refactor: make bubblewrap the default Linux sandbox (#13996)

## Summary
- make bubblewrap the default Linux sandbox and keep
`use_legacy_landlock` as the only override
- remove `use_linux_sandbox_bwrap` from feature, config, schema, and
docs surfaces
- update Linux sandbox selection, CLI/config plumbing, and related
tests/docs to match the new default
- fold in the follow-up CI fixes for request-permissions responses and
Linux read-only sandbox error text

codex-rs/linux-sandbox/tests/suite/landlock.rs

@@ -72,7 +72,7 @@ async fn run_cmd_result_with_writable_roots(
     cmd: &[&str],
     writable_roots: &[PathBuf],
     timeout_ms: u64,
-    use_bwrap_sandbox: bool,
+    use_legacy_landlock: bool,
     network_access: bool,
 ) -> Result<codex_core::exec::ExecToolCallOutput> {
     let sandbox_policy = SandboxPolicy::WorkspaceWrite {
@@ -96,7 +96,7 @@ async fn run_cmd_result_with_writable_roots(
         file_system_sandbox_policy,
         network_sandbox_policy,
         timeout_ms,
-        use_bwrap_sandbox,
+        use_legacy_landlock,
     )
     .await
 }
@@ -108,7 +108,7 @@ async fn run_cmd_result_with_policies(
     file_system_sandbox_policy: FileSystemSandboxPolicy,
     network_sandbox_policy: NetworkSandboxPolicy,
     timeout_ms: u64,
-    use_bwrap_sandbox: bool,
+    use_legacy_landlock: bool,
 ) -> Result<codex_core::exec::ExecToolCallOutput> {
     let cwd = std::env::current_dir().expect("cwd should exist");
     let sandbox_cwd = cwd.clone();
@@ -133,7 +133,7 @@ async fn run_cmd_result_with_policies(
         network_sandbox_policy,
         sandbox_cwd.as_path(),
         &codex_linux_sandbox_exe,
-        use_bwrap_sandbox,
+        use_legacy_landlock,
         None,
     )
     .await
@@ -155,7 +155,7 @@ async fn should_skip_bwrap_tests() -> bool {
         &["bash", "-lc", "true"],
         &[],
         NETWORK_TIMEOUT_MS,
-        true,
+        false,
         true,
     )
     .await
@@ -216,7 +216,7 @@ async fn test_dev_null_write() {
         // We have seen timeouts when running this test in CI on GitHub,
         // so we are using a generous timeout until we can diagnose further.
         LONG_TIMEOUT_MS,
-        true,
+        false,
         true,
     )
     .await
@@ -240,7 +240,7 @@ async fn bwrap_populates_minimal_dev_nodes() {
         ],
         &[],
         LONG_TIMEOUT_MS,
-        true,
+        false,
         true,
     )
     .await
@@ -278,7 +278,7 @@ async fn bwrap_preserves_writable_dev_shm_bind_mount() {
         ],
         &[PathBuf::from("/dev/shm")],
         LONG_TIMEOUT_MS,
-        true,
+        false,
         true,
     )
     .await
@@ -442,7 +442,7 @@ async fn sandbox_blocks_git_and_codex_writes_inside_writable_root() {
             ],
             &[tmpdir.path().to_path_buf()],
             LONG_TIMEOUT_MS,
-            true,
+            false,
             true,
         )
         .await,
@@ -458,7 +458,7 @@ async fn sandbox_blocks_git_and_codex_writes_inside_writable_root() {
             ],
             &[tmpdir.path().to_path_buf()],
             LONG_TIMEOUT_MS,
-            true,
+            false,
             true,
         )
         .await,
@@ -495,7 +495,7 @@ async fn sandbox_blocks_codex_symlink_replacement_attack() {
             ],
             &[tmpdir.path().to_path_buf()],
             LONG_TIMEOUT_MS,
-            true,
+            false,
             true,
         )
         .await,
@@ -548,7 +548,7 @@ async fn sandbox_blocks_explicit_split_policy_carveouts_under_bwrap() {
             file_system_sandbox_policy,
             NetworkSandboxPolicy::Enabled,
             LONG_TIMEOUT_MS,
-            true,
+            false,
         )
         .await,
         "explicit split-policy carveout should be denied under bubblewrap",
@@ -599,7 +599,7 @@ async fn sandbox_blocks_root_read_carveouts_under_bwrap() {
             file_system_sandbox_policy,
             NetworkSandboxPolicy::Enabled,
             LONG_TIMEOUT_MS,
-            true,
+            false,
         )
         .await,
         "root-read carveout should be denied under bubblewrap",

codex-rs/linux-sandbox/tests/suite/managed_proxy.rs

@@ -133,7 +133,6 @@ async fn run_linux_sandbox_direct(
         cwd.to_string_lossy().to_string(),
         "--sandbox-policy".to_string(),
         policy_json,
-        "--use-bwrap-sandbox".to_string(),
     ];
     if allow_network_for_proxy {
         args.push("--allow-network-for-proxy".to_string());