diff --git a/backend/src/tht/tht-runner.ts b/backend/src/tht/tht-runner.ts
index e14d6f7d..c93409b6 100644
--- a/backend/src/tht/tht-runner.ts
+++ b/backend/src/tht/tht-runner.ts
@@ -26,6 +26,15 @@ export interface SessionDocument {
   content: string;
 }
 
+export interface OllamaEnsureResult {
+  ok: boolean;
+  stage?: string;
+  error?: string;
+  server?: string;
+  model?: string;
+  model_name?: string;
+}
+
 export class ThtRunner {
   constructor(private cfg: ThtConfig) {}
 
@@ -129,4 +138,19 @@ export class ThtRunner {
   unarchive(id: string) { return this.ok(["session", "unarchive", id]); }
   deleteSession(id: string) { return this.ok(["session", "delete", id]); }
   documents(id: string) { return this.json<SessionDocument[]>(["session", "documents", id, "--json"]); }
+
+  async ollamaEnsure(workspace: string, timeoutSec: number): Promise<OllamaEnsureResult> {
+    const { code, stdout, stderr } = await this.run(
+      ["ollama", "ensure", "--json", "--timeout", String(timeoutSec)],
+      workspace,
+    );
+    let parsed: Partial<OllamaEnsureResult> = {};
+    try { parsed = JSON.parse(stdout.trim() || "{}"); } catch { /* leave {} */ }
+    if (code === 0) return { ok: true, ...parsed };
+    return {
+      ok: false,
+      stage: parsed.stage,
+      error: parsed.error ?? (stderr.trim() || `tht ollama ensure exit ${code}`),
+    };
+  }
 }
diff --git a/backend/test/tht-runner.test.ts b/backend/test/tht-runner.test.ts
index a4f1d7e5..39c3f709 100644
--- a/backend/test/tht-runner.test.ts
+++ b/backend/test/tht-runner.test.ts
@@ -114,3 +114,28 @@ test("documents parses the JSON array", async () => {
   const docs = await r.documents("sid");
   expect(docs[0].key).toBe("question");
 });
+
+test("ollamaEnsure builds argv with --json --timeout and the workspace -c", async () => {
+  let calledArgs: string[] = [];
+  let calledWs: string | undefined;
+  const r = new ThtRunner({ thtBin: "tht", harnessDir: "/nope", configPath: "config/tht.yaml" });
+  r.run = async (args, ws) => { calledArgs = args; calledWs = ws; return { code: 0, stdout: '{"ok":true,"server":"up","model":"warmed","model_name":"m"}', stderr: "" }; };
+  const res = await r.ollamaEnsure("psd", 60);
+  expect(calledArgs).toEqual(["ollama", "ensure", "--json", "--timeout", "60"]);
+  expect(calledWs).toBe("psd");
+  expect(res).toEqual({ ok: true, server: "up", model: "warmed", model_name: "m" });
+});
+
+test("ollamaEnsure maps a non-zero exit to ok:false with stage/error from stdout JSON", async () => {
+  const r = new ThtRunner({ thtBin: "tht", harnessDir: "/nope", configPath: "config/tht.yaml" });
+  r.run = async () => ({ code: 1, stdout: '{"ok":false,"stage":"model","error":"missing"}', stderr: "" });
+  expect(await r.ollamaEnsure("psd", 60)).toEqual({ ok: false, stage: "model", error: "missing" });
+});
+
+test("ollamaEnsure falls back to stderr when stdout is not JSON on failure", async () => {
+  const r = new ThtRunner({ thtBin: "tht", harnessDir: "/nope", configPath: "config/tht.yaml" });
+  r.run = async () => ({ code: 1, stdout: "", stderr: "boom" });
+  const res = await r.ollamaEnsure("psd", 60);
+  expect(res.ok).toBe(false);
+  expect(res.error).toContain("boom");
+});