Two defects found by running migration 0004 against a seeded legacy database.
A unique index on org_id treats a missing org_id as null. Renaming the field
strips it, so the second document collided and the whole update failed:
E11000 duplicate key error collection: instance_oidc index: org_id_1
dup key: { org_id: null }
The index cleanup therefore has to run BEFORE the field rename, not after.
rename-rollback needs the symmetric step for instance_id, or reverting hits
the same wall.
The detection also silently matched nothing: the driver decodes an index key
document as bson.D, not bson.M, so the type assertion always failed and no
index was ever dropped. IndexKeyedOn now handles both.
mrhid6