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/core/src/session/session.rs

@@ -149,19 +149,19 @@ impl SessionConfiguration {
             );
         let file_system_policy_matches_legacy = current_file_system_sandbox_policy
             .is_semantically_equivalent_to(&legacy_file_system_projection, &self.cwd);
-        let file_system_policy_has_rebindable_cwd_write = current_file_system_sandbox_policy
-            .entries
-            .iter()
-            .any(|entry| {
-                entry.access.can_write()
-                    && matches!(
-                        &entry.path,
-                        FileSystemPath::Special {
-                            value: FileSystemSpecialPath::CurrentWorkingDirectory
-                                | FileSystemSpecialPath::ProjectRoots { subpath: None },
-                        }
-                    )
-            });
+        let file_system_policy_has_rebindable_project_root_write =
+            current_file_system_sandbox_policy
+                .entries
+                .iter()
+                .any(|entry| {
+                    entry.access.can_write()
+                        && matches!(
+                            &entry.path,
+                            FileSystemPath::Special {
+                                value: FileSystemSpecialPath::ProjectRoots { subpath: None },
+                            }
+                        )
+                });
         if let Some(collaboration_mode) = updates.collaboration_mode.clone() {
             next_configuration.collaboration_mode = collaboration_mode;
         }
@@ -228,7 +228,7 @@ impl SessionConfiguration {
             )?;
         } else if cwd_changed
             && file_system_policy_matches_legacy
-            && file_system_policy_has_rebindable_cwd_write
+            && file_system_policy_has_rebindable_project_root_write
         {
             // Preserve richer split policies across cwd-only updates; only
             // rederive when the session is already using a structurally

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

@@ -2874,7 +2874,7 @@ async fn session_configuration_apply_preserves_profile_file_system_policy_on_cwd
     let file_system_sandbox_policy = FileSystemSandboxPolicy::restricted(vec![
         FileSystemSandboxEntry {
             path: FileSystemPath::Special {
-                value: FileSystemSpecialPath::CurrentWorkingDirectory,
+                value: FileSystemSpecialPath::project_roots(/*subpath*/ None),
             },
             access: FileSystemAccessMode::Write,
         },
@@ -3187,7 +3187,7 @@ async fn session_configuration_apply_preserves_absolute_cwd_write_root_on_cwd_up
         !updated
             .file_system_sandbox_policy()
             .can_write_path_with_cwd(next_cwd.as_path(), updated.cwd.as_path()),
-        "cwd-only update must not reinterpret an absolute old-cwd grant as :cwd"
+        "cwd-only update must not reinterpret an absolute old-cwd grant as :project_roots"
     );
 }
 
@@ -3850,7 +3850,7 @@ async fn request_permissions_response_materializes_session_cwd_grants_before_rec
         file_system: Some(FileSystemPermissions {
             entries: vec![FileSystemSandboxEntry {
                 path: FileSystemPath::Special {
-                    value: FileSystemSpecialPath::CurrentWorkingDirectory,
+                    value: FileSystemSpecialPath::project_roots(/*subpath*/ None),
                 },
                 access: FileSystemAccessMode::Write,
             }],