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/README.md

@@ -909,7 +909,7 @@ Run a standalone command (argv vector) in the server’s sandbox without creatin
         "type": "managed",
         "fileSystem": { "type": "restricted", "entries": [
             { "path": { "type": "special", "value": { "kind": "root" } }, "access": "read" },
-            { "path": { "type": "special", "value": { "kind": "current_working_directory" } }, "access": "write" }
+            { "path": { "type": "special", "value": { "kind": "project_roots", "subpath": null } }, "access": "write" }
         ] },
         "network": { "enabled": false }
     },
@@ -1255,7 +1255,7 @@ the client can offer session-scoped and/or persistent approval choices.
 
 ### Permission requests
 
-The built-in `request_permissions` tool sends an `item/permissions/requestApproval` JSON-RPC request to the client with the requested permission profile. This v2 payload mirrors the command-execution `additionalPermissions` shape: it can request network access and additional filesystem access. The `cwd` field identifies the directory used to resolve cwd-relative permissions such as `:cwd`, `:project_roots`, and relative deny globs.
+The built-in `request_permissions` tool sends an `item/permissions/requestApproval` JSON-RPC request to the client with the requested permission profile. This v2 payload mirrors the command-execution `additionalPermissions` shape: it can request network access and additional filesystem access. The `cwd` field identifies the directory used to resolve project-root permissions and relative deny globs.
 
 ```json
 {