permissions: make SessionConfigured profile-only (#19774)

## Why

`SessionConfiguredEvent` is the internal event that tells clients what
permissions are active for a session. Emitting both `sandbox_policy` and
`permission_profile` leaves two possible authorities and forces every
consumer to decide which one to honor. At this point in the migration,
the profile is expressive enough to represent managed, disabled, and
external sandbox enforcement, so the internal event can be profile-only.

The wire compatibility concern is older serialized events or rollout
data that only contain `sandbox_policy`; those still need to
deserialize.

## What Changed

- Removes `sandbox_policy` from `SessionConfiguredEvent` and makes
`permission_profile` required.
- Adds custom deserialization so old payloads with only `sandbox_policy`
are upgraded to a cwd-anchored `PermissionProfile`.
- Updates core event emission and TUI session handling to sync
permissions from the profile directly.
- Updates app-server response construction to derive the legacy
`sandbox` response field from the active thread snapshot instead of from
`SessionConfiguredEvent`.
- Updates yolo-mode display logic to treat both
`PermissionProfile::Disabled` and managed unrestricted filesystem plus
enabled network as full-access, while still preserving the distinction
between no sandbox and external sandboxing.

## Verification

- `cargo test -p codex-protocol session_configured_event --lib`
- `cargo test -p codex-protocol serialize_event --lib`
- `cargo test -p codex-exec session_configured --lib`
- `cargo test -p codex-app-server
thread_response_permission_profile_preserves_enforcement --lib`
- `cargo test -p codex-core
session_configured_reports_permission_profile_for_external_sandbox
--lib`
- `cargo test -p codex-tui session_configured --lib`
- `cargo test -p codex-tui
yolo_mode_includes_managed_full_access_profiles --lib`


































---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/openai/codex/pull/19774).
* #19900
* #19899
* #19776
* #19775
* __->__ #19774

codex-rs/exec/tests/event_processor_with_json_output.rs

@@ -28,9 +28,9 @@ use codex_app_server_protocol::TurnStartedNotification;
 use codex_app_server_protocol::TurnStatus;
 use codex_app_server_protocol::WebSearchAction as ApiWebSearchAction;
 use codex_protocol::ThreadId;
+use codex_protocol::models::PermissionProfile;
 use codex_protocol::models::WebSearchAction;
 use codex_protocol::protocol::AskForApproval;
-use codex_protocol::protocol::SandboxPolicy;
 use codex_protocol::protocol::SessionConfiguredEvent;
 use codex_utils_absolute_path::test_support::PathBufExt;
 use codex_utils_absolute_path::test_support::test_path_buf;
@@ -114,8 +114,7 @@ fn session_configured_produces_thread_started_event() {
         service_tier: None,
         approval_policy: AskForApproval::Never,
         approvals_reviewer: codex_protocol::config_types::ApprovalsReviewer::User,
-        sandbox_policy: SandboxPolicy::new_read_only_policy(),
-        permission_profile: None,
+        permission_profile: PermissionProfile::read_only(),
         cwd: test_path_buf("/tmp/project").abs(),
         reasoning_effort: None,
         history_log_id: 0,