Inherit locale and template_scope in subclassed messengers

[ahmeij]

Summary

BaseMessenger.locale and BaseMessenger.template_scope store their value in a class-instance variable and returned only what was set directly on the receiving class. Because class-instance variables are not inherited, a messenger that subclasses another (for example an STI-derived messenger) silently returned nil for these — losing its parent's configuration.

The concrete impact downstream: a subclassed messenger with no explicit template_scope caused select_templates to skip the scope entirely (the default template scope is unrestricted), so template selection ran across all records instead of the intended (e.g. per-label) subset.

This changes both getters to fall back to the superclass value when the subclass has not set its own, walking up the ancestry until a BaseMessenger descendant is found. Setting a value on a subclass still only affects that subclass (no parent mutation).

Changes

• locale / template_scope: return own value if set, otherwise delegate to superclass.
• New test/messengers/messenger_inheritance_test.rb covering:
  • a subclass inherits locale from its parent messenger
  • a subclass inherits template_scope from its parent messenger
  • overriding template_scope on a subclass does not mutate the parent

Test plan

• bin/rails test test/messengers test/life_cycle_test.rb test/state_machine_test.rb test/models/nuntius/template_test.rb (0 failures)
• New inheritance test fails before the fix (subclass returns nil) and passes after

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