[nazarli-shabnam]

Closes #5173

Problem

When some incidents fail to merge, POST /incidents/merge runs raise HTTPException(f"Some incidents failed to merge. {message}"). The first argument of HTTPException is status_code, so the message is used as a status code and Starlette fails with 'Some incidents failed to merge. ...' is not a valid HTTPStatus. The client gets a broken response instead of the error, which fits the "unexpected end of JSON input" in #5173.

Fix

Pass status_code=500 and the message as detail.

This does not explain why a merge of three or more incidents fails in the first place. merge_incidents_to_id loops over every source incident, so I could not find the original cause by reading the code; this PR only makes the failure report correctly. The linked-issue check requires a closing keyword, so this PR says Closes; if you want the issue to stay open until the cause of the failed merges is found, please reopen it.

Tests

Added test_merge_incidents_app_reports_partial_failure in tests/test_incidents.py. It patches merge_incidents_to_id to report one failed incident and expects a 500 with the message in detail.

Run in a throwaway python:3.12 container after poetry install --no-root --with dev. Before the fix it failed with ValueError: ... is not a valid HTTPStatus; after the fix it passed.

Not verified

• I only ran this one test, not the rest of tests/test_incidents.py. The existing test_merge_incidents_app is inside a string literal in that file (disabled), so nothing else covers this route.
• 500 is my choice of status for a partial failure; say if you prefer another.
• I did not run black or isort. I wrapped the line by hand.

AI disclosure

Claude (Anthropic) helped investigate the bug and draft the change and this description. I reviewed the diff.