Isolate dev DB per git worktree

config/database.yml now derives the development DB name from the
checkout's git state: the main checkout (.git is a directory) keeps
using build_new_development, while git worktrees (.git is a pointer
file) get build_new_development_<dirname>. Parallel Conductor
worktrees, and apps forked from this template into a sibling checkout,
no longer share or clobber each other's schemas. Override with
DATABASE_NAME if needed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Brian Casel

CLAUDE.md

@@ -10,6 +10,8 @@ Rails 8 + React 19 + PostgreSQL, bridged by **Inertia.js** (no separate API laye
 
 Background jobs, caching, and WebSockets use the Rails 8 "Solid" trifecta (Solid Queue, Solid Cache, Solid Cable), all database-backed. **All four share the single PostgreSQL database** (`build_new_<env>` by default) — there are no separate cache/cable/queue databases, no `db/cache_schema.rb` / `db/cable_schema.rb` / `db/queue_schema.rb`, and `config/cache.yml` / `config/cable.yml` / `config/queue.yml` have no separate connection blocks. Override the connection via `DATABASE_URL` or the `DATABASE_USER` / `DATABASE_PASSWORD` / `DATABASE_HOST` / `DATABASE_PORT` env vars (see `config/database.yml`).
 
+**Per-worktree dev DB isolation.** `config/database.yml` derives the development DB name from the checkout's git state. The main checkout (where `.git` is a directory) keeps using `build_new_development`. Each git worktree (where `.git` is a pointer file written by `git worktree add`, e.g. Conductor workspaces) gets its own DB suffixed with the worktree directory name — `build_new_development_<dirname>` — so parallel worktrees never share or clobber each other's schemas. This matters when forking this template into a new app: if two checkouts share a dev DB, migrations from one will land in the other and `db:schema:dump` will commit phantom tables. Override the derived name with `DATABASE_NAME` if needed.
+
 ## Commands
 
 ```bash

config/database.yml

@@ -20,9 +20,24 @@ default: &default
   host: <%= ENV.fetch("DATABASE_HOST") { "localhost" } %>
   port: <%= ENV.fetch("DATABASE_PORT") { 5432 } %>
 
+<%
+  # Per-worktree dev DB isolation. The main checkout (.git is a directory)
+  # keeps using build_new_development; each git worktree (.git is a pointer
+  # file written by `git worktree add`) gets its own DB suffixed with the
+  # worktree directory name, so parallel Conductor worktrees never share or
+  # clobber each other's schemas. Override with DATABASE_NAME to force a name.
+  app_root = Dir.pwd
+  worktree_db_suffix =
+    if File.file?(File.join(app_root, ".git"))
+      "_#{File.basename(app_root).gsub(/[^a-z0-9_]/i, "_").downcase}"
+    else
+      ""
+    end
+%>
+
 development:
   <<: *default
-  database: build_new_development
+  database: <%= ENV.fetch("DATABASE_NAME") { "build_new_development#{worktree_db_suffix}" } %>
 
 # Warning: The database defined as "test" will be erased and
 # re-generated from your development database when you run "rake".