fix: return ETag header on GET for config resource endpoints

[KirylKurnosenka]

Applicable issues

• fixes #

Description of changes

GET v1/applications/public/{name} (handled by ResourceController) correctly returns an ETag response header and enforces RFC 7232 conditional headers. However, GET v1/roles/platform/{name}, GET v1/models/public/{name}, and other config resource endpoints handled by ConfigResourceController had two issues:

1. Missing ETag on 200 responses — ConfigResourceController already fetched blob metadata (including the ETag) to support If-None-Match / 304 conditional GET, but the fetched ETag was discarded and never added to the response header on the normal 200 path.

2. If-Match silently ignored on GET — the evaluateConditionalGet method caught all HttpExceptions from EtagHeader.validate() and only surfaced the 304 case, silently swallowing If-Match failures. RFC 7232 §3.1 does not exempt GET from If-Match evaluation, so a mismatched If-Match header should return 412, consistent with ResourceController.

Fix:

• evaluateConditionalGet now calls etag.validate() without a try-catch, letting HttpException (304 or 412) propagate through the Future failure chain to handleWriteError, exactly as ResourceController does.
• Simplified the return type of evaluateConditionalGet from a GetResult record to Future<String> (the ETag or null), removing the now-unnecessary wrapper.
• Both handleSingleGet and handleSchemaGet set the ETag response header on 200 OK when the entity has a blob-backed ETag.
• Entities without a blob backing (file-sourced, invalid records) return 200 with no ETag header.

Tests (ConfigResourceConditionalHeaderTest):

• testGet200IncludesEtagHeader — plain GET on a blob-backed model asserts ETag header is present on the 200 response.
• testGet200OnStaleIfNoneMatch — asserts ETag is returned on 200 when the client sends a stale If-None-Match.
• testGet200OnMatchingIfMatch — GET with a matching If-Match returns 200 with an ETag header.
• testGet412OnStaleIfMatch — GET with a mismatched If-Match returns 412.

Checklist

• Title of the pull request follows Conventional Commits specification

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[ai-dial-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[KirylKurnosenka]

/deploy-review

GitHub actions run: 27817445939

Stage	Status
deploy-review	Failed ❌
matrix.application	Skipped ➖

[KirylKurnosenka]

/deploy-review

GitHub actions run: 27818241376

Stage	Status
deploy-review	Success ✅
chat	Success ✅