permissions: make legacy profile conversion cwd-free (#19414)

## Why

The profile conversion path still required a `cwd` even when it was only
translating a legacy `SandboxPolicy` into a `PermissionProfile`. That
made profile producers invent an ambient `cwd`, which is exactly the
anchoring we are trying to remove from permission-profile data. A legacy
workspace-write policy can be represented symbolically instead: `:cwd =
write` plus read-only `:project_roots` metadata subpaths.

This PR creates that cwd-free base so the rest of the stack can stop
threading cwd through profile construction. Callers that actually need a
concrete runtime filesystem policy for a specific cwd still have an
explicitly named cwd-bound conversion.

## What Changed

- `PermissionProfile::from_legacy_sandbox_policy` now takes only
`&SandboxPolicy`.
- `FileSystemSandboxPolicy::from_legacy_sandbox_policy` is now the
symbolic, cwd-free projection for profiles.
- The old concrete projection is retained as
`FileSystemSandboxPolicy::from_legacy_sandbox_policy_for_cwd` for
runtime/boundary code that must materialize legacy cwd behavior.
- Workspace-write profiles preserve `CurrentWorkingDirectory` and
`ProjectRoots` special entries instead of materializing cwd into
absolute paths.

## Verification

- `cargo check -p codex-protocol -p codex-core -p
codex-app-server-protocol -p codex-app-server -p codex-exec -p
codex-exec-server -p codex-tui -p codex-sandboxing -p
codex-linux-sandbox -p codex-analytics --tests`
- `just fix -p codex-protocol -p codex-core -p codex-app-server-protocol
-p codex-app-server -p codex-exec -p codex-exec-server -p codex-tui -p
codex-sandboxing -p codex-linux-sandbox -p codex-analytics`




---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/openai/codex/pull/19414).
* #19395
* #19394
* #19393
* #19392
* #19391
* __->__ #19414

codex-rs/tui/src/chatwidget/tests/history_replay.rs

@@ -321,13 +321,20 @@ async fn session_configured_syncs_widget_config_permissions_and_cwd() {
     let updated_sandbox = SandboxPolicy::new_workspace_write_policy();
     chat.set_sandbox_policy(updated_sandbox.clone())
         .expect("set sandbox policy");
+    let updated_file_system_policy = FileSystemSandboxPolicy::from_legacy_sandbox_policy_for_cwd(
+        &updated_sandbox,
+        &expected_cwd,
+    );
     assert_eq!(
         chat.config_ref().permissions.permission_profile(),
-        codex_protocol::models::PermissionProfile::from_legacy_sandbox_policy(
-            &updated_sandbox,
-            &expected_cwd
+        codex_protocol::models::PermissionProfile::from_runtime_permissions_with_enforcement(
+            codex_protocol::models::SandboxEnforcement::from_legacy_sandbox_policy(
+                &updated_sandbox
+            ),
+            &updated_file_system_policy,
+            NetworkSandboxPolicy::from(&updated_sandbox),
         ),
-        "local sandbox changes should replace SessionConfigured profile-derived runtime permissions"
+        "local sandbox changes should replace SessionConfigured profile-derived runtime permissions using the widget cwd"
     );
 }