diff --git a/bun.lock b/bun.lock
index 0d77bca2..525a040f 100644
--- a/bun.lock
+++ b/bun.lock
@@ -637,6 +637,11 @@
         "@intx/workflow": "workspace:*",
         "arktype": "catalog:",
       },
+      "devDependencies": {
+        "@intx/inference-testing": "workspace:*",
+        "@intx/storage-isogit": "workspace:*",
+        "@intx/workflow-host": "workspace:*",
+      },
     },
   },
   "patchedDependencies": {
diff --git a/workflows/writer/package.json b/workflows/writer/package.json
index ccc576c3..c92a1f25 100644
--- a/workflows/writer/package.json
+++ b/workflows/writer/package.json
@@ -16,5 +16,10 @@
     "@intx/agent": "workspace:*",
     "@intx/workflow": "workspace:*",
     "arktype": "catalog:"
+  },
+  "devDependencies": {
+    "@intx/inference-testing": "workspace:*",
+    "@intx/storage-isogit": "workspace:*",
+    "@intx/workflow-host": "workspace:*"
   }
 }
diff --git a/workflows/writer/src/model-turns.test.ts b/workflows/writer/src/model-turns.test.ts
new file mode 100644
index 00000000..a6c5288d
--- /dev/null
+++ b/workflows/writer/src/model-turns.test.ts
@@ -0,0 +1,149 @@
+import { afterEach, expect, test } from "bun:test";
+import { mkdtemp, rm } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { defineTool } from "@intx/agent/authoring";
+import { noopAuditStore } from "@intx/agent/testing";
+import { createDefaultDirectorRegistry } from "@intx/agent";
+import { setupHarness, type Harness } from "@intx/inference-testing";
+import { createIsogitStore } from "@intx/storage-isogit/node";
+import {
+  runLocal,
+  type RunResult,
+  type WorkflowAuthorizeFn,
+  type WorkflowRun,
+} from "@intx/workflow";
+import { createWorkflowStepInvoker } from "@intx/workflow-host/local";
+import { createWriterAgent } from "./agent.ts";
+import { writerTaskMessage } from "./contract.ts";
+import { createWriterWorkflow } from "./workflow.ts";
+
+const source = {
+  id: "openai-compatible:model",
+  provider: "openai-compatible",
+  baseURL: "https://model.test/v1",
+  credentialId: "model-key",
+  model: "model",
+};
+const constraints = {
+  kind: "constraints",
+  title: "Constraints",
+  content: "# Constraints\n\nRuns in the browser.",
+};
+
+// Stands in for the hub's write_artifact, which the writer is given at deploy time.
+const filed: unknown[] = [];
+const writeArtifact = defineTool({
+  id: "@corbits-builder/writer-test/artifacts",
+  definitions: [{ name: "write_artifact" }],
+  factory: () => ({
+    definitions: [
+      {
+        name: "write_artifact",
+        description: "Write the next version of one project document.",
+        inputSchema: { type: "object" },
+      },
+    ],
+    run: async (call) => {
+      filed.push(call.arguments);
+      return { callId: call.id, content: "filed" };
+    },
+  }),
+});
+
+const workflow = createWriterWorkflow({
+  id: "writer",
+  address: "writer",
+  agent: createWriterAgent({
+    id: "writer",
+    inference: { provider: source.provider, model: source.model },
+    tools: [writeArtifact],
+    capabilities: [],
+  }),
+  inference: { literal: {} },
+});
+
+const allow: WorkflowAuthorizeFn = async () => ({
+  effect: "allow",
+  matchingGrants: [],
+  resolvedBy: null,
+});
+
+// The harness serves model calls only while it runs, so it runs until the workflow settles.
+async function runUntilSettled(
+  harness: Harness,
+  run: WorkflowRun,
+): Promise<RunResult> {
+  let settled = false;
+  async function settle() {
+    try {
+      return await run.complete;
+    } finally {
+      settled = true;
+    }
+  }
+  const settling = settle();
+  while (!settled) {
+    await harness.run({ wallClockBudgetMs: 2000 });
+    await new Promise((resolve) => setTimeout(resolve, 0));
+  }
+  return settling;
+}
+
+const cleanup: (() => unknown)[] = [];
+afterEach(async () => {
+  for (const step of cleanup.splice(0).reverse()) await step();
+});
+
+test("a writer files its one document, then replies", async () => {
+  const harness = setupHarness();
+  cleanup.push(() => harness.dispose());
+  const baseDir = await mkdtemp(join(tmpdir(), "writer-model-turns-"));
+  cleanup.push(() => rm(baseDir, { recursive: true, force: true }));
+  harness.scenario.replyOnce("openai", {
+    toolCalls: [
+      { callId: "call-write", name: "write_artifact", args: constraints },
+    ],
+  });
+  harness.scenario.replyOnce("openai", { text: "Filed the constraints." });
+
+  const directors = createDefaultDirectorRegistry();
+  const invokeStep = createWorkflowStepInvoker({
+    workflowAuthorize: allow,
+    buildEnv: async () => ({
+      sources: [source],
+      defaultSource: source.id,
+      storage: await createIsogitStore(join(baseDir, "context")),
+      workdir: join(baseDir, "workspace"),
+      audit: noopAuditStore(),
+      directors,
+      readCurrentMaterial: () => ({ secret: "model-key" }),
+      deps: harness.deps,
+    }),
+  });
+
+  const result = await runUntilSettled(
+    harness,
+    runLocal(workflow, {
+      authorize: allow,
+      directors,
+      invokeStep,
+      hasUpstreamSignalResolver: false,
+      triggerPayload: writerTaskMessage({
+        task: "Write the constraints for a habit tracker.",
+        documents: [
+          {
+            ref: "brief-1",
+            kind: "problem_brief",
+            title: "Problem brief",
+            content: "A habit tracker for one person.",
+          },
+        ],
+        artifact: "constraints",
+      }),
+    }),
+  );
+
+  expect(result.terminalStatus).toBe("completed");
+  expect(filed).toEqual([constraints]);
+});