0533 — Field absence is the zero value, never a nil pointer

Context

Read-models mark optional scalar fields with // "" if unset (Message.RoutingKey, CompactionKey). The question was whether to adopt pointer-typed optional fields (*string) repo-wide instead.

Decision

• Zero value = unset, legal only where the zero can never be real data (nobody binds routing key ""; time.Time has IsZero). The field carries the // "" if unset comment; the datastore’s SQL-side NULLIF/COALESCE shaping keeps ""<->NULL from diverging.
• Pointer-optionals were rejected: they reverse the standing “outside the error path a pointer is never nil” invariant, put a nil guard (or a panic) at every read site, and reintroduce the banned nil-safe receivers.
• The ambiguous cases keep their established answers: whole-entity absence is a nil struct return from Get ((nil, nil) comma-ok); a tri-state scalar widens its domain (ShutdownGrace < 0) or gets a named state; a bool whose default would be true takes the inverted Disable* name so zero stays the default under WithDefaults.
• The one honest pointer-optional use case is a partial-update (PATCH) write shape, where nil = leave unchanged. Vulkan has none; if one appears, the pointer rule may apply to that write shape only.

Consequences

• CONVENTIONS “Pointers & receivers” gains the rule.
• Pointer-typed read-model fields (Message.Options and siblings) must be never-nil end to end — a nilable Options is a bug under this rule.