Add canonical chunk plan source model

docs/adr/0005-cache-canonical-chunk-plans-by-source.md

@@ -1,6 +1,6 @@
 # ADR-0005: Cache one canonical chunk plan per source
 
-**Status:** Proposed
+**Status:** Accepted
 **Date:** 2026-07-17
 
 ## Context
@@ -70,6 +70,9 @@ Notarius state.
 
 One mutable active plan is stored under the canonical source identity and
 retains provenance for the module and relevant runtime inputs that produced it.
+Refreshing the active plan atomically replaces that one mutable record; readers
+must observe either the previous complete plan or the replacement complete
+plan, never a partial update.
 The effective plan producer is reported separately from the chunk module
 requested by the current pipeline; reuse must not attribute cached boundaries
 or annotations to a module that did not produce them.