fix: compose extensions when any parent is active#39
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The UCP intersection algorithm states: “Remove any capability where `extends` is set but none of its parent capabilities are in the intersection.” “For multi-parent extensions (`extends: ["a", "b"]`): at least one parent must be present.” — docs/specification/overview.md, “Intersection Algorithm” The composer instead required every declared parent to be active. Discount extending `[Cart, Checkout]` therefore failed to compose into a Checkout response when Cart was absent. Remove the all-parents-present check and retain root-reachability validation. Extensions with no path to the active root remain rejected. Add Cart and Checkout regressions for root-specific `$defs` selection, parent ordering, orphan rejection, and cycle termination.
damaz91
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damaz91
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July 13, 2026 07:52
damaz91
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Jul 13, 2026
| if let Some(parents) = &cap.extends { | ||
| for parent in parents { | ||
| if !cap_map.contains_key(parent.as_str()) { | ||
| return Err(ComposeError::UnknownParent { |
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consider cleaning up this error variant from src/error.rs if, after this PR, it's not referenced elsewhere
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The UCP intersection algorithm states:
The composer required every parent in
extends[]to be present in the active response graph. For example, Discount can extend either Cart or Checkout:{ "dev.ucp.shopping.discount": [{ "extends": [ "dev.ucp.shopping.cart", "dev.ucp.shopping.checkout" ] }] }A response containing Checkout + Discount capability, but not Cart, previously failed with:
Updated logic allows above / aligns with normative requirement in the UCP spec.
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