Define relation cardinality validation

[tonyketcham]

Source: flatbread-flow-pmf-audit.md

Project metadata

• Phase: Core relational model and validation
• Sequence: 10
• Priority: P1
• Suggested owner role: backend
• Supporting roles: none
• Dependency status: blocked
• Blocked by: Define Flatbread relational primitives glossary #143 Define Flatbread relational primitives glossary; Normalize ID semantics across collections and query args #148 Normalize ID semantics across collections and query args

Task details

• Specify and validate supported one-to-one, one-to-many, and many-to-many relation shapes.
• Reject unsupported cardinality or ambiguous shapes with clear errors rather than implicit behavior.

Acceptance criteria

• Supported cardinality shapes are documented against the glossary terms.
• Validation covers one-to-one, one-to-many, and many-to-many examples, or explicitly rejects unsupported shapes.
• Tests cover valid and invalid relation cardinality cases.