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`



































































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[//]: # (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/app-server/src/codex_message_processor.rs

@@ -2278,9 +2278,11 @@ impl CodexMessageProcessor {
                 codex_protocol::models::PermissionProfile::from(permission_profile);
             let (mut file_system_sandbox_policy, network_sandbox_policy) =
                 permission_profile.to_runtime_permissions();
+            let configured_file_system_sandbox_policy =
+                self.config.permissions.file_system_sandbox_policy();
             Self::preserve_configured_deny_read_restrictions(
                 &mut file_system_sandbox_policy,
-                &self.config.permissions.file_system_sandbox_policy,
+                &configured_file_system_sandbox_policy,
             );
             let effective_permission_profile =
                 codex_protocol::models::PermissionProfile::from_runtime_permissions_with_enforcement(