FlatteningService now treats IsInherited rows as placeholders: when a
derived template carries an inherited attribute or script, the live base
value resolves through the ParentTemplateId chain instead of the
(possibly stale) copy. An IsInherited=false row is a real override and
wins as before.
ValidateLockedInDerived runs once per chain (main + composed) and returns
a flatten-time failure if a derived template overrides a base row that
the base marked LockedInDerived.
TemplateService.Update{Attribute,Script}Async reject mid-flight when a
derived target tries to override a LockedInDerived base member, and now
persist IsInherited/LockedInDerived from the proposed payload so the UI
can flip override state or set base-locks via the same endpoints.
AddCompositionAsync creates a derived Template ("<parent>.<slot>") that
inherits from the base via ParentTemplateId. Base attributes and scripts
are copied with IsInherited=true so the derived template carries its own
override-able rows. The composition row points at the derived template,
and the derived's OwnerCompositionId back-refs the composition for cascade
delete.
DeleteCompositionAsync cascade-deletes the owned derived template.
DeleteTemplateAsync blocks direct deletion of derived templates and
distinguishes derivatives from regular children, listing slot owners
("'Pump' (as 'TempSensor')") in the error.
Composing a derived template is rejected — only bases can be composed.
Existing compositions still resolve until phase 3 migrates them.
Template inheritance is set once at create time and immutable on update.
UpdateTemplateAsync now returns "Parent template cannot be changed after
creation." when the caller sends a parent that differs from the stored
value — server-side enforcement covers UI, ManagementService, and CLI.
TemplateEdit renders the parent as static plaintext rather than an
editable dropdown; TemplateCreate's parent picker is unchanged.
