feat: DuckDB S3 credential-chain support for IRSA-backed Iceberg reads

[velo]

Reopens/supersedes #2096 (that PR's branch was deleted so it can't be reopened in place).

Problem

When the Vert.x server reads an S3-backed Iceberg table through the DuckDB engine from an in-cluster pod (EKS IRSA), the query fails with HTTP 403 Forbidden / AccessDenied — No credentials are provided.

DuckDB's httpfs only auto-detects env-var credentials (AWS_ACCESS_KEY_ID/SECRET/SESSION_TOKEN) or an explicit credential secret. It does not use the projected web-identity token that backs IRSA, so on an IRSA-only pod it sends an anonymous request → 403. (Flink writes succeed because Flink's S3 layer does the web-identity exchange.)

This was proven directly inside a running server pod: anonymous iceberg_scan('s3://…') → 403 No credentials; after adding the credential-chain secret below, the same read returned 1,810,576 rows.

Change

Opt-in use-credential-chain flag on the DuckDB engine. When enabled, the connection init SQL adds:

LOAD aws;
CREATE OR REPLACE SECRET sqrl_s3_credential_chain (TYPE S3, PROVIDER credential_chain);

PROVIDER credential_chain (with no explicit CHAIN) delegates to the AWS SDK default provider chain, which includes the web-identity provider used by IRSA — so DuckDB obtains temporary creds from the projected service-account token, exactly like Flink.

Note: an explicit CHAIN 'env;config;sts;…' does not work — DuckDB maps sts to AssumeRole and rejects it without an ASSUME_ROLE_ARN. The default chain is required. (This is the correction vs the original #2096.)

The flag defaults to false, preserving today's behavior.

Files

• DuckDbExtensions.java — emit LOAD aws + default-chain CREATE SECRET when the flag is set; @VisibleForTesting buildInitSql(extensionDir) overload for unit testing.
• JdbcConfig.DuckDbConfig — new use-credential-chain boolean.
• packageSchema.json — register the new key.
• Dockerfile.duckdb-extensions — INSTALL aws so the extension is bundled (the credential_chain provider requires it; confirmed it is not bundled today).
• documentation/docs/configuration-engine/duckdb.md — document the flag + IRSA rationale.
• DuckDbExtensionsTest.java — covers default vs credential-chain init SQL, ordering, all-flags, and that no explicit CHAIN is emitted.

Validation

• DuckDbExtensionsTest — 4 tests green (JDK 17).
• The credential_chain secret was validated live in a server pod (IRSA-only): private-bucket iceberg_scan returned 1.8M rows with the secret, 403 without it.
• Downstream: IcebergDeploymentIT in cloud-compilation has the full datagen→Iceberg(Glue/S3FileIO/s3://)→Flink-write path green; this PR closes the read-side gap. Setting use-credential-chain: true on the duckdb engine turns that IT's GraphQL read green.

Draft until a maintainer confirms the secret name + bundling the aws extension.

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 13.62%. Comparing base (33ba2e3) to head (df10424).
⚠️ Report is 8 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
.../main/java/com/datasqrl/util/DuckDbExtensions.java	83.33%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2098      +/-   ##
============================================
+ Coverage     13.55%   13.62%   +0.07%     
- Complexity      835      840       +5     
============================================
  Files           605      605              
  Lines         17259    17264       +5     
  Branches       2084     2085       +1     
============================================
+ Hits           2339     2352      +13     
+ Misses        14700    14692       -8     
  Partials        220      220              

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[mbroecheler]

@velo This change makes sense to me.
@ferenc-csaky One thing we want to look into is how we support the different clouds with this one to load things dynamically.

Note, that this is currently blocked on a DuckDB fix.

[ferenc-csaky]

Logic LGTM, added 1 comment about the docs.

[ferenc-csaky]

Can we make this a bit more general and hopefully more concise? IMO this is way too much implementation detail for a general user facing doc. For example referencing that DuckDB PR is completely unnecessary.