cp_write: true -> state-tx (test-validate@1, frozen-fixture-emit@1) and, in
the archived bug-ancestor-auto-advance@1, tag-set + state-tx.
cp_write: false -> every other script node (verdict-gate, policy-pick,
preflight-*, frozen-fixture-emit, parent-link-check).
tests/invariants/test_cp_write_field_set_correctly.py pins the set.
HOLD: do not merge until the CP release that adds WorkflowNode.cp_write.
The current CP schema is extra="forbid" and rejects the new key
(verified: nodes.0.cp_write extra_forbidden), so on the old CP these
template edits are NOT inert.
Claude-Session: https://claude.ai/code/session_01N218bERyNeLhbLmDRDvbWF
