fix(storage): increase gRPC response metadata limit

[span-lh]

Why

The gRPC Storage client currently inherits gRPC's 8 KiB inbound metadata limit. Larger response headers can fail with INTERNAL: http2 exception and Header size exceeded max allowed size (10240). For appendable uploads, losing the first acknowledgement can also leave a retry using the original generation condition after the server has already created a new generation.

Change

Set a bounded 64 KiB inbound metadata limit on the Storage client's GAX channel provider. Add real-transport regression tests covering small response metadata, an 18,000-byte response header, and rejection of a 96 KiB response header. Generation conditions, request retries, and upload behavior are unchanged.

Validation

• Regression test failed with the exact 10,240-byte header error before the change and passes afterward.
• mvn -f java-storage/google-cloud-storage/pom.xml -DskipITs test: 1,377 tests, zero failures/errors.
• mvn -f java-storage/google-cloud-storage/pom.xml com.spotify.fmt:fmt-maven-plugin:check: passed with JDK 21.
• Separately reproduced the appendable-upload header-rejection/precondition sequence with Storage 2.75.0 against a synthetic loopback GCS service; the same upload completes with the larger metadata limit.

Scope and limitations

The default changes for gRPC Storage clients only; response metadata remains bounded. The larger cap increases the worst-case accepted metadata size. Cloud-backed integration tests were not run. CodeScene could not run because the local CLI is not authenticated. This draft does not change a downstream application's dependencies or deploy a client.

Co-Authored-By: Codex (GPT-5) noreply@openai.com

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[gemini-code-assist]

Code Review

This pull request configures the maximum inbound metadata size for the gRPC channel provider to 64 KB in GrpcStorageOptions and introduces a new test suite, GrpcResponseMetadataTest, to verify that metadata sizes up to this limit are accepted while larger sizes are rejected. There are no review comments, and I have no feedback to provide.