docs(6209): forty test files — design cascade and stylesheet, embeddings, family canon, forge, backup round trips, inception, placement, platforms, moments, rule move and verification, search scope, facets

Module and test docstrings state what is pinned without the record number
or step that introduced it. Incident accounts become the failure shape in
the present tense: the pipefail head, the code_shapes import, the export
order, the facet dialects, the cross-kind repeat, the write-once kind.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_integration_placement.py

@@ -1,4 +1,4 @@
-"""Real-Postgres tests for task placement (milestone 409 step 1).
+"""Real-Postgres tests for task placement.
 
 What a mock cannot show: that step order is creation order rather than update
 order, that position and progress are computed over the steps the CALLER may