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ADR-025 — Selection-vector semantics

  • Identifier: ADR-025
  • Title: Selection-vector semantics
  • Status: Accepted
  • Source: extracted verbatim from the Engineering PRD, docs/prd/08-kernel-design.md (REQ-DOC-004). From M0 onward this file is the canonical, living ADR record; status changes happen here and in the index, with the PRD text remaining the historical record.

Status: Accepted. Context: Charter §6.2 fixes sorted-unique for selection and arbitrary for take; the engineering question is enforcement. Alternatives: (1) validate eagerly in release — rejected: O(n) tax on every call contradicts the performance identity of the library; (2) tolerate unsorted input in selection kernels ("works by accident") — rejected: forecloses forward-scan algorithms and in-place filter safety; (3) contract + debug assertion (selected): sortedness/in-range checked fully under QUIVER_ENABLE_ASSERTS (O(n) scan acceptable in debug), UB in release, fuzz harnesses generate only contract-valid selections while separately fuzzing K8's untrusted-input surface. Consequences: documented loudly on every SelVec API; inv_selvec_sorted validates producers, assert tests validate consumers. Related: REQ-MEM-007, REQ-K5-001/002.