D273 — Knowledge gaps are Contradiction concepts with a reserved, non-blocking kind

Decision. A gap is a Contradiction concept whose contradiction_kind is missing_context (the KB lacks information it should have) or open_question (a question raised and not yet answered). kb.GapKinds / kb.IsGapKind name the two kinds; commit_gate and gate_check never block on a gap, whatever its involves, and involves is optional for one. kb_status counts open gaps in open_gaps (total, by_kind, 10 newest in recent) and excludes them from open_contradictions; contradiction_report takes a kind filter (an exact kind, gap, or contradiction).

Why. A KB could record that two claims disagree but not that something is not known, so an unknown stayed prose no tool could find. The Contradiction lifecycle (open → resolved with a resolution), contradiction_report, conflict_resolve and the kb_status count already fit; only the gate semantics differ, since an open question must not block the writes that answer it.

Alternatives rejected. - A new Gap concept type with its own tools: duplicates a lifecycle that is identical, and adds tools to a public contract. - Letting gaps block like contradictions: writing is how a gap is answered, so it would deadlock the KB on its own to-do list. - Reusing search_misses (D247): it shows what readers hit, not what writers already know is missing.

Consequences. open_contradictions is narrowed: it no longer counts gap kinds (no KB used them before). The two kinds are reserved: any other contradiction_kind keeps blocking. kb_status is the agent's view of gaps; the advanced tools (D123) stay callable by name.