feat(core): add structured network approval plumbing and policy decision model (#11672)

### Description
#### Summary
Introduces the core plumbing required for structured network approvals

#### What changed
- Added structured network policy decision modeling in core.
- Added approval payload/context types needed for network approval
semantics.
- Wired shell/unified-exec runtime plumbing to consume structured
decisions.
- Updated related core error/event surfaces for structured handling.
- Updated protocol plumbing used by core approval flow.
- Included small CLI debug sandbox compatibility updates needed by this
layer.

#### Why
establishes the minimal backend foundation for network approvals without
yet changing high-level orchestration or TUI behavior.

#### Notes
- Behavior remains constrained by existing requirements/config gating.
- Follow-up PRs in the stack handle orchestration, UX, and app-server
integration.

---------

Co-authored-by: Codex <199175422+chatgpt-codex-connector[bot]@users.noreply.github.com>

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

@@ -2476,6 +2476,7 @@ async fn exec_approval_emits_proposed_command_and_decision_history() {
         reason: Some(
             "this is a test reason such as one that would be produced by the model".into(),
         ),
+        network_approval_context: None,
         proposed_execpolicy_amendment: None,
         parsed_cmd: vec![],
     };
@@ -2520,6 +2521,7 @@ async fn exec_approval_decision_truncates_multiline_and_long_commands() {
         reason: Some(
             "this is a test reason such as one that would be produced by the model".into(),
         ),
+        network_approval_context: None,
         proposed_execpolicy_amendment: None,
         parsed_cmd: vec![],
     };
@@ -2570,6 +2572,7 @@ async fn exec_approval_decision_truncates_multiline_and_long_commands() {
         command: vec!["bash".into(), "-lc".into(), long],
         cwd: std::env::current_dir().unwrap_or_else(|_| PathBuf::from(".")),
         reason: None,
+        network_approval_context: None,
         proposed_execpolicy_amendment: None,
         parsed_cmd: vec![],
     };
@@ -5450,6 +5453,7 @@ async fn approval_modal_exec_snapshot() -> anyhow::Result<()> {
         reason: Some(
             "this is a test reason such as one that would be produced by the model".into(),
         ),
+        network_approval_context: None,
         proposed_execpolicy_amendment: Some(ExecPolicyAmendment::new(vec![
             "echo".into(),
             "hello".into(),
@@ -5506,6 +5510,7 @@ async fn approval_modal_exec_without_reason_snapshot() -> anyhow::Result<()> {
         command: vec!["bash".into(), "-lc".into(), "echo hello world".into()],
         cwd: std::env::current_dir().unwrap_or_else(|_| PathBuf::from(".")),
         reason: None,
+        network_approval_context: None,
         proposed_execpolicy_amendment: Some(ExecPolicyAmendment::new(vec![
             "echo".into(),
             "hello".into(),
@@ -5553,6 +5558,7 @@ async fn approval_modal_exec_multiline_prefix_hides_execpolicy_option_snapshot()
         command: command.clone(),
         cwd: std::env::current_dir().unwrap_or_else(|_| PathBuf::from(".")),
         reason: None,
+        network_approval_context: None,
         proposed_execpolicy_amendment: Some(ExecPolicyAmendment::new(command)),
         parsed_cmd: vec![],
     };
@@ -5912,6 +5918,7 @@ async fn status_widget_and_approval_modal_snapshot() {
         reason: Some(
             "this is a test reason such as one that would be produced by the model".into(),
         ),
+        network_approval_context: None,
         proposed_execpolicy_amendment: Some(ExecPolicyAmendment::new(vec![
             "echo".into(),
             "hello world".into(),