fix: improve condition check for streaming token callback in handle_on_chain_stream

[ricofurtado]

This pull request makes a minor update to the logic for streaming token events in the handle_on_chain_stream function. The change improves the condition that checks whether to send a token event, ensuring it is more explicit and reliable.

Summary by CodeRabbit

• Bug Fixes
  • Refined token callback emission logic for more consistent handling of output validation.

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Walkthrough

A condition check in the handle_on_chain_stream function was modified to explicitly validate that output_text is not None and not an empty string, replacing a truthiness-based check with explicit equality comparisons.

Changes

Cohort / File(s)	Summary
Token callback guard condition src/lfx/src/lfx/base/agents/events.py	Updated the condition for emitting a token callback from output_text and output_text.strip() to output_text is not None and output_text != "", changing from implicit truthiness checks to explicit None and empty string validation

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

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Important

Pre-merge checks failed

Please resolve all errors before merging. Addressing warnings is optional.

❌ Failed checks (1 error, 2 warnings)

Check name	Status	Explanation	Resolution
Test Coverage For New Implementations	❌ Error	PR implements a bug fix to condition check for streaming token callbacks but includes no new tests to validate the fix or prevent regressions.	Add regression tests for whitespace-only strings, None values, empty strings, and a test case reproducing the original bug to validate the condition change.
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Test Quality And Coverage	⚠️ Warning	PR changes token emission condition from filtering whitespace-only strings to allowing them, but existing test expects whitespace-only strings to be skipped.	Update test_agent_streaming_skips_empty_chunks() to reflect new behavior or add new test explicitly validating the condition change with clear assertions.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main change: improving condition checks for streaming token callbacks in a specific function.
Test File Naming And Structure	✅ Passed	The test file follows correct patterns with 45 fully implemented test functions using proper pytest structure and comprehensive coverage.
Excessive Mock Usage Warning	✅ Passed	Test file demonstrates appropriate use of mocks for external dependencies while using real objects to test actual behavior, with 30+ tests validating improved condition logic.

✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch lfoss-3036-streaming-output-bug

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[github-actions]

Frontend Unit Test Coverage Report

Coverage Summary

Lines	Statements	Branches	Functions
	17.49% (4997/28566)	10.83% (2388/22036)	11.58% (724/6248)

Unit Test Results

Tests	Skipped	Failures	Errors	Time
1998	0 💤	0 ❌	0 🔥	26.269s ⏱️

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 31.64%. Comparing base (5497f93) to head (3b618a9).

Files with missing lines	Patch %	Lines
src/lfx/src/lfx/base/agents/events.py	0.00%	1 Missing ⚠️

❌ Your project check has failed because the head coverage (42.66%) is below the target coverage (55.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11362      +/-   ##
==========================================
- Coverage   34.23%   31.64%   -2.60%     
==========================================
  Files        1409     1414       +5     
  Lines       66923    67202     +279     
  Branches     9877     9910      +33     
==========================================
- Hits        22914    21267    -1647     
- Misses      42808    44719    +1911     
- Partials     1201     1216      +15     

Flag	Coverage Δ
backend	42.66% <ø> (-10.88%)	⬇️
frontend	16.03% <ø> (ø)
lfx	41.60% <0.00%> (+0.79%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/lfx/src/lfx/base/agents/events.py	16.58% <0.00%> (ø)

... and 112 files with indirect coverage changes

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[Adam-Aghili]

Do we want to allow whitespace only stings, such as " "?

[ricofurtado]

Yes, we want. That was the original issue; the chunks outputs were different from the text outputs. e.g. "PISA 2022" was becoming "PISA2022" when accumulating the chunks.

[Adam-Aghili]

Suggested change

	if output_text is not None and output_text != "" and send_token_callback and message_id:
	if output_text is not None and output_text.lstrip() and output_text.rstrip() and output_text != "" and send_token_callback and message_id:

Based on the tests failing I think it would be safe to use either lstrip or rstrip to preserve the previous intent of ignoring " " but allowing "PISA 2022".

We could use both but that seems unnecessary