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/exec-server/src/file_system.rs

@@ -1,10 +1,12 @@
 use async_trait::async_trait;
 use codex_protocol::config_types::WindowsSandboxLevel;
 use codex_protocol::models::PermissionProfile;
+use codex_protocol::models::SandboxEnforcement;
 use codex_protocol::permissions::FileSystemPath;
 use codex_protocol::permissions::FileSystemSandboxKind;
 use codex_protocol::permissions::FileSystemSandboxPolicy;
 use codex_protocol::permissions::FileSystemSpecialPath;
+use codex_protocol::permissions::NetworkSandboxPolicy;
 use codex_protocol::protocol::SandboxPolicy;
 use codex_utils_absolute_path::AbsolutePathBuf;
 use std::path::Path;
@@ -57,8 +59,13 @@ pub struct FileSystemSandboxContext {
 
 impl FileSystemSandboxContext {
     pub fn from_legacy_sandbox_policy(sandbox_policy: SandboxPolicy, cwd: AbsolutePathBuf) -> Self {
-        let permissions =
-            PermissionProfile::from_legacy_sandbox_policy(&sandbox_policy, cwd.as_path());
+        let file_system_sandbox_policy =
+            FileSystemSandboxPolicy::from_legacy_sandbox_policy_for_cwd(&sandbox_policy, &cwd);
+        let permissions = PermissionProfile::from_runtime_permissions_with_enforcement(
+            SandboxEnforcement::from_legacy_sandbox_policy(&sandbox_policy),
+            &file_system_sandbox_policy,
+            NetworkSandboxPolicy::from(&sandbox_policy),
+        );
         Self::from_permission_profile_with_cwd(permissions, cwd)
     }