Migrate legacy exec policy allow rules (#34271)

## What changed

- On session startup, remove exact `allow` entries from `rules/default.rules`
  for command prefixes that Codex no longer suggests as policy amendments.
- Record the migration in `.sandbox_migration` so it runs only once, preserving
  rules created after the migration.
- Skip the migration when user and project exec policy rules are ignored.
- Expand the protected prefix list across shells, interpreters, package runners,
  and destructive or privilege-related commands.

## Testing

- Cover selective removal, case-insensitive matching, one-time behavior, and the
  startup path with ignored policy rules.

GitOrigin-RevId: a0c60e3f82b9630e621fd034b40462e3ab775102

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

@@ -33,7 +33,9 @@ use crate::context::world_state::WorldState;
 use crate::current_time::TimeProvider;
 use crate::default_skill_metadata_budget;
 use crate::environment_selection::TurnEnvironmentSnapshot;
+use crate::exec_policy::BANNED_PREFIX_SUGGESTIONS;
 use crate::exec_policy::ExecPolicyManager;
+use crate::exec_policy::default_policy_path;
 use crate::image_preparation::prepare_response_items as prepare_image_response_items;
 use crate::parse_turn_item;
 use crate::realtime_conversation::RealtimeConversationManager;
@@ -57,6 +59,7 @@ use codex_connectors::connector_runtime_context_key;
 use codex_core_skills::injection::HostSkillsCatalogInWorldState;
 use codex_exec_server::Environment;
 use codex_exec_server::EnvironmentManager;
+use codex_execpolicy::prefix_rule_migration;
 use codex_extension_api::ExtensionDataInit;
 use codex_extension_api::LoadedUserInstructions;
 use codex_extension_api::PromptFragment;
@@ -549,6 +552,22 @@ impl Session {
         } else if let Some(exec_policy) = &inherited_exec_policy {
             Arc::clone(exec_policy)
         } else {
+            if !config
+                .config_layer_stack
+                .ignore_user_and_project_exec_policy_rules()
+            {
+                let codex_home = config.codex_home.clone();
+                let policy_path = default_policy_path(codex_home.as_path());
+                if let Err(err) = prefix_rule_migration(
+                    codex_home.as_path(),
+                    policy_path.as_path(),
+                    BANNED_PREFIX_SUGGESTIONS,
+                )
+                .await
+                {
+                    tracing::warn!(error = %err, "failed to run prefix rule migration");
+                }
+            }
             Arc::new(
                 ExecPolicyManager::load(&config.config_layer_stack)
                     .await