docs: add source-fresh performance postmortem

.phrase/phases/phase-kp-overhaul-20260726/change_post_audit_hardening_20260820.md

@@ -50,7 +50,7 @@
   conflict, and non-regression checks true. The high-row full matrix was
   stopped after a source DP cell exceeded two minutes of CPU; it is not
   claimed as complete evidence.
-- **Commit:** Pending documentation commit.
+- **Commit:** `60b299b` and `postmortem` follow-up commit.
 
 ## Verification
 

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

@@ -0,0 +1,48 @@
+# 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-file`s 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 p95/p99 are 23.294 ms for C and 78.593
+ms for Elisp, so the evaluator correctly remains red. 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.
+
+Profiling attributes the Elisp structural cost primarily to the incremental
+1D DP pass and the C cost to live-plan construction/publication around the
+native call. No single 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 correctness hardening change.
+
+## 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.
+
+## 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.