Why AWS Bedrock Returned an Empty Agent Response

Bedrock reported generated output tokens, but the user received an empty assistant message. No exception explained the failure.

INC-003 came from an adapter that only extracted ordinary text blocks. Bedrock Converse can return reasoningContent, guardContent, toolUse, empty text, and unknown future block types. A second layer discarded the message because it used a truthiness check instead of preserving an empty string.

Adapter controls

• Validate the provider content-block schema.
• Preserve empty text when a message exists.
• Log reasoning and guardrail diagnostics without exposing internal reasoning.
• Add fixtures for reasoning-only, guardrail, tool-use, empty-text, and unknown blocks.

Provider adapters are reliability boundaries. A graph can be correct while its translation layer silently drops the response.

Review source patterns with:

prevention-scanner scan . --format json

Confirm the fix with provider contract tests, not only a happy-path mock.

Read the full INC-003 incident.

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