fix: Add validation for empty request body and message content in chat handler

[Ragini-Microsoft]

Purpose

This pull request adds improved input validation to the unified chat endpoint in app.py. The main changes ensure that the endpoint returns clear error messages for missing or empty request data, which helps prevent processing invalid requests and improves the API's robustness.

Input validation improvements:

• Added a check to return a 400 error if the request body is missing, with a descriptive error message in the response.
• Added a check to return a 400 error if both the action and message fields are empty or missing, ensuring that chat requests include meaningful content.

Does this introduce a breaking change?

• Yes
• No

Golden Path Validation

• I have tested the primary workflows (the "golden path") to ensure they function correctly without errors.

Deployment Validation

• I have validated the deployment process successfully and all services are running as expected with this change.

[github-actions]

Coverage Report •

File	Stmts	Miss	Cover	Missing
src/backend
app.py	720	135	81%	47, 64, 71–76, 79, 84, 119–120, 165, 244, 262, 281, 288, 412–413, 519, 522, 525–527, 536–537, 540, 542–544, 553–556, 566–567, 570–576, 579–581, 587–588, 590, 601, 603–608, 611–613, 620, 630–631, 633, 730–734, 742, 745, 753, 756–759, 768–769, 772, 781, 783, 811, 820–821, 835–836, 855–856, 858–859, 866–867, 870–871, 1013–1015, 1019–1021, 1060–1061, 1099, 1102, 1104, 1130–1131, 1133–1135, 1137, 1156–1157, 1159–1160, 1229–1230, 1261–1262, 1339–1340, 1600–1602, 1604–1605, 1612–1614, 1616, 1751, 1769, 1831–1832, 1836–1837
src/tests
test_app.py	1588	6	99%	1088, 1114, 3356–3357, 3375–3376
TOTAL	7680	379	95%

Tests	Skipped	Failures	Errors	Time
422	0 💤	0 ❌	0 🔥	12.855s ⏱️

[Copilot]

Pull request overview

This PR tightens input validation for the Quart unified chat endpoint (/api/chat) to reject missing/empty request bodies and empty message content when no action is provided, improving API robustness and error clarity.

Changes:

• Added an early 400 response when the request JSON body is missing/empty.
• Added a 400 response when both action is absent and message is empty/whitespace.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

[github-actions]

🎉 This PR is included in version 2.5.2 🎉

The release is available on GitHub release

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