feat(backend): Ollama embeddings preflight on session create/resume (503 hard-fail)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/test/routes-sessions.test.ts

@@ -9,7 +9,7 @@ const SCRIPT = path.resolve("../harness/tests/fake_pi/scripts/f1_disambiguation.
 
 function mutApp(thtRunner: any) {
   return buildApp(loadConfig({ THT_HARNESS_DIR: "../harness" }), {
-    thtRunner,
+    thtRunner: { ollamaEnsure: async () => ({ ok: true }), ...thtRunner },
     getSettings: () => ({ workspace: "w" }) as any,
     spawnFn: () => nodeSpawn("node", [FAKE, SCRIPT]) as any,
   });
@@ -20,6 +20,7 @@ test("POST /sessions usa i settings (workspace/provider/model/thinking) e crea+a
   let spawnArg: any;
   const app = buildApp(loadConfig({ THT_HARNESS_DIR: "../harness" }), {
     thtRunner: {
+      ollamaEnsure: async () => ({ ok: true }),
       sessionNew: async (o: any) => { sessionNewArg = o; return { id: "s1" }; },
       sessionList: async () => [{ id: "s1" }],
     } as any,
@@ -40,6 +41,7 @@ test("POST /sessions usa i settings (workspace/provider/model/thinking) e crea+a
 test("POST /sessions/:id/response inoltra al bridge (no error)", async () => {
   const app = buildApp(loadConfig({ THT_HARNESS_DIR: "../harness" }), {
     thtRunner: {
+      ollamaEnsure: async () => ({ ok: true }),
       sessionNew: async () => ({ id: "s1" }),
       sessionList: async () => [],
     } as any,
@@ -118,3 +120,47 @@ test("POST resume on an archived session is refused with 409", async () => {
   const res = await app.inject({ method: "POST", url: "/sessions/s1/resume" });
   expect(res.statusCode).toBe(409);
 });
+
+test("POST /sessions refuses with 503 when ollamaEnsure fails (no session created)", async () => {
+  let createdCalled = false;
+  const app = buildApp(loadConfig({ THT_HARNESS_DIR: "../harness" }), {
+    thtRunner: {
+      ollamaEnsure: async () => ({ ok: false, stage: "model", error: "modello non installato" }),
+      sessionNew: async () => { createdCalled = true; return { id: "s1" }; },
+    } as any,
+    getSettings: () => ({ workspace: "psd" }) as any,
+    spawnFn: () => nodeSpawn("node", [FAKE, SCRIPT]) as any,
+  });
+  const res = await app.inject({ method: "POST", url: "/sessions", payload: { question: "q" } });
+  expect(res.statusCode).toBe(503);
+  expect(res.json().error).toContain("non installato");
+  expect(createdCalled).toBe(false);
+});
+
+test("POST /sessions proceeds when ollamaEnsure succeeds", async () => {
+  let ensureWs: string | undefined;
+  const app = buildApp(loadConfig({ THT_HARNESS_DIR: "../harness" }), {
+    thtRunner: {
+      ollamaEnsure: async (ws: string) => { ensureWs = ws; return { ok: true }; },
+      sessionNew: async () => ({ id: "s1" }),
+    } as any,
+    getSettings: () => ({ workspace: "psd" }) as any,
+    spawnFn: () => nodeSpawn("node", [FAKE, SCRIPT]) as any,
+  });
+  const res = await app.inject({ method: "POST", url: "/sessions", payload: { question: "q" } });
+  expect(res.json()).toEqual({ id: "s1" });
+  expect(ensureWs).toBe("psd");
+});
+
+test("POST /sessions/:id/resume refuses with 503 when ollamaEnsure fails", async () => {
+  const app = buildApp(loadConfig({ THT_HARNESS_DIR: "../harness" }), {
+    thtRunner: {
+      ollamaEnsure: async () => ({ ok: false, error: "Ollama down" }),
+      sessionShow: async () => ({ status: "open", archived: false }),
+    } as any,
+    getSettings: () => ({ workspace: "psd" }) as any,
+    spawnFn: () => nodeSpawn("node", [FAKE, SCRIPT]) as any,
+  });
+  const res = await app.inject({ method: "POST", url: "/sessions/s1/resume" });
+  expect(res.statusCode).toBe(503);
+});