refactor: Split engine.rs into submodules

Break the 4733-line engine.rs into engine/mod.rs (2650 lines) plus
11 focused submodules. All extracted methods remain as `impl Engine`
blocks — no public API changes, all 130 tests pass unmodified.

New structure:
- engine/definitions/{templates,agent_defs,swarm_defs,schedules,triggers}.rs
- engine/{scheduler,trigger_executor,session_repair,pty_operations,subscriptions}.rs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: 2witstudios

crates/pu-engine/src/engine/definitions/agent_defs.rs

@@ -0,0 +1,163 @@
+use std::path::Path;
+
+use pu_core::paths;
+use pu_core::protocol::{AgentDefInfo, Response};
+
+use super::super::Engine;
+
+impl Engine {
+    pub(in crate::engine) async fn handle_list_agent_defs(&self, project_root: &str) -> Response {
+        let pr = project_root.to_string();
+        match tokio::task::spawn_blocking(move || {
+            let root = Path::new(&pr);
+            let defs = pu_core::agent_def::list_agent_defs(root);
+            let infos: Vec<AgentDefInfo> = defs
+                .into_iter()
+                .map(|d| AgentDefInfo {
+                    name: d.name,
+                    agent_type: d.agent_type,
+                    template: d.template,
+                    inline_prompt: d.inline_prompt,
+                    tags: d.tags,
+                    scope: d.scope,
+                    available_in_command_dialog: d.available_in_command_dialog,
+                    icon: d.icon,
+                    command: d.command,
+                })
+                .collect();
+            infos
+        })
+        .await
+        {
+            Ok(agent_defs) => Response::AgentDefList { agent_defs },
+            Err(e) => Response::Error {
+                code: "INTERNAL_ERROR".into(),
+                message: format!("task join error: {e}"),
+            },
+        }
+    }
+
+    pub(in crate::engine) async fn handle_get_agent_def(
+        &self,
+        project_root: &str,
+        name: &str,
+    ) -> Response {
+        let pr = project_root.to_string();
+        let n = name.to_string();
+        match tokio::task::spawn_blocking(move || {
+            pu_core::agent_def::find_agent_def(Path::new(&pr), &n)
+        })
+        .await
+        {
+            Ok(Some(d)) => Response::AgentDefDetail {
+                name: d.name,
+                agent_type: d.agent_type,
+                template: d.template,
+                inline_prompt: d.inline_prompt,
+                tags: d.tags,
+                scope: d.scope,
+                available_in_command_dialog: d.available_in_command_dialog,
+                icon: d.icon,
+                command: d.command,
+            },
+            Ok(None) => Response::Error {
+                code: "NOT_FOUND".into(),
+                message: format!("agent def '{name}' not found"),
+            },
+            Err(e) => Response::Error {
+                code: "INTERNAL_ERROR".into(),
+                message: format!("task join error: {e}"),
+            },
+        }
+    }
+
+    #[allow(clippy::too_many_arguments)]
+    pub(in crate::engine) async fn handle_save_agent_def(
+        &self,
+        project_root: &str,
+        name: &str,
+        agent_type: &str,
+        template: Option<String>,
+        inline_prompt: Option<String>,
+        tags: Vec<String>,
+        scope: &str,
+        available_in_command_dialog: bool,
+        icon: Option<String>,
+        command: Option<String>,
+    ) -> Response {
+        let dir = match Self::resolve_scope_dir(
+            project_root,
+            scope,
+            paths::agents_dir,
+            paths::global_agents_dir,
+        ) {
+            Ok(d) => d,
+            Err(msg) => {
+                return Response::Error {
+                    code: "IO_ERROR".into(),
+                    message: msg,
+                };
+            }
+        };
+        let def = pu_core::agent_def::AgentDef {
+            name: name.to_string(),
+            agent_type: agent_type.to_string(),
+            template,
+            inline_prompt,
+            tags,
+            scope: scope.to_string(),
+            available_in_command_dialog,
+            icon,
+            command,
+        };
+        match tokio::task::spawn_blocking(move || pu_core::agent_def::save_agent_def(&dir, &def))
+            .await
+        {
+            Ok(Ok(())) => Response::Ok,
+            Ok(Err(e)) => Response::Error {
+                code: "IO_ERROR".into(),
+                message: format!("failed to save agent def: {e}"),
+            },
+            Err(e) => Response::Error {
+                code: "INTERNAL_ERROR".into(),
+                message: format!("task join error: {e}"),
+            },
+        }
+    }
+
+    pub(in crate::engine) async fn handle_delete_agent_def(
+        &self,
+        project_root: &str,
+        name: &str,
+        scope: &str,
+    ) -> Response {
+        let dir = match Self::resolve_scope_dir(
+            project_root,
+            scope,
+            paths::agents_dir,
+            paths::global_agents_dir,
+        ) {
+            Ok(d) => d,
+            Err(msg) => {
+                return Response::Error {
+                    code: "IO_ERROR".into(),
+                    message: msg,
+                };
+            }
+        };
+        let n = name.to_string();
+        match tokio::task::spawn_blocking(move || pu_core::agent_def::delete_agent_def(&dir, &n))
+            .await
+        {
+            Ok(Ok(_)) => Response::Ok,
+            Ok(Err(e)) => Response::Error {
+                code: "IO_ERROR".into(),
+                message: format!("failed to delete agent def: {e}"),
+            },
+            Err(e) => Response::Error {
+                code: "INTERNAL_ERROR".into(),
+                message: format!("task join error: {e}"),
+            },
+        }
+    }
+}

crates/pu-engine/src/engine/definitions/mod.rs

@@ -0,0 +1,5 @@
+mod agent_defs;
+mod schedules;
+mod swarm_defs;
+mod templates;
+mod triggers;