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Pattern Matching

Open and deferred

Open and deferred. Future design is tracked in CEP-0002: Pattern Matching and Narrowing.

V1 has no match expression or general pattern-narrowing syntax. Plain enums, enum unions, closed error sets, concrete type unions, and future discriminated unions should all use the shared narrowing model proposed in CEP-0002 rather than separate local rules.

Boundary

Pattern-matching syntax is rejected in V1. Optional payload binding remains the only accepted source-level payload-narrowing form.