feat: include available decisions in command approval requests (#12758)

Command-approval clients currently infer which choices to show from
side-channel fields like `networkApprovalContext`,
`proposedExecpolicyAmendment`, and `additionalPermissions`. That makes
the request shape harder to evolve, and it forces each client to
replicate the server's heuristics instead of receiving the exact
decision list for the prompt.

This PR introduces a mapping between `CommandExecutionApprovalDecision`
and `codex_protocol::protocol::ReviewDecision`:

```rust
impl From<CoreReviewDecision> for CommandExecutionApprovalDecision {
    fn from(value: CoreReviewDecision) -> Self {
        match value {
            CoreReviewDecision::Approved => Self::Accept,
            CoreReviewDecision::ApprovedExecpolicyAmendment {
                proposed_execpolicy_amendment,
            } => Self::AcceptWithExecpolicyAmendment {
                execpolicy_amendment: proposed_execpolicy_amendment.into(),
            },
            CoreReviewDecision::ApprovedForSession => Self::AcceptForSession,
            CoreReviewDecision::NetworkPolicyAmendment {
                network_policy_amendment,
            } => Self::ApplyNetworkPolicyAmendment {
                network_policy_amendment: network_policy_amendment.into(),
            },
            CoreReviewDecision::Abort => Self::Cancel,
            CoreReviewDecision::Denied => Self::Decline,
        }
    }
}
```

And updates `CommandExecutionRequestApprovalParams` to have a new field:

```rust
available_decisions: Option<Vec<CommandExecutionApprovalDecision>>
```

when, if specified, should make it easier for clients to display an
appropriate list of options in the UI.

This makes it possible for `CoreShellActionProvider::prompt()` in
`unix_escalation.rs` to specify the `Vec<ReviewDecision>` directly,
adding support for `ApprovedForSession` when approving a skill script,
which was previously missing in the TUI.

Note this results in a significant change to `exec_options()` in
`approval_overlay.rs`, as the displayed options are now derived from
`available_decisions: &[ReviewDecision]`.

## What Changed

- Add `available_decisions` to
[`ExecApprovalRequestEvent`](de00e932dd/codex-rs/protocol/src/approvals.rs (L111-L175)),
including helpers to derive the legacy default choices when older
senders omit the field.
- Map `codex_protocol::protocol::ReviewDecision` to app-server
`CommandExecutionApprovalDecision` and expose the ordered list as
experimental `availableDecisions` in
[`CommandExecutionRequestApprovalParams`](de00e932dd/codex-rs/app-server-protocol/src/protocol/v2.rs (L3798-L3807)).
- Thread optional `available_decisions` through the core approval path
so Unix shell escalation can explicitly request `ApprovedForSession` for
session-scoped approvals instead of relying on client heuristics.
[`unix_escalation.rs`](de00e932dd/codex-rs/core/src/tools/runtimes/shell/unix_escalation.rs (L194-L214))
- Update the TUI approval overlay to build its buttons from the ordered
decision list, while preserving the legacy fallback when
`available_decisions` is missing.
- Update the app-server README, test client output, and generated schema
artifacts to document and surface the new field.

## Testing

- Add `approval_overlay.rs` coverage for explicit decision lists,
including the generic `ApprovedForSession` path and network approval
options.
- Update `chatwidget/tests.rs` and app-server protocol tests to populate
the new optional field and keep older event shapes working.

## Developers Docs

- If we document `item/commandExecution/requestApproval` on
[developers.openai.com/codex](https://developers.openai.com/codex), add
experimental `availableDecisions` as the preferred source of approval
choices and note that older servers may omit it.

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

@@ -2790,6 +2790,7 @@ async fn exec_approval_emits_proposed_command_and_decision_history() {
         proposed_execpolicy_amendment: None,
         proposed_network_policy_amendments: None,
         additional_permissions: None,
+        available_decisions: None,
         parsed_cmd: vec![],
     };
     chat.handle_codex_event(Event {
@@ -2839,6 +2840,7 @@ async fn exec_approval_uses_approval_id_when_present() {
             proposed_execpolicy_amendment: None,
             proposed_network_policy_amendments: None,
             additional_permissions: None,
+            available_decisions: None,
             parsed_cmd: vec![],
         }),
     });
@@ -2875,6 +2877,7 @@ async fn exec_approval_decision_truncates_multiline_and_long_commands() {
         proposed_execpolicy_amendment: None,
         proposed_network_policy_amendments: None,
         additional_permissions: None,
+        available_decisions: None,
         parsed_cmd: vec![],
     };
     chat.handle_codex_event(Event {
@@ -2929,6 +2932,7 @@ async fn exec_approval_decision_truncates_multiline_and_long_commands() {
         proposed_execpolicy_amendment: None,
         proposed_network_policy_amendments: None,
         additional_permissions: None,
+        available_decisions: None,
         parsed_cmd: vec![],
     };
     chat.handle_codex_event(Event {
@@ -6748,6 +6752,7 @@ async fn approval_modal_exec_snapshot() -> anyhow::Result<()> {
         ])),
         proposed_network_policy_amendments: None,
         additional_permissions: None,
+        available_decisions: None,
         parsed_cmd: vec![],
     };
     chat.handle_codex_event(Event {
@@ -6808,6 +6813,7 @@ async fn approval_modal_exec_without_reason_snapshot() -> anyhow::Result<()> {
         ])),
         proposed_network_policy_amendments: None,
         additional_permissions: None,
+        available_decisions: None,
         parsed_cmd: vec![],
     };
     chat.handle_codex_event(Event {
@@ -6855,6 +6861,7 @@ async fn approval_modal_exec_multiline_prefix_hides_execpolicy_option_snapshot()
         proposed_execpolicy_amendment: Some(ExecPolicyAmendment::new(command)),
         proposed_network_policy_amendments: None,
         additional_permissions: None,
+        available_decisions: None,
         parsed_cmd: vec![],
     };
     chat.handle_codex_event(Event {
@@ -7221,6 +7228,7 @@ async fn status_widget_and_approval_modal_snapshot() {
         ])),
         proposed_network_policy_amendments: None,
         additional_permissions: None,
+        available_decisions: None,
         parsed_cmd: vec![],
     };
     chat.handle_codex_event(Event {