Fixes #XXXXX - Fix RHSM OS TOCTOU race during concurrent registration

[pablomh]

Summary

• Under concurrent bulk registration, create_or_find_by in RhsmFactParser#operatingsystem can return an unpersisted Operatingsystem object when the model-level uniqueness validation catches a duplicate committed between the initial find_by_attributes lookup and the create attempt
• Rails create_or_find_by only rescues RecordNotUnique (DB constraint), not RecordInvalid (model validation). Assigning the invalid object to the host silently sets operatingsystem_id=NULL, causing step 3 POST /register to fail with 422 "Must provide an operating system"
• Replace create_or_find_by with create! + rescue for both RecordInvalid and RecordNotUnique, retrying the find on either. Re-raise if the retry also returns nil (genuine validation failure, not a race)

Root cause

Operatingsystem has three model-level uniqueness validations (name scoped to major/minor, description, and title). During the first registration burst when the OS record does not yet exist:

1. Thread A: find_by_attributes → nil, create_or_find_by → creates OS (id=4), commits
2. Thread B: find_by_attributes → nil (Thread A not yet committed), create_or_find_by → internal create runs model validations → SELECT finds OS (Thread A now committed) → validation fails → returns unpersisted object (id=nil) → no RecordNotUnique raised → create_or_find_by returns the invalid object
3. host.operatingsystem = invalid_os → host.operatingsystem_id = nil
4. host.save persists architecture_id but operatingsystem_id stays NULL
5. Step 3 POST /register → initial_configuration_template → 422

Test plan

• test_operatingsystem_returns_existing_os_after_record_not_unique — DB constraint race path
• test_operatingsystem_returns_existing_os_after_uniqueness_validation_conflict — model validation race path (the confirmed production failure)
• test_operatingsystem_raises_non_race_validation_failure — genuine validation errors propagate instead of being silently swallowed

🤖 Generated with Claude Code