fix: make the policy health check satisfy json object mode

[Barsoomx]

An OpenAI curation policy could never pass engram_validate_policies / the console's Test connection button.

Observed on the stand right after migrating it to OpenAI:

curation   openai gpt-5-mini            status=FAIL error=provider_http_error (400)
digest     openai gpt-5-nano            status=PASS
generation openai gpt-5-nano            status=PASS
embedding  openai text-embedding-3-small status=PASS

Only curation failed, because it is the only task type whose health check uses a structured response kind: _validation_response_kind returns candidates for curation, candidates is in _STRUCTURED_RESPONSE_KINDS, and openai_json_mode_override therefore sets response_format: json_object for an OpenAI policy. OpenAI rejects that unless the messages mention json, and VALIDATION_PROMPT did not.

Proved against the real API, both prompts, same policy shape:

OLD  HTTP 400 'messages' must contain the word 'json' in some form, to use 'response_format'...
NEW  OK  out=14  content={"ok": true}

Fix is the prompt itself. The test pins the relationship rather than the wording: it asserts that the curation health check's response kind really is a structured one, and that the prompt satisfies the mode that implies.

Pre-existing — it would have hit any OpenAI curation policy before this week; nobody had one until now.

Backend suites: 815 passed.

🤖 Generated with Claude Code

[Barsoomx]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues

💻 Catch issues earlier using the plugins for VS Code, JetBrains IDEs, Visual Studio, and Eclipse.

[codecov-commenter]

Bundle Report

Bundle size has no change ✅

Affected Assets, Files, and Routes:

view changes for bundle: engram-frontend-client-array-push

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
server/middleware-*.js	2.72kB	3.21kB	548.89% ⚠️
server/middleware-*.js	-2.72kB	495 bytes	-84.59%
static/A3RWyqOJYQIawHj4nWJHS/_buildManifest.js (New)	1.51kB	1.51kB	100.0% 🚀
static/A3RWyqOJYQIawHj4nWJHS/_ssgManifest.js (New)	77 bytes	77 bytes	100.0% 🚀
static/fT1P5ugzkNt6fxJqQJY2R/_buildManifest.js (Deleted)	-1.51kB	0 bytes	-100.0% 🗑️
static/fT1P5ugzkNt6fxJqQJY2R/_ssgManifest.js (Deleted)	-77 bytes	0 bytes	-100.0% 🗑️

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.03%. Comparing base (ba194b4) to head (fafe322).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #300   +/-   ##
=======================================
  Coverage   91.03%   91.03%           
=======================================
  Files         221      221           
  Lines       23099    23099           
=======================================
  Hits        21029    21029           
  Misses       2070     2070           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.