fix: unblock subscriptions-smoke (S3 loader without R4; smoke ids via PUT)

[smunini]

Summary

Two independent problems kept subscriptions-smoke.yml from running at all; both predate #1342 and neither is backend-specific.

1. hfs did not compile without the R4 feature when s3 was on

S3Backend::reload_stored_cache_for_tenant (crates/persistence/src/backends/s3/storage.rs:403) built its SearchParameterLoader with FhirVersion::default(), which only exists when the R4 feature is enabled:

error[E0599]: no variant, associated function, or constant named `default` found for enum `FhirVersion`
   --> crates/persistence/src/backends/s3/storage.rs:403:62

That failed 10 of the 16 build jobs (run 35516683520). Switched to FhirVersion::default_enabled(), the helper intended for code that must compile in any single-version build. The companion validator error was fixed in #1375.

2. The smoke script asserted on ids the server no longer keeps

crates/hfs/tests/subscriptions/run_external_subscriptions_smoke.sh POSTed its topic, Subscriptions and Encounters with a client-chosen id, then asserted that delivered notifications reference Encounter/<that id>. HFS assigns the id on POST, so every leg failed with rest-hook event bundle missing expected focus (run 35629993565: the captured bundle carried Encounter/01a0c55f-…, the script expected Encounter/enc-rest-…). The nine create calls now use PUT <Type>/<id> (update-as-create), which keeps the chosen id.

Test plan

• cargo check -p helios-hfs --no-default-features --features "<V>,subscriptions,sqlite,elasticsearch,postgres,mongodb,s3" for R5, R4B, R6, and R4B,R6
• CI: all 15 build subsets compiled in run 35629993565 (previously 10 failed)
• Patched smoke script run locally against an in-memory sqlite hfs, R4 (backport topic) and R5 (native SubscriptionTopic): rest-hook, websocket and messaging pass
• Email channel re-run locally against a mailpit container (R5): passes, and the delivered bundle carries the client-chosen focus Encounter/enc-email-… — the exact assertion that was failing
• subscriptions-smoke.yml on this branch (run 35644104645): green — all 168 smoke legs pass, including the first-ever run of the postgres-elasticsearch / mongodb-elasticsearch legs added in ci: add postgres-elasticsearch and mongodb-elasticsearch legs to backend matrices #1342. Two legs initially failed on GitHub's artifact service (403 Forbidden: Error from intermediary on FinalizeArtifact / ListArtifacts, unrelated to storage behaviour); re-running just those two passed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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