feat(sandbox): enforce proxy-aware network routing in sandbox (#11113)

## Summary
- expand proxy env injection to cover common tool env vars
(`HTTP_PROXY`/`HTTPS_PROXY`/`ALL_PROXY`/`NO_PROXY` families +
tool-specific variants)
- harden macOS Seatbelt network policy generation to route through
inferred loopback proxy endpoints and fail closed when proxy env is
malformed
- thread proxy-aware Linux sandbox flags and add minimal bwrap netns
isolation hook for restricted non-proxy runs
- add/refresh tests for proxy env wiring, Seatbelt policy generation,
and Linux sandbox argument wiring

codex-rs/core/src/unified_exec/mod.rs

@@ -4,7 +4,7 @@
 //! - Manages interactive processes (create, reuse, buffer output with caps).
 //! - Uses the shared ToolOrchestrator to handle approval, sandbox selection, and
 //!   retry semantics in a single, descriptive flow.
-//! - Spawns the PTY from a sandbox‑transformed `ExecEnv`; on sandbox denial,
+//! - Spawns the PTY from a sandbox-transformed `ExecRequest`; on sandbox denial,
 //!   retries without sandbox when policy allows (no re‑prompt thanks to caching).
 //! - Uses the shared `is_likely_sandbox_denied` heuristic to keep denial messages
 //!   consistent with other exec paths.
@@ -12,7 +12,7 @@
 //! Flow at a glance (open process)
 //! 1) Build a small request `{ command, cwd }`.
 //! 2) Orchestrator: approval (bypass/cache/prompt) → select sandbox → run.
-//! 3) Runtime: transform `CommandSpec` → `ExecEnv` → spawn PTY.
+//! 3) Runtime: transform `CommandSpec` -> `ExecRequest` -> spawn PTY.
 //! 4) If denial, orchestrator retries with `SandboxType::None`.
 //! 5) Process handle is returned with streaming output + metadata.
 //!
@@ -27,6 +27,7 @@ use std::path::PathBuf;
 use std::sync::Arc;
 use std::time::Duration;
 
+use codex_network_proxy::NetworkProxy;
 use rand::Rng;
 use rand::rng;
 use tokio::sync::Mutex;
@@ -79,6 +80,7 @@ pub(crate) struct ExecCommandRequest {
     pub yield_time_ms: u64,
     pub max_output_tokens: Option<usize>,
     pub workdir: Option<PathBuf>,
+    pub network: Option<NetworkProxy>,
     pub tty: bool,
     pub sandbox_permissions: SandboxPermissions,
     pub justification: Option<String>,
@@ -203,6 +205,7 @@ mod tests {
                     yield_time_ms,
                     max_output_tokens: None,
                     workdir: None,
+                    network: None,
                     tty: true,
                     sandbox_permissions: SandboxPermissions::UseDefault,
                     justification: None,