collab-stack: import collab stack with local repairs

Start from the pinned `origin/dev/friel/collab-stack` snapshot and fold in the
local follow-up repairs that made that imported stack usable here: watchdog
spawn/registration plumbing, deferred-tool fallback behavior, collab discovery
fixture alignment, schema mirroring, and subagent-panel fixes.

Original imported source:
- source ref: `refs/remotes/origin/dev/friel/collab-stack`
- source tip: `599ed9dc05eafd116192184bd54a2a55a2c49366`
- original base: `c1d18ceb6f22ae3acd67bbd6badad0f475b31dfc`

codex-rs/cli/src/main.rs

@@ -768,12 +768,16 @@ async fn cli_main(arg0_paths: Arg0DispatchPaths) -> anyhow::Result<()> {
             .await?;
             handle_app_exit(exit_info)?;
         }
-        Some(Subcommand::Exec(mut exec_cli)) => {
+        Some(Subcommand::Exec(exec_cli)) => {
             reject_remote_mode_for_subcommand(
                 root_remote.as_deref(),
                 root_remote_auth_token_env.as_deref(),
                 "exec",
             )?;
+            let mut exec_cli = match exec_cli.validate() {
+                Ok(exec_cli) => exec_cli,
+                Err(err) => err.exit(),
+            };
             exec_cli
                 .shared
                 .inherit_exec_root_options(&interactive.shared);
@@ -1411,8 +1415,13 @@ async fn run_debug_models_command(
         let config = Config::load_with_cli_overrides(cli_overrides).await?;
         let auth_manager =
             AuthManager::shared_from_config(&config, /*enable_codex_api_key_env*/ true).await;
-        let models_manager =
-            build_models_manager(&config, auth_manager, CollaborationModesConfig::default());
+        let models_manager = build_models_manager(
+            &config,
+            auth_manager,
+            config.model_catalog.clone(),
+            config.custom_models.clone(),
+            CollaborationModesConfig::default(),
+        );
         models_manager
             .raw_model_catalog(RefreshStrategy::OnlineIfUncached)
             .await
@@ -1795,6 +1804,40 @@ mod tests {
         assert_eq!(args.session_id.as_deref(), Some("session-123"));
         assert_eq!(args.prompt.as_deref(), Some("re-review"));
     }
+    #[test]
+    fn exec_fork_accepts_prompt_positional() {
+        let cli = MultitoolCli::try_parse_from([
+            "codex",
+            "exec",
+            "--json",
+            "--fork",
+            "session-123",
+            "2+2",
+        ])
+        .expect("parse should succeed");
+
+        let Some(Subcommand::Exec(exec)) = cli.subcommand else {
+            panic!("expected exec subcommand");
+        };
+
+        assert_eq!(exec.fork_session_id.as_deref(), Some("session-123"));
+        assert!(exec.command.is_none());
+        assert_eq!(exec.prompt.as_deref(), Some("2+2"));
+    }
+
+    #[test]
+    fn exec_fork_conflicts_with_resume_subcommand() {
+        let cli =
+            MultitoolCli::try_parse_from(["codex", "exec", "--fork", "session-123", "resume"])
+                .expect("parse should succeed");
+
+        let Some(Subcommand::Exec(exec)) = cli.subcommand else {
+            panic!("expected exec subcommand");
+        };
+
+        let validate_result = exec.validate();
+        assert!(validate_result.is_err());
+    }
 
     #[test]
     fn dangerous_bypass_conflicts_with_approval_policy() {