diff --git a/.changeset/FN-5770-workflow-interpreter-authoritative.md b/.changeset/FN-5770-workflow-interpreter-authoritative.md
new file mode 100644
index 0000000000..59f8da2a68
--- /dev/null
+++ b/.changeset/FN-5770-workflow-interpreter-authoritative.md
@@ -0,0 +1,5 @@
+---
+"@runfusion/fusion": minor
+---
+
+Add a guarded interpreter-authoritative workflow cutover for coding-task lifecycle execution. The new capability stays default-off behind `experimentalFeatures.workflowInterpreterAuthoritative` and only activates when rollout-readiness checks pass, preserving legacy execution as the fallback path.
diff --git a/docs/architecture.md b/docs/architecture.md
index 7b9e8dccf8..3109da5b67 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -1820,6 +1820,7 @@ Reliability-layer changes are in scope. Interaction regression backstops live in
 - FN-5741 backstop: `packages/engine/src/__tests__/reliability-interactions/merge-request-shadow-handoff.test.ts` guards Phase-1 merge-request contract shadow writes: flag OFF is a no-op, flag ON writes marker/record strictly after legacy handoff, and `autoMerge:false` remains `manual-required` without shadow running transitions.
 - FN-5742 backstop: `packages/engine/src/__tests__/reliability-interactions/dual-observe-merge-seam.test.ts` guards Phase-2 dual-observe invariants: legacy dependency satisfaction remains authoritative while parity diffs emit, and shadow dequeue selection never advances `manual-required` rows.
 - FN-5743 backstop: `packages/engine/src/__tests__/reliability-interactions/merge-request-cancel-on-hard-cancel.test.ts` and `packages/core/src/__tests__/merge-request-record.test.ts` guard Phase-3 cutover invariants: transient merge retries mutate merge-request state (no column rebound), user hard-cancel after accepted handoff cancels pending merge requests, and non-user rebounds preserve legacy fail-soft semantics.
+- FN-5770 backstop: `packages/engine/src/__tests__/reliability-interactions/workflow-interpreter-cutover.test.ts` guards the interpreter-authoritative lifecycle seam. The cutover remains opt-in (`workflowInterpreterAuthoritative` default OFF), readiness-gated by dual-observe parity evidence, reversible by flipping one flag back OFF, and must preserve file-scope, squash-overlap, `autoMerge:false`, hard-cancel, and self-healing interaction invariants.
 - FN-5337 backstop: `packages/engine/src/__tests__/reliability-interactions/orphan-detected-no-requeue.test.ts` locks observation-only orphan detection across FN-5279 repro metadata desync, worktree-present and worktree-missing candidates, FN-5219 ordering, FN-5147 in-review isolation, FN-5083 branch-cleared composition, lease-manager non-invocation, and per-sweep idempotent audit emission.
 - FN-5256 backstop: `packages/engine/src/__tests__/reliability-interactions/dependency-cycle-reconcile.test.ts` covers persisted dependency-cycle detection via `reconcileDependencyCycles`, bounded umbrella-back-edge auto-repair, ambiguous-cycle observe-only behavior, composition ordering with `reconcileSelfDefeatingDependencies`, and the post-sweep write-time guard invariant. Core write-boundary regressions (FN-5240/5241/5242 signature, indirect cycle, umbrella back-edge rejection) live in `packages/core/src/__tests__/store-dependency-cycle.test.ts`.
 - FN-5325 backstop: `packages/engine/src/__tests__/reliability-interactions/scheduler-overlap-priority-inversion.test.ts` covers queued-overlap priority/age deferral, equal-priority age ordering, FN-4969 fanout composition, and transition-only `scheduler:overlap-priority-inversion` audit surfacing across unchanged, changed-blocker, and clear→reappear states.
diff --git a/docs/settings-reference.md b/docs/settings-reference.md
index c13e065959..94712f71a3 100644
--- a/docs/settings-reference.md
+++ b/docs/settings-reference.md
@@ -1216,7 +1216,7 @@ The Experimental Features section in Settings shows:
 - Global scope indicator (features are shared across projects)
 - Description explaining the purpose of experimental features
 
-Common built-in dashboard flags include:
+Common built-in dashboard/runtime flags include:
 - `insights`
 - `roadmap`
 - `memoryView`
@@ -1226,6 +1226,9 @@ Common built-in dashboard flags include:
 - `todoView` (enables dashboard Todo View; see [Todo View](./todo-view.md))
 - `researchView`
 - `evalsView` (gates Evals dashboard view, Settings → Scheduled Evals section, and scheduled-eval cron execution)
+- `workflowGraphExecutor` (enables the workflow-IR interpreter path)
+- `workflowInterpreterDualObserve` (observe-only parity instrumentation for interpreter rollout)
+- `workflowInterpreterAuthoritative` (readiness-gated authoritative interpreter lifecycle cutover; legacy remains default/fallback when OFF)
 - `remoteAccess`
 - `agentOnboarding` (enables the **AI Interview** option inside the New Agent dialog)
 
diff --git a/docs/workflow-steps.md b/docs/workflow-steps.md
index 59dc51b1c7..698ec0b53b 100644
--- a/docs/workflow-steps.md
+++ b/docs/workflow-steps.md
@@ -410,7 +410,7 @@ Run-audit events emitted in `database` domain:
 
 The parity contract is exported from `@fusion/core` (`compareWorkflowRunObservations`, `compareWorkflowRunAudits`) and produces deterministic drift reports shaped as `{ agree, diffs[] }`, where each diff includes field name, legacy/interpreter values, category, and severity.
 
-This is a dual-observe stage only; interpreter-authoritative cutover is deferred to a later phase.
+Dual-observe remains the rollout evidence path for the later authoritative cutover: the interpreter may only become authoritative when the separate `experimentalFeatures.workflowInterpreterAuthoritative` flag is ON **and** the cutover-readiness guard reports zero unresolved parity drift.
 
 #### Self-healing recovery for parked review tasks
 
@@ -480,6 +480,26 @@ Traversal semantics:
 
 Parity coverage includes flag-OFF no-op behavior, lifecycle ordering parity vs legacy seams, merge/file-scope-like failure routing, and downstream halt behavior for hard-cancel/self-healing style failures.
 
+### Interpreter-authoritative cutover
+
+A second default-OFF flag, `experimentalFeatures.workflowInterpreterAuthoritative`, promotes the interpreter from shadow/selected-workflow sequencing to the **authoritative** lifecycle driver for default coding tasks.
+
+The cutover stays opt-in, guarded, and reversible:
+- **Default OFF:** legacy executor/reviewer/merger/scheduler flow remains authoritative.
+- **Guarded ON:** the engine only routes through the authoritative driver when `evaluateInterpreterCutoverReadiness(...)` reports ready. The guard consumes explicit rollout evidence (cutover flag enabled, dual-observe enabled, non-empty parity observations, zero unresolved drift).
+- **Rollback:** turning `workflowInterpreterAuthoritative` back OFF immediately restores the legacy path; no migration or cleanup step is required.
+
+When the guard passes, the runtime binds real DI seams from `TaskExecutor` into the built-in coding IR and drives `BUILTIN_CODING_WORKFLOW_IR` through `WorkflowGraphExecutor`. The interpreter does **not** reimplement lifecycle behavior: it delegates execute/review/merge to the same legacy seams already used by the imperative path.
+
+Reliability invariants preserved under authoritative mode:
+- file-scope enforcement including `FileScopeViolationError`
+- squash/file-scope overlap enforcement via `assertSquashOverlapsFileScope`
+- `autoMerge: false` terminal-until-merged behavior in `in-review`
+- `moveTask(in-progress → todo)` hard-cancel semantics without stray `userPaused` rebounds
+- existing self-healing routing and fail-soft fallback behavior
+
+The interaction backstop lives in `packages/engine/src/__tests__/reliability-interactions/workflow-interpreter-cutover.test.ts`.
+
 ## Workflow Step APIs
 
 | Endpoint | Purpose |
diff --git a/packages/core/src/__tests__/workflow-cutover.test.ts b/packages/core/src/__tests__/workflow-cutover.test.ts
new file mode 100644
index 0000000000..246bc7192d
--- /dev/null
+++ b/packages/core/src/__tests__/workflow-cutover.test.ts
@@ -0,0 +1,68 @@
+import { describe, expect, it } from "vitest";
+
+import { evaluateInterpreterCutoverReadiness } from "../workflow-cutover.js";
+
+describe("workflow interpreter authoritative cutover readiness", () => {
+  it("is ready when the cutover flag, dual-observe, and clean parity evidence are present", () => {
+    const result = evaluateInterpreterCutoverReadiness({
+      authoritativeFlagEnabled: true,
+      dualObserveEnabled: true,
+      paritySummary: { observed: 5, drift: 0, recentDrift: [] },
+      minimumObservedRuns: 3,
+    });
+
+    expect(result).toEqual({ ready: true, reasons: [] });
+  });
+
+  it("enumerates every failed criterion deterministically", () => {
+    const result = evaluateInterpreterCutoverReadiness({
+      authoritativeFlagEnabled: false,
+      dualObserveEnabled: false,
+      paritySummary: null,
+    });
+
+    expect(result.ready).toBe(false);
+    expect(result.reasons).toEqual([
+      "experimentalFeatures.workflowInterpreterAuthoritative is disabled",
+      "experimentalFeatures.workflowInterpreterDualObserve is disabled",
+      "workflow parity summary unavailable",
+    ]);
+  });
+
+  it("blocks when parity drift is present in the summary or unresolved drift reports", () => {
+    const result = evaluateInterpreterCutoverReadiness({
+      authoritativeFlagEnabled: true,
+      dualObserveEnabled: true,
+      paritySummary: {
+        observed: 8,
+        drift: 2,
+        recentDrift: [
+          { taskId: "FN-1", timestamp: "2026-06-01T00:00:00.000Z", diffs: [] },
+        ],
+      },
+      unresolvedDriftReports: [
+        { agree: false, diffs: [{ field: "terminalColumn", legacy: "done", interpreter: "in-review", category: "lifecycle", severity: "error" }] },
+      ],
+    });
+
+    expect(result.ready).toBe(false);
+    expect(result.reasons).toEqual([
+      "workflow parity drift above zero (2 drift events)",
+      "workflow parity has unresolved drift reports (1)",
+    ]);
+  });
+
+  it("normalizes minimum observed runs to at least one", () => {
+    const result = evaluateInterpreterCutoverReadiness({
+      authoritativeFlagEnabled: true,
+      dualObserveEnabled: true,
+      paritySummary: { observed: 0, drift: 0, recentDrift: [] },
+      minimumObservedRuns: 0,
+    });
+
+    expect(result.ready).toBe(false);
+    expect(result.reasons).toEqual([
+      "workflow parity observation window too small (0/1 observed)",
+    ]);
+  });
+});
diff --git a/packages/core/src/index.ts b/packages/core/src/index.ts
index 90802a24c8..8b4589aaba 100644
--- a/packages/core/src/index.ts
+++ b/packages/core/src/index.ts
@@ -1446,6 +1446,14 @@ export type {
   WorkflowColumnsGraduationReport,
   GraduationReportInputs,
 } from "./workflow-parity.js";
+export {
+  WORKFLOW_INTERPRETER_AUTHORITATIVE_FLAG,
+  evaluateInterpreterCutoverReadiness,
+} from "./workflow-cutover.js";
+export type {
+  InterpreterCutoverReadinessInput,
+  InterpreterCutoverReadinessResult,
+} from "./workflow-cutover.js";
 export { isResearchExperimentalEnabled, resolveResearchSettings } from "./research-settings.js";
 export type { ResolvedResearchSettings } from "./research-settings.js";
 export { isEvalsExperimentalEnabled, resolveEvalSettings } from "./eval-settings.js";
diff --git a/packages/core/src/workflow-cutover.ts b/packages/core/src/workflow-cutover.ts
new file mode 100644
index 0000000000..8b793eed74
--- /dev/null
+++ b/packages/core/src/workflow-cutover.ts
@@ -0,0 +1,81 @@
+import type { WorkflowParityDriftReport, WorkflowParitySummary } from "./workflow-parity.js";
+
+/**
+ * Opt-in authoritative cutover flag for routing the coding lifecycle through the
+ * workflow interpreter. The cutover is guarded by rollout-readiness checks and
+ * remains reversible by disabling the flag.
+ */
+export const WORKFLOW_INTERPRETER_AUTHORITATIVE_FLAG = "workflowInterpreterAuthoritative" as const;
+
+export interface InterpreterCutoverReadinessInput {
+  /** Explicit operator opt-in; default runtime remains legacy when false. */
+  authoritativeFlagEnabled: boolean;
+  /** The dual-observe rollout must stay enabled/proven before cutover. */
+  dualObserveEnabled: boolean;
+  /** Aggregated parity signal from the audit trail (for example `store.getWorkflowParitySummary()`). */
+  paritySummary?: Pick<WorkflowParitySummary, "observed" | "drift" | "recentDrift"> | null;
+  /** Optional unresolved drift reports surfaced directly by the caller. */
+  unresolvedDriftReports?: readonly Pick<WorkflowParityDriftReport, "agree" | "diffs">[] | null;
+  /** Minimum observed parity runs required before cutover may proceed. Default: 1. */
+  minimumObservedRuns?: number;
+}
+
+export interface InterpreterCutoverReadinessResult {
+  ready: boolean;
+  reasons: string[];
+}
+
+function normalizeMinimumObservedRuns(value: number | undefined): number {
+  if (!Number.isFinite(value)) return 1;
+  return Math.max(1, Math.floor(value!));
+}
+
+function countUnresolvedDriftReports(
+  reports: readonly Pick<WorkflowParityDriftReport, "agree" | "diffs">[] | null | undefined,
+): number {
+  if (!reports || reports.length === 0) return 0;
+  return reports.filter((report) => report.agree === false || report.diffs.length > 0).length;
+}
+
+/**
+ * Pure rollout-readiness guard for the interpreter-authoritative cutover.
+ * Callers supply explicit parity evidence; this function performs no I/O.
+ */
+export function evaluateInterpreterCutoverReadiness(
+  input: InterpreterCutoverReadinessInput,
+): InterpreterCutoverReadinessResult {
+  const reasons: string[] = [];
+  const minimumObservedRuns = normalizeMinimumObservedRuns(input.minimumObservedRuns);
+
+  if (!input.authoritativeFlagEnabled) {
+    reasons.push("experimentalFeatures.workflowInterpreterAuthoritative is disabled");
+  }
+
+  if (!input.dualObserveEnabled) {
+    reasons.push("experimentalFeatures.workflowInterpreterDualObserve is disabled");
+  }
+
+  const paritySummary = input.paritySummary;
+  if (!paritySummary) {
+    reasons.push("workflow parity summary unavailable");
+  } else {
+    if (paritySummary.observed < minimumObservedRuns) {
+      reasons.push(
+        `workflow parity observation window too small (${paritySummary.observed}/${minimumObservedRuns} observed)`,
+      );
+    }
+    if (paritySummary.drift > 0) {
+      reasons.push(`workflow parity drift above zero (${paritySummary.drift} drift events)`);
+    }
+  }
+
+  const unresolvedDriftCount = countUnresolvedDriftReports(input.unresolvedDriftReports);
+  if (unresolvedDriftCount > 0) {
+    reasons.push(`workflow parity has unresolved drift reports (${unresolvedDriftCount})`);
+  }
+
+  return {
+    ready: reasons.length === 0,
+    reasons,
+  };
+}
diff --git a/packages/engine/src/__tests__/openclaw-runtime-e2e.test.ts b/packages/engine/src/__tests__/openclaw-runtime-e2e.test.ts
index d6202e8bed..960b4e2fe9 100644
--- a/packages/engine/src/__tests__/openclaw-runtime-e2e.test.ts
+++ b/packages/engine/src/__tests__/openclaw-runtime-e2e.test.ts
@@ -42,6 +42,7 @@ vi.mock("../pi.js", () => ({
 }));
 
 vi.mock("node:child_process", () => ({
+  execFile: vi.fn(),
   spawn: (...args: unknown[]) => mockSpawn(...args),
 }));
 
diff --git a/packages/engine/src/__tests__/pi-layers-wiring.test.ts b/packages/engine/src/__tests__/pi-layers-wiring.test.ts
index 7dd78f0fb7..8c242edbab 100644
--- a/packages/engine/src/__tests__/pi-layers-wiring.test.ts
+++ b/packages/engine/src/__tests__/pi-layers-wiring.test.ts
@@ -64,7 +64,7 @@ vi.mock("node:child_process", () => {
         }
       });
     });
-  return { execSync: execSyncFn, exec: execFn };
+  return { execSync: execSyncFn, exec: execFn, execFile: vi.fn() };
 });
 
 vi.mock("node:fs", async () => {
diff --git a/packages/engine/src/__tests__/reliability-interactions/branch-recovery-live-zero-commits.test.ts b/packages/engine/src/__tests__/reliability-interactions/branch-recovery-live-zero-commits.test.ts
index 2e37d2f4a0..82d0fbc6d1 100644
--- a/packages/engine/src/__tests__/reliability-interactions/branch-recovery-live-zero-commits.test.ts
+++ b/packages/engine/src/__tests__/reliability-interactions/branch-recovery-live-zero-commits.test.ts
@@ -12,7 +12,7 @@ vi.mock("node:child_process", async () => {
       .catch((err: Error) => callback?.(err, "", err.message));
   };
   execFn[promisify.custom] = (cmd: string, opts?: any) => execMock(cmd, opts).then((stdout: string) => ({ stdout, stderr: "" }));
-  return { exec: execFn, execSync: vi.fn() };
+  return { exec: execFn, execSync: vi.fn(), execFile: vi.fn() };
 });
 
 import { SelfHealingManager } from "../../self-healing.js";
diff --git a/packages/engine/src/__tests__/reliability-interactions/branch-recovery-stale-cached-base.test.ts b/packages/engine/src/__tests__/reliability-interactions/branch-recovery-stale-cached-base.test.ts
index f745d77ed7..366e79ccef 100644
--- a/packages/engine/src/__tests__/reliability-interactions/branch-recovery-stale-cached-base.test.ts
+++ b/packages/engine/src/__tests__/reliability-interactions/branch-recovery-stale-cached-base.test.ts
@@ -12,7 +12,7 @@ vi.mock("node:child_process", async () => {
       .catch((err: Error) => callback?.(err, "", err.message));
   };
   execFn[promisify.custom] = (cmd: string, opts?: any) => execMock(cmd, opts).then((stdout: string) => ({ stdout, stderr: "" }));
-  return { exec: execFn, execSync: vi.fn() };
+  return { exec: execFn, execSync: vi.fn(), execFile: vi.fn() };
 });
 
 import { SelfHealingManager } from "../../self-healing.js";
diff --git a/packages/engine/src/__tests__/reliability-interactions/workflow-interpreter-cutover.test.ts b/packages/engine/src/__tests__/reliability-interactions/workflow-interpreter-cutover.test.ts
new file mode 100644
index 0000000000..74d3a45e76
--- /dev/null
+++ b/packages/engine/src/__tests__/reliability-interactions/workflow-interpreter-cutover.test.ts
@@ -0,0 +1,306 @@
+import { mkdir, writeFile } from "node:fs/promises";
+import { join } from "node:path";
+
+import { DEFAULT_SETTINGS, type Settings, type TaskDetail } from "@fusion/core";
+import { afterEach, describe, expect, it, vi } from "vitest";
+
+import { assertSquashOverlapsFileScope, FileScopeViolationError } from "../../merger.js";
+import type { WorkflowLegacySeams } from "../../workflow-node-handlers.js";
+import { WorkflowAuthoritativeDriver } from "../../workflow-authoritative-driver.js";
+import { git, hasGit, makeReliabilityFixture } from "./_helpers.js";
+
+const readyParity = {
+  observed: 5,
+  agreed: 5,
+  drift: 0,
+  agreeRate: 1,
+  driftFieldCounts: {},
+  recentDrift: [],
+};
+
+const baseTask = {
+  id: "FN-5770",
+  column: "in-progress",
+  steps: [],
+  review: null,
+  mergeDetails: null,
+} as unknown as TaskDetail;
+
+function settingsWith(flags: Record<string, boolean>, overrides: Partial<Settings> = {}): Settings {
+  return {
+    ...DEFAULT_SETTINGS,
+    ...overrides,
+    experimentalFeatures: {
+      ...(DEFAULT_SETTINGS.experimentalFeatures ?? {}),
+      ...flags,
+    },
+  } as Settings;
+}
+
+function createStore(options: {
+  settings?: Settings;
+  selection?: { workflowId: string; stepIds: string[] } | undefined;
+  task?: TaskDetail;
+  paritySummary?: typeof readyParity | undefined;
+} = {}) {
+  return {
+    getSettings: vi.fn(async () => options.settings ?? settingsWith({ workflowInterpreterAuthoritative: true, workflowInterpreterDualObserve: true })),
+    getTask: vi.fn(async () => options.task ?? baseTask),
+    getTaskWorkflowSelection: vi.fn(() => options.selection),
+    getWorkflowParitySummary: vi.fn(() => options.paritySummary ?? readyParity),
+  };
+}
+
+function createExecutor(seams: WorkflowLegacySeams) {
+  return {
+    createAuthoritativeWorkflowSeams: vi.fn(() => seams),
+  };
+}
+
+describe("workflow interpreter authoritative cutover", () => {
+  it("is a strict no-op when the cutover flag is off", async () => {
+    const store = createStore({
+      settings: settingsWith({ workflowInterpreterAuthoritative: false, workflowInterpreterDualObserve: true }),
+    });
+    const executor = createExecutor({
+      planning: vi.fn(async () => ({ outcome: "success" as const })),
+      execute: vi.fn(async () => ({ outcome: "success" as const })),
+      review: vi.fn(async () => ({ outcome: "success" as const })),
+      merge: vi.fn(async () => ({ outcome: "success" as const })),
+      schedule: vi.fn(async () => ({ outcome: "success" as const })),
+    });
+
+    const result = await new WorkflowAuthoritativeDriver({ store, executor }).maybeRun(baseTask as any);
+
+    expect(result.handled).toBe(false);
+    expect(result.disposition).toBe("fell-back");
+    expect(executor.createAuthoritativeWorkflowSeams).not.toHaveBeenCalled();
+  });
+
+  it("falls back when readiness fails even if the cutover flag is on", async () => {
+    const store = createStore({
+      paritySummary: { ...readyParity, observed: 4, drift: 1 },
+    });
+    const executor = createExecutor({
+      planning: vi.fn(async () => ({ outcome: "success" as const })),
+      execute: vi.fn(async () => ({ outcome: "success" as const })),
+      review: vi.fn(async () => ({ outcome: "success" as const })),
+      merge: vi.fn(async () => ({ outcome: "success" as const })),
+      schedule: vi.fn(async () => ({ outcome: "success" as const })),
+    });
+
+    const result = await new WorkflowAuthoritativeDriver({ store, executor }).maybeRun(baseTask as any);
+
+    expect(result.handled).toBe(false);
+    expect(result.reason).toMatch(/drift above zero/);
+    expect(executor.createAuthoritativeWorkflowSeams).not.toHaveBeenCalled();
+  });
+
+  it("drives execute → review → merge through authoritative seams on a clean run", async () => {
+    const calls: string[] = [];
+    const executor = createExecutor({
+      planning: async () => ({ outcome: "success" as const }),
+      execute: async () => {
+        calls.push("execute");
+        return { outcome: "success" as const };
+      },
+      review: async () => {
+        calls.push("review");
+        return { outcome: "success" as const };
+      },
+      merge: async () => {
+        calls.push("merge");
+        return { outcome: "success" as const };
+      },
+      schedule: async () => ({ outcome: "success" as const }),
+    });
+
+    const result = await new WorkflowAuthoritativeDriver({ store: createStore(), executor }).maybeRun(baseTask as any);
+
+    expect(result.handled).toBe(true);
+    expect(result.disposition).toBe("completed");
+    expect(calls).toEqual(["execute", "review", "merge"]);
+  });
+
+  it("keeps autoMerge:false tasks terminal in review by stopping before merge", async () => {
+    const merge = vi.fn(async () => ({ outcome: "success" as const }));
+    const executor = createExecutor({
+      planning: async () => ({ outcome: "success" as const }),
+      execute: async () => ({ outcome: "success" as const }),
+      review: async () => ({ outcome: "failure" as const, value: "manual-merge-required" }),
+      merge,
+      schedule: async () => ({ outcome: "success" as const }),
+    });
+
+    const result = await new WorkflowAuthoritativeDriver({
+      store: createStore({ settings: settingsWith({ workflowInterpreterAuthoritative: true, workflowInterpreterDualObserve: true }, { autoMerge: false }) }),
+      executor,
+    }).maybeRun(baseTask as any);
+
+    expect(result.handled).toBe(true);
+    expect(result.disposition).toBe("failed");
+    expect(merge).not.toHaveBeenCalled();
+  });
+
+  it("preserves moveTask hard-cancel semantics by halting downstream seams without setting userPaused", async () => {
+    const review = vi.fn(async () => ({ outcome: "success" as const }));
+    const merge = vi.fn(async () => ({ outcome: "success" as const }));
+    const task = { ...baseTask, userPaused: undefined } as TaskDetail;
+    const executor = createExecutor({
+      planning: async () => ({ outcome: "success" as const }),
+      execute: async () => ({ outcome: "failure" as const, value: "hard-cancel" }),
+      review,
+      merge,
+      schedule: async () => ({ outcome: "success" as const }),
+    });
+
+    const result = await new WorkflowAuthoritativeDriver({
+      store: createStore({ task }),
+      executor,
+    }).maybeRun(task as any);
+
+    expect(result.handled).toBe(true);
+    expect(result.disposition).toBe("failed");
+    expect(review).not.toHaveBeenCalled();
+    expect(merge).not.toHaveBeenCalled();
+    expect(task.userPaused).toBeUndefined();
+  });
+
+  it("routes self-healing style execute failures without divergent downstream lifecycle mutations", async () => {
+    const review = vi.fn(async () => ({ outcome: "success" as const }));
+    const merge = vi.fn(async () => ({ outcome: "success" as const }));
+    const executor = createExecutor({
+      planning: async () => ({ outcome: "success" as const }),
+      execute: async () => ({ outcome: "failure" as const, value: "recoverable" }),
+      review,
+      merge,
+      schedule: async () => ({ outcome: "success" as const }),
+    });
+
+    const result = await new WorkflowAuthoritativeDriver({ store: createStore(), executor }).maybeRun(baseTask as any);
+
+    expect(result.handled).toBe(true);
+    expect(result.disposition).toBe("failed");
+    expect(review).not.toHaveBeenCalled();
+    expect(merge).not.toHaveBeenCalled();
+  });
+
+  it("immediately rolls back to legacy when the cutover flag is flipped back off", async () => {
+    let settings = settingsWith({ workflowInterpreterAuthoritative: true, workflowInterpreterDualObserve: true });
+    const store = createStore();
+    store.getSettings.mockImplementation(async () => settings);
+    const executor = createExecutor({
+      planning: async () => ({ outcome: "success" as const }),
+      execute: async () => ({ outcome: "success" as const }),
+      review: async () => ({ outcome: "success" as const }),
+      merge: async () => ({ outcome: "success" as const }),
+      schedule: async () => ({ outcome: "success" as const }),
+    });
+    const driver = new WorkflowAuthoritativeDriver({ store, executor });
+
+    const first = await driver.maybeRun(baseTask as any);
+    settings = settingsWith({ workflowInterpreterAuthoritative: false, workflowInterpreterDualObserve: true });
+    const second = await driver.maybeRun(baseTask as any);
+
+    expect(first.handled).toBe(true);
+    expect(second.handled).toBe(false);
+    expect(executor.createAuthoritativeWorkflowSeams).toHaveBeenCalledTimes(1);
+  });
+
+  it("defers to existing selected custom workflows instead of double-driving", async () => {
+    const executor = createExecutor({
+      planning: async () => ({ outcome: "success" as const }),
+      execute: async () => ({ outcome: "success" as const }),
+      review: async () => ({ outcome: "success" as const }),
+      merge: async () => ({ outcome: "success" as const }),
+      schedule: async () => ({ outcome: "success" as const }),
+    });
+
+    const result = await new WorkflowAuthoritativeDriver({
+      store: createStore({ selection: { workflowId: "WF-123", stepIds: [] } }),
+      executor,
+    }).maybeRun(baseTask as any);
+
+    expect(result.handled).toBe(false);
+    expect(result.reason).toContain("workflow selection already present");
+    expect(executor.createAuthoritativeWorkflowSeams).not.toHaveBeenCalled();
+  });
+});
+
+const describeIfGit = hasGit ? describe : describe.skip;
+
+describeIfGit("workflow interpreter authoritative cutover + file-scope invariants", () => {
+  const fixtures: Array<Awaited<ReturnType<typeof makeReliabilityFixture>>> = [];
+
+  afterEach(async () => {
+    while (fixtures.length) {
+      await fixtures.pop()!.cleanup();
+    }
+  });
+
+  async function createRealDriverFixture() {
+    const fx = await makeReliabilityFixture({
+      taskId: "FN-5770-FS",
+      task: {
+        column: "in-progress",
+      },
+    });
+    fixtures.push(fx);
+    vi.spyOn(fx.store, "parseFileScopeFromPrompt").mockResolvedValue(["packages/engine/src/**"]);
+    let mergeChecked = false;
+
+    const driver = new WorkflowAuthoritativeDriver({
+      store: {
+        getSettings: async () => settingsWith({ workflowInterpreterAuthoritative: true, workflowInterpreterDualObserve: true }),
+        getTask: (taskId) => fx.store.getTask(taskId) as Promise<TaskDetail>,
+        getTaskWorkflowSelection: () => undefined,
+        getWorkflowParitySummary: () => readyParity,
+      },
+      executor: createExecutor({
+        planning: async () => ({ outcome: "success" as const }),
+        execute: async () => ({ outcome: "success" as const }),
+        review: async () => ({ outcome: "success" as const }),
+        merge: async () => {
+          mergeChecked = true;
+          await assertSquashOverlapsFileScope({
+            store: fx.store,
+            rootDir: fx.rootDir,
+            taskId: fx.task.id,
+            task: await fx.store.getTask(fx.task.id) as any,
+          });
+          return { outcome: "success" as const };
+        },
+        schedule: async () => ({ outcome: "success" as const }),
+      }),
+    });
+
+    return { fx, driver, wasMergeChecked: () => mergeChecked };
+  }
+
+  it("trips FileScopeViolationError under interpreter authority for off-scope staged changes", async () => {
+    const { fx, driver, wasMergeChecked } = await createRealDriverFixture();
+    await mkdir(join(fx.rootDir, "packages/core/src"), { recursive: true });
+    await writeFile(join(fx.rootDir, "packages/core/src/offscope.txt"), "x\n", "utf-8");
+    git(fx.rootDir, "git add packages/core/src/offscope.txt");
+
+    const result = await driver.maybeRun(fx.task as any);
+
+    expect(result.handled).toBe(true);
+    expect(result.disposition).toBe("failed");
+    expect(result.graphResult?.outcome).toBe("failure");
+    expect(wasMergeChecked()).toBe(true);
+  });
+
+  it("preserves the squash/merge contract when staged changes stay inside file scope", async () => {
+    const { fx, driver, wasMergeChecked } = await createRealDriverFixture();
+    await mkdir(join(fx.rootDir, "packages/engine/src"), { recursive: true });
+    await writeFile(join(fx.rootDir, "packages/engine/src/inscope.txt"), "ok\n", "utf-8");
+    git(fx.rootDir, "git add packages/engine/src/inscope.txt");
+
+    const result = await driver.maybeRun(fx.task as any);
+
+    expect(result.handled).toBe(true);
+    expect(result.disposition).toBe("completed");
+    expect(wasMergeChecked()).toBe(true);
+  });
+});
diff --git a/packages/engine/src/__tests__/self-healing-completion-fanout.test.ts b/packages/engine/src/__tests__/self-healing-completion-fanout.test.ts
index faecf0b24b..dfd4b5c1cc 100644
--- a/packages/engine/src/__tests__/self-healing-completion-fanout.test.ts
+++ b/packages/engine/src/__tests__/self-healing-completion-fanout.test.ts
@@ -6,7 +6,7 @@ const { execMock, existsSyncMock } = vi.hoisted(() => ({
   execMock: vi.fn(),
   existsSyncMock: vi.fn(() => false),
 }));
-vi.mock("node:child_process", () => ({ exec: execMock, execSync: vi.fn() }));
+vi.mock("node:child_process", () => ({ exec: execMock, execSync: vi.fn(), execFile: vi.fn() }));
 
 vi.mock("node:fs", async (importOriginal) => {
   const actual = await importOriginal<typeof import("node:fs")>();
diff --git a/packages/engine/src/__tests__/self-healing-ghost-branch-recovery.test.ts b/packages/engine/src/__tests__/self-healing-ghost-branch-recovery.test.ts
index 7b2ef2f2dd..b5f6f008d2 100644
--- a/packages/engine/src/__tests__/self-healing-ghost-branch-recovery.test.ts
+++ b/packages/engine/src/__tests__/self-healing-ghost-branch-recovery.test.ts
@@ -14,7 +14,7 @@ vi.mock("node:child_process", async () => {
   };
   execFn[promisify.custom] = (cmd: string, opts?: any) =>
     execMock(cmd, opts).then((stdout: string) => ({ stdout, stderr: "" }));
-  return { exec: execFn, execSync: vi.fn() };
+  return { exec: execFn, execSync: vi.fn(), execFile: vi.fn() };
 });
 
 import { SelfHealingManager } from "../self-healing.js";
diff --git a/packages/engine/src/__tests__/self-healing-orphan-only-scope.test.ts b/packages/engine/src/__tests__/self-healing-orphan-only-scope.test.ts
index 39f6c5482e..0c4df8e381 100644
--- a/packages/engine/src/__tests__/self-healing-orphan-only-scope.test.ts
+++ b/packages/engine/src/__tests__/self-healing-orphan-only-scope.test.ts
@@ -28,7 +28,7 @@ vi.mock("node:child_process", async () => {
       }
     });
   });
-  return { execSync: execSyncFn, exec: execFn };
+  return { execSync: execSyncFn, exec: execFn, execFile: vi.fn() };
 });
 
 import { EventEmitter } from "node:events";
diff --git a/packages/engine/src/__tests__/self-healing-reclaim-live-zero-commits.test.ts b/packages/engine/src/__tests__/self-healing-reclaim-live-zero-commits.test.ts
index a64414cca5..4c407e0f3c 100644
--- a/packages/engine/src/__tests__/self-healing-reclaim-live-zero-commits.test.ts
+++ b/packages/engine/src/__tests__/self-healing-reclaim-live-zero-commits.test.ts
@@ -14,7 +14,7 @@ vi.mock("node:child_process", async () => {
   };
   execFn[promisify.custom] = (cmd: string, opts?: any) =>
     execMock(cmd, opts).then((stdout: string) => ({ stdout, stderr: "" }));
-  return { exec: execFn, execSync: vi.fn() };
+  return { exec: execFn, execSync: vi.fn(), execFile: vi.fn() };
 });
 
 import { SelfHealingManager } from "../self-healing.js";
diff --git a/packages/engine/src/__tests__/self-healing-stale-merger-status.test.ts b/packages/engine/src/__tests__/self-healing-stale-merger-status.test.ts
index bf4e2cbcf8..26daa07096 100644
--- a/packages/engine/src/__tests__/self-healing-stale-merger-status.test.ts
+++ b/packages/engine/src/__tests__/self-healing-stale-merger-status.test.ts
@@ -5,7 +5,7 @@ import type { Settings, Task, TaskStore } from "@fusion/core";
 const { execMock } = vi.hoisted(() => ({
   execMock: vi.fn(),
 }));
-vi.mock("node:child_process", () => ({ exec: execMock, execSync: vi.fn() }));
+vi.mock("node:child_process", () => ({ exec: execMock, execSync: vi.fn(), execFile: vi.fn() }));
 
 const { logger } = vi.hoisted(() => ({
   logger: { log: vi.fn(), warn: vi.fn(), error: vi.fn() },
diff --git a/packages/engine/src/__tests__/step-session-executor.test.ts b/packages/engine/src/__tests__/step-session-executor.test.ts
index 001656622f..c69f488f75 100644
--- a/packages/engine/src/__tests__/step-session-executor.test.ts
+++ b/packages/engine/src/__tests__/step-session-executor.test.ts
@@ -685,7 +685,7 @@ vi.mock("node:child_process", async () => {
         }
       });
     });
-  return { execSync: execSyncFn, exec: execFn };
+  return { execSync: execSyncFn, exec: execFn, execFile: vi.fn() };
 });
 vi.mock("node:fs", () => ({
   existsSync: vi.fn().mockReturnValue(true),
diff --git a/packages/engine/src/__tests__/worktree-admin-entry-prune.test.ts b/packages/engine/src/__tests__/worktree-admin-entry-prune.test.ts
index 78c21d6d79..882cb1c0cd 100644
--- a/packages/engine/src/__tests__/worktree-admin-entry-prune.test.ts
+++ b/packages/engine/src/__tests__/worktree-admin-entry-prune.test.ts
@@ -21,7 +21,7 @@ describe("worktree prune wiring", () => {
 
     execMock.mockRejectedValueOnce(new Error("create failed")).mockResolvedValueOnce({ stdout: "", stderr: "" });
 
-    vi.doMock("node:child_process", () => ({ exec: execMock }));
+    vi.doMock("node:child_process", () => ({ exec: execMock, execFile: vi.fn() }));
     vi.doMock("../worktree-prune.js", async (importOriginal) => {
       const actual = await importOriginal<typeof import("../worktree-prune.js")>();
       return { ...actual, pruneWorktreeAdminEntries: pruneSpy };
@@ -61,7 +61,7 @@ describe("worktree prune wiring", () => {
     (execMock as any)[Symbol.for("nodejs.util.promisify.custom")] = execMock;
     execMock.mockRejectedValueOnce(new Error("create failed")).mockResolvedValueOnce({ stdout: "", stderr: "" });
 
-    vi.doMock("node:child_process", () => ({ exec: execMock }));
+    vi.doMock("node:child_process", () => ({ exec: execMock, execFile: vi.fn() }));
     vi.doMock("../worktree-prune.js", async (importOriginal) => {
       const actual = await importOriginal<typeof import("../worktree-prune.js")>();
       return { ...actual, pruneWorktreeAdminEntries: pruneSpy };
@@ -91,7 +91,7 @@ describe("worktree prune wiring", () => {
     (execMock as any)[Symbol.for("nodejs.util.promisify.custom")] = execMock;
     execMock.mockResolvedValueOnce({ stdout: "", stderr: "" }).mockResolvedValueOnce({ stdout: "", stderr: "" });
 
-    vi.doMock("node:child_process", () => ({ exec: execMock }));
+    vi.doMock("node:child_process", () => ({ exec: execMock, execFile: vi.fn() }));
     vi.doMock("../worktree-prune.js", async (importOriginal) => {
       const actual = await importOriginal<typeof import("../worktree-prune.js")>();
       return { ...actual, pruneWorktreeAdminEntries: pruneSpy };
@@ -122,7 +122,7 @@ describe("pruneWorktreeAdminEntries helper", () => {
     execMock.mockRejectedValue(new Error("boom"));
     vi.doMock("node:child_process", async () => {
       const actual = await vi.importActual<typeof import("node:child_process")>("node:child_process");
-      return { ...actual, exec: execMock };
+      return { ...actual, exec: execMock, execFile: vi.fn() };
     });
 
     vi.unmock("../worktree-prune.js");
diff --git a/packages/engine/src/executor.ts b/packages/engine/src/executor.ts
index 66e83d3db2..8d33579a77 100644
--- a/packages/engine/src/executor.ts
+++ b/packages/engine/src/executor.ts
@@ -1129,6 +1129,10 @@ export interface TaskExecutorOptions {
   onStart?: (task: Task, worktreePath: string) => void;
   onComplete?: (task: Task) => void;
   onError?: (task: Task, error: Error) => void;
+  /** Optional runtime-owned dispatch seam that lets a flag-gated workflow
+   * interpreter own the authoritative lifecycle for default coding tasks.
+   * Return true when the task was fully handled and legacy execute() should stop. */
+  workflowAuthoritativeDispatch?: (task: Task) => Promise<boolean>;
   onAgentText?: (taskId: string, delta: string) => void;
   onAgentTool?: (taskId: string, toolName: string) => void;
   autoRecoveryDispatcher?: AutoRecoveryDispatcher;
@@ -3704,7 +3708,7 @@ export class TaskExecutor {
       const runner = new WorkflowGraphTaskRunner({
         store: this.store,
         runId: resolvedRunId,
-        seams: this.createGraphSeams(settings),
+        seams: this.createAuthoritativeWorkflowSeams(settings),
         runCustomNode: (node, nodeTask) =>
           this.runGraphCustomNode(node, nodeTask, settings, resolveBindingForNode(node.id)),
         onEvent: (event) => executorLog.log(`[workflow-graph] ${event.type} ${event.taskId}: ${event.detail}`),
@@ -4543,8 +4547,9 @@ export class TaskExecutor {
     return only;
   }
 
-  /** Seam implementations delegating to the legacy engine (KTD-1: delegate, never reimplement). */
-  private createGraphSeams(_settings: Settings): WorkflowLegacySeams {
+  /** Public authoritative-driver seam factory: exposes the same real lifecycle
+   * seams the internal graph runner uses, without changing legacy behavior. */
+  public createAuthoritativeWorkflowSeams(_settings: Settings): WorkflowLegacySeams {
     return {
       // Built-in triage/spec generation runs upstream of the interpreter today,
       // so planning is a no-op for already-specified tasks. Custom planning
@@ -5568,6 +5573,8 @@ export class TaskExecutor {
         executorLog.log(`execute() called for ${task.id} while graph routing is active — skipping duplicate`);
         return;
       }
+      const authoritativeOwned = await this.options.workflowAuthoritativeDispatch?.(task);
+      if (authoritativeOwned) return;
       const graphOwned = await this.maybeExecuteWorkflowGraph(task);
       if (graphOwned) return;
     }
diff --git a/packages/engine/src/index.ts b/packages/engine/src/index.ts
index 8f5642569c..1110472ac9 100644
--- a/packages/engine/src/index.ts
+++ b/packages/engine/src/index.ts
@@ -201,6 +201,12 @@ export {
   type WorkflowParityObserverLegacyRunResult,
   type WorkflowParityObserverShadowRunResult,
 } from "./workflow-parity-observer.js";
+export {
+  WorkflowAuthoritativeDriver,
+  type WorkflowAuthoritativeDriverDeps,
+  type WorkflowAuthoritativeDriverResult,
+  type WorkflowAuthoritativeDriverStore,
+} from "./workflow-authoritative-driver.js";
 export {
   auditSquashMerge,
   formatSquashAuditReport,
diff --git a/packages/engine/src/runtimes/in-process-runtime.ts b/packages/engine/src/runtimes/in-process-runtime.ts
index 19f14f163c..c83aa10650 100644
--- a/packages/engine/src/runtimes/in-process-runtime.ts
+++ b/packages/engine/src/runtimes/in-process-runtime.ts
@@ -17,6 +17,7 @@ import { Scheduler } from "../scheduler.js";
 import type { PrMonitor, PrComment } from "../pr-monitor.js";
 import type { PrInfo } from "@fusion/core";
 import { TaskExecutor, type TaskExecutorOptions } from "../executor.js";
+import { WorkflowAuthoritativeDriver } from "../workflow-authoritative-driver.js";
 import { buildPrNodeDeps } from "../pr-nodes.js";
 import { isExperimentalFeatureEnabled } from "@fusion/core";
 import { createCliAgentRuntime, type BootstrappedCliAgentRuntime } from "../cli-agent/runtime.js";
@@ -474,6 +475,7 @@ export class InProcessRuntime
       }
 
       const prNodeGithubOps = this.config.prNodeGithubOps;
+      const workflowAuthoritativeDriverRef: { current?: WorkflowAuthoritativeDriver } = {};
       const executorOptions: TaskExecutorOptions = {
         semaphore: this.globalSemaphore,
         pool: this.worktreePool,
@@ -494,6 +496,8 @@ export class InProcessRuntime
         onSliceComplete: (slice) => {
           void this.scheduler.onSliceComplete(slice);
         },
+        workflowAuthoritativeDispatch: async (task) =>
+          (await workflowAuthoritativeDriverRef.current?.maybeRun(task))?.handled ?? false,
         onStart: (task, worktreePath) => {
           this.recordActivity();
           runtimeLog.log(`Started executing task ${task.id} in ${worktreePath}`);
@@ -536,6 +540,10 @@ export class InProcessRuntime
         this.config.workingDirectory,
         executorOptions
       );
+      workflowAuthoritativeDriverRef.current = new WorkflowAuthoritativeDriver({
+        store: this.taskStore,
+        executor: this.executor,
+      });
       if (this.mergeRequester) {
         this.executor.setMergeRequester(this.mergeRequester);
       }
diff --git a/packages/engine/src/workflow-authoritative-driver.ts b/packages/engine/src/workflow-authoritative-driver.ts
new file mode 100644
index 0000000000..77c115981f
--- /dev/null
+++ b/packages/engine/src/workflow-authoritative-driver.ts
@@ -0,0 +1,154 @@
+import {
+  BUILTIN_CODING_WORKFLOW_IR,
+  WORKFLOW_INTERPRETER_AUTHORITATIVE_FLAG,
+  evaluateInterpreterCutoverReadiness,
+  isExperimentalFeatureEnabled,
+  type Settings,
+  type Task,
+  type TaskDetail,
+  type WorkflowDefinition,
+  type WorkflowParitySummary,
+} from "@fusion/core";
+
+import type { TaskExecutor } from "./executor.js";
+import { executorLog } from "./logger.js";
+import { WORKFLOW_INTERPRETER_DUAL_OBSERVE_FLAG } from "./workflow-parity-observer.js";
+import { WorkflowGraphTaskRunner, type WorkflowGraphTaskRunResult } from "./workflow-graph-task-runner.js";
+
+const AUTHORITATIVE_WORKFLOW_ID = "builtin:workflow-interpreter-authoritative";
+
+export interface WorkflowAuthoritativeDriverStore {
+  getSettings(): Promise<Settings>;
+  getTask(taskId: string): Promise<TaskDetail>;
+  getTaskWorkflowSelection?(taskId: string): { workflowId: string; stepIds: string[] } | undefined;
+  getWorkflowParitySummary?(options?: { since?: string; limit?: number }): WorkflowParitySummary;
+}
+
+export interface WorkflowAuthoritativeDriverDeps {
+  store: WorkflowAuthoritativeDriverStore;
+  executor: Pick<TaskExecutor, "createAuthoritativeWorkflowSeams">;
+  minimumObservedRuns?: number;
+}
+
+export interface WorkflowAuthoritativeDriverResult {
+  handled: boolean;
+  disposition: "completed" | "failed" | "fell-back";
+  reason?: string;
+  readinessReasons: string[];
+  graphResult?: WorkflowGraphTaskRunResult;
+}
+
+function buildAuthoritativeSettings(settings: Settings): Settings {
+  return {
+    ...settings,
+    experimentalFeatures: {
+      ...(settings.experimentalFeatures ?? {}),
+      workflowGraphExecutor: true,
+      [WORKFLOW_INTERPRETER_AUTHORITATIVE_FLAG]: true,
+    },
+  };
+}
+
+export class WorkflowAuthoritativeDriver {
+  public constructor(private readonly deps: WorkflowAuthoritativeDriverDeps) {}
+
+  public async maybeRun(task: Task): Promise<WorkflowAuthoritativeDriverResult> {
+    let settings: Settings;
+    let paritySummary: WorkflowParitySummary | undefined;
+    try {
+      settings = await this.deps.store.getSettings();
+      paritySummary = this.deps.store.getWorkflowParitySummary?.();
+    } catch (error) {
+      const message = error instanceof Error ? error.message : String(error);
+      executorLog.warn(`[workflow-authoritative] ${task.id}: readiness probe failed — falling back to legacy (${message})`);
+      return {
+        handled: false,
+        disposition: "fell-back",
+        reason: `store-unavailable: ${message}`,
+        readinessReasons: ["workflow parity readiness probe unavailable"],
+      };
+    }
+    const authoritativeFlagEnabled = isExperimentalFeatureEnabled(
+      settings,
+      WORKFLOW_INTERPRETER_AUTHORITATIVE_FLAG,
+    );
+    const dualObserveEnabled = isExperimentalFeatureEnabled(
+      settings,
+      WORKFLOW_INTERPRETER_DUAL_OBSERVE_FLAG,
+    );
+    const readiness = evaluateInterpreterCutoverReadiness({
+      authoritativeFlagEnabled,
+      dualObserveEnabled,
+      paritySummary,
+      minimumObservedRuns: this.deps.minimumObservedRuns,
+    });
+    if (!readiness.ready) {
+      return {
+        handled: false,
+        disposition: "fell-back",
+        reason: readiness.reasons.join("; "),
+        readinessReasons: readiness.reasons,
+      };
+    }
+
+    const existingSelection = this.deps.store.getTaskWorkflowSelection?.(task.id);
+    if (existingSelection) {
+      return {
+        handled: false,
+        disposition: "fell-back",
+        reason: `workflow selection already present (${existingSelection.workflowId})`,
+        readinessReasons: [],
+      };
+    }
+
+    let liveTask: TaskDetail;
+    try {
+      liveTask = await this.deps.store.getTask(task.id);
+    } catch (error) {
+      const message = error instanceof Error ? error.message : String(error);
+      executorLog.warn(`[workflow-authoritative] ${task.id}: failed to load live task — falling back to legacy (${message})`);
+      return {
+        handled: false,
+        disposition: "fell-back",
+        reason: `task-load-failed: ${message}`,
+        readinessReasons: [],
+      };
+    }
+    const runner = new WorkflowGraphTaskRunner({
+      store: {
+        getTaskWorkflowSelection: () => ({ workflowId: AUTHORITATIVE_WORKFLOW_ID, stepIds: [] }),
+        getWorkflowDefinition: async () => ({
+          id: AUTHORITATIVE_WORKFLOW_ID,
+          name: "Workflow interpreter authoritative cutover",
+          ir: BUILTIN_CODING_WORKFLOW_IR,
+        } satisfies Pick<WorkflowDefinition, "id" | "name" | "ir"> as WorkflowDefinition),
+      },
+      seams: this.deps.executor.createAuthoritativeWorkflowSeams(settings),
+      runCustomNode: async (node) => {
+        throw new Error(`unexpected custom node in builtin authoritative workflow: ${node.id}`);
+      },
+      onEvent: (event) => {
+        executorLog.log(`[workflow-authoritative] ${event.type} ${event.taskId}: ${event.detail}`);
+      },
+    });
+
+    const graphResult = await runner.run(liveTask, buildAuthoritativeSettings(settings));
+    if (graphResult.disposition === "fell-back") {
+      return {
+        handled: false,
+        disposition: "fell-back",
+        reason: graphResult.reason,
+        readinessReasons: [],
+        graphResult,
+      };
+    }
+
+    return {
+      handled: true,
+      disposition: graphResult.disposition,
+      reason: graphResult.reason,
+      readinessReasons: [],
+      graphResult,
+    };
+  }
+}