Create Engine Installer

Apply the execution contract before this procedure.

Validation Workflow (HARD-GATE)

When building or reviewing an install generator, follow these steps in order. DO NOT ship a generator without completing steps 3 and 4.

1. GENERATE: Run the generator against a clean host app. Show command + terminal output labeled Observed output for the first run. Confirm files are created in correct host paths (initializer at config/initializers/, migrations at db/migrate/, route mount in config/routes.rb).
2. VERIFY: Check output files exist in the correct host paths. List shell commands confirming the initializer, routes, and migrations exist.
3. RERUN: Run the generator a second time; confirm no duplicate files, routes, or initializer blocks are inserted. Show command + terminal output labeled Observed output demonstrating idempotent behavior (skipping/conflict resolution). Use unique, scenario-specific values rather than copying verbatim from templates.
4. TEST: Cover both single-run and rerun behavior in generator specs (see spec template below).
5. DOCUMENT: List what was generated vs. what the user must do manually, including required env vars, rollback steps, and any install docs — verified against what the generator actually produces.

Key implementation rules:

• Configure only in initializers (avoid boot-time mutation).
• Document all required env vars alongside rollback steps.
• Provide sensible defaults that are easy to edit.