From 42022d84f14aa67b22aa790c09cfdc3dffb6be86 Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Sun, 1 Nov 2026 19:27:25 +0000
Subject: [PATCH] Require classifying each contributed SSA and S.770 node in
 the reference test

No node under gov.contrib.congress.s770 or gov.contrib.ssa is removed from
the calculator reference any more, so a new calculator-only node left
unlisted would stay in both models and a legacy formula that read it by
accident would go undetected. The new test reads both namespaces' children
from the live tree and fails unless each appears exactly once, either in
NEW_PARAMETER_NODES or in REFERENCE_PARAMETER_NODES, whose entries name
their non-calculator readers.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 ...or-reference-contrib-node-guard.changed.md |  1 +
 .../unit/test_ss_calculator_differential.py   | 62 +++++++++++++++++++
 2 files changed, 63 insertions(+)
 create mode 100644 changelog.d/ss-calculator-reference-contrib-node-guard.changed.md

diff --git a/changelog.d/ss-calculator-reference-contrib-node-guard.changed.md b/changelog.d/ss-calculator-reference-contrib-node-guard.changed.md
new file mode 100644
index 00000000000..2f68693f852
--- /dev/null
+++ b/changelog.d/ss-calculator-reference-contrib-node-guard.changed.md
@@ -0,0 +1 @@
+Require every S.770 and SSA contributed parameter node to be classified in the household calculator reference test.
diff --git a/policyengine_us/tests/unit/test_ss_calculator_differential.py b/policyengine_us/tests/unit/test_ss_calculator_differential.py
index 6597c4d557e..d59466ec760 100644
--- a/policyengine_us/tests/unit/test_ss_calculator_differential.py
+++ b/policyengine_us/tests/unit/test_ss_calculator_differential.py
@@ -31,6 +31,26 @@
     "gov.ssa.social_security.pia.bend_points",
     "gov.ssa.social_security.cola",
 )
+# Contributed namespaces whose every child node must be classified: either
+# calculator-only (listed in NEW_PARAMETER_NODES, so the reference drops it)
+# or kept in the reference (listed below with the code outside the household
+# calculator that reads it).
+CLASSIFIED_CONTRIB_NAMESPACES = ("gov.contrib.congress.s770", "gov.contrib.ssa")
+REFERENCE_PARAMETER_NODES = (
+    # tools/social_security/population.py: reported-benefit PIA ratios.
+    "gov.contrib.congress.s770.section_2",
+    # reforms/congress/s770/section_8.py reads it at simulation start; the
+    # s770 tax variables read it in formulas.
+    "gov.contrib.congress.s770.section_8",
+    # The social_security_*_payable_factor and across-the-board variables,
+    # the COLA means-test reform and the reported-benefit PIA ratios.
+    "gov.contrib.ssa.benefit_levers",
+    # reforms/ssa/owners_draw.py and s770_active_business_income; system.py
+    # writes current_law_cap into it at every system build.
+    "gov.contrib.ssa.owners_draw",
+    # tools/social_security/population.py: reported-benefit PIA ratios.
+    "gov.contrib.ssa.pia",
+)
 YEAR = 2026
 
 
@@ -87,6 +107,48 @@ def apply(self):
 )
 
 
+def _node(root, path):
+    node = root
+    for part in path.split("."):
+        node = node.children[part]
+    return node
+
+
+def test_every_contributed_calculator_namespace_child_is_classified():
+    """A new node under these namespaces must be calculator-only or kept.
+
+    If an unlisted calculator-only node stayed in the reference, a legacy
+    formula that read it by accident would compute the same in both models,
+    and the differential below could not detect the dependency.
+    """
+    parameters = Simulation.default_tax_benefit_system_instance.parameters
+    classified = NEW_PARAMETER_NODES + REFERENCE_PARAMETER_NODES
+    problems = [
+        f"{path} is listed {classified.count(path)} times"
+        for path in sorted(set(classified))
+        if classified.count(path) > 1
+    ]
+    children = set()
+    for namespace in CLASSIFIED_CONTRIB_NAMESPACES:
+        for name in _node(parameters, namespace).children:
+            path = f"{namespace}.{name}"
+            children.add(path)
+            if path not in classified:
+                problems.append(
+                    f"{path} is unclassified: add it to NEW_PARAMETER_NODES if "
+                    "only the household calculator reads it, or to "
+                    "REFERENCE_PARAMETER_NODES with a comment naming the "
+                    "legacy formula, reform start-up or system build that "
+                    "reads it"
+                )
+    problems += [
+        f"{path} is listed in REFERENCE_PARAMETER_NODES but does not exist"
+        for path in REFERENCE_PARAMETER_NODES
+        if path not in children
+    ]
+    assert not problems, "\n".join(problems)
+
+
 def _situation(age, benefits, earnings=0, investment_income=0, joint=False):
     amounts = dict(zip(LEGACY_SSA_OUTPUTS[:4], benefits))
     person = {