fix: include reasoning block with empty text and non-empty signature

[gaurav71531]

Motivation

Some models like Opus 4.7 emit reasoning content blocks that carry only a signature with no accompanying reasoningText. The prior condition in handle_content_block_stop checked only reasoning_text, which evaluated to falsy for an empty string, causing the entire reasoning content block (including the signature) to be silently dropped from the assembled message content.

Public API Changes

No public API changes. This is an internal streaming assembly fix.

Change

The condition in handle_content_block_stop is broadened from:

elif reasoning_text:

to:

elif reasoning_text or "signature" in state:

This ensures that reasoning blocks carrying only a signature are preserved in the output content, matching the behavior models like Opus 4.7 expect.

Testing

Added two tests covering the signature-only reasoning scenario:

• A parametrized case in test_handle_content_block_stop for empty reasoningText with a signature present
• An end-to-end test_process_stream_with_signature_only that simulates the Opus 4.7 streaming pattern (signature-only reasoning block followed by a text response)

[poshinchen]

/strands

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[poshinchen]

Could you add / update the unit tests so we know what the expected behaviors are?