feat: streaming (SSE) end-to-end

- Provider::chat_stream; OpenAI provider streams via stream_options.include_usage
- pipeline.run_stream: shared route/select, failover before first byte
- /v1/chat/completions forwards SSE verbatim with X-Cortiq-* headers; usage tapped for stats
- admin /test/stream + live streaming in Playground (stream toggle, 7 langs)

web/js/api.js

@@ -91,3 +91,51 @@ export const api = {
   // playground
   test: (b) => j("POST", "/test", b),
 };
+
+// Streaming playground: POST /test/stream, calls onDelta(text) per content chunk,
+// returns the routing decision read from X-Cortiq-* response headers.
+export async function testStream(body, onDelta) {
+  const r = await fetch(BASE + "/test/stream", {
+    method: "POST",
+    headers: { Authorization: "Bearer " + getToken(), "content-type": "application/json" },
+    body: JSON.stringify(body),
+  });
+  if (r.status === 401) {
+    if (onUnauthorized) onUnauthorized();
+    throw new Error("unauthorized");
+  }
+  if (!r.ok || !r.body) {
+    throw new Error((await r.text()) || r.statusText);
+  }
+  const reader = r.body.getReader();
+  const dec = new TextDecoder();
+  let buf = "";
+  for (;;) {
+    const { done, value } = await reader.read();
+    if (done) break;
+    buf += dec.decode(value, { stream: true });
+    let idx;
+    while ((idx = buf.indexOf("\n\n")) >= 0) {
+      const line = buf.slice(0, idx).split("\n").find((l) => l.startsWith("data:"));
+      buf = buf.slice(idx + 2);
+      if (!line) continue;
+      const data = line.slice(5).trim();
+      if (!data || data === "[DONE]") continue;
+      try {
+        const d = JSON.parse(data).choices?.[0]?.delta?.content;
+        if (d) onDelta(d);
+      } catch {
+        /* ignore malformed chunk */
+      }
+    }
+  }
+  const h = r.headers;
+  return {
+    task_label: h.get("x-cortiq-task-label") || "",
+    tier: h.get("x-cortiq-complexity-tier") || "",
+    score: parseFloat(h.get("x-cortiq-complexity-score") || "0"),
+    selected_model: h.get("x-cortiq-selected-model") || "",
+    route_source: h.get("x-cortiq-route-source") || "",
+    cost_usd: parseFloat(h.get("x-cortiq-cost-usd") || "0"),
+  };
+}

web/js/i18n/de.js

@@ -200,6 +200,7 @@ export default {
   "pg.temp": "Temperatur",
   "pg.maxTokens": "Max. Tokens",
   "pg.send": "Senden",
+  "pg.stream": "Streamen",
   "pg.sending": "Wird gesendet…",
   "pg.answer": "Antwort",
   "pg.empty": "Antwort und Routing-Entscheidung erscheinen hier.",

web/js/i18n/en.js

@@ -201,6 +201,7 @@ export default {
   "pg.temp": "Temperature",
   "pg.maxTokens": "Max tokens",
   "pg.send": "Send",
+  "pg.stream": "Stream",
   "pg.sending": "Sending…",
   "pg.answer": "Answer",
   "pg.empty": "The answer and routing decision will appear here.",

web/js/i18n/es.js

@@ -200,6 +200,7 @@ export default {
   "pg.temp": "Temperatura",
   "pg.maxTokens": "Tokens máx.",
   "pg.send": "Enviar",
+  "pg.stream": "Streaming",
   "pg.sending": "Enviando…",
   "pg.answer": "Respuesta",
   "pg.empty": "La respuesta y la decisión de enrutamiento aparecerán aquí.",

web/js/i18n/fr.js

@@ -200,6 +200,7 @@ export default {
   "pg.temp": "Température",
   "pg.maxTokens": "Tokens max",
   "pg.send": "Envoyer",
+  "pg.stream": "Streaming",
   "pg.sending": "Envoi…",
   "pg.answer": "Réponse",
   "pg.empty": "La réponse et la décision de routage s'afficheront ici.",

web/js/i18n/ru.js

@@ -200,6 +200,7 @@ export default {
   "pg.temp": "Температура",
   "pg.maxTokens": "Макс. токены",
   "pg.send": "Отправить",
+  "pg.stream": "Стриминг",
   "pg.sending": "Отправка…",
   "pg.answer": "Ответ",
   "pg.empty": "Ответ и решение роутера появятся здесь.",

web/js/i18n/tr.js

@@ -200,6 +200,7 @@ export default {
   "pg.temp": "Sıcaklık",
   "pg.maxTokens": "Maks. token",
   "pg.send": "Gönder",
+  "pg.stream": "Akış",
   "pg.sending": "Gönderiliyor…",
   "pg.answer": "Yanıt",
   "pg.empty": "Yanıt ve yönlendirme kararı burada görünecek.",

web/js/i18n/zh.js

@@ -200,6 +200,7 @@ export default {
   "pg.temp": "温度",
   "pg.maxTokens": "最大 Token 数",
   "pg.send": "发送",
+  "pg.stream": "流式",
   "pg.sending": "发送中…",
   "pg.answer": "回答",
   "pg.empty": "回答和路由决策将在此显示。",

web/js/views/playground.js

@@ -1,7 +1,7 @@
 // Playground — send a prompt through the live pipeline, inspect routing decision.
-import { h, mount, money, ms, num } from "../ui.js";
+import { h, mount, money, ms } from "../ui.js";
 import { t } from "../i18n.js";
-import { api } from "../api.js";
+import { api, testStream } from "../api.js";
 import { appState } from "../app.js";
 
 export async function renderPlayground() {
@@ -16,6 +16,7 @@ export async function renderPlayground() {
   const promptIn = h("textarea", { placeholder: t("pg.promptPlaceholder"), rows: 5 });
   const tempIn = h("input", { type: "number", step: "0.1", value: 0.7 });
   const maxTokIn = h("input", { type: "number", value: 512 });
+  const streamCb = h("input", { type: "checkbox", checked: true });
   const profileSel = h("select", {}, ...(meta.profiles || []).map((p) => h("option", { value: p }, p)));
   const modelSel = h("select", {}, ...ids.map((id) => h("option", { value: id }, id)));
 
@@ -62,19 +63,43 @@ export async function renderPlayground() {
     sendBtn.disabled = true;
     sendBtn.textContent = t("pg.sending");
     mount(out, h("div", { class: "flex" }, h("span", { class: "spinner" }), " ", t("pg.sending")));
+    const body = {
+      model,
+      messages,
+      temperature: parseFloat(tempIn.value),
+      max_tokens: parseInt(maxTokIn.value) || null,
+    };
     try {
-      const r = await api.test({
-        model,
-        messages,
-        temperature: parseFloat(tempIn.value),
-        max_tokens: parseInt(maxTokIn.value) || null,
-      });
-      if (r.ok) {
-        mount(out, r.answer || h("span", { class: "muted" }, "—"));
-        renderDecision(r);
+      if (streamCb.checked) {
+        const started = performance.now();
+        let acc = "";
+        out.textContent = "";
+        const info = await testStream(body, (d) => {
+          acc += d;
+          out.textContent = acc;
+        });
+        out.textContent = acc || "—";
+        renderDecision({
+          cortiq: {
+            task_label: info.task_label,
+            complexity: { score: info.score, tier: info.tier },
+            selected_model: info.selected_model,
+            route_source: info.route_source,
+            cost_usd: info.cost_usd,
+            failover: false,
+          },
+          usage: {},
+          latency_ms: Math.round(performance.now() - started),
+        });
       } else {
-        mount(out, h("div", { class: "callout" }, h("b", {}, t("pg.error") + ": "), r.error || ""));
-        mount(decision, h("div", { class: "card-head" }, h("h3", {}, t("pg.decision"))), h("div", { class: "empty" }, "—"));
+        const r = await api.test(body);
+        if (r.ok) {
+          mount(out, r.answer || h("span", { class: "muted" }, "—"));
+          renderDecision(r);
+        } else {
+          mount(out, h("div", { class: "callout" }, h("b", {}, t("pg.error") + ": "), r.error || ""));
+          mount(decision, h("div", { class: "card-head" }, h("h3", {}, t("pg.decision"))), h("div", { class: "empty" }, "—"));
+        }
       }
     } catch (e) {
       mount(out, h("div", { class: "callout" }, String(e.message || e)));
@@ -126,7 +151,12 @@ export async function renderPlayground() {
           h("label", { class: "field" }, h("span", {}, t("pg.mode")), modeSeg),
           modeExtra,
           h("div", { class: "row" }, h("label", { class: "field" }, h("span", {}, t("pg.temp")), tempIn), h("label", { class: "field" }, h("span", {}, t("pg.maxTokens")), maxTokIn)),
-          h("div", { class: "flex", style: "justify-content:flex-end" }, sendBtn)
+          h(
+            "div",
+            { class: "flex", style: "justify-content:space-between" },
+            h("label", { class: "check", style: "margin:0" }, streamCb, t("pg.stream")),
+            sendBtn
+          )
         ),
         h("div", { class: "card" }, h("div", { class: "card-head" }, h("h3", {}, t("pg.answer"))), out)
       ),