exec-server: route remote network policy decisions

[viyatb-oai]

Summary

• route executor-local proxy policy misses back to the process-scoped core policy decider
• preserve environment, execution, command, and tool-call attribution for Guardian decisions
• correlate concurrent decisions and fail closed on disconnect, process exit, missing deciders, mismatched process IDs, and stale responses
• keep the callback opt-in backward compatible; MITM, credential injection, and hooks remain out of scope

Stack

Depends on #31453, which starts and owns the managed proxy on the executor.

Testing

• just test -p codex-network-proxy policy_decision_callback_opt_in_is_backward_compatible
• just test -p codex-exec-server network_policy_decisions
• just test -p codex-core remote_guardian_receives_exact_trigger_for_network_request (compiled and completed through the standard no-remote-environment skip locally)
• just fix -p codex-exec-server -p codex-network-proxy -p codex-core
• just fix -p codex-exec-server
• just fmt

A final core rebuild after extracting the relay module hit the machine's local disk ceiling while writing Cargo metadata; the extracted executor tests and scoped Clippy pass completed successfully.