core: derive active permission profiles (#18277)

## Why

`Permissions` should not store a separate `PermissionProfile` that can
drift from the constrained `SandboxPolicy` and network settings. The
active profile needs to be derived from the same constrained values that
already honor `requirements.toml`.

## What changed

This adds derivation of the active `PermissionProfile` from the
constrained runtime permission settings and exposes that derived value
through config snapshots and thread state. The app-server can then
report the active profile without introducing a second source of truth.

## Verification

- `cargo test -p codex-core --test all permissions_messages --
--nocapture`
- `cargo test -p codex-core --test all request_permissions --
--nocapture`



























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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/18277).
* #18288
* #18287
* #18286
* #18285
* #18284
* #18283
* #18282
* #18281
* #18280
* #18279
* #18278
* __->__ #18277

codex-rs/core/src/codex_thread.rs

@@ -11,6 +11,7 @@ use codex_protocol::error::CodexErr;
 use codex_protocol::error::Result as CodexResult;
 use codex_protocol::mcp::CallToolResult;
 use codex_protocol::models::ContentItem;
+use codex_protocol::models::PermissionProfile;
 use codex_protocol::models::ResponseInputItem;
 use codex_protocol::models::ResponseItem;
 use codex_protocol::openai_models::ReasoningEffort;
@@ -42,6 +43,7 @@ pub struct ThreadConfigSnapshot {
     pub approval_policy: AskForApproval,
     pub approvals_reviewer: ApprovalsReviewer,
     pub sandbox_policy: SandboxPolicy,
+    pub permission_profile: PermissionProfile,
     pub cwd: AbsolutePathBuf,
     pub ephemeral: bool,
     pub reasoning_effort: Option<ReasoningEffort>,