permissions: derive compatibility policies from profiles (#19392)

## Why

After #19391, `PermissionProfile` and the split filesystem/network
policies could still be stored in parallel. That creates drift risk: a
profile can preserve deny globs, external enforcement, or split
filesystem entries while a cached projection silently loses those
details. This PR makes the profile the runtime source and derives
compatibility views from it.

## What Changed

- Removes stored filesystem/network sandbox projections from
`Permissions` and `SessionConfiguration`; their accessors now derive
from the canonical `PermissionProfile`.
- Derives legacy `SandboxPolicy` snapshots from profiles only where an
older API still needs that field.
- Updates MCP connection and elicitation state to track
`PermissionProfile` instead of `SandboxPolicy` for auto-approval
decisions.
- Adds semantic filesystem-policy comparison so cwd changes can preserve
richer profiles while still recognizing equivalent legacy projections
independent of entry ordering.
- Updates config/session tests to assert profile-derived projections
instead of parallel stored fields.

## Verification

- `cargo test -p codex-core direct_write_roots`
- `cargo test -p codex-core runtime_roots_to_legacy_projection`
- `cargo test -p codex-app-server
requested_permissions_trust_project_uses_permission_profile_intent`



































































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

codex-rs/core/src/unified_exec/process_manager.rs

@@ -788,6 +788,8 @@ impl UnifiedExecProcessManager {
             self,
             context.turn.tools_config.unified_exec_shell_mode.clone(),
         );
+        let file_system_sandbox_policy = context.turn.file_system_sandbox_policy();
+        let sandbox_policy = context.turn.sandbox_policy();
         let exec_approval_requirement = context
             .session
             .services
@@ -795,8 +797,8 @@ impl UnifiedExecProcessManager {
             .create_exec_approval_requirement_for_command(ExecApprovalRequest {
                 command: &request.command,
                 approval_policy: context.turn.approval_policy.value(),
-                sandbox_policy: context.turn.sandbox_policy.get(),
-                file_system_sandbox_policy: &context.turn.file_system_sandbox_policy,
+                sandbox_policy: &sandbox_policy,
+                file_system_sandbox_policy: &file_system_sandbox_policy,
                 sandbox_permissions: if request.additional_permissions_preapproved {
                     crate::sandboxing::SandboxPermissions::UseDefault
                 } else {