The workshop + managed-global overlay surface fully covers the
admin-SFTP flow that 'external' was a placeholder for. Drop the type
from the model defaults, builder registry, routes, template, and
tests, and add migration 0004 that deletes any leftover external
rows along with their blueprint and job references.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Adds l4d2web/services/overlay_builders.py with a BUILDERS dict mapping
Overlay.type to a builder class. ExternalBuilder is a no-op that just
ensures the overlay directory exists. WorkshopBuilder diff-applies
absolute symlinks under left4dead2/addons/ against the overlay's current
WorkshopItem associations: creates new ones, removes obsolete, leaves
unrelated files alone, and skips uncached items with a warning rather
than producing dangling symlinks.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
