test(codex): coverage for MCP tool calls (SIG-198)#171
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GuyMoses merged 2 commits intoJul 15, 2026
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Verified on Codex 0.142.5 that MCP tool calls fire PreToolUse/PostToolUse hooks and that the hook payload's tool_name uses the canonical mcp__<server>__<tool> form (e.g. mcp__everything__echo) — identical to Claude Code. Codex's internal trace name flattens this to "mcp__everythingecho", but the hook the plugin consumes is canonical, so the pipeline's generic ExtractMCPServer / NormalizeMCPToolName handle it with zero Codex-specific code. Captured a real mcp__everything__echo call and added the PreToolUse/ PostToolUse pair to the golden fixture. The resulting span is "execute_tool echo" with gen_ai.tool.name=echo and dash0.gen_ai.tool.mcp_server=everything. Added an explicit invariant so a regression fails even if the golden is re-blessed. Note: MCP tools are gated behind Codex's ToolSearchAlwaysDeferMcpTools feature (tool_search), and stdio MCP servers must complete their handshake within the startup timeout to be indexed — orthogonal to plugin capture. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Closes SIG-198.
What this verifies
MCP tool calls on the Codex path were likely-works-but-unverified — the pipeline handles
mcp__<server>__<tool>generically, but there was no proof for Codex and an open risk that older Codex might not fire tool hooks for MCP at all.Verified live on Codex 0.142.5 (the pinned version):
mcp__everything__echocall produced bothPreToolUseandPostToolUsehook events.tool_nameis canonical —mcp__everything__echo, with the__separator, identical to Claude Code. (Codex's internal trace name flattens this tomcp__everythingecho, but the hook the plugin consumes is canonical.)ExtractMCPServer/NormalizeMCPToolNamehandle it with zero Codex-specific code.Changes
PreToolUse/PostToolUsepair tocaptured_events.jsonl(injected into the simplest existing session).golden_spans.json. The MCP call becomes spanexecute_tool echowithgen_ai.tool.name=echoanddash0.gen_ai.tool.mcp_server=everything.TestGoldenSpanTreeso a regression fails even if the golden is blindly re-blessed.Notes for reviewers
golden_spans.jsondiff is mostly span/trace token renumbering +durationMsshifts from inserting one event mid-session; the only new span is the MCP one.ToolSearchAlwaysDeferMcpToolsfeature (tool_search), and stdio MCP servers must finish their handshake within the startup timeout to be indexed — both orthogonal to plugin capture.