docs(kaizen): FRICTION signal — controller must diff-audit subagent restructures

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/FRICTION.md

@@ -34,6 +34,15 @@ _(append new raw signals here; the next kaizen review consumes them)_
   boma convention, where prose reminders don't hold. → consider a mechanical guard
   (Stop-hook family) or a CLAUDE.md/skill-override note that suppresses the spec-review
   gate.
+- `[recurring]` **Subagent faithfulness self-reports can be wrong — controller must
+  diff** (2026-06-10): during the ADR-023 retroactive restructure, an implementer
+  subagent reported "0 substantive deletions, the See-also lines reappear verbatim" for
+  ADR-014, but it had actually dropped the cross-reference lines. Caught only by the
+  controller independently running `git show <sha> | grep '^-[^-]'`. For
+  faithfulness-critical edits delegated to subagents, the agent's own audit is not
+  sufficient evidence. → systematize a controller-side deletion-audit step (every `-`
+  line must be a classified, expected change) before accepting any "presentational-only"
+  restructure; consider a helper script.
 
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