fix: Capture systemPrompt in Strands agent model span input - #2311
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Alex Jean-Baptiste (justcodebruh) wants to merge 2 commits into
Open
fix: Capture systemPrompt in Strands agent model span input#2311Alex Jean-Baptiste (justcodebruh) wants to merge 2 commits into
Alex Jean-Baptiste (justcodebruh) wants to merge 2 commits into
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The TypeScript Strands plugin read event.agent.messages to build the
model span input but never read event.agent.systemPrompt, so the system
prompt was silently absent from every model span — even though it was
set on the agent and visible in other observability tools.
Add buildModelSpanInput() which prepends a { role: "system", content }
message to the input array when systemPrompt is present, matching the
behavior already documented for the Python integration.
Also add systemPrompt to the StrandsAgent vendor type.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Alex Jean-Baptiste (justcodebruh)
marked this pull request as ready for review
July 30, 2026 16:38
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Summary
Linear Issue: https://linear.app/braintrustdata/issue/SDK-109/typescript-strands-sdk-wrapper-drops-systemprompt-from-model-span
event.agent.messagesto build the model span input but never readevent.agent.systemPrompt, so the system prompt was silently absent from every model spanbuildModelSpanInput()which prepends a{ role: "system", content }message to the input array whensystemPromptis present, matching the behavior already documented for the Python integrationsystemPrompt?: stringto theStrandsAgentvendor typeTest plan
src/instrumentation/plugins/strands-agent-sdk-plugin.test.ts— 7 tests ✓)systemPromptset viawrapStrandsAgentSDKor auto-instrumentation and confirm theStrands modelspan input includes a leading{ role: "system" }messagesystemPromptare unaffected (input falls back to messages array only)References