planning: lower batch-write trigger threshold from 3+ to 2+ files

Author: cowwoc

.cat/issues/v2/v2.1/refactor-batch-write-instructions/plan.md

@@ -3,7 +3,7 @@
 ## Goal
 
 Run instruction-builder on cat:batch-write-agent skill to redesign and improve its instructions; add
-e2e post-condition verifying subagents invoke this skill when they need to write 3+ independent files
+e2e post-condition verifying subagents invoke this skill when they need to write 2+ independent files
 in a single operation.
 
 ## Pre-conditions
@@ -15,5 +15,5 @@ in a single operation.
 - [ ] Instruction-builder workflow completed for cat:batch-write-agent (design, benchmark, adversarial TDD, compression)
 - [ ] Skill instructions improved with clearer trigger conditions and usage guidance
 - [ ] All tests pass after changes
-- [ ] E2e verification: spawn a subagent with a task requiring writing 3+ independent files and confirm it invokes cat:batch-write-agent instead of making individual Write calls
+- [ ] E2e verification: spawn a subagent with a task requiring writing 2+ independent files and confirm it invokes cat:batch-write-agent instead of making individual Write calls
 - [ ] No regressions in existing behavior