docs(release): the 10.4.0 entry, the index-health concept doc, and the API surfaces — written from the tree, not the plan

tests/lifecycle/README.md

@@ -14,3 +14,9 @@ from the message alone. `biography.test.ts` is split into two `it` blocks
 (Ch1-3, then Ch4-6) purely for reporting; it is still ONE fixed-order story.
 Chapters must never be reordered, skipped, or made conditional, and a
 failing chapter's assertion must never be weakened to force green.
+
+Lab notes (hard-won, keep):
+- `git reset --hard` does NOT remove untracked files — a "clean" tree can still
+  carry stray test stores; use `git clean -fd tests/lifecycle-tmp` equivalents.
+- `silent: true` patches `console` process-wide — never assert narration through
+  `console` spies in this lane; the engine's always-on channel is `prodLog`.