Port gRPC URI and resolver stack

Scope

Port Bun corpus position 3988, js/third_party/grpc-js/test-resolver.test.ts.

Required contracts

• parse gRPC URIs and map unknown/bare schemes through the default DNS resolver
• register DNS, Unix-domain-socket, IPv4, IPv6, and custom resolver implementations
• default missing ports to 443
• resolve localhost and stable upstream DNS fixtures deterministically
• represent endpoint/address lists and equality correctly
• support repeated explicit resolution attempts without autonomous retry loops
• compute custom resolver authorities
• preserve resolver failures as causes with scheme, target, operation, and source-module stack context

Verification

• all active focused upstream tests pass with upstream todo/skip counts preserved
• permanent diagnostics cover custom schemes and failed-resolution context
• existing gRPC, SQL adapter, and third-party gates remain green

Implemented and pushed in 83a49f5b8.

Completed contracts:

• parsed gRPC URIs and mapped bare/unknown schemes through the default DNS resolver
• registered DNS, UDS, IPv4, IPv6, and custom resolvers
• defaulted missing ports to 443
• resolved localhost and stable upstream DNS fixtures deterministically
• represented endpoint/address equality and formatting correctly
• supported repeated explicit resolution attempts without autonomous retry loops
• computed custom resolver authorities
• failed resolutions return UNAVAILABLE with preserved causes and scheme/target/operation/source stack context

Verification:

• focused Bun corpus: 20 passed, 4 upstream todo, 0 failed, 0 unsupported
• permanent gRPC diagnostics: 15 passed
• SQL adapter contracts: passed
• permanent third-party JWT/utility mini-suite: passed
• zig fmt --check and git diff --check: passed

Cumulative through position 3988: 330 files, 2,763 passed, 213 todo, 0 failed, 0 unsupported, 171 allowed-empty.