ActiveRecordOptional: attribute type casts don't unwrap Options — Boolean.cast(Some(false)) silently stores true #60

Summary

ActiveModel type casts don't unwrap Options, so assigning an Option through an attribute writer behaves differently per column type — including one case of silent data corruption: ActiveModel::Type::Boolean.cast(Some(false)) returns true.

Context

b.attr = a.attr (record-to-record copy, dup-then-tweak, form round-trips, update_all) is one of the most common idioms in a converted app: the reader returns an Option and the writer hands it to the type cast. Found during a full-codebase conversion audit (107 models, errgonomic 0.8.3, Rails 8.1.3.1). The gem already unwraps at the SQL quoting and predicate-builder boundaries (active_record_optional.rb:231-244, :276-317); the attribute-cast boundary is the missing third seam.

Current State

Measured per type, assigning Some(x) through a writer:

update_all(col: Some(x)) raises SerializeError for the same reason.

Desired State

Assigning an Option through any attribute writer behaves exactly like assigning its inner value (None like nil), for every type, with no deprecation output.

Acceptance Criteria

• record.bool_col = Some(false) stores false; = None() stores nil
• String/text/jsonb/date/datetime writers accept Options without raising and without storing a wrapper
• Numeric writers no longer route through Option#presence (no stderr nudge)
• changes / attribute_before_type_cast contain raw values after an Option assignment
• update_all accepts Option values
• Tests cover each cast type with Some(x), Some(falsy), and None()

Technical Notes

• Validated prototype from the audit: prepend a module on ActiveModel::Type::Value that unwraps in #cast and #serialize, then super. Two methods, covers every type including custom ones.
• Interaction warning worth a line in the docs: once casts unwrap, a truthiness bug like self.col = col || default (where col reads as truthy None) stops leaking a wrapper and instead silently persists nil — the write succeeds. Cast unwrapping should ship alongside truthiness-linting guidance, not instead of it.

Related Files

• lib/errgonomic/rails/active_record_optional.rb:231-244 — existing quoting-boundary unwrap (type_cast), the pattern to extend
• lib/errgonomic/rails/active_record_optional.rb:276-317 — existing predicate-builder unwrap
• lib/errgonomic/option.rb:624-626 — the presence_nudge the numeric path currently triggers

References

• ActiveRecordOptional: class_eval reader wrapping silently destroys (or is destroyed by) model-defined methods — wrap via a module #59 (module-based wrapping) — independent, but both change what a reader/writer round-trip looks like; coordinate test coverage