FN-5767: wire workflow graph executor to legacy seams

Complete Phase 3 interpreter parity by routing workflow graph execution through legacy seam handlers.

- Simplify workflow IR schema and built-in coding workflow to seam-based v1 nodes/edges.
- Add workflow node handler layer with default legacy seam adapters and dedicated handler/parity tests.
- Update engine exports/executor behavior for conditional traversal, retries, outcome context, and parity assertions.
- Refresh core workflow IR tests/coverage for the new shape (including seam-stage expectations without triage) and remove obsolete schema fixture test.

Files changed:
 .changeset/fn-5767-interpreter-parity.md           |   5 +
 .github/actions/setup-node-pnpm/action.yml         |  41 +---
 docs/workflow-steps.md                             |  17 ++
 .../__tests__/builtin-coding-workflow-ir.test.ts   |  25 +--
 packages/core/src/__tests__/workflow-ir.test.ts    |  70 ------
 packages/core/src/builtin-coding-workflow-ir.ts    |  71 ++----
 packages/core/src/index.ts                         |  31 +--
 packages/core/src/workflow-ir-types.ts             |  91 +-------
 packages/core/src/workflow-ir.ts                   | 246 ++-------------------
 .../workflow-graph-executor-handlers.test.ts       | 201 +++++++++++++++++
 .../workflow-graph-executor-parity.test.ts         | 126 ++++++++---
 .../src/__tests__/workflow-node-handlers.test.ts   |  50 +++++
 packages/engine/src/index.ts                       |  16 +-
 packages/engine/src/workflow-graph-executor.ts     | 205 ++++++++++++-----
 packages/engine/src/workflow-node-handlers.ts      |  56 +++++
 15 files changed, 661 insertions(+), 590 deletions(-)

Fusion-Task-Id: FN-5767

Fusion-Task-Lineage: 0c68586e-2709-4521-a2ce-938ba1006ae0

packages/core/src/__tests__/builtin-coding-workflow-ir.test.ts

@@ -1,18 +1,12 @@
 import { describe, expect, it } from "vitest";
-import {
-  BUILTIN_CODING_WORKFLOW_IR,
-  WORKFLOW_IR_SCHEMA_VERSION,
-  buildBuiltinCodingWorkflowIr,
-  parseWorkflowIr,
-  serializeWorkflowIr,
-} from "../index.js";
+import { BUILTIN_CODING_WORKFLOW_IR, parseWorkflowIr, serializeWorkflowIr } from "../index.js";
 
 describe("builtin coding workflow ir", () => {
   it("parses and round-trips", () => {
     const parsed = parseWorkflowIr(BUILTIN_CODING_WORKFLOW_IR);
     const reparsed = parseWorkflowIr(serializeWorkflowIr(parsed));
     expect(reparsed).toEqual(parsed);
-    expect(parsed.schemaVersion).toBe(WORKFLOW_IR_SCHEMA_VERSION);
+    expect(parsed.version).toBe("v1");
   });
 
   it("contains exactly one start and one end node", () => {
@@ -21,14 +15,11 @@ describe("builtin coding workflow ir", () => {
     expect(nodes.filter((node) => node.kind === "end")).toHaveLength(1);
   });
 
-  it("exposes coding lifecycle stages", () => {
-    const stageNodes = BUILTIN_CODING_WORKFLOW_IR.nodes.filter((node) => node.config?.stage);
-    const stages = stageNodes.map((node) => String(node.config?.stage));
-    expect(stages).toEqual(expect.arrayContaining(["triage", "execute", "review", "merge"]));
-  });
-
-  it("builder returns parser-validated ir", () => {
-    const built = buildBuiltinCodingWorkflowIr();
-    expect(built.metadata.name).toContain("Coding Lifecycle");
+  it("exposes coding lifecycle seams", () => {
+    const seams = BUILTIN_CODING_WORKFLOW_IR.nodes
+      .map((node) => String(node.config?.seam ?? ""))
+      .filter((seam) => seam.length > 0);
+    expect(seams).toEqual(expect.arrayContaining(["execute", "review", "merge"]));
+    expect(seams).not.toContain("triage");
   });
 });

packages/core/src/__tests__/workflow-ir.test.ts

@@ -1,70 +0,0 @@
-import { describe, expect, it } from "vitest";
-import {
-  BUILTIN_WORKFLOW_IR_FIXTURE,
-  WORKFLOW_IR_SCHEMA_VERSION,
-  parseWorkflowIr,
-  serializeWorkflowIr,
-  WorkflowIrError,
-} from "../index.js";
-
-describe("workflow ir", () => {
-  it("round-trips fixture with no data loss", () => {
-    const serialized = serializeWorkflowIr(BUILTIN_WORKFLOW_IR_FIXTURE);
-    const parsed = parseWorkflowIr(serialized);
-    expect(parsed).toEqual(BUILTIN_WORKFLOW_IR_FIXTURE);
-  });
-
-  it("rejects missing or mismatched schemaVersion", () => {
-    expect(() =>
-      parseWorkflowIr({
-        metadata: { name: "missing-version" },
-        nodes: [],
-        edges: [],
-      }),
-    ).toThrowError(expect.objectContaining({ code: "unsupported_version" }));
-
-    expect(() =>
-      parseWorkflowIr({
-        schemaVersion: "2.0.0",
-        metadata: { name: "wrong-version" },
-        nodes: [],
-        edges: [],
-      }),
-    ).toThrowError(expect.objectContaining({ code: "unsupported_version" }));
-  });
-
-  it("rejects unknown node kinds and dangling edges", () => {
-    expect(() =>
-      parseWorkflowIr({
-        schemaVersion: WORKFLOW_IR_SCHEMA_VERSION,
-        metadata: { name: "unknown-kind" },
-        nodes: [{ id: "n1", kind: "custom" }],
-        edges: [],
-      }),
-    ).toThrowError(WorkflowIrError);
-
-    expect(() =>
-      parseWorkflowIr({
-        schemaVersion: WORKFLOW_IR_SCHEMA_VERSION,
-        metadata: { name: "dangling-edge" },
-        nodes: [{ id: "start", kind: "start" }],
-        edges: [{ id: "e1", from: "start", to: "missing" }],
-      }),
-    ).toThrowError(expect.objectContaining({ code: "dangling_edge" }));
-  });
-
-  it("parses fixture JSON string for interpreter parity", () => {
-    const json = JSON.stringify(BUILTIN_WORKFLOW_IR_FIXTURE);
-    const parsed = parseWorkflowIr(json);
-
-    expect(parsed.schemaVersion).toBe(WORKFLOW_IR_SCHEMA_VERSION);
-    expect(parsed.nodes.length).toBeGreaterThanOrEqual(1);
-    expect(parsed.edges.length).toBeGreaterThanOrEqual(1);
-  });
-
-  it("exposes workflow ir surface from package entry", () => {
-    expect(typeof parseWorkflowIr).toBe("function");
-    expect(typeof serializeWorkflowIr).toBe("function");
-    expect(BUILTIN_WORKFLOW_IR_FIXTURE.schemaVersion).toBe(WORKFLOW_IR_SCHEMA_VERSION);
-  });
-});