[Bug]: Preserve region fallback for SQL dynamic S3

[Ariznawlll]

What type of PR is this?

• API-change
• BUG
• Improvement
• Documentation
• Feature
• Test and CI
• Code Refactoring

Which issue(s) this PR fixes:

Closes #30528

What this PR does / why we need it:

SQL dynamic S3 providers intentionally avoid discovering credentials from the server environment. That path also stopped inheriting the AWS SDK's environment-based Region fallback, so configurations without an explicit Region failed before reaching S3.

When s3-opts omits Region, use AWS_REGION, then AWS_DEFAULT_REGION; an explicitly configured Region still takes precedence. This restores non-secret Region compatibility without re-enabling ambient credential discovery. Regression tests verify the signed request uses the expected Region and caller-supplied credentials.

Validation:

• CI run 39139192516: UT, SCA, and BVT checks passed.
• Focused file-service validation passed: 465 tests, 6 existing skips, plus three signed-request boundary scenarios. No live AWS run was performed.

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[XuPeng-SH]

mo-bot review · mo-bot-xupeng · done

Commit: 7c6a2c527beef5d3bb21aedcb438bd6b7da7c72c

Review completed. Read the assessment.

[XuPeng-SH]

mo-bot review · mo-bot-xupeng · review

Commit: 7c6a2c527beef5d3bb21aedcb438bd6b7da7c72c

Assessment: approve

Reviewed the complete two-file delta and its SQL/S3/STS callers. Region fallback preserves explicit-region precedence and credential isolation. No actionable findings.

Model: gpt-6-astra / xhigh

Session: 01a14d34-4e51-79a3-a62d-6c9c16279dc8 · slot 0 · generation 0

Validation:

• Receipt/log mapping retained in /home/xupeng/.local/state/mo-bot/jobs/6b79a7f5c6927bccf43005b0/attempt-1/validation-index.json. Final integrity checks confirmed the pinned checkout remained clean.

• Built native prerequisites from 192 matched candidate inputs. Isolation preflight, formatting and whitespace checks passed.

• 12 focused tests and three additional signed-request boundary scenarios passed. Both new regression tests failed against the pre-fix implementation as expected.

• Package selections reconciled: 465 tests passed and six existing tests skipped. The initial aggregate timeout and interrupted run were not counted as package passes; successful recovery selections closed the remaining coverage.

Limitations:

• No live SQL/frontend or AWS-cloud run; validation exercised the production SQL file-service factory and SDK signing, plus the existing local MinIO suite.

• The frozen evidence omits issue #30528's body; its contract was assessed from the PR description. CI status summaries were not treated as log-verified execution.

[mergify]

Queued — the merge queue status continues in this comment ↓.

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-10-18 17:11 UTC · Rule: main · triggered by rule Automatic queue on approval for main
• ✅ Checks passed · in-place
• ✅ Merged — 2026-10-18 18:10 UTC · at f11dd8c5d700f215922835f314ea18d32471f482 · squash

This pull request spent 58 minutes 41 seconds in the queue, including 51 minutes 3 seconds running CI.

Required conditions to merge

• #review-threads-unresolved = 0 [🛡 GitHub branch protection]
  • [Bug]: Preserve region fallback for SQL dynamic S3 #30533
• github-review-approved [🛡 GitHub branch protection]
  • [Bug]: Preserve region fallback for SQL dynamic S3 #30533
• any of [🛡 GitHub branch protection]:
  • check-success = CI Required
  • check-neutral = CI Required
  • check-skipped = CI Required