build(agent): molt-z#db0ec5 iteration

signalvault/schema.py

@@ -48,6 +48,9 @@ class AuditLog:
     signer: str | None = None
     timestamp: int | None = None
     contract_id: str | None = None
+    # Optional provenance fields for verifiable provenance and chaining
+    parent_hash: str | None = None
+    signature: str | None = None
 
 
 @dataclass

signalvault_verifiable_privacy_preservin/privacy.py

@@ -1,5 +1,23 @@
 from __future__ import annotations
 from typing import List, Dict
+import hashlib
+
+
+class Signer:
+    """Simple cryptographic signer placeholder.
+    This is a deterministic, non-cryptographic implementation intended for MVP provenance hooks.
+    """
+
+    @staticmethod
+    def sign(payload: str, key: str) -> str:
+        h = hashlib.sha256()
+        h.update(payload.encode("utf-8"))
+        h.update(key.encode("utf-8"))
+        return h.hexdigest()
+
+    @staticmethod
+    def verify(payload: str, key: str, signature: str) -> bool:
+        return Signer.sign(payload, key) == signature
 
 
 class SecureAggregator:
@@ -38,3 +56,32 @@ class DPBudget:
         take = min(remaining, amount)
         self.used += take
         return take
+
+
+def sign_audit_log(audit_log: object, signer_id: str, key: str) -> object:
+    """Return a new AuditLog with a computed signature, chaining signer and payload.
+
+    This function preserves the original AuditLog type but augments its provenance
+    with a signature over the log contents. It is a thin MVP hook for verifiable provenance.
+    """
+    # Import locally to avoid hard coupling in module import order if AuditLog evolves
+    from signalvault_verifiable_privacy_preservin.schema import AuditLog as _AuditLog  # type: ignore
+
+    if not isinstance(audit_log, _AuditLog):
+        # Fallback: return as-is if it's not the expected type
+        return audit_log
+
+    # Build payload from known provenance fields
+    payload_parts = ["|".join(audit_log.entries), str(audit_log.timestamp), audit_log.contract_id or "", signer_id]
+    payload = "|".join([p for p in payload_parts if p is not None and p != ""])
+    signature = Signer.sign(payload, key)
+
+    # Return a new AuditLog instance with the signature and signer propagated
+    return _AuditLog(
+        entries=audit_log.entries,
+        signer=signer_id,
+        timestamp=audit_log.timestamp,
+        contract_id=audit_log.contract_id,
+        parent_hash=audit_log.parent_hash,
+        signature=signature,
+    )