Isolate IPC in Bubblewrap sandboxes (#39586)

## What changed

- Pass `--unshare-ipc` when building Bubblewrap arguments for both restricted-filesystem and full-filesystem sandbox paths.
- Update the Bubblewrap argument tests to cover the new namespace flag.

GitOrigin-RevId: 61fb1d5150d09626a3b6ee7a9c6a508108c52e80

codex-rs/linux-sandbox/src/bwrap.rs

@@ -282,6 +282,7 @@ fn create_bwrap_flags_full_filesystem(command: Vec<String>, options: BwrapOption
         // not need ambient CAP_SYS_ADMIN to create the remaining namespaces.
         "--unshare-user".to_string(),
         "--unshare-pid".to_string(),
+        "--unshare-ipc".to_string(),
     ];
     if options.network_mode.should_unshare_network() {
         args.push("--unshare-net".to_string());
@@ -331,6 +332,7 @@ fn create_bwrap_flags(
     // auto-enable behavior, which is skipped when the caller runs as uid 0.
     args.push("--unshare-user".to_string());
     args.push("--unshare-pid".to_string());
+    args.push("--unshare-ipc".to_string());
     if options.network_mode.should_unshare_network() {
         args.push("--unshare-net".to_string());
     }
@@ -1422,6 +1424,7 @@ mod tests {
                 "/dev/shm".to_string(),
                 "--unshare-user".to_string(),
                 "--unshare-pid".to_string(),
+                "--unshare-ipc".to_string(),
                 "--unshare-net".to_string(),
                 "--proc".to_string(),
                 "/proc".to_string(),

codex-rs/linux-sandbox/src/linux_run_main_tests.rs

@@ -81,6 +81,7 @@ fn inserts_bwrap_argv0_before_command_separator() {
             "/dev".to_string(),
             "--unshare-user".to_string(),
             "--unshare-pid".to_string(),
+            "--unshare-ipc".to_string(),
             "--proc".to_string(),
             "/proc".to_string(),
             "--cap-drop".to_string(),