fix: surface MaxTokensError when max_tokens truncates tool input JSON#2620
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JackYPCOnline merged 1 commit intoJun 4, 2026
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When a model hits the max_tokens limit mid-stream, the tool input JSON can be truncated and fail to parse. Previously the SyntaxError from JSON.parse was thrown immediately, masking the more actionable MaxTokensError that the maxTokens stop reason should produce. Defer the tool input parse error and only surface it after checking the stop reason: MaxTokensError takes precedence when stopReason is maxTokens, otherwise the SyntaxError is attached as the cause of a ModelError. If the stream ends without a stop event, the SyntaxError is attached as the cause of the "Stream ended" ModelError. Ported from strands-agents/sdk-typescript#1065 by @cmbullock.
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Assessment: Comment Clean, well-scoped bug fix that correctly prioritizes Review Details
Solid fix — the inline comments are suggestions for hardening, not blockers. |
zastrowm
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zastrowm
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Description
Port of strands-agents/sdk-typescript#1065 by @cmbullock.
Resolves : #2451
When a model hits the
max_tokenslimit mid-stream, the tool input JSON can be truncated and failJSON.parse. Previously the resultingSyntaxErrorwas thrown immediately fromstreamAggregated, masking the more actionableMaxTokensErrorthat themaxTokensstop reason is supposed to surface.The fix defers the tool input parse error instead of throwing it inline, then resolves precedence after the stop reason is known:
stopReason === 'maxTokens'→MaxTokensError(the real, actionable failure).ModelError('unable to parse tool input JSON')with theSyntaxErrorattached ascause.ModelError('Stream ended without completing a message')with theSyntaxErrorattached ascause.Type of Change
Bug fix
Testing
npm run test -w strands-ts— full unit suite passes (lint, format, and type-check included via the prepare checks).Checklist
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