diff --git a/README.md b/README.md
index 160face..1876e22 100644
--- a/README.md
+++ b/README.md
@@ -8,10 +8,12 @@ Key Primitives
 - PlanDelta: incremental routing/size/timing decisions with metadata
 - Attestation/AuditLog: cryptographic attestations and an append-only log
 - GraphOfContracts: registry for adapters and data-contract schemas
+- compute_delta / compute_plan_delta: deterministic, replayable routing plans for a task/context pair
 
 How to use
 - Install dependencies and run tests via the provided test script (test.sh).
-- The core models are defined under exprove.contracts and can be composed by a solver.
+- The core models are defined under `exprove.contracts`; the reference planner lives in `exprove.engine`.
+- All public dataclasses expose `to_dict()` and/or `to_json()` helpers for audit trails and export.
 
 Development notes
 - This repo focuses on a production-ready, minimal core that can be extended to a full edge-native solver and delta-sync pipeline.
diff --git a/exprove/__init__.py b/exprove/__init__.py
index 37ea5fe..a231265 100644
--- a/exprove/__init__.py
+++ b/exprove/__init__.py
@@ -13,6 +13,7 @@ from .contracts import (
     Attestation,
     AuditLog,
     GraphOfContracts,
+    compute_delta,
 )
 
 __all__ = [
@@ -22,4 +23,5 @@ __all__ = [
     "Attestation",
     "AuditLog",
     "GraphOfContracts",
+    "compute_delta",
 ]
diff --git a/exprove/contracts.py b/exprove/contracts.py
index 42e95d6..bbd2714 100644
--- a/exprove/contracts.py
+++ b/exprove/contracts.py
@@ -1,7 +1,12 @@
 from __future__ import annotations
 
-from dataclasses import dataclass, asdict
-from typing import Dict, Any, List
+import json
+from dataclasses import dataclass, asdict, field
+from typing import Dict, Any, List, Optional
+
+
+def to_json(obj: Any) -> str:
+    return json.dumps(obj, default=lambda o: o.__dict__, sort_keys=True)
 
 
 @dataclass
@@ -11,7 +16,10 @@ class LocalExecutionTask:
     instrument: str
     venue: str
     objective: str
-    constraints: Dict[str, Any]
+    constraints: Dict[str, Any] = field(default_factory=dict)
+
+    def to_json(self) -> str:
+        return to_json(asdict(self))
 
     def to_dict(self) -> Dict[str, Any]:
         return asdict(self)
@@ -24,6 +32,9 @@ class SharedMarketContext:
     version: int
     contract_id: str
 
+    def to_json(self) -> str:
+        return to_json(asdict(self))
+
     def to_dict(self) -> Dict[str, Any]:
         return asdict(self)
 
@@ -35,7 +46,10 @@ class PlanDelta:
     timestamp: float
     author: str
     contract_id: str
-    privacy_budget: float
+    privacy_budget: Optional[float] = None
+
+    def to_json(self) -> str:
+        return to_json(asdict(self))
 
     def to_dict(self) -> Dict[str, Any]:
         return asdict(self)
@@ -50,6 +64,9 @@ class Attestation:
     contract_id: str
     version: int
 
+    def to_json(self) -> str:
+        return to_json(asdict(self))
+
     def to_dict(self) -> Dict[str, Any]:
         return asdict(self)
 
@@ -57,7 +74,13 @@ class Attestation:
 @dataclass
 class AuditLog:
     """Append-only log of attestations and approvals."""
-    entries: List[Attestation]
+    entries: List[Attestation] = field(default_factory=list)
+
+    def add(self, attestation: Attestation) -> None:
+        self.entries.append(attestation)
+
+    def to_json(self) -> str:
+        return to_json([asdict(entry) for entry in self.entries])
 
     def to_dict(self) -> Dict[str, Any]:
         return {"entries": [e.to_dict() for e in self.entries]}
@@ -67,17 +90,19 @@ class AuditLog:
 class GraphOfContracts:
     """Registry for adapters and data-contract schemas."""
     registry: Dict[str, Any]
+    version: int = 1
+    adapters: Optional[Dict[str, Any]] = None
+
+    def __post_init__(self) -> None:
+        if self.adapters is None:
+            self.adapters = self.registry
 
     def to_dict(self) -> Dict[str, Any]:
-        return {"registry": self.registry}
+        return {"registry": self.registry, "version": self.version, "adapters": self.adapters}
 
 
 def compute_delta(task: LocalExecutionTask, ctx: SharedMarketContext) -> PlanDelta:
-    """Deterministic, minimal PlanDelta from inputs.
-
-    This is intentionally deterministic (timestamp=0.0) for replayability in tests
-    and backtesting scenarios. Real deployments can replace this with a richer solver.
-    """
+    """Deterministic, minimal PlanDelta from inputs."""
     delta = {
         "action": "hold",
         "reason": "base-case",
diff --git a/exprove/engine.py b/exprove/engine.py
new file mode 100644
index 0000000..04b9be6
--- /dev/null
+++ b/exprove/engine.py
@@ -0,0 +1,29 @@
+"""Deterministic execution planner for ExProve."""
+
+from __future__ import annotations
+
+import hashlib
+from typing import Any, Dict
+
+from .contracts import LocalExecutionTask, SharedMarketContext, PlanDelta
+
+
+def _deterministic_delta(task: LocalExecutionTask, ctx: SharedMarketContext) -> Dict[str, Any]:
+    seed_input = f"{task.task_id}:{task.instrument}:{task.venue}:{ctx.version}:{ctx.contract_id}"
+    digest = hashlib.sha256(seed_input.encode("utf-8")).hexdigest()
+    return {
+        "route": [task.venue],
+        "size_adjustment": int(digest[:6], 16) % 1000,
+        "timestamp": 0.0,
+        "hash_seed": digest,
+    }
+
+
+def compute_plan_delta(task: LocalExecutionTask, ctx: SharedMarketContext, *, author: str) -> PlanDelta:
+    return PlanDelta(
+        delta=_deterministic_delta(task, ctx),
+        timestamp=0.0,
+        author=author,
+        contract_id=ctx.contract_id,
+        privacy_budget=None,
+    )
diff --git a/pyproject.toml b/pyproject.toml
index 9aca510..f95fa53 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -8,7 +8,7 @@ version = "0.1.0"
 description = "Open-source Execution Provenance Engine for cross-venue equity trading (core primitives)"
 readme = "README.md"
 requires-python = ">=3.8"
-license = {text = "MIT"}
+license = "MIT"
 authors = [ { name = "ExProve Team" } ]
 dependencies = [
   "dataclasses; python_version < '3.7'",