docs(agents): add incremental verification rule for multi-step refactors

Add a bullet to the Required Baseline section: for multi-step refactors
such as splitting a large .cpp into several files, build and commit after
each step rather than batching all changes before verification.

Author: abacus_fixer

AGENTS.md

@@ -31,6 +31,10 @@ rules. Read the complete governance document before making or reviewing changes:
   is required.
 - Report the exact verification performed. Do not claim completion without
   fresh test or check output.
+- For multi-step refactors (e.g., splitting a large `.cpp` into several
+  files), build and commit after each step rather than batching all changes
+  before verification. This keeps the blast radius small when a step
+  surfaces a missing include or instantiation error.
 
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