The core chain already owns and reproduces the full bundled schema (deploys run
`flask db upgrade` only). The per-plugin Alembic baselines duplicated those
tables, so `flask plugin upgrade-all` would conflict - a footgun. Remove the 6
bundled plugin migration dirs; the per-plugin Alembic helpers
(alembic_template, PluginMigrationRunner) remain for external/filesystem
plugins. upgrade-all now cleanly no-ops for bundled plugins.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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