feat: expose plugin migration commands

Forward ash.codegen and ecto.migration through the Aether plugin wrapper and update agent guidance to prefer AshPostgres codegen for resource-backed schema changes.

AGENTS.md

@@ -5,8 +5,9 @@ contract, migrations, assets, and tests owned by this repo.
 
 ## Required Workflow
 
-- Use `scripts/plugin` for plugin-aware commands: `scripts/plugin validate`,
-  `scripts/plugin test`, `scripts/plugin precommit`, and `scripts/plugin smoke`.
+- Use `plugin` for plugin-aware commands in the devenv shell: `plugin validate`,
+  `plugin test`, `plugin precommit`, and `plugin smoke`. Outside the devenv
+  shell, use the local `scripts/plugin` wrapper.
 - Use `devenv shell -- <command>` when running repo commands from outside the
   devenv shell.
 - Raw `mix test` is not the normal entrypoint for this repo; `plugin test`
@@ -14,6 +15,11 @@ contract, migrations, assets, and tests owned by this repo.
   plugin-manager paths.
 - Keep browser assets under the plugin asset pipeline and avoid host app
   internals unless the plugin API requires them.
+- For AshPostgres resource changes, generate migrations with
+  `plugin ash.codegen <name>`. Use `plugin ecto.migration <name>` only for rare
+  manual schema migrations that are not derived from Ash resources.
+- Do not edit an existing migration after it may have run; add a new migration
+  instead.
 
 ## Plugin Contract
 

scripts/plugin

@@ -7,6 +7,8 @@ Usage:
   plugin validate
   plugin test [mix test args...]
   plugin precommit [mix precommit args...]
+  plugin ecto.migration <name> [mix ecto.gen.migration args...]
+  plugin ash.codegen <name> [mix ash_postgres.generate_migrations args...]
   plugin smoke
   plugin shell
 EOF
@@ -77,7 +79,7 @@ fi
 shift
 
 case "$command_name" in
-  validate | test | precommit | smoke | shell) ;;
+  validate | test | precommit | ecto.migration | ash.codegen | smoke | shell) ;;
   -h | --help | help)
     usage
     exit 0