permissions: remove cwd special path (#19841)

## Why

The experimental `PermissionProfile` API had both `:cwd` and
`:project_roots` special filesystem paths, which made the permission
root ambiguous. This PR removes the unstable `current_working_directory`
special path before the permissions API is stabilized, so callers use
`:project_roots` for symbolic project-root access.

## What changed

- Removes `FileSystemSpecialPath::CurrentWorkingDirectory` from protocol
and app-server protocol models, plus regenerated app-server
JSON/TypeScript schemas.
- Replaces internal `:cwd` permission entries with `:project_roots`
entries.
- Keeps the existing cwd-update behavior for legacy-shaped
workspace-write profiles, while removing the deleted
`CurrentWorkingDirectory` case from that compatibility path.
- Keeps `PermissionProfile::workspace_write()` as the reusable symbolic
workspace-write helper, with docs noting that `:project_roots` entries
resolve at enforcement time.
- Updates app-server docs/examples and approval UI labeling to stop
advertising `:cwd` as a permission token.

## Compatibility

Persisted rollout items may contain the old
`{"kind":"current_working_directory"}` tag from earlier experimental
`permissionProfile` snapshots. This PR keeps that tag as a
deserialize-only alias for `ProjectRoots { subpath: None }`, while
continuing to serialize only the new `project_roots` tag.

## Follow-up

This PR intentionally does not introduce an explicit project-root set on
`SessionConfiguration` or runtime sandbox resolution. Today, the
resolver still uses the active cwd as the single implicit project root.
A follow-up should model project roots separately from tool cwd so
`:project_roots` entries can resolve against the configured project
roots, and resolve to no entries when there are no project roots.

## Verification

- `cargo test -p codex-protocol permissions:: --lib`
- `cargo test -p codex-app-server-protocol`
- `cargo test -p codex-sandboxing -p codex-exec-server --lib`
- `cargo test -p codex-core session_configuration_apply_ --lib`
- `cargo test -p codex-app-server
command_exec_permission_profile_project_roots_use_command_cwd --test
all`
- `cargo test -p codex-tui
thread_read_session_state_does_not_reuse_primary_permission_profile
--lib`
- `cargo test -p codex-tui
preset_matching_accepts_workspace_write_with_extra_roots --lib`
- `cargo test -p codex-config --lib`

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -1434,7 +1434,7 @@ v2_enum_from_core!(
 pub enum FileSystemSpecialPath {
     Root,
     Minimal,
-    CurrentWorkingDirectory,
+    #[serde(alias = "current_working_directory")]
     ProjectRoots {
         subpath: Option<PathBuf>,
     },
@@ -1451,7 +1451,6 @@ impl From<CoreFileSystemSpecialPath> for FileSystemSpecialPath {
         match value {
             CoreFileSystemSpecialPath::Root => Self::Root,
             CoreFileSystemSpecialPath::Minimal => Self::Minimal,
-            CoreFileSystemSpecialPath::CurrentWorkingDirectory => Self::CurrentWorkingDirectory,
             CoreFileSystemSpecialPath::ProjectRoots { subpath } => Self::ProjectRoots { subpath },
             CoreFileSystemSpecialPath::Tmpdir => Self::Tmpdir,
             CoreFileSystemSpecialPath::SlashTmp => Self::SlashTmp,
@@ -1465,7 +1464,6 @@ impl From<FileSystemSpecialPath> for CoreFileSystemSpecialPath {
         match value {
             FileSystemSpecialPath::Root => Self::Root,
             FileSystemSpecialPath::Minimal => Self::Minimal,
-            FileSystemSpecialPath::CurrentWorkingDirectory => Self::CurrentWorkingDirectory,
             FileSystemSpecialPath::ProjectRoots { subpath } => Self::ProjectRoots { subpath },
             FileSystemSpecialPath::Tmpdir => Self::Tmpdir,
             FileSystemSpecialPath::SlashTmp => Self::SlashTmp,
@@ -8111,6 +8109,26 @@ mod tests {
         .expect_err("zero glob scan depth should fail deserialization");
     }
 
+    #[test]
+    fn legacy_current_working_directory_special_path_deserializes_as_project_roots() {
+        let special_path = serde_json::from_value::<FileSystemSpecialPath>(json!({
+            "kind": "current_working_directory",
+        }))
+        .expect("legacy cwd special path should deserialize");
+
+        assert_eq!(
+            special_path,
+            FileSystemSpecialPath::ProjectRoots { subpath: None }
+        );
+        assert_eq!(
+            serde_json::to_value(&special_path).expect("serialize special path"),
+            json!({
+                "kind": "project_roots",
+                "subpath": null,
+            })
+        );
+    }
+
     #[test]
     fn permissions_request_approval_response_uses_granted_permission_profile_without_macos() {
         let read_only_path = if cfg!(windows) {