LCORE-1323: Add text/event-stream Header for Streaming Query

[Jdubrick]

Description

• Adds text/event-stream header back after it was dropped during the refactor and defaulted to text/plain

Type of change

• Refactor
• New feature
• Bug fix
• CVE fix
• Optimization
• Documentation Update
• Configuration Update
• Bump-up service version
• Bump-up dependent library
• Bump-up library or tool used for development (does not change the final image)
• CI configuration change
• Konflux configuration change
• Unit tests improvement
• Integration tests improvement
• End to end tests improvement
• Benchmarks improvement

Tools used to create PR

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• Assisted-by: Claude
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Related Tickets & Documents

• Related Issue #
• Closes #

Checklist before requesting a review

• I have performed a self-review of my code.
• PR has passed all pre-merge test jobs.
• If it is a core feature, I have added thorough tests.

Testing

• Please provide detailed steps to perform tests related to this code change.
• How were the fix/results from this change verified? Please provide relevant screenshots or results.

Summary by CodeRabbit

• Bug Fixes

  • Ensure streaming responses default to Server-Sent Events (SSE) for non-text requests while preserving text format when explicitly requested.

• New Features

  • Introduced a named media-type constant for SSE to standardize streaming content type across endpoints.

• Tests

  • Added tests validating streaming media-type headers and behavior for text vs. SSE responses.

[coderabbitai]

Walkthrough

Sets a new constant MEDIA_TYPE_EVENT_STREAM and updates streaming endpoints to use a computed response_media_type: use MEDIA_TYPE_TEXT only when explicitly requested, otherwise use MEDIA_TYPE_EVENT_STREAM. Updates OpenAPI response media type and adds a unit test asserting text media-type behavior.

Changes

Cohort / File(s)	Summary
Streaming endpoints src/app/endpoints/streaming_query.py, src/app/endpoints/a2a.py	Introduce and use MEDIA_TYPE_EVENT_STREAM constant; streaming handlers compute response_media_type and set StreamingResponse media type to SSE by default unless request explicitly asks for text.
Constants & models src/constants.py, src/models/responses.py	Add MEDIA_TYPE_EVENT_STREAM = "text/event-stream" and update StreamingQueryResponse.openapi_response to reference the new constant instead of hard-coded string.
Tests tests/unit/app/endpoints/test_streaming_query.py	Add test_streaming_query_text_media_type_header and assertions verifying StreamingResponse media type/header for text requests.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• LCORE-282: ensure compatibility with OLS streaming query #519: Touches streaming_query media-type handling and related tests; closely related changes.
• LCORE-956: Bump llama stack to 0.3.0 #866: Standardizes SSE media type usage across streaming endpoints; likely related.

Suggested reviewers

• tisnik
• jrobertboos
• are-ces

🚥 Pre-merge checks | ✅ 3 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into main
Title check	✅ Passed	The title accurately describes the main change—extracting the text/event-stream media type into a constant and applying it across streaming endpoints to restore the correct header for streaming queries.

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[tisnik]

LGTM

[jrobertboos]

Overall the PR looks good. However could you make an issue in the LCORE JIRA and attach it to the PR, we are just trying to get better about attaching PR's to issues.

The ticket should be in the title like:

LCORE-XXX: Add text/event-stream Header for Streaming Query

As well as in the Closes Ticket section of the PR description.

Thanks so much!