feat: implement GEWU service and local agent workflows

docs/development/MODULARITY_PROTOCOL.md

@@ -63,4 +63,4 @@ At scaffolding, add import/dependency checks and reusable contract test suites f
 
 Early acceptance examples: swap an embedding provider and rebuild without changing search consumers; substitute an extraction-stage implementation while preserving old citations; replace a frontend evidence panel without changing the read API; resume an agent run with its original pinned skill version after a newer version is installed. These are required design tests to implement, not existing passes.
 
-Primary documentation above was checked on 13 October 2026. No module implementation or replacement test exists yet.
+Primary documentation above was checked on 13 October 2026. The canonical repository port now owns its stable errors, path rules, revision-history semantics and a shared behavioral contract run against both the Git adapter and an independent in-memory implementation. `CanonicalNodeReader` also returns the same accepted node and citations against the substitute without consumer changes. This demonstrates dependency isolation and the checked contract subset; it does not establish durability, locking, crash recovery or production equivalence for another backend. Broader fault, concurrency and filesystem-specific qualification remains required.