ekp/postmortem/20260820-source-fresh-live-commit-gate.md

Source-Fresh Live-Commit Gate

Context

The first post-audit task030 report claimed pass:true, while the source-loaded public benchmark still exceeded the 16 ms structural-commit budget. The evaluator loaded the candidate by name and therefore allowed an ignored local .elc to win. The report was not evidence for the locked source contract.

Decision

tests/run-live-commit-evaluator.sh now passes each baseline/candidate root through EKP_LIVE_COMMIT_CODE_ROOT, and tests/ekp-live-commit-evaluator.el explicitly load-files the four production sources from that root before measuring. A bytecode-backed result cannot satisfy the source gate.

Evidence

The corrected width-80, two-row, GC-excluded matrix preserves layout parity, zero-work ordinary keys, valid GC exclusion, conflict freedom, and non-regression. Its source candidate total p95/p99 are 23.217/23.217 ms for C and 79.724/79.724 ms for Elisp, so the evaluator correctly remains red. The newly measured append owners account for C at 17.161 ms append and 1.187 ms append-DP p95, and Elisp at 73.293 ms append and 57.063 ms append-DP p95. The public source benchmark independently records C append/hard-boundary p99 near 19.9/30.7 ms and Elisp near 49.3/50.8 ms; byte-compiled production remains below 16 ms.

The evaluator now attributes the Elisp structural cost primarily to the incremental 1D DP pass and the C cost to live-plan construction around the native call. No cache-key or validation call owns enough time to make a safe one-line optimization. A broad DP or projection rewrite would need a new red/green parity matrix and architecture decision; it is not smuggled into this measurement change.

The finer attribution separates the latest source-fresh append p95 into append_para/append_plan: C 9.753/5.663 ms and Elisp 9.753/5.663 ms. The Elisp append_dp remains 55.970 ms; C append_dp remains 1.015 ms. This is why a C-only change cannot close the locked gate.

Rejected experiment

An append-only strict-DP specialization was prototyped and gated against the existing general strict-reuse result. It required duplicating roughly 160 lines of transition logic, and the first parity run returned nil; it was not benchmarked or connected to ekp--dp-cache-append. The experiment was fully discarded. Maintaining a second transition kernel would create rule drift, so the next attempt must optimize a shared kernel or change the data structure/ownership boundary under a new architecture decision.

Consequences

• issue028 is closed as an evaluator-integrity defect.
• issue018/task030 remain open with honest source-fresh evidence.
• Compiled production interaction remains within the documented budget.
• The next performance task must optimize a measured structural owner while preserving exact C/Elisp parity, source-clean projection, and zero-work point motion.
• Every run now keeps nonempty baseline/candidate JSONL under a unique raw directory and replaces the report only after comparison, so interruption cannot erase the last evidence.

Rollback

Revert the evaluator source bootstrap and its test-gate documentation only; runtime layout behavior and valid C/API contracts are independent of this decision.

Resolution update — 2026-08-20

The user-selected native automatic live-append backend is now enabled by default for prepared 1D append DP, while full/string dispatch remains governed by ekp-use-c-module. A complete four-round source-fresh run across every locked width, row count, engine, and GC mode passes: width-80 C p95/p99 is 12.010/14.622 ms and the Elisp-configured live path is 10.980/11.194 ms. Ordinary-key p99 is 0.551 ms; parity, zero-work, GC, conflict, and non-regression checks are green. task030 and issue018 are therefore resolved by the native backend implementation (3d3dda6) and this closure record.