (including MCP connector tool calls) are captured "with its input and result ... named after the tool" as dedicated spans. This confirms the capability is documented/expected, just not delivered correctly by the Java SDK.

Why this isn't speculative

The identical bug (same mechanism: literal match on "server_tool_use", suffix-based result matching that doesn't require a paired call) was already found and fixed in Braintrust's Python SDK — see braintrustdata/braintrust-sdk-python#797 (fixed in py-sdk-v0.44.1) — and is tracked as still-open for the Go SDK in braintrustdata/braintrust-sdk-go#107. The fix was never ported to the Java SDK.

Upstream sources

Local repo files inspected

  • braintrust-sdk/src/main/java/dev/braintrust/instrumentation/InstrumentationSemConv.java — ANTHROPIC_SERVER_TOOL_USE_TYPE constant and dispatch check; addAnthropicServerSideChildSpans (call registration loop); isAnthropicToolResultType (suffix-based result matching); emitAnthropicServerToolSpan, anthropicToolSpanName, anthropicToolSpanInput (fallback behavior when call == null).
  • braintrust-sdk/instrumentation/anthropic_2_2_0/src/test/java/dev/braintrust/instrumentation/anthropic/v2_2_0/BraintrustAnthropicServerSideSpansTest.java — only exercises web_search/server_tool_use; no mcp_tool_use/mcp_tool_result test coverage exists.
  • Repo-wide search for mcp_tool_use / mcp_tool_result / "MCP connector" — zero matches outside this finding.

Suggested fix

Recognize "mcp_tool_use" as an additional call-type alongside "server_tool_use" when populating the call-tracking map (the existing suffix-based result matching already handles "mcp_tool_result" correctly once a matching call is registered), and add a test mirroring the existing server_tool_use test for the MCP connector block pair.

Lingua principale
Java
Stelle
21
Fork
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Merge medio
1g 1h
PR unite (30g)
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