Activate nesting per GH-DEC-2026-015: view_hash carries binding.digest

approval-engine met the condition. Verified here rather than taken on report:
their docs/approval-claim.md carries "Presentation exclusion — GH-DEC-2026-015
§4" in normative language, and I ran
tests/test_claim_contract.py::test_presentation_changes_cannot_change_the_approved_act
myself — 1 passed. That test pins the digest input set from BOTH sides, and the
narrowing half is what makes it real: without it a digest over four fields, or
over a constant, would pass the widening half perfectly.

view_hash now carries binding.digest and the act-scope is no longer
independently canonicalized here, so the act has exactly one canonicalization
computed by the layer that owns it. approval_binding_digest is validated for
shape and refused without its approval id — it is carried, never computed.

The three published vectors are unchanged: they do not carry the new key, so
pick omits it. Asserted, not assumed.

The cycle condition did not disappear, its protection moved — from refusing
nesting to approval-engine's normative exclusion. layer.yaml carries it as
cycle_condition with a test, so a future widening meets a rule rather than
silence.

One thing not assumed. Both gate-house and approval-engine said our binding
slice canonicalizes principal and target, two of their five fields. target
plainly is act material and is now dropped. But their principal is the party ON
WHOSE BEHALF the approval was issued, while ours is the person being BOUND — the
approver. Different roles, and dropping ours would remove who was shown this
from view_hash and gut the promise. Kept it, declared principal_role_overlap
open in layer.yaml, tested that changing the approver still moves view_hash, and
raised it rather than silently resolving it either way.

L0/L2 are unaffected: with no approval there is no digest to defer to, and
test_act_scope_still_binds_when_there_is_no_carried_digest pins that.

100 tests pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V3W1dQG7GFFM9d94jFx7iR

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 1565372@bnt-lap001
Assistant-Session: 16bb2f25-b34c-49ef-8e94-5fec3567a568

tests/test_layer_conformance.py

@@ -160,11 +160,28 @@ def test_presentation_claim_carries_all_three_limits(layer_doc):
     }
 
 
-def test_binding_digest_relationship_is_co_reference_not_nesting(layer_doc):
+def test_binding_digest_relationship_is_nesting_and_declares_its_condition(layer_doc):
+    """GH-DEC-2026-015, activated once approval-engine met the condition."""
     rel = layer_doc["binding_digest_relationship"]
-    assert rel["linkage"] == "co-reference"
+    assert rel["linkage"] == "nesting"
     assert rel["substitutable"] is False
-    assert "nesting_forbidden" in rel
+    assert rel["nesting_permission_active"] is True
+    assert rel["nesting_condition_evidence"]["test"]
+
+
+def test_the_cycle_condition_is_still_declared(layer_doc):
+    """Nesting is safe only while binding.digest excludes presentation.
+
+    The protection moved from refusing nesting to approval-engine's normative
+    exclusion. The condition itself must stay written down, or a future
+    widening ships against a rule nobody can find.
+    """
+    assert "cycle_condition" in layer_doc["binding_digest_relationship"]
+
+
+def test_the_principal_role_overlap_is_declared_open(layer_doc):
+    """We kept our own principal in view_hash rather than assuming it is theirs."""
+    assert layer_doc["binding_digest_relationship"]["principal_role_overlap"] == "open"
 
 
 def test_residual_is_declared_not_closed(layer_doc):