Day 3a: Rails worker — real substrate copy + Ruby AST rename

[dadachi]

Summary

• src/agents/workers/rails.ts — real implementation: copy \$NATEMPLATE_API → ./out/<slug>/rails (filtered: no .git, node_modules, tmp, log, vendor/bundle, sockets/FIFOs), invoke rename.rb, run git init -q -b main. Stub path preserved behind isStub("rails").
• scripts/ruby/rename.rb — takes {renamePlan, root} on stdin, rewrites file contents AND renames paths (deepest-first) for PascalCase / snake_case / plural / SCREAMING variants.
• src/ruby.ts — thin execFile wrapper per CLAUDE.md convention; JSON on stdin/stdout, propagates non-zero exit codes with stderr tail.

Tricky bit worth flagging

Ruby's \b treats _ as a word char, so \bshops\b silently fails to match inside shops_controller or accounts_shopkeeper. First attempt left 10+ files unrenamed. Fix: letter-aware boundary (?<![A-Za-z])...(?![A-Za-z]) — treats _, ., digits, punctuation as boundaries; only letters block a match. After the fix, 2220 substitutions vs 1334 before.

Verified against clinic-queue (stub planner for determinism)

Metric	Value
Files scanned	305
Files changed (content)	125
Substitutions	2,220
File/dir renames	49
Leftover Shop/Shopkeeper tokens	0 (grep returned empty)
ruby -c on renamed models	Syntax OK across spot-checks
Migration filename + class-name coherence	Confirmed (e.g. change_vet_foreign_keys_to_nullify_on_delete.rb / class ChangeVetForeignKeysToNullifyOnDelete)
config/routes.rb	clean — resources :clinics, namespace :vet_auth, accounts_vets

What this doesn't do (deferred)

• Actual bin/dev boot verification — that's Layer 2 (Day 5 morning).
• acts_as_tenant / devise_token_auth deeper semantic edits — rename is complete; any missing wiring surfaces when Day 5 Layer 2 boots the server.
• Migration table-name validation — we rename class + filename, but DB table rename (if any) would need explicit AST work. Not needed for the hackathon specs.

Test plan

• npm run ci — green (stub path still used in tests under NATEMPLATE_STUB_ALL=1)
• NATEMPLATE_STUB_PLANNER=1 npm run dev -- "a walk-in clinic queue..." — real copy + rename runs, no errors
• Spot check: grep -rln '\\bshop\\|\\bshopkeeper\\|shops_\\|shopkeepers_' out/clinic-queue/rails returns empty
• Spot check: ruby -c on 3 renamed model files — all Syntax OK
• Full bin/dev boot — deferred to Day 5 Layer 2 validation