fix(compact): validate compact_threshold is at least 1000 (#838)

[Artemon-line]

Summary

Validate compact_threshold as at least 1000 when parsing the compaction entry in context_management. Invalid or missing proxy-consumed values produce an invalid_request_error rather than silently skipping or executing compaction.

Related issue

Closes #838

Validation

• Unit tests (cargo test -p praxis-ai-apis -- compact)
• Integration or functional tests (cargo test -p praxis-tests-integration -- compact)
• make lint

Verification Proof

To test the rejection for an invalid threshold (< 1000), send a value below 1000 (e.g. 50):

curl -i -X POST http://localhost:8080/v1/responses \
  -H "Content-Type: application/json" \
  -d '{"model":"llama3.2:1b","input":"Hello","context_management":[{"type":"compaction","compact_threshold":50}]}'

The proxy will intercept it and return HTTP 400 Bad Request directly:

HTTP/1.1 400 Bad Request
Content-Type: application/json

{"error":{"code":"invalid_request_error","message":"compact_threshold must be an integer of at least 1000","param":null,"type":"invalid_request_error"}}

Checklist

• I reviewed every changed line and can explain the change.
• New capabilities include an example config and functional example test.
• User-facing behavior and generated documentation are updated.
• Performance-sensitive changes include appropriate benchmark or load-test evidence.
• Commits are signed and include a Signed-off-by trailer.

Breaking changes

None.

[praxis-bot]

PR Review

Summary: Validates compact_threshold as at least 1000, converting extract_compaction_config and should_compact to return Result so invalid values produce invalid_request_error instead of being silently skipped. Clean refactor with good test coverage for threshold edge cases.

Overall: The validation logic, error messaging, and integration test are solid. One new validation path lacks test coverage.

Severity	Count
Critical	0
Large	0
Medium	1