RAC (Requirements as Code) — the relationship vocabulary

Normative reference: SPEC.md §8. The vocabulary is closed. Relationships are declared as ## body sections; the section heading maps to the edge name by lowercasing and replacing spaces with underscores (## Related Decisions → related_decisions). Each non-empty line of the section body is one reference (a leading Markdown list marker is stripped; the remaining line text is the reference, verbatim).

The edges

Edge	Declared by (domain)	Target (range)	Direction	Inverse	Cardinality	Validation level
related_requirements	all five types	requirement	undirected	—	many	resolve + range + status: error/blocking on failure
related_decisions	all five types	decision	undirected	—	many	resolve + range + status
related_roadmaps	all five types	roadmap	undirected	—	many	resolve + range + status
related_prompts	requirement, roadmap, design	prompt	undirected	—	many	resolve + range + status
related_designs	requirement, decision, roadmap, prompt	design	undirected	—	many	resolve + range + status
supersedes	decision	decision	directed, acyclic	superseded-by	many	resolve + range + acyclicity; exempt from the retired-target rule
related_tickets	all five types	external ticket key or URL	undirected	—	many	format lint against the configured provider (malformed-ticket-reference, blocking); never resolved in-corpus
verified_by	requirement	external test/trace file path	directed	verifies	many	recorded only; not resolved, not existence-checked
applies_to	decision	repository path, glob, or component label	directed	governed_by	many	literal path entries existence-checked (applies-to-target-not-found, blocking); globs and labels recorded only

Cardinality is declared (many) and not otherwise enforced. Inverse labels are display semantics for consumers rendering the graph; only the forward direction is authored.

Findings

Code	Trigger	Intrinsic severity	Default enforcement
relationship-target-not-found	reference resolves to nothing	error	blocking
relationship-target-ambiguous	reference resolves to more than one artifact	error	blocking
relationship-target-type-mismatch	resolved target's type outside the edge's range (untyped targets exempt)	error	blocking
relationship-cycle	cycle in an acyclic edge kind (supersedes); one finding per strongly connected component	error	blocking
duplicate-artifact-identifier	two artifacts share a canonical identifier	error	blocking
applies-to-target-not-found	literal applies_to path missing from the working tree	error	blocking
relationship-target-superseded	live artifact references a retired one outside supersedes	warning	blocking
relationship-self-reference	reference resolves to the declaring artifact	warning	blocking
relationship-edge-unsupported	vocabulary section populated on a type that does not declare it	warning	blocking

Note the last three: warning-severity but blocking by default — the annotation level and the enforcement class are independent (SPEC.md §9.1). Every relationship finding fails rac relationships --validate (exit 1) regardless of severity; a corpus policy may reclassify a specific code (SPEC.md §9.5).

Out-of-vocabulary sections

A populated vocabulary section on a type that does not declare it is relationship-edge-unsupported. A ## section whose name is outside the vocabulary entirely (e.g. ## Related Widgets) is ordinary body content: no edge and no finding — it is indistinguishable from prose. Extension is via tags or free body sections, never via new relationship section names (SPEC.md §11); adding an edge to this vocabulary is a minor spec version, removing or re-defining one a major version.