Phase 5c slice A. Pulls the structural rules out of the Postgres
triggers into a Go-side validator. The trigger stays as defence in
depth; the validator is the human-facing error path.
- docs/plans/itemwrite-validation.md enumerates every rule the
triggers in 0001 + 0010 enforce, with the ValidationError.Kind
callers will see for each. Eleven rules total (two SQL-only safety
rails kept untranslated).
- internal/itemwrite/itemwrite.go: ValidationError + Input + Reader
interface + ValidateFormat (pure: missing fields, slug format,
status whitelist, self-parent) + ValidateAgainstStore (DB-aware:
unknown-parent, slug-collision under any common parent, cycle via
ancestor-closure DFS capped at 64 hops to mirror the trigger).
- Eight kind constants exported: missing-required, invalid-slug-format,
invalid-status, slug-collision, cycle, self-parent, unknown-parent,
unresolvable-path.
Tests cover every kind on both happy and reject paths: missing /
whitespace fields, slug containing dot / upper / whitespace, invalid
status enum, self-parent guard, unknown parent id, root slug collision,
sibling slug collision under common parent, cycle on ancestor closure,
and the "Reader returns ListAll error → validator returns nil" path
(callers see the infra error later, validator doesn't mask it).
No caller migrates yet. Same Go-linker DCE caveat as 5a/5b slice A:
`strings <binary> | grep internal/itemwrite` returns 0 until slice B
imports.
Task: t-projax-5c-itemwrite
mAi
df65e4b586