Admit live E2 from a value-safe custody receipt

WH-ENG-20260822-AUDIT-E2-02 projected and then aborted: admit-plane had no
receipt adapter, so the runner sent zero packets. Consume custody receipts
as handles only, keep unconnected admission fail-closed, and retire -02.

Assistant: grok
Assistant-Session: 01a02670-3345-76f2-a014-70fde8e2a2bb

schemas/projection-receipt.schema.json

@@ -0,0 +1,21 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "whitehat-projection-receipt/v1",
+  "type": "object",
+  "additionalProperties": false,
+  "required": [
+    "engagement_id", "projected_at", "expires_at", "identities",
+    "mounted_secret", "mounted_keys", "target_ready", "secret_values_observed"
+  ],
+  "properties": {
+    "engagement_id": {"type": "string", "minLength": 1},
+    "projected_at": {"type": "string", "format": "date-time"},
+    "expires_at": {"type": "string", "format": "date-time"},
+    "identities": {"type": "array", "minItems": 1, "items": {"type": "string"}},
+    "mounted_secret": {"type": "string", "pattern": "^whitehat/"},
+    "mounted_keys": {"type": "array", "items": {"type": "string"}},
+    "target_image_matches": {"type": "boolean"},
+    "target_ready": {"const": true},
+    "secret_values_observed": {"const": false}
+  }
+}