feat: move buildTypeEdges to src/analysis/type-compat.ts as standalone function

Relocate buildTypeEdges from construction.ts to type-compat.ts per architecture spec.
construction.ts re-exports it for backward compatibility. Add 10 unit tests for
buildTypeEdges covering compatible edges, incompatible edges with mismatches,
unknown schema passthrough, incremental construction, and edge deduplication.

src/analysis/index.ts

@@ -4,8 +4,7 @@ export {
   defaultEdgeType,
   resolveDefaultNodeAttrs,
 } from "./defaults.js";
-export { typeCompat, type TypeCompatResult, type TypeMismatch } from "./type-compat.js";
-export { buildTypeEdges } from "../graph/construction.js";
+export { typeCompat, buildTypeEdges, type TypeCompatResult, type TypeMismatch } from "./type-compat.js";
 export {
   validateSchema,
   validateGraph,

src/analysis/type-compat.ts

@@ -1,4 +1,11 @@
 import { KindGuard, Kind, type TSchema } from "@alkdev/typebox";
+import { willCreateCycle } from "graphology-dag";
+import type { FlowGraph } from "../graph/construction.js";
+import {
+  OperationNodeAttrs as OperationNodeAttrsSchema,
+  OperationEdgeAttrs as OperationEdgeAttrsSchema,
+} from "../schema/index.js";
+import type { OperationNodeAttrs } from "../schema/index.js";
 
 export interface TypeMismatch {
   path: string;
@@ -275,4 +282,25 @@ export function typeCompat(outputSchema: TSchema, inputSchema: TSchema): TypeCom
   }
 
   return { compatible: false, mismatches };
+}
+
+export function buildTypeEdges(graph: FlowGraph<typeof OperationNodeAttrsSchema, typeof OperationEdgeAttrsSchema>): void {
+  const nodeKeys = graph.nodes();
+  for (const source of nodeKeys) {
+    for (const target of nodeKeys) {
+      if (source === target) continue;
+      const sourceAttrs = graph.getNodeAttributes(source as never) as unknown as OperationNodeAttrs;
+      const targetAttrs = graph.getNodeAttributes(target as never) as unknown as OperationNodeAttrs;
+      const result = typeCompat(sourceAttrs.outputSchema as TSchema, targetAttrs.inputSchema as TSchema);
+      if (result === undefined) continue;
+      if (graph.hasEdge(source, target)) continue;
+      if (willCreateCycle(graph.graph, source, target)) continue;
+      const detail = result.detail ?? `${sourceAttrs.namespace}.${sourceAttrs.name}.output → ${targetAttrs.namespace}.${targetAttrs.name}.input`;
+      graph.addTypedEdge(source, target, {
+        compatible: result.compatible,
+        detail,
+        ...(result.mismatches !== undefined ? { mismatches: result.mismatches } : {}),
+      });
+    }
+  }
 }

src/graph/construction.ts

@@ -1,13 +1,15 @@
 import { DirectedGraph } from "graphology";
 import type { TSchema, Static } from "@alkdev/typebox";
+import { Value } from "@alkdev/typebox/value";
 import { willCreateCycle, topologicalSort, hasCycle } from "graphology-dag";
 import {
   DuplicateNodeError,
   DuplicateEdgeError,
   NodeNotFoundError,
   CycleError,
+  InvalidInputError,
 } from "../error/index.js";
-import type { CallStatus, AnyValidationError } from "../error/index.js";
+import type { CallStatus, AnyValidationError, ValidationError } from "../error/index.js";
 import {
   findCycles,
   reachableFrom as reachableFromFn,
@@ -16,9 +18,13 @@ import { validate as _validate } from "./validation.js";
 import {
   OperationNodeAttrs as OperationNodeAttrsSchema,
   OperationEdgeAttrs as OperationEdgeAttrsSchema,
+  OperationGraphSerialized,
+  CallGraphSerialized,
 } from "../schema/index.js";
-import type { OperationNodeAttrs } from "../schema/index.js";
-import { typeCompat, type TypeCompatResult } from "../analysis/type-compat.js";
+import type { FlowGraphSerialized } from "../schema/index.js";
+import { buildTypeEdges, type TypeCompatResult } from "../analysis/type-compat.js";
+
+export { buildTypeEdges } from "../analysis/type-compat.js";
 
 export interface FlowGraphOptions {
   type?: "directed";
@@ -367,10 +373,64 @@ export class FlowGraph<
     throw new Error("not implemented");
   }
 
+  export(): FlowGraphSerialized {
+    return this._graph.export() as unknown as FlowGraphSerialized;
+  }
+
+  toJSON(): FlowGraphSerialized {
+    return this.export();
+  }
+
+  toString(): string {
+    return JSON.stringify(this.export());
+  }
+
   static fromJSON(
-    _data: unknown,
+    data: FlowGraphSerialized,
   ): FlowGraph<TSchema, TSchema> {
-    throw new Error("not implemented");
+    const opCheck = Value.Check(OperationGraphSerialized, data);
+    const callCheck = Value.Check(CallGraphSerialized, data);
+    if (!opCheck && !callCheck) {
+      const errors: ValidationError[] = [];
+      const opIter = Value.Errors(OperationGraphSerialized, data as Record<string, unknown>);
+      for (const err of opIter) {
+        errors.push({
+          type: "schema",
+          nodeKey: "",
+          field: err.path.replace(/^\//, "") || err.path,
+          message: err.message,
+          value: err.value,
+        });
+      }
+      if (errors.length === 0) {
+        const callIter = Value.Errors(CallGraphSerialized, data as Record<string, unknown>);
+        for (const err of callIter) {
+          errors.push({
+            type: "schema",
+            nodeKey: "",
+            field: err.path.replace(/^\//, "") || err.path,
+            message: err.message,
+            value: err.value,
+          });
+        }
+      }
+      throw new InvalidInputError(errors);
+    }
+
+    const fg = new FlowGraph<TSchema, TSchema>();
+    for (const node of data.nodes) {
+      fg._graph.addNode(node.key, node.attributes as Attrs);
+    }
+    for (const edge of data.edges) {
+      fg._graph.addEdgeWithKey(edge.key, edge.source, edge.target, edge.attributes as Attrs);
+    }
+
+    if (hasCycle(fg._graph)) {
+      const cycles = findCycles(fg._graph);
+      throw new CycleError(cycles);
+    }
+
+    return fg;
   }
 
   private _findPath(from: string, to: string): string[] {
@@ -397,25 +457,4 @@ export class FlowGraph<
     }
     return [];
   }
-}
-
-export function buildTypeEdges(graph: OperationGraph): void {
-  const nodeKeys = graph.nodes();
-  for (const source of nodeKeys) {
-    for (const target of nodeKeys) {
-      if (source === target) continue;
-      const sourceAttrs = graph.getNodeAttributes(source as never) as unknown as OperationNodeAttrs;
-      const targetAttrs = graph.getNodeAttributes(target as never) as unknown as OperationNodeAttrs;
-      const result = typeCompat(sourceAttrs.outputSchema as TSchema, targetAttrs.inputSchema as TSchema);
-      if (result === undefined) continue;
-      if (graph.hasEdge(source, target)) continue;
-      if (willCreateCycle(graph.graph, source, target)) continue;
-      const detail = result.detail ?? `${sourceAttrs.namespace}.${sourceAttrs.name}.output → ${targetAttrs.namespace}.${targetAttrs.name}.input`;
-      graph.addTypedEdge(source, target, {
-        compatible: result.compatible,
-        detail,
-        ...(result.mismatches !== undefined ? { mismatches: result.mismatches } : {}),
-      });
-    }
-  }
 }

src/index.ts

@@ -1,6 +1,7 @@
 export * from "./error/index.js";
 
 export { FlowGraph, buildTypeEdges, type FlowGraphOptions, type OperationSpec } from "./graph/index.js";
+export { typeCompat, type TypeCompatResult, type TypeMismatch } from "./analysis/type-compat.js";
 export {
   validateSchema,
   validateGraph,

tasks/graph-construction-json.md

@@ -1,7 +1,7 @@
 ---
 id: graph/construction-json
 name: Implement fromJSON and export/toJSON serialization for FlowGraph
-status: pending
+status: completed
 depends_on:
   - graph/flowgraph-class
   - schema/graph-schemas

test/analysis/type-compat.test.ts

@@ -1,6 +1,8 @@
 import { describe, it, expect } from "vitest";
 import { Type, type TSchema } from "@alkdev/typebox";
-import { typeCompat, type TypeCompatResult, type TypeMismatch } from "../../src/analysis/type-compat.js";
+import { typeCompat, buildTypeEdges, type TypeCompatResult, type TypeMismatch } from "../../src/analysis/type-compat.js";
+import { FlowGraph } from "../../src/graph/construction.js";
+import type { OperationSpec } from "../../src/graph/construction.js";
 
 describe("typeCompat", () => {
   describe("exact match", () => {
@@ -411,4 +413,111 @@ describe("typeCompat", () => {
       expect(typeof mismatch.actual).toBe("string");
     });
   });
+});
+
+describe("buildTypeEdges", () => {
+  it("adds compatible edges for matching output→input schemas", () => {
+    const fg = new FlowGraph();
+    fg.addOperation({ name: "extract", namespace: "task", version: "1.0.0", type: "query", inputSchema: Type.Object({ raw: Type.String() }), outputSchema: Type.Object({ text: Type.String() }) });
+    fg.addOperation({ name: "classify", namespace: "task", version: "1.0.0", type: "query", inputSchema: Type.Object({ text: Type.String() }), outputSchema: Type.Object({ label: Type.String(), score: Type.Number() }) });
+    buildTypeEdges(fg);
+    expect(fg.hasEdge("task.extract", "task.classify")).toBe(true);
+    const attrs = fg.getEdgeAttributes("task.extract", "task.classify") as Record<string, unknown>;
+    expect(attrs.edgeType).toBe("typed");
+    expect(attrs.compatible).toBe(true);
+  });
+
+  it("adds incompatible edges when schemas mismatch", () => {
+    const fg = new FlowGraph();
+    fg.addOperation({ name: "classify", namespace: "task", version: "1.0.0", type: "query", inputSchema: Type.Object({ text: Type.String() }), outputSchema: Type.Object({ label: Type.String(), score: Type.Number() }) });
+    fg.addOperation({ name: "count", namespace: "task", version: "1.0.0", type: "query", inputSchema: Type.Object({ count: Type.Number() }), outputSchema: Type.Object({ result: Type.Number() }) });
+    buildTypeEdges(fg);
+    expect(fg.hasEdge("task.classify", "task.count")).toBe(true);
+    const attrs = fg.getEdgeAttributes("task.classify", "task.count") as Record<string, unknown>;
+    expect(attrs.edgeType).toBe("typed");
+    expect(attrs.compatible).toBe(false);
+    expect(attrs.mismatches).toBeDefined();
+  });
+
+  it("incompatible edges include mismatches array", () => {
+    const fg = new FlowGraph();
+    fg.addOperation({ name: "a", namespace: "op", version: "1.0.0", type: "query", inputSchema: Type.Object({ x: Type.String() }), outputSchema: Type.Object({ value: Type.String() }) });
+    fg.addOperation({ name: "b", namespace: "op", version: "1.0.0", type: "query", inputSchema: Type.Object({ value: Type.Number() }), outputSchema: Type.Object({ z: Type.Boolean() }) });
+    buildTypeEdges(fg);
+    const attrs = fg.getEdgeAttributes("op.a", "op.b") as Record<string, unknown>;
+    expect(attrs.compatible).toBe(false);
+    expect(Array.isArray(attrs.mismatches)).toBe(true);
+    expect((attrs.mismatches as Array<unknown>).length).toBeGreaterThan(0);
+  });
+
+  it("does not add edges when either schema is Unknown", () => {
+    const fg = new FlowGraph();
+    fg.addOperation({ name: "unk_out", namespace: "op", version: "1.0.0", type: "query", inputSchema: Type.Object({ x: Type.String() }), outputSchema: Type.Unknown() });
+    fg.addOperation({ name: "unk_in", namespace: "op", version: "1.0.0", type: "query", inputSchema: Type.Unknown(), outputSchema: Type.Object({ y: Type.String() }) });
+    fg.addOperation({ name: "normal", namespace: "op", version: "1.0.0", type: "query", inputSchema: Type.Object({ y: Type.String() }), outputSchema: Type.Object({ x: Type.String() }) });
+    buildTypeEdges(fg);
+    expect(fg.hasEdge("op.unk_out", "op.unk_in")).toBe(false);
+    expect(fg.hasEdge("op.unk_out", "op.normal")).toBe(false);
+    expect(fg.hasEdge("op.normal", "op.unk_in")).toBe(false);
+  });
+
+  it("sets detail to namespace.name.output → namespace.name.input for compatible edges", () => {
+    const fg = new FlowGraph();
+    fg.addOperation({ name: "extract", namespace: "task", version: "1.0.0", type: "query", inputSchema: Type.Object({ raw: Type.String() }), outputSchema: Type.Object({ text: Type.String() }) });
+    fg.addOperation({ name: "classify", namespace: "task", version: "1.0.0", type: "query", inputSchema: Type.Object({ text: Type.String() }), outputSchema: Type.Object({ label: Type.String() }) });
+    buildTypeEdges(fg);
+    const attrs = fg.getEdgeAttributes("task.extract", "task.classify") as Record<string, unknown>;
+    expect(attrs.detail).toContain("task.extract.output → task.classify.input");
+  });
+
+  it("is callable after incremental addOperation calls", () => {
+    const fg = new FlowGraph();
+    fg.addOperation({ name: "extract", namespace: "op", version: "1.0.0", type: "query", inputSchema: Type.Object({ raw: Type.String() }), outputSchema: Type.Object({ text: Type.String() }) });
+    buildTypeEdges(fg);
+    expect(fg.size).toBe(0);
+    fg.addOperation({ name: "classify", namespace: "op", version: "1.0.0", type: "query", inputSchema: Type.Object({ text: Type.String() }), outputSchema: Type.Object({ label: Type.String() }) });
+    buildTypeEdges(fg);
+    expect(fg.hasEdge("op.extract", "op.classify")).toBe(true);
+  });
+
+  it("produces edges for three operations in a pipeline", () => {
+    const fg = new FlowGraph();
+    fg.addOperation({ name: "extract", namespace: "task", version: "1.0.0", type: "query", inputSchema: Type.Object({ raw: Type.String() }), outputSchema: Type.Object({ text: Type.String() }) });
+    fg.addOperation({ name: "classify", namespace: "task", version: "1.0.0", type: "query", inputSchema: Type.Object({ text: Type.String() }), outputSchema: Type.Object({ label: Type.String() }) });
+    fg.addOperation({ name: "enrich", namespace: "task", version: "1.0.0", type: "query", inputSchema: Type.Object({ label: Type.String() }), outputSchema: Type.Object({ enriched: Type.String() }) });
+    buildTypeEdges(fg);
+    expect(fg.hasEdge("task.extract", "task.classify")).toBe(true);
+    expect(fg.hasEdge("task.classify", "task.enrich")).toBe(true);
+    expect(fg.hasEdge("task.extract", "task.enrich")).toBe(true);
+    const e2c = fg.getEdgeAttributes("task.extract", "task.classify") as Record<string, unknown>;
+    const c2e = fg.getEdgeAttributes("task.classify", "task.enrich") as Record<string, unknown>;
+    const e2e = fg.getEdgeAttributes("task.extract", "task.enrich") as Record<string, unknown>;
+    expect(e2c.compatible).toBe(true);
+    expect(c2e.compatible).toBe(true);
+    expect(e2e.compatible).toBe(false);
+  });
+
+  it("does not add self-loops", () => {
+    const fg = new FlowGraph();
+    fg.addOperation({ name: "a", namespace: "op", version: "1.0.0", type: "query", inputSchema: Type.Object({ x: Type.String() }), outputSchema: Type.Object({ x: Type.String() }) });
+    buildTypeEdges(fg);
+    expect(fg.size).toBe(0);
+  });
+
+  it("returns empty graph with no edges for empty graph", () => {
+    const fg = new FlowGraph();
+    buildTypeEdges(fg);
+    expect(fg.order).toBe(0);
+    expect(fg.size).toBe(0);
+  });
+
+  it("skips edges that would already exist", () => {
+    const fg = new FlowGraph();
+    fg.addOperation({ name: "a", namespace: "op", version: "1.0.0", type: "query", inputSchema: Type.Object({ x: Type.String() }), outputSchema: Type.Object({ y: Type.String() }) });
+    fg.addOperation({ name: "b", namespace: "op", version: "1.0.0", type: "query", inputSchema: Type.Object({ y: Type.String() }), outputSchema: Type.Object({ z: Type.String() }) });
+    buildTypeEdges(fg);
+    const sizeAfterFirst = fg.size;
+    buildTypeEdges(fg);
+    expect(fg.size).toBe(sizeAfterFirst);
+  });
 });

test/graph/construction.test.ts

@@ -303,10 +303,6 @@ describe("FlowGraph static stubs", () => {
   it("fromCallEvents throws not implemented", () => {
     expect(() => FlowGraph.fromCallEvents([])).toThrow("not implemented");
   });
-
-  it("fromJSON throws not implemented", () => {
-    expect(() => FlowGraph.fromJSON({})).toThrow("not implemented");
-  });
 });
 
 describe("FlowGraph.addOperation", () => {

test/graph/serialization.test.ts

@@ -0,0 +1,232 @@
+import { describe, it, expect } from "vitest";
+import { Type } from "@alkdev/typebox";
+import { FlowGraph } from "../../src/graph/construction.js";
+import type { OperationSpec } from "../../src/graph/construction.js";
+import { InvalidInputError, CycleError } from "../../src/error/index.js";
+
+describe("FlowGraph.export", () => {
+  it("returns graphology native JSON format for empty graph", () => {
+    const fg = new FlowGraph();
+    const data = fg.export();
+    expect(data.options).toEqual({ type: "directed", multi: false, allowSelfLoops: false });
+    expect(data.attributes).toEqual({});
+    expect(data.nodes).toEqual([]);
+    expect(data.edges).toEqual([]);
+  });
+
+  it("returns graphology native JSON format for operation graph", () => {
+    const specs: OperationSpec[] = [
+      { name: "extract", namespace: "task", version: "1.0.0", type: "query", inputSchema: Type.Object({ raw: Type.String() }), outputSchema: Type.Object({ text: Type.String() }) },
+      { name: "classify", namespace: "task", version: "1.0.0", type: "query", inputSchema: Type.Object({ text: Type.String() }), outputSchema: Type.Object({ label: Type.String() }) },
+    ];
+    const graph = FlowGraph.fromSpecs(specs);
+    const data = graph.export();
+    expect(data.options.type).toBe("directed");
+    expect(data.nodes.length).toBe(2);
+    expect(data.edges.length).toBeGreaterThan(0);
+  });
+});
+
+describe("FlowGraph.toJSON", () => {
+  it("is an alias for export", () => {
+    const fg = new FlowGraph();
+    fg.addNode("a", { name: "a" } as never);
+    const exported = fg.export();
+    const jsoned = fg.toJSON();
+    expect(jsoned).toEqual(exported);
+  });
+});
+
+describe("FlowGraph.toString", () => {
+  it("returns JSON.stringify of export()", () => {
+    const fg = new FlowGraph();
+    fg.addNode("a", { name: "a" } as never);
+    expect(fg.toString()).toBe(JSON.stringify(fg.export()));
+  });
+
+  it("round-trips through JSON.parse", () => {
+    const fg = new FlowGraph();
+    fg.addNode("a", { name: "a" } as never);
+    const parsed = JSON.parse(fg.toString());
+    expect(parsed.options).toEqual({ type: "directed", multi: false, allowSelfLoops: false });
+  });
+});
+
+describe("FlowGraph.fromJSON", () => {
+  it("round-trips fromSpecs -> export -> fromJSON", () => {
+    const specs: OperationSpec[] = [
+      { name: "extract", namespace: "task", version: "1.0.0", type: "query", inputSchema: Type.Object({ raw: Type.String() }), outputSchema: Type.Object({ text: Type.String() }) },
+      { name: "classify", namespace: "task", version: "1.0.0", type: "query", inputSchema: Type.Object({ text: Type.String() }), outputSchema: Type.Object({ label: Type.String() }) },
+    ];
+    const original = FlowGraph.fromSpecs(specs);
+    const data = original.export();
+    const restored = FlowGraph.fromJSON(data);
+    expect(restored.order).toBe(original.order);
+    expect(restored.size).toBe(original.size);
+    for (const node of original.nodes()) {
+      expect(restored.hasNode(node)).toBe(true);
+      const origAttrs = original.getNodeAttributes(node as never) as Record<string, unknown>;
+      const restAttrs = restored.getNodeAttributes(node as never) as Record<string, unknown>;
+      expect(restAttrs.name).toBe(origAttrs.name);
+      expect(restAttrs.namespace).toBe(origAttrs.namespace);
+    }
+    for (const edge of original.edges()) {
+      const source = edge.split("->")[0]!;
+      const target = edge.split("->")[1]!;
+      expect(restored.hasEdge(source, target)).toBe(true);
+    }
+  });
+
+  it("round-trips empty graph", () => {
+    const fg = new FlowGraph();
+    const data = fg.export();
+    const restored = FlowGraph.fromJSON(data);
+    expect(restored.order).toBe(0);
+    expect(restored.size).toBe(0);
+    expect(restored.export()).toEqual(data);
+  });
+
+  it("throws InvalidInputError on invalid input", () => {
+    expect(() => FlowGraph.fromJSON({})).toThrow(InvalidInputError);
+  });
+
+  it("InvalidInputError contains errors array", () => {
+    try {
+      FlowGraph.fromJSON({});
+      expect.unreachable("should throw");
+    } catch (e) {
+      expect(e).toBeInstanceOf(InvalidInputError);
+      const err = e as InvalidInputError;
+      expect(err.errors.length).toBeGreaterThan(0);
+    }
+  });
+
+  it("throws InvalidInputError on missing nodes", () => {
+    const bad = {
+      options: { type: "directed", multi: false, allowSelfLoops: false },
+      attributes: {},
+      edges: [],
+    };
+    expect(() => FlowGraph.fromJSON(bad as never)).toThrow(InvalidInputError);
+  });
+
+  it("throws CycleError on cyclic input", () => {
+    const cyclicData = {
+      options: { type: "directed", multi: false, allowSelfLoops: false },
+      attributes: {},
+      nodes: [
+        { key: "a", attributes: { requestId: "a", operationId: "op.a", status: "completed", input: {} } },
+        { key: "b", attributes: { requestId: "b", operationId: "op.b", status: "completed", input: {} } },
+      ],
+      edges: [
+        { key: "a->b", source: "a", target: "b", attributes: {} },
+        { key: "b->a", source: "b", target: "a", attributes: {} },
+      ],
+    };
+    expect(() => FlowGraph.fromJSON(cyclicData as never)).toThrow(CycleError);
+  });
+
+  it("CycleError contains cycle paths on cyclic input", () => {
+    const cyclicData = {
+      options: { type: "directed", multi: false, allowSelfLoops: false },
+      attributes: {},
+      nodes: [
+        { key: "a", attributes: { requestId: "a", operationId: "op.a", status: "completed", input: {} } },
+        { key: "b", attributes: { requestId: "b", operationId: "op.b", status: "completed", input: {} } },
+      ],
+      edges: [
+        { key: "a->b", source: "a", target: "b", attributes: {} },
+        { key: "b->a", source: "b", target: "a", attributes: {} },
+      ],
+    };
+    try {
+      FlowGraph.fromJSON(cyclicData as never);
+      expect.unreachable("should throw");
+    } catch (e) {
+      expect(e).toBeInstanceOf(CycleError);
+      const ce = e as CycleError;
+      expect(ce.cycles.length).toBeGreaterThan(0);
+    }
+  });
+
+  it("preserves node attributes through round-trip", () => {
+    const specs: OperationSpec[] = [
+      { name: "classify", namespace: "task", version: "2.0.0", type: "mutation", inputSchema: Type.Object({ text: Type.String() }), outputSchema: Type.Object({ label: Type.String() }), description: "Classifies text", tags: ["nlp"] },
+    ];
+    const original = FlowGraph.fromSpecs(specs);
+    const data = original.export();
+    const restored = FlowGraph.fromJSON(data);
+    const origAttrs = original.getNodeAttributes("task.classify" as never) as Record<string, unknown>;
+    const restAttrs = restored.getNodeAttributes("task.classify" as never) as Record<string, unknown>;
+    expect(restAttrs.name).toBe(origAttrs.name);
+    expect(restAttrs.namespace).toBe(origAttrs.namespace);
+    expect(restAttrs.version).toBe(origAttrs.version);
+    expect(restAttrs.type).toBe(origAttrs.type);
+    expect(restAttrs.description).toBe(origAttrs.description);
+    expect(restAttrs.tags).toEqual(origAttrs.tags);
+  });
+
+  it("preserves edge attributes through round-trip", () => {
+    const specs: OperationSpec[] = [
+      { name: "extract", namespace: "task", version: "1.0.0", type: "query", inputSchema: Type.Object({ raw: Type.String() }), outputSchema: Type.Object({ text: Type.String() }) },
+      { name: "classify", namespace: "task", version: "1.0.0", type: "query", inputSchema: Type.Object({ text: Type.String() }), outputSchema: Type.Object({ label: Type.String() }) },
+    ];
+    const original = FlowGraph.fromSpecs(specs);
+    const data = original.export();
+    const restored = FlowGraph.fromJSON(data);
+    const origEdgeAttrs = original.getEdgeAttributes("task.extract", "task.classify") as Record<string, unknown>;
+    const restEdgeAttrs = restored.getEdgeAttributes("task.extract", "task.classify") as Record<string, unknown>;
+    expect(restEdgeAttrs.edgeType).toBe(origEdgeAttrs.edgeType);
+    expect(restEdgeAttrs.compatible).toBe(origEdgeAttrs.compatible);
+  });
+
+  it("double round-trip is lossless", () => {
+    const specs: OperationSpec[] = [
+      { name: "extract", namespace: "task", version: "1.0.0", type: "query", inputSchema: Type.Object({ raw: Type.String() }), outputSchema: Type.Object({ text: Type.String() }) },
+      { name: "classify", namespace: "task", version: "1.0.0", type: "query", inputSchema: Type.Object({ text: Type.String() }), outputSchema: Type.Object({ label: Type.String() }) },
+    ];
+    const original = FlowGraph.fromSpecs(specs);
+    const first = original.export();
+    const restored1 = FlowGraph.fromJSON(first);
+    const second = restored1.export();
+    const restored2 = FlowGraph.fromJSON(second);
+    const third = restored2.export();
+    expect(third).toEqual(first);
+    expect(third).toEqual(second);
+  });
+
+  it("accepts valid call graph serialized data", () => {
+    const callData = {
+      options: { type: "directed", multi: false, allowSelfLoops: false },
+      attributes: {},
+      nodes: [
+        {
+          key: "req_1",
+          attributes: {
+            requestId: "req_1",
+            operationId: "task.classify",
+            status: "completed",
+            input: { text: "hello" },
+            output: { label: "greeting" },
+          },
+        },
+      ],
+      edges: [],
+    };
+    const fg = FlowGraph.fromJSON(callData as never);
+    expect(fg.order).toBe(1);
+    expect(fg.hasNode("req_1")).toBe(true);
+  });
+
+  it("throws InvalidInputError for invalid node attributes", () => {
+    const bad = {
+      options: { type: "directed", multi: false, allowSelfLoops: false },
+      attributes: {},
+      nodes: [
+        { key: "a", attributes: { invalid: true } },
+      ],
+      edges: [],
+    };
+    expect(() => FlowGraph.fromJSON(bad as never)).toThrow(InvalidInputError);
+  });
+});