diff --git a/src/capability-model/evolution.ts b/src/capability-model/evolution.ts
index 32e0cf0..f6ec15a 100644
--- a/src/capability-model/evolution.ts
+++ b/src/capability-model/evolution.ts
@@ -26,43 +26,80 @@ export const contentDigest = (value: unknown) =>
  * event loop while verifying large immutable metadata. No validation is skipped.
  * This is for asynchronous loading, not a different build/wire identity. */
 export async function contentDigestAsync(value: unknown): Promise<string> {
-  function* parts(value: unknown): Generator<string> {
-    if (Array.isArray(value)) {
-      yield "[";
-      for (let index = 0; index < value.length; index++) {
-        if (index) yield ",";
-        // Match canonicalJson's Array.map behavior for sparse arrays too.
-        if (index in value) yield* parts(value[index]);
-      }
-      yield "]";
-    } else if (value !== null && typeof value === "object") {
-      if (Object.getPrototypeOf(value) !== Object.prototype && Object.getPrototypeOf(value) !== null)
-        throw new Error("Expected a plain JSON object");
-      yield "{";
-      let first = true;
-      for (const key of Object.keys(value).sort(compareText)) {
-        const entry = (value as Record<string, unknown>)[key];
-        if (entry === undefined) continue;
-        if (!first) yield ",";
-        first = false;
-        yield JSON.stringify(key) + ":";
-        yield* parts(entry);
-      }
-      yield "}";
-    } else yield canonicalJson(value);
-  }
-  const hash = createHash("sha256");
+  // An explicit stack visits each node once; recursive generator delegation
+  // otherwise forwards every token through every ancestor of a deep plan.
+  type Frame = { kind: "value" | "array" | "object"; value: unknown; index?: number; keys?: string[]; wrote?: boolean };
+  const hash = createHash("sha256"),
+    stack: Frame[] = [{ kind: "value", value }],
+    active = new WeakSet<object>();
   let buffer = "",
-    sliceStarted = performance.now();
-  for (const part of parts(value)) {
+    sliceStarted = performance.now(),
+    steps = 0;
+  const append = (part: string) => {
     buffer += part;
     if (buffer.length >= 65536) {
       hash.update(buffer);
       buffer = "";
-      if (performance.now() - sliceStarted >= 8) {
-        await setImmediate();
-        sliceStarted = performance.now();
+    }
+  };
+  while (stack.length) {
+    const frame = stack[stack.length - 1]!;
+    if (frame.kind === "value") {
+      const value = frame.value;
+      if (value !== null && typeof value === "object") {
+        if (active.has(value)) throw new Error("Cannot hash cyclic JSON values");
+        active.add(value);
+        frame.index = 0;
+        if (Array.isArray(value)) {
+          frame.kind = "array";
+          append("[");
+        } else {
+          if (Object.getPrototypeOf(value) !== Object.prototype && Object.getPrototypeOf(value) !== null)
+            throw new Error("Expected a plain JSON object");
+          frame.kind = "object";
+          frame.keys = Object.keys(value).sort(compareText);
+          frame.wrote = false;
+          append("{");
+        }
+      } else {
+        append(canonicalJson(value));
+        stack.pop();
       }
+    } else if (frame.kind === "array") {
+      const array = frame.value as unknown[];
+      if (frame.index === array.length) {
+        append("]");
+        active.delete(array);
+        stack.pop();
+      } else {
+        const index = frame.index!;
+        frame.index = index + 1;
+        if (index) append(",");
+        // Match canonicalJson's Array.map behavior for sparse arrays too.
+        if (index in array) stack.push({ kind: "value", value: array[index] });
+      }
+    } else {
+      const object = frame.value as Record<string, unknown>;
+      if (frame.index === frame.keys!.length) {
+        append("}");
+        active.delete(object);
+        stack.pop();
+      } else {
+        const index = frame.index!;
+        frame.index = index + 1;
+        const key = frame.keys![index]!,
+          entry = object[key];
+        if (entry !== undefined) {
+          if (frame.wrote) append(",");
+          frame.wrote = true;
+          append(JSON.stringify(key) + ":");
+          stack.push({ kind: "value", value: entry });
+        }
+      }
+    }
+    if (++steps % 512 === 0 && performance.now() - sliceStarted >= 8) {
+      await setImmediate();
+      sliceStarted = performance.now();
     }
   }
   hash.update(buffer);
diff --git a/src/execution-world/artifacts.ts b/src/execution-world/artifacts.ts
index d0a2e1d..b53e2d0 100644
--- a/src/execution-world/artifacts.ts
+++ b/src/execution-world/artifacts.ts
@@ -1,13 +1,13 @@
-import { createHash } from "node:crypto";
-import { canonicalJson } from "../capability-model/evolution.js";
 import {
+  executionPlanDigestAsync,
   type ExecutionPlan,
   type PlanPackage,
   ExecutionPlanError,
   hexDigest,
-  hexDigestAsync,
   executionVersions,
 } from "./plan.js";
+import { createHash } from "node:crypto";
+import { canonicalJson } from "../capability-model/evolution.js";
 
 export interface ArtifactFile {
   path: string;
@@ -366,7 +366,7 @@ export async function checkExecutionWorld(
 ): Promise<CheckedWorld> {
   if (canonicalJson(plan.definition.versions) !== canonicalJson(executionVersions))
     fail("world", "Unsupported plan codec versions");
-  if ((await hexDigestAsync(plan.definition)) !== plan.digest) fail("plan", "Plan digest mismatch");
+  if ((await executionPlanDigestAsync(plan)) !== plan.digest) fail("plan", "Plan digest mismatch");
   const manifests = inputs.map(parsePackageArtifacts);
   unique(
     manifests.map((m) => m.packageRevisionId),
diff --git a/src/execution-world/candidate.ts b/src/execution-world/candidate.ts
index 9a0e0b5..f9fd215 100644
--- a/src/execution-world/candidate.ts
+++ b/src/execution-world/candidate.ts
@@ -1,7 +1,7 @@
 import { graphExecutionRepresentation } from "./graph-execution.js";
 import { lstat } from "node:fs/promises";
 import { join } from "node:path";
-import { hexDigest, hexDigestAsync, ExecutionPlanError, type ExecutionPlan } from "./plan.js";
+import { hexDigest, hexDigestAsync, sealExecutionPlan, ExecutionPlanError, type ExecutionPlan } from "./plan.js";
 import {
   loadExecutionInstallation,
   createClientContractCatalog,
@@ -72,7 +72,7 @@ export async function loadCheckedInstallationCandidate(
     const [plan, artifacts, source, entryRequest, kernel, queries] = values;
     if (
       plan?.definition?.codec !== "camino-execution-plan-v1" ||
-      (await hexDigestAsync(plan.definition)) !== plan.digest ||
+      !(await sealExecutionPlan(plan)) ||
       workspaceDigest !== (await hexDigestAsync(plan.definition.workspace))
     )
       throw new ExecutionPlanError(
diff --git a/src/execution-world/client-contracts.ts b/src/execution-world/client-contracts.ts
index 59f2e7b..11ebdd2 100644
--- a/src/execution-world/client-contracts.ts
+++ b/src/execution-world/client-contracts.ts
@@ -1,3 +1,4 @@
+import { executionPlanDigest, type ExecutionPlan, resolvePlannedOperation, ExecutionPlanError } from "./plan.js";
 import type {
   InterfaceRevision,
   InterfaceOperation,
@@ -6,7 +7,7 @@ import type {
 } from "../capability-model/types.js";
 import { canonicalJson } from "../capability-model/evolution.js";
 import { portableValueSchema, tsType } from "../bindings/portable.js";
-import { type ExecutionPlan, resolvePlannedOperation, hexDigest, ExecutionPlanError } from "./plan.js";
+
 import type { BindingSchema } from "../bindings/index.js";
 import type { PackageBuildContract } from "./build-contract.js";
 import { preparationArtifact, type ReactPreparationArtifact } from "../react-build/declarations.js";
@@ -55,7 +56,7 @@ export function publicOperationContract(
 }
 /** Resolve a public contract to internal dispatch. This does not authorize the receiver. */
 export function linkInterfaceOperation(plan: ExecutionPlan, atom: string, contract: PublicOperationContract) {
-  if (hexDigest(plan.definition) !== plan.digest)
+  if (executionPlanDigest(plan) !== plan.digest)
     throw new ExecutionPlanError("INVALID_PLAN", atom, "Invalid execution plan digest");
   const iface = plan.definition.workspace.interfaceImports.find((i) => i.revisionId === contract.interface);
   const operation = iface?.members.flatMap((m) => m.operations).find((o) => o.id === contract.operation);
@@ -97,7 +98,7 @@ export function publicQueryContract(pkg: PackageRevision, queryId: string): Publ
   };
 }
 export function linkPackageQuery(plan: ExecutionPlan, contract: PublicQueryContract) {
-  if (hexDigest(plan.definition) !== plan.digest)
+  if (executionPlanDigest(plan) !== plan.digest)
     throw new ExecutionPlanError("INVALID_PLAN", contract.query, "Invalid execution plan digest");
   const pkg = plan.definition.workspace.packageImports.find((p) => p.revisionId === contract.package);
   if (!pkg || canonicalJson(publicQueryContract(pkg, contract.query)) !== canonicalJson(contract))
diff --git a/src/execution-world/execution-groups.ts b/src/execution-world/execution-groups.ts
index ad4b8dd..116ade0 100644
--- a/src/execution-world/execution-groups.ts
+++ b/src/execution-world/execution-groups.ts
@@ -1,3 +1,4 @@
+import { executionPlanDigestAsync, type ExecutionPlan, hexDigest, hexDigestAsync, ExecutionPlanError } from "./plan.js";
 import { portableReflectionValue } from "./reflection.js";
 import type {
   BoundDependency,
@@ -6,7 +7,6 @@ import type {
   PersistentAttachment,
 } from "../capability-model/types.js";
 import { type ExecutionInstallation, type ExecutionGroupIdentity } from "./installation.js";
-import { type ExecutionPlan, hexDigest, hexDigestAsync, ExecutionPlanError } from "./plan.js";
 
 export interface ExecutionEnvironment {
   /** Explicit host placement. Merely including an optional module does not select it. */
@@ -28,7 +28,7 @@ export async function compileExecutionGroups(
   installation: ExecutionInstallation,
   environments: Readonly<Record<string, ExecutionEnvironment>>,
 ): Promise<InstalledExecutionGroup[]> {
-  if (installation.plan !== plan.digest || (await hexDigestAsync(plan.definition)) !== plan.digest)
+  if (installation.plan !== plan.digest || (await executionPlanDigestAsync(plan)) !== plan.digest)
     throw new ExecutionPlanError("GROUP_PLAN_MISMATCH", plan.digest, "Expected one checked installation");
   const workspace = plan.definition.workspace;
   const packages = new Map(workspace.packageImports.map((p) => [p.revisionId as string, p]));
diff --git a/src/execution-world/graph-execution.ts b/src/execution-world/graph-execution.ts
index 93fb031..ab2b009 100644
--- a/src/execution-world/graph-execution.ts
+++ b/src/execution-world/graph-execution.ts
@@ -1,4 +1,5 @@
-import { ExecutionPlanError, hexDigest, type ExecutionPlan } from "./plan.js";
+import { executionPlanDigest, ExecutionPlanError, hexDigest, type ExecutionPlan } from "./plan.js";
+
 import type { ExecutionInstallation } from "./installation.js";
 
 /** Execution inputs, not build evidence. Nominal revision IDs remain dispatch
@@ -10,7 +11,7 @@ export function graphExecutionRepresentation(
   kernel: unknown,
   queries: unknown,
 ) {
-  if (installation.plan !== plan.digest || hexDigest(plan.definition) !== plan.digest)
+  if (installation.plan !== plan.digest || executionPlanDigest(plan) !== plan.digest)
     throw new ExecutionPlanError("GRAPH_PLAN_MISMATCH", "graph", "Expected one checked installation");
   if (
     !kernel ||
diff --git a/src/execution-world/installation.ts b/src/execution-world/installation.ts
index b5eb379..92d9d22 100644
--- a/src/execution-world/installation.ts
+++ b/src/execution-world/installation.ts
@@ -1,9 +1,10 @@
+import { executionPlanDigestAsync, ExecutionPlanError, type ExecutionPlan } from "./plan.js";
 import { compileInspectionTemplates, type InspectionTemplate, type InspectionKernel } from "./inspection.js";
 import path from "node:path";
 import { loadCheckedArtifactWorld } from "./receipts.js";
 import { contentArtifactUrl, loadArtifactWorld, type LoadedArtifactWorld } from "./files.js";
 import { selectArtifactImplementation, type ArtifactImplementation, type ComponentArtifact } from "./artifacts.js";
-import { ExecutionPlanError, hexDigestAsync, type ExecutionPlan } from "./plan.js";
+
 import {
   publicOperationContract,
   publicQueryContract,
@@ -47,7 +48,7 @@ export async function clientContractCatalog(
   requestedPackages: readonly string[],
   checkedKernel?: InspectionKernel,
 ): Promise<ClientContractCatalog> {
-  if (installation.plan !== plan.digest || (await hexDigestAsync(plan.definition)) !== plan.digest)
+  if (installation.plan !== plan.digest || (await executionPlanDigestAsync(plan)) !== plan.digest)
     throw new ExecutionPlanError(
       "CATALOG_PLAN_MISMATCH",
       plan.digest,
diff --git a/src/execution-world/kernel.ts b/src/execution-world/kernel.ts
index 47d9ff5..4a23a0c 100644
--- a/src/execution-world/kernel.ts
+++ b/src/execution-world/kernel.ts
@@ -1,3 +1,4 @@
+import { executionPlanDigest, type ExecutionPlan, ExecutionPlanError, hexDigest } from "./plan.js";
 import { portableReflectionType, portableReflectionValue } from "./reflection.js";
 import type {
   ValueType,
@@ -7,7 +8,7 @@ import type {
   BoundDependency,
   PackageExport,
 } from "../capability-model/types.js";
-import { type ExecutionPlan, ExecutionPlanError, hexDigest } from "./plan.js";
+
 import { portableValueSchema } from "../bindings/portable.js";
 import { subscriptionContract } from "../capability-model/journals.js";
 type PreparedStep = string | null | { case: string; id: string };
@@ -25,7 +26,7 @@ function preparedInputPaths(type: ValueType, path: PreparedStep[] = []): Prepare
 }
 /** Small data-only interpreter input; no compiler, parser, Node module or SQL dependency reaches the browser. */
 export function compileKernelProgram(plan: ExecutionPlan): unknown {
-  if (hexDigest(plan.definition) !== plan.digest)
+  if (executionPlanDigest(plan) !== plan.digest)
     throw new ExecutionPlanError("INVALID_PLAN", "kernel", "Plan digest mismatch");
   const workspace = plan.definition.workspace;
   if (workspace.sharedAttachments.some((attachment) => attachment.kind !== "edge"))
diff --git a/src/execution-world/placement.ts b/src/execution-world/placement.ts
index 569b96a..e00e77f 100644
--- a/src/execution-world/placement.ts
+++ b/src/execution-world/placement.ts
@@ -1,6 +1,7 @@
+import { executionPlanDigest, ExecutionPlanError, hexDigest, type ExecutionPlan } from "./plan.js";
 import { parse } from "@babel/parser";
 import { builtinModules } from "node:module";
-import { ExecutionPlanError, hexDigest, type ExecutionPlan } from "./plan.js";
+
 import type { ExecutionInstallation } from "./installation.js";
 import type { ArtifactImplementation, ArtifactReader } from "./artifacts.js";
 
@@ -212,7 +213,7 @@ export async function reportExecutionPlacement(
   installation: ExecutionInstallation,
   read: ArtifactReader,
 ) {
-  if (installation.plan !== plan.digest || hexDigest(plan.definition) !== plan.digest)
+  if (installation.plan !== plan.digest || executionPlanDigest(plan) !== plan.digest)
     throw new ExecutionPlanError(
       "PLACEMENT_PLAN_MISMATCH",
       plan.digest,
diff --git a/src/execution-world/plan.ts b/src/execution-world/plan.ts
index bc5cd6d..e941965 100644
--- a/src/execution-world/plan.ts
+++ b/src/execution-world/plan.ts
@@ -17,6 +17,7 @@ import { linkQueries, type LinkedQuery } from "../query/link.js";
 import { type BindingSchema } from "../bindings/index.js";
 import { unsupportedQueryOperator } from "./query-operators.js";
 import { packageBuildContexts } from "./build-contract.js";
+import { setImmediate } from "node:timers/promises";
 
 export class ExecutionPlanError extends Error {
   constructor(
@@ -31,6 +32,54 @@ export class ExecutionPlanError extends Error {
 export const hexDigest = (value: unknown): string => contentDigest(value).slice("sha256:".length);
 export const hexDigestAsync = async (value: unknown): Promise<string> =>
   (await contentDigestAsync(value)).slice("sha256:".length);
+// Checked runtime metadata is owned JSON, not live Graph data. Reuse its proof
+// only after every reachable record is immutable. Weak keys retain neither old
+// Candidates nor an application cache; unsealed compiler inputs are rehashed.
+const sealedPlanDigests = new WeakMap<ExecutionPlan, string>();
+export const executionPlanDigest = (plan: ExecutionPlan): string =>
+  sealedPlanDigests.get(plan) ?? hexDigest(plan.definition);
+export const executionPlanDigestAsync = async (plan: ExecutionPlan): Promise<string> =>
+  sealedPlanDigests.get(plan) ?? (await hexDigestAsync(plan.definition));
+/** Transfers owned parsed JSON into immutable runtime metadata. Freeze before
+ * yielding to hashing so concurrent mutation cannot invalidate the proof. */
+export async function sealExecutionPlan(plan: ExecutionPlan): Promise<boolean> {
+  if (sealedPlanDigests.has(plan)) return true;
+  if (!Object.hasOwn(plan, "definition") || !Object.hasOwn(plan, "digest")) return false;
+  const pending: object[] = [plan],
+    seen = new WeakSet<object>();
+  let sliceStarted = performance.now(),
+    count = 0;
+  while (pending.length) {
+    const value = pending.pop()!;
+    if (seen.has(value)) continue;
+    if (
+      !Array.isArray(value) &&
+      Object.getPrototypeOf(value) !== Object.prototype &&
+      Object.getPrototypeOf(value) !== null
+    )
+      throw new ExecutionPlanError("INVALID_PLAN_JSON", "plan", "Expected owned JSON records");
+    for (const key of Reflect.ownKeys(value)) {
+      const descriptor = Object.getOwnPropertyDescriptor(value, key)!;
+      if (typeof key !== "string" || !Object.hasOwn(descriptor, "value"))
+        throw new ExecutionPlanError(
+          "INVALID_PLAN_JSON",
+          "plan",
+          "Runtime metadata cannot contain accessors or symbols",
+        );
+      if (descriptor.value !== null && typeof descriptor.value === "object") pending.push(descriptor.value);
+    }
+    Object.freeze(value);
+    seen.add(value);
+    if (++count % 1024 === 0 && performance.now() - sliceStarted >= 8) {
+      await setImmediate();
+      sliceStarted = performance.now();
+    }
+  }
+  const digest = await hexDigestAsync(plan.definition);
+  if (digest !== plan.digest) return false;
+  sealedPlanDigests.set(plan, digest);
+  return true;
+}
 const sorted = <T>(values: readonly T[], key: (value: T) => string): T[] =>
   [...values].sort((a, b) => (key(a) < key(b) ? -1 : key(a) > key(b) ? 1 : 0));
 export const publicOperationKey = (atom: string, iface: string, operation: string): string =>
diff --git a/src/execution-world/projections.ts b/src/execution-world/projections.ts
index 2eb24af..d00913a 100644
--- a/src/execution-world/projections.ts
+++ b/src/execution-world/projections.ts
@@ -1,4 +1,5 @@
-import { ExecutionPlanError, hexDigest, type ExecutionPlan, type PlannedQuery } from "./plan.js";
+import { executionPlanDigest, ExecutionPlanError, type ExecutionPlan, type PlannedQuery } from "./plan.js";
+
 /** Contracts promised by a direct result. Interface dependencies are explicit; accidental
  * overlap among today's implementations does not silently widen an exported interface contract. */
 export function resultInterfaces(plan: ExecutionPlan, operationKey: string): string[] {
@@ -23,7 +24,7 @@ export function resultInterfaces(plan: ExecutionPlan, operationKey: string): str
 }
 /** Compile-time observeResult compatibility. Observation does not grant read or mutation authority. */
 export function checkResultProjection(plan: ExecutionPlan, operationKey: string, queryId: string): PlannedQuery {
-  if (hexDigest(plan.definition) !== plan.digest)
+  if (executionPlanDigest(plan) !== plan.digest)
     throw new ExecutionPlanError("INVALID_PLAN", "projection", "Plan digest mismatch");
   const query = plan.definition.queries.find((q) => q.id === queryId);
   if (!query) throw new ExecutionPlanError("UNKNOWN_PROJECTION", queryId, "No installed query");
diff --git a/src/execution-world/queries.ts b/src/execution-world/queries.ts
index 1513014..a924cdc 100644
--- a/src/execution-world/queries.ts
+++ b/src/execution-world/queries.ts
@@ -1,7 +1,8 @@
+import { executionPlanDigest, ExecutionPlanError, type ExecutionPlan } from "./plan.js";
 import { compileKernelProgram } from "./kernel.js";
 import { compileInspectionTemplates } from "./inspection.js";
 import { portableValueSchema } from "../bindings/portable.js";
-import { ExecutionPlanError, hexDigest, type ExecutionPlan } from "./plan.js";
+
 import type { ValueType } from "../capability-model/types.js";
 import { compileQueryComposition } from "../query/composition.js";
 import { queryTreeBlueprint } from "./query-trees.js";
@@ -24,7 +25,7 @@ const lowerTypes = (value: unknown): unknown =>
 /** Checked query IR and installed getter identities, without GraphQL schemas/parsers or SQL adapters.
  * Keep authored selection names only for output paths; field access uses resolved interface/member IDs. */
 export function compileQueryProgram(plan: ExecutionPlan): unknown {
-  if (hexDigest(plan.definition) !== plan.digest)
+  if (executionPlanDigest(plan) !== plan.digest)
     throw new ExecutionPlanError("INVALID_PLAN", "queries", "Plan digest mismatch");
   const allQueries = new Map(plan.definition.queries.map(({ id, query }) => [id, query.checked]));
   const compositions = plan.definition.workspace.packageImports.flatMap((pkg) =>
diff --git a/src/execution-world/query-document.ts b/src/execution-world/query-document.ts
index a897ab8..570a465 100644
--- a/src/execution-world/query-document.ts
+++ b/src/execution-world/query-document.ts
@@ -1,8 +1,9 @@
+import { executionPlanDigest, hexDigest, type ExecutionPlan, type PlannedQuery } from "./plan.js";
 import { compileQuery } from "../query/compile.js";
 import { linkQueries } from "../query/link.js";
 import { capabilityId } from "../capability-model/types.js";
 import { portableValueSchema } from "../bindings/portable.js";
-import { hexDigest, type ExecutionPlan, type PlannedQuery } from "./plan.js";
+
 import { compileKernelProgram } from "./kernel.js";
 import { queryProgramEntry } from "./queries.js";
 import { unsupportedQueryOperator } from "./query-operators.js";
@@ -17,7 +18,7 @@ export interface QueryDocument {
 /** Runtime query documents use the same language, nominal contracts, linking
  * and interpreter as packaged queries. They introduce no resources or code. */
 export async function compilePublicQuery(plan: ExecutionPlan, request: QueryDocument) {
-  if (hexDigest(plan.definition) !== plan.digest) throw Error("INVALID_PLAN");
+  if (executionPlanDigest(plan) !== plan.digest) throw Error("INVALID_PLAN");
   if (
     typeof request.document !== "string" ||
     Buffer.byteLength(request.document) > 32768 ||
diff --git a/test/evolution.test.ts b/test/evolution.test.ts
index 8a40286..754fe45 100644
--- a/test/evolution.test.ts
+++ b/test/evolution.test.ts
@@ -55,10 +55,22 @@ test("hashing is canonical and rejects values outside the persisted JSON contrac
 test("cooperative hashing preserves canonical identities and services the event loop", async () => {
   const sparse = [1, 2, 3];
   delete sparse[1];
-  const values = [null, false, -0, "中\\n\ud800", sparse, { z: 1, a: { omitted: undefined, b: [false, 1e100] } }];
+  const values: unknown[] = [
+    null,
+    false,
+    -0,
+    "中\\n\ud800",
+    sparse,
+    { z: 1, a: { omitted: undefined, b: [false, 1e100] } },
+  ];
+  const shared = { text: "中😀".repeat(22000) };
+  values.push({ first: shared, second: shared });
   for (const value of values) assert.equal(await contentDigestAsync(value), contentDigest(value));
   for (const value of [undefined, NaN, Infinity, new Date(), [undefined]])
     await assert.rejects(contentDigestAsync(value));
+  const cyclic: { next?: unknown } = {};
+  cyclic.next = cyclic;
+  await assert.rejects(contentDigestAsync(cyclic), /cyclic JSON/);
   const large = Array.from({ length: 50000 }, (_, index) => ({ z: "definition".repeat(8), a: index }));
   const expected = contentDigest(large);
   let serviced = false;
diff --git a/test/execution-world.test.ts b/test/execution-world.test.ts
index 471a62c..ab2047b 100644
--- a/test/execution-world.test.ts
+++ b/test/execution-world.test.ts
@@ -9,6 +9,9 @@ import {
   implementationDigest,
   clientContractCatalog,
   hexDigest,
+  executionPlanDigest,
+  executionPlanDigestAsync,
+  sealExecutionPlan,
   parsePackageArtifacts,
   artifactPath,
   type PackageArtifacts,
@@ -21,6 +24,54 @@ import { compileKernelProgram } from "../src/execution-world/kernel.js";
 import { loadCompositeWorkspace } from "./composite-fixture.js";
 import { standardNativeBackends } from "../src/execution-world/native-backends.js";
 
+test("sealed runtime plans reuse verified integrity while mutable copies are rechecked", async () => {
+  const workspace = await loadReaderWorkspace();
+  const compiled = compileExecutionPlan(workspace);
+  const plan: ExecutionPlan = JSON.parse(JSON.stringify(compiled));
+  assert.equal(await sealExecutionPlan(plan), true);
+  assert.equal(executionPlanDigest(plan), compiled.digest);
+  assert.equal(await executionPlanDigestAsync(plan), compiled.digest);
+  assert.throws(() => {
+    plan.definition.workspace.sourceRootCommit = "f".repeat(40);
+  }, TypeError);
+  assert.throws(() => {
+    plan.digest = "0".repeat(64);
+  }, TypeError);
+
+  const stringify = JSON.stringify;
+  JSON.stringify = () => {
+    throw Error("Repeated serialization of sealed metadata");
+  };
+  try {
+    assert.equal(executionPlanDigest(plan), compiled.digest);
+    assert.equal(await executionPlanDigestAsync(plan), compiled.digest);
+  } finally {
+    JSON.stringify = stringify;
+  }
+
+  const changed: ExecutionPlan = structuredClone(plan);
+  changed.definition.workspace.sourceRootCommit = "f".repeat(40);
+  Object.freeze(changed);
+  assert.notEqual(executionPlanDigest(changed), plan.digest);
+  assert.notEqual(await executionPlanDigestAsync(changed), plan.digest);
+  assert.equal(await sealExecutionPlan(changed), false, "shallow freezing is not an integrity proof");
+
+  const resigned: ExecutionPlan = structuredClone(plan);
+  resigned.definition.workspace.sourceRootCommit = "e".repeat(40);
+  resigned.digest = executionPlanDigest(resigned);
+  assert.equal(await sealExecutionPlan(resigned), true);
+  assert.notEqual(executionPlanDigest(resigned), plan.digest);
+  workspace.sourceRootCommit = "d".repeat(40);
+  assert.equal(workspace.sourceRootCommit, "d".repeat(40), "sealing owned JSON leaves compiler inputs editable");
+});
+
+test("runtime plan sealing rejects accessor-backed metadata", async () => {
+  const plan: ExecutionPlan = compileExecutionPlan(await loadReaderWorkspace());
+  assert.equal(await sealExecutionPlan(Object.create(plan)), false, "inherited integrity fields cannot be sealed");
+  Object.defineProperty(plan.definition, "codec", { get: () => "camino-execution-plan-v1", enumerable: true });
+  await assert.rejects(sealExecutionPlan(plan), /INVALID_PLAN_JSON/);
+});
+
 test("optional targets close over calls into another package", async () => {
   const workspace = await loadCompositeWorkspace();
   const before = compileExecutionPlan(workspace).definition.operations.find(