refactor: Split engine.rs (4734 LoC) into 17 submodules (1139 LoC core)

[2witstudios]

Summary

• Splits the monolithic engine.rs (4,734 lines) into 17 focused submodule files under engine/
• Core mod.rs reduced to 1,139 lines (struct definitions, new(), handle_request() dispatch, initialization, and tests)
• All impl Engine blocks — Rust allows splitting these across files in submodules
• Zero behavioral changes — pure code-move refactoring
• Rebased onto main (includes PR feat: Make triggers opt-in and fix inject submission #131 trigger opt-in changes)

Module breakdown

Module	Lines	Contents
mod.rs	1,139	Engine struct, dispatch, init, reaper, tests
spawn.rs	519	handle_spawn, handle_spawn_shell
agent_lifecycle.rs	516	kill, rename, suspend, resume, assign_trigger
status.rs	303	status, pulse, diff, agent status reports
worktree_ops.rs	200	create/delete worktree, rollback
helpers.rs	191	parse_agent_command, reconcile, reap, error helpers
definitions/	1,239	CRUD for templates, agent defs, swarm defs, schedules, triggers
subscriptions.rs	128	grid + status pub/sub
scheduler.rs	178	periodic schedule evaluation
trigger_executor.rs	287	idle trigger evaluation + inject
session_repair.rs	232	session file repair + prompt injection
pty_operations.rs	157	PTY I/O: logs, attach, input, resize

Test plan

• cargo test -p pu-engine — all 130 tests pass (119 unit + 11 integration)
• cargo fmt --all — no formatting issues
• cargo test -p pu-engine --no-run — zero warnings
• PR feat: Make triggers opt-in and fix inject submission #131 trigger opt-in changes fully integrated

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 86fb5b2f-0c05-40a0-9c18-3a9bcd14baff

📥 Commits

Reviewing files that changed from the base of the PR and between 8d8ff39 and ce7f9cf.

📒 Files selected for processing (18)

• crates/pu-engine/src/engine.rs
• crates/pu-engine/src/engine/agent_lifecycle.rs
• crates/pu-engine/src/engine/definitions/agent_defs.rs
• crates/pu-engine/src/engine/definitions/mod.rs
• crates/pu-engine/src/engine/definitions/schedules.rs
• crates/pu-engine/src/engine/definitions/swarm_defs.rs
• crates/pu-engine/src/engine/definitions/templates.rs
• crates/pu-engine/src/engine/definitions/triggers.rs
• crates/pu-engine/src/engine/helpers.rs
• crates/pu-engine/src/engine/mod.rs
• crates/pu-engine/src/engine/pty_operations.rs
• crates/pu-engine/src/engine/scheduler.rs
• crates/pu-engine/src/engine/session_repair.rs
• crates/pu-engine/src/engine/spawn.rs
• crates/pu-engine/src/engine/status.rs
• crates/pu-engine/src/engine/subscriptions.rs
• crates/pu-engine/src/engine/trigger_executor.rs
• crates/pu-engine/src/engine/worktree_ops.rs

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch pu/refactor-engine

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