fix(mcp): prefer application/json over SSE when client accepts both

[Vishnuujain]

• fixes: MCP tools not working via ai-sdk #28557
• When a client says it can read both JSON and streaming (SSE) responses, the server now sends plain JSON.
• This fixes a bug from fix(mcp): emit SSE response when client negotiates text/event-stream #27917 where the server sent a streaming response (data: ...) to clients that expected JSON, so they couldn't read it (e.g. the ai-sdk Python client).
• The server still sends a streaming response to clients that only accept streaming (like Databricks).

[github-actions]

Hi there 👋 Thanks for your contribution!

The OpenMetadata team will review the PR shortly! Once it has been labeled as safe to test, the CI workflows
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[gitar-bot]

Code Review ✅ Approved 1 resolved / 1 findings

Updates MCP response negotiation to prioritize application/json over SSE, fixing response parsing issues for compliant clients. Add a test case for the shouldEmitSse(false, false) scenario to ensure full coverage.

✅ 1 resolved

✅ Edge Case: Missing test for shouldEmitSse(false, false)

📄 openmetadata-mcp/src/test/java/org/openmetadata/mcp/server/transport/HttpServletStatelessServerTransportTest.java:128-141
The test suite covers three of the four boolean combinations for shouldEmitSse(acceptsJson, acceptsSse) but omits (false, false) — the case where a client sends an Accept header that includes neither JSON nor SSE (e.g. */* or some other media type). Adding this case documents the expected behaviour and guards against future regressions.

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[github-actions]

🟡 Playwright Results — all passed (18 flaky)

✅ 4253 passed · ❌ 0 failed · 🟡 18 flaky · ⏭️ 88 skipped

Shard	Passed	Failed	Flaky	Skipped
🟡 Shard 1	298	0	1	4
🟡 Shard 2	801	0	6	9
🟡 Shard 3	803	0	3	8
🟡 Shard 4	844	0	2	12
🟡 Shard 5	719	0	1	47
🟡 Shard 6	788	0	5	8

🟡 18 flaky test(s) (passed on retry)

• Pages/AuditLogs.spec.ts › should handle audit logs access for non-admin users (shard 1, 1 retry)
• Features/ContextCenter.spec.ts › searching documents filters the list to matching results (shard 2, 1 retry)
• Features/DataQuality/TestCaseImportExportE2eFlow.spec.ts › Admin: Complete export-import-validate flow (shard 2, 1 retry)
• Features/DataQuality/TestCaseImportExportE2eFlow.spec.ts › EditAll User: Complete export-import-validate flow (shard 2, 1 retry)
• Features/DataQuality/TestCaseResultPermissions.spec.ts › User with TEST_CASE.EDIT_ALL can see edit action on test case (shard 2, 1 retry)
• Features/DataQuality/TestCaseResultPermissions.spec.ts › User with only VIEW cannot PATCH results (shard 2, 1 retry)
• Features/Glossary/GlossaryWorkflow.spec.ts › should start term as Draft when glossary has reviewers (shard 2, 1 retry)
• Features/LandingPageWidgets/DomainDataProductsWidgets.spec.ts › Data Product asset count should update when assets are added (shard 3, 1 retry)
• Features/RTL.spec.ts › Verify Following widget functionality (shard 3, 1 retry)
• Features/Table.spec.ts › Tags term should be consistent for search (shard 3, 1 retry)
• Flow/PersonaDeletionUserProfile.spec.ts › User profile loads correctly before and after persona deletion (shard 4, 1 retry)
• Flow/PersonaFlow.spec.ts › Set default persona for team should work properly (shard 4, 1 retry)
• Pages/ExplorePageRightPanel_KnowledgeCenter.spec.ts › Should remove user owner for knowledgeCenter (shard 5, 1 retry)
• Pages/Glossary.spec.ts › Cancel glossary delete operation (shard 6, 1 retry)
• Pages/Lineage/LineageFilters.spec.ts › Verify lineage schema filter selection (shard 6, 1 retry)
• Pages/Lineage/LineageInteraction.spec.ts › Verify edge delete button in drawer (shard 6, 1 retry)
• Pages/ServiceEntity.spec.ts › Tier Add, Update and Remove (shard 6, 1 retry)
• Pages/Users.spec.ts › Create and Delete user (shard 6, 1 retry)

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How to debug locally

# Download playwright-test-results-<shard> artifact and unzip
npx playwright show-trace path/to/trace.zip    # view trace

[github-actions]

Changes have been cherry-picked to the 1.12.10 branch.

[github-actions]

Changes have been cherry-picked to the 1.13 branch.