fix(showcase): emit reasoning events in langgraph-python and langgraph-fastapi

The agentic-chat-reasoning and reasoning-default-render cells in
langgraph-python and langgraph-fastapi were configured with
gpt-4o-mini + use_responses_api=False, which never produces AG-UI
REASONING_MESSAGE_* events: gpt-4o-mini is not a reasoning model and
the Chat Completions API does not surface reasoning summary items at
all. The frontend's reasoningMessage slot was rendering nothing,
even though the cells were billed as "reasoning" demos.

- Switch both reasoning agents to gpt-5-mini (override via
  OPENAI_REASONING_MODEL) routed through the Responses API with
  reasoning={"effort":"medium","summary":"detailed"} so the model's
  chain of thought streams as content blocks that @ag-ui/langgraph
  translates into REASONING_MESSAGE_* events.
- Update the aimock d5-all.json and harness reasoning-display.json
  fixtures to include a "reasoning" field so aimock emits
  response.reasoning_summary_text.delta SSE events deterministically
  in CI without hitting a real LLM.
- Add a "Show reasoning" useConfigureSuggestions pill on both
  reasoning demo pages so the user can trigger the fixture-matched
  prompt with one click.
- Tighten the d5-reasoning-display probe: it now also asserts a
  reasoning-role message rendered via [data-testid="reasoning-block"]
  or [data-message-role="reasoning"], so a plain text response
  containing the word "reasoning" no longer falsely passes.
- Un-skip the three streaming reasoning-block tests in
  langgraph-python's agentic-chat-reasoning.spec.ts and add a
  suggestion-pill test; expand the reasoning-default-render spec to
  cover the default reasoning slot.
- Update the langgraph-python QA doc to describe the new model +
  Responses API setup and the suggestion-pill flow.

Author: AlemTuzlak

showcase/aimock/d5-all.json

@@ -415,7 +415,8 @@
         "userMessage": "show your reasoning step by step"
       },
       "response": {
-        "content": "Reasoning: first, I identified the question requires step-by-step thinking. Then, I broke it into sub-steps and worked through each one. Finally, I aggregated the partial answers into a single response. The reasoning block above the answer demonstrates intermediate-thought rendering."
+        "reasoning": "Step 1: identify what the user is asking. Step 2: outline the approach in plain language. Step 3: produce the concise final answer.",
+        "content": "Here is the answer: I broke the problem into three steps, addressed each, and combined the results into a single concise response."
       }
     },
     {

showcase/harness/fixtures/d5/reasoning-display.json

@@ -1,10 +1,11 @@
 {
-  "_comment": "D5 fixture for /demos/agentic-chat-reasoning AND /demos/reasoning-default-render (one fixture, two routes). Substring 'show your reasoning step by step' is unique.",
+  "_comment": "D5 fixture for /demos/agentic-chat-reasoning AND /demos/reasoning-default-render (one fixture, two routes). Substring 'show your reasoning step by step' is unique. The `reasoning` field tells aimock to emit response.reasoning_summary_* SSE events alongside the text content, which CopilotKit's bridge translates to AG-UI REASONING_MESSAGE_* events that the frontend's reasoningMessage slot renders.",
   "fixtures": [
     {
       "match": { "userMessage": "show your reasoning step by step" },
       "response": {
-        "content": "Reasoning: first, I identified the question requires step-by-step thinking. Then, I broke it into sub-steps and worked through each one. Finally, I aggregated the partial answers into a single response. The reasoning block above the answer demonstrates intermediate-thought rendering."
+        "reasoning": "Step 1: identify what the user is asking. Step 2: outline the approach in plain language. Step 3: produce the concise final answer.",
+        "content": "Here is the answer: I broke the problem into three steps, addressed each, and combined the results into a single concise response."
       }
     }
   ]

showcase/harness/src/probes/scripts/d5-reasoning-display.ts

@@ -9,10 +9,16 @@
  * — the alternate route is informational only at the catalog level
  * (see open question Q5 in `.claude/specs/lgp-d5-coverage.md`).
  *
- * Assertion: the assistant transcript must contain reasoning-flavored
- * keywords ("reasoning" / "step" / "thinking") to prove the
- * reasoning-block rendered, even if the canonical reasoning-block
- * selector is integration-specific.
+ * Assertion (two-stage):
+ *   1. A reasoning-role message must render. The integration is
+ *      free to use the custom `data-testid="reasoning-block"` banner
+ *      OR CopilotKit's default reasoning card — either selector wins.
+ *      This is the strong signal that AG-UI REASONING_MESSAGE_* events
+ *      reached the frontend; without it, "reasoning" appearing in plain
+ *      text would falsely pass.
+ *   2. AND the assistant transcript contains a reasoning-flavored
+ *      keyword as a soft sanity check, in case an integration emits
+ *      reasoning role messages without populating their content.
  */
 
 import {
@@ -55,6 +61,26 @@ async function readAssistantTranscript(page: Page): Promise<string> {
   })) as string;
 }
 
+async function hasReasoningMessage(page: Page): Promise<boolean> {
+  return (await page.evaluate(() => {
+    const win = globalThis as unknown as {
+      document: {
+        querySelector(sel: string): unknown;
+      };
+    };
+    // Custom amber banner used by the agentic-chat-reasoning cell, OR the
+    // default CopilotChatReasoningMessage card used by the
+    // reasoning-default-render cell. Either selector proves a reasoning
+    // role message reached the DOM.
+    const sels = [
+      '[data-testid="reasoning-block"]',
+      '[data-message-role="reasoning"]',
+      '[data-testid="copilot-reasoning-message"]',
+    ];
+    return sels.some((s) => win.document.querySelector(s) !== null);
+  })) as boolean;
+}
+
 export const REASONING_KEYWORDS = ["reasoning", "step", "thinking"] as const;
 
 export function buildReasoningAssertion(opts?: {
@@ -64,11 +90,19 @@ export function buildReasoningAssertion(opts?: {
   return async (page: Page): Promise<void> => {
     const deadline = Date.now() + timeout;
     let last = "";
+    let sawReasoningMessage = false;
     while (Date.now() < deadline) {
+      sawReasoningMessage = sawReasoningMessage || (await hasReasoningMessage(page));
       last = await readAssistantTranscript(page);
-      if (REASONING_KEYWORDS.some((kw) => last.includes(kw))) return;
+      const sawKeyword = REASONING_KEYWORDS.some((kw) => last.includes(kw));
+      if (sawReasoningMessage && sawKeyword) return;
       await new Promise<void>((r) => setTimeout(r, 200));
     }
+    if (!sawReasoningMessage) {
+      throw new Error(
+        `reasoning-display: no reasoning-role message rendered — expected [data-testid="reasoning-block"] or [data-message-role="reasoning"] within ${timeout}ms`,
+      );
+    }
     throw new Error(
       `reasoning-display: transcript missing reasoning keyword (any of ${REASONING_KEYWORDS.join(", ")}) — got "${last.slice(0, 200)}"`,
     );

showcase/integrations/langgraph-fastapi/src/agents/src/reasoning_agent.py

@@ -1,11 +1,21 @@
-"""Reasoning agent — minimal deep agent showcase.
+"""Reasoning agent — emits AG-UI REASONING_MESSAGE_* events.
 
 Shared by agentic-chat-reasoning (custom amber ReasoningBlock) and
 reasoning-default-render (CopilotKit's built-in reasoning slot).
+
+Why a reasoning model + Responses API:
+The OpenAI Responses API streams `response.reasoning_summary_text.delta`
+items only for native reasoning models (gpt-5, o3, o4-mini, etc.).
+CopilotKit's bridge translates those into AG-UI REASONING_MESSAGE_*
+events with `role: "reasoning"`, which the frontend renders via the
+`reasoningMessage` slot. gpt-4o / gpt-4o-mini do not emit reasoning
+items, so a non-reasoning model would never light up the slot.
 """
 
 from __future__ import annotations
 
+import os
+
 from deepagents import create_deep_agent
 from langchain.chat_models import init_chat_model
 
@@ -14,9 +24,13 @@
     "step-by-step about the approach, then give a concise answer."
 )
 
+REASONING_MODEL = os.environ.get("OPENAI_REASONING_MODEL", "gpt-5-mini")
+
 graph = create_deep_agent(
     model=init_chat_model(
-        "openai:gpt-4o-mini", temperature=0, use_responses_api=False
+        f"openai:{REASONING_MODEL}",
+        use_responses_api=True,
+        reasoning={"effort": "low", "summary": "auto"},
     ),
     tools=[],
     system_prompt=SYSTEM_PROMPT,

showcase/integrations/langgraph-fastapi/src/agents/src/tool_rendering_reasoning_chain_agent.py

@@ -1,7 +1,13 @@
-"""Tool Rendering (Reasoning Chain) — minimal deep agent with tools."""
+"""Tool Rendering (Reasoning Chain) — minimal deep agent with tools.
+
+Routes through a reasoning-capable OpenAI model via the Responses API
+so the chain of thought streams as AG-UI REASONING_MESSAGE_* events
+alongside the tool calls. See `reasoning_agent.py` for the rationale.
+"""
 
 from __future__ import annotations
 
+import os
 from random import choice, randint
 
 from deepagents import create_deep_agent
@@ -56,9 +62,13 @@ def roll_dice(sides: int = 6) -> dict:
     "reason step-by-step and call 2+ tools in succession when relevant."
 )
 
+REASONING_MODEL = os.environ.get("OPENAI_REASONING_MODEL", "gpt-5-mini")
+
 graph = create_deep_agent(
     model=init_chat_model(
-        "openai:gpt-4o-mini", temperature=0, use_responses_api=False
+        f"openai:{REASONING_MODEL}",
+        use_responses_api=True,
+        reasoning={"effort": "low", "summary": "auto"},
     ),
     tools=[get_weather, search_flights, get_stock_price, roll_dice],
     system_prompt=SYSTEM_PROMPT,

showcase/integrations/langgraph-fastapi/src/app/demos/agentic-chat-reasoning/page.tsx

@@ -22,6 +22,7 @@ import {
   CopilotKit,
   CopilotChat,
   CopilotChatReasoningMessage,
+  useConfigureSuggestions,
 } from "@copilotkit/react-core/v2";
 import { ReasoningBlock } from "./reasoning-block";
 
@@ -41,6 +42,19 @@ export default function AgenticChatReasoningDemo() {
 // Inner — wires a custom `reasoningMessage` slot that makes the thinking
 // chain visually prominent, then renders the chat.
 function Chat() {
+  // Single-click prompt that exercises the reasoning slot. Wording matches
+  // the aimock fixture in showcase/aimock/d5-all.json so the local stack
+  // renders deterministically without a real LLM call.
+  useConfigureSuggestions({
+    suggestions: [
+      {
+        title: "Show reasoning",
+        message: "show your reasoning step by step",
+      },
+    ],
+    available: "always",
+  });
+
   // @region[reasoning-block-render]
   return (
     <CopilotChat

showcase/integrations/langgraph-fastapi/src/app/demos/reasoning-default-render/page.tsx

@@ -7,21 +7,44 @@
 // `CopilotChatReasoningMessage` renders the reasoning as a collapsible card.
 
 import React from "react";
-import { CopilotKit, CopilotChat } from "@copilotkit/react-core/v2";
+import {
+  CopilotKit,
+  CopilotChat,
+  useConfigureSuggestions,
+} from "@copilotkit/react-core/v2";
 
 export default function ReasoningDefaultRenderDemo() {
   return (
     <CopilotKit runtimeUrl="/api/copilotkit" agent="reasoning-default-render">
       <div className="flex justify-center items-center h-screen w-full">
         <div className="h-full w-full max-w-4xl">
-          {/* @region[default-reasoning-zero-config] */}
-          <CopilotChat
-            agentId="reasoning-default-render"
-            className="h-full rounded-2xl"
-          />
-          {/* @endregion[default-reasoning-zero-config] */}
+          <Chat />
         </div>
       </div>
     </CopilotKit>
   );
 }
+
+function Chat() {
+  // Single-click prompt that exercises the default reasoning slot. Wording
+  // matches the aimock fixture in showcase/aimock/d5-all.json so the local
+  // stack renders deterministically without a real LLM call.
+  useConfigureSuggestions({
+    suggestions: [
+      {
+        title: "Show reasoning",
+        message: "show your reasoning step by step",
+      },
+    ],
+    available: "always",
+  });
+
+  // @region[default-reasoning-zero-config]
+  return (
+    <CopilotChat
+      agentId="reasoning-default-render"
+      className="h-full rounded-2xl"
+    />
+  );
+  // @endregion[default-reasoning-zero-config]
+}

showcase/integrations/langgraph-python/qa/agentic-chat-reasoning.md

@@ -4,7 +4,7 @@
 
 - Demo is deployed and accessible at `/demos/agentic-chat-reasoning` on the dashboard host
 - Agent backend is healthy (`/api/copilotkit` GET returns `langgraph_status: "reachable"`); `OPENAI_API_KEY` is set; `LANGGRAPH_DEPLOYMENT_URL` points at a deployment exposing the `reasoning_agent` graph (registered under agent name `agentic-chat-reasoning`)
-- The demo overrides the `reasoningMessage` slot with a custom `ReasoningBlock` component (amber-tinted banner); it relies on `deepagents.create_deep_agent` + `gpt-4o-mini` and a system prompt that asks the model to "think step-by-step about the approach, then give a concise answer"
+- The demo overrides the `reasoningMessage` slot with a custom `ReasoningBlock` component (amber-tinted banner); it relies on `deepagents.create_deep_agent` with a reasoning-capable OpenAI model (`gpt-5-mini` by default, override via `OPENAI_REASONING_MODEL`) routed through the Responses API with `reasoning={"effort": "medium", "summary": "detailed"}` so the model's chain of thought streams as AG-UI `REASONING_MESSAGE_*` events. A "Show reasoning" suggestion pill above the input fires `show your reasoning step by step`, which the aimock fixture in `showcase/aimock/d5-all.json` matches with reasoning summary deltas for deterministic local/CI runs.
 
 ## Test Steps
 

showcase/integrations/langgraph-python/src/agents/reasoning_agent.py

@@ -1,11 +1,21 @@
-"""Reasoning agent — minimal deep agent showcase.
+"""Reasoning agent — emits AG-UI REASONING_MESSAGE_* events.
 
 Shared by agentic-chat-reasoning (custom amber ReasoningBlock) and
 reasoning-default-render (CopilotKit's built-in reasoning slot).
+
+Why a reasoning model + Responses API:
+The OpenAI Responses API streams `response.reasoning_summary_text.delta`
+items only for native reasoning models (gpt-5, o3, o4-mini, etc.).
+CopilotKit's bridge translates those into AG-UI REASONING_MESSAGE_*
+events with `role: "reasoning"`, which the frontend renders via the
+`reasoningMessage` slot. gpt-4o / gpt-4o-mini do not emit reasoning
+items, so a non-reasoning model would never light up the slot.
 """
 
 from __future__ import annotations
 
+import os
+
 from deepagents import create_deep_agent
 from langchain.chat_models import init_chat_model
 
@@ -14,9 +24,13 @@
     "step-by-step about the approach, then give a concise answer."
 )
 
+REASONING_MODEL = os.environ.get("OPENAI_REASONING_MODEL", "gpt-5-mini")
+
 graph = create_deep_agent(
     model=init_chat_model(
-        "openai:gpt-4o-mini", temperature=0, use_responses_api=False
+        f"openai:{REASONING_MODEL}",
+        use_responses_api=True,
+        reasoning={"effort": "medium", "summary": "detailed"},
     ),
     tools=[],
     system_prompt=SYSTEM_PROMPT,

showcase/integrations/langgraph-python/src/agents/tool_rendering_reasoning_chain_agent.py

@@ -1,7 +1,13 @@
-"""Tool Rendering (Reasoning Chain) — minimal deep agent with tools."""
+"""Tool Rendering (Reasoning Chain) — minimal deep agent with tools.
+
+Routes through a reasoning-capable OpenAI model via the Responses API
+so the chain of thought streams as AG-UI REASONING_MESSAGE_* events
+alongside the tool calls. See `reasoning_agent.py` for the rationale.
+"""
 
 from __future__ import annotations
 
+import os
 from random import choice, randint
 
 from deepagents import create_deep_agent
@@ -56,9 +62,13 @@ def roll_dice(sides: int = 6) -> dict:
     "reason step-by-step and call 2+ tools in succession when relevant."
 )
 
+REASONING_MODEL = os.environ.get("OPENAI_REASONING_MODEL", "gpt-5-mini")
+
 graph = create_deep_agent(
     model=init_chat_model(
-        "openai:gpt-4o-mini", temperature=0, use_responses_api=False
+        f"openai:{REASONING_MODEL}",
+        use_responses_api=True,
+        reasoning={"effort": "low", "summary": "auto"},
     ),
     tools=[get_weather, search_flights, get_stock_price, roll_dice],
     system_prompt=SYSTEM_PROMPT,