Honor DefaultHostMetadataResolverFactory in host-metadata resolver wrapper

[Divyansh-db]

Summary

Fixes a pre-existing bug where the provider silently ignored config.DefaultHostMetadataResolverFactory.

During provider configuration the provider installs a wrapper around the SDK's host-metadata resolver (cfg.HostMetadataResolver) so it can observe the host's workspace_id from the single /.well-known/databricks-config fetch. The SDK only consults the DefaultHostMetadataResolverFactory global when cfg.HostMetadataResolver is nil — but because the wrapper always sets cfg.HostMetadataResolver, that factory was never reached. The wrapper's own fallback went straight to the built-in HTTP fetch, so any resolver installed through the factory was silently bypassed.

Fix

The wrapper now replicates the SDK's resolver precedence when choosing what to delegate to: a pre-existing resolver, then DefaultHostMetadataResolverFactory, then the built-in HTTP fetch. It still performs exactly one metadata fetch.

Testing

Adds a regression test that installs a factory and asserts it is consulted (the config is back-filled from the factory's metadata). The test fails without the fix — the factory is called zero times and no back-fill happens — and passes with it. make fmt lint ws clean; existing configuration tests pass.

Note

This is the standalone fix for a bug that predates and is independent of the eager-workspace-id work; it is being sent separately so it can be reviewed and merged on its own.

[github-actions]

Unit tests

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Inputs:

• PR number: 5940
• Commit SHA: 65d99547961aeb9d929516a8f3acd201f9dba3ce

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