Port Bun gRPC channel and server idle timers

Scope

Port Bun corpus position 3981, js/third_party/grpc-js/test-idle-timer.test.ts, into Home's shared Node/gRPC compatibility bootstrap.

Required contracts

• client channels become READY after requests and waitForReady
• client idle timeouts transition channels to IDLE, with the gRPC minimum of one second
• requests reconnect successfully after an idle transition
• Unix-domain-socket targets follow the same lifecycle
• server grpc.max_connection_idle_ms disconnects idle clients
• watchConnectivityState supports deadline-bounded state observation
• lifecycle failures retain causes and add actionable operation/target stack frames

Verification

• focused Bun corpus file passes with no unsupported cases
• shared gRPC diagnostics remain green
• SQL adapter and permanent third-party regression gates remain green

Implemented and pushed in a46582776.

Completed contracts:

• client request and waitForReady activity transitions channels to READY
• grpc.client_idle_timeout_ms transitions inactive clients to IDLE and enforces the one-second minimum
• requests reconnect after an idle transition
• Unix-domain-socket targets use the same lifecycle through target-aware server lookup
• grpc.max_connection_idle_ms transitions inactive clients to IDLE
• watchConnectivityState supports deadline-bounded transition observation
• watcher deadline errors preserve cause and add operation, target, and source-module stack context

Verification:

• focused Bun corpus: 8 passed, 0 failed, 0 todo, 0 unsupported
• permanent gRPC diagnostics: 8 passed
• SQL adapter contracts: passed
• permanent third-party JWT/utility mini-suite: passed
• zig fmt --check and git diff --check: passed

The cumulative checkpoint is now 323 files, 2,661 passed, 209 todo, 0 failed, 0 unsupported, and 171 allowed-empty through position 3981.