Align SoF async export to the simplified async interaction pattern

[smunini]

Summary

Updates the $viewdefinition-export and $sqlquery-export operations to follow the FHIR Asynchronous Interaction Request Pattern per HL7/sql-on-fhir#369, replacing the prior Bulk Data completion behavior.

The core behavioral change: completion (and failure) is now signalled by a 303 See Other redirect from the status poll to a separate result URL — instead of returning 200 OK with the manifest directly on the status poll.

Changes

crates/rest

• routing/fhir_routes.rs — Added GET /export/{job_id}/result. The static result segment takes priority over the existing {filename} download route (matchit 0.8 supports this overlap).
• handlers/sof/export.rs
  • get_export_status_handler — the Completed/Failed arms now return 303 See Other with an empty body and a Location header carrying the absolute result URL. The status endpoint no longer communicates job outcome (still 202 while running, 404 for unknown/cancelled).
  • Added get_export_result_handler — serves the manifest Parameters with 200 OK + Expires (24h) on success, the error status + OperationOutcome on failure, and 404 when the job is unknown/cancelled/still running.
  • Updated the module-level doc comment.
• handlers/sof/mod.rs — re-exported the new handler.

Tests (crates/rest/tests/sof_export.rs)

• Updated the poll_to_manifest helper to follow the 303 → result URL → 200 flow.
• Reworked the three tests that assumed the old direct-200-on-poll completion, and the failure test (now asserts 303 → 500 at the result URL).
• Added test_export_completion_redirects_to_result (empty-body 303, Location, stable repeat fetch, Expires) and test_export_result_unknown_job_returns_404.

Not implemented (optional / client-side)

• 429 Too Many Requests for excessive polling — spec says the server MAY; we don't rate-limit polls.
• Opaque-URL requirement — a client-side MUST; our URLs are already non-guessable (UUID job IDs).

Caveat

HL7/sql-on-fhir#369 is still open, and the cited async-interaction pattern currently links an in-progress incubator branch — the exact 303/result-URL contract could shift before it lands.

Test plan

• cargo fmt --all
• cargo clippy --all-targets --all-features -- -D warnings ... (clean)
• cargo test -p helios-rest --test sof_export — 44 passed, 0 failed

[codecov]

Codecov Report

❌ Patch coverage is 92.10526% with 6 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/rest/src/handlers/sof/export.rs	91.78%	6 Missing ⚠️

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