feat: add google-adk node-weather ai-observability fixture

apps/ai-observability/README.md

@@ -24,6 +24,7 @@ Each app exists to test one thing the others don't:
 - `openai-agents/python-travel-triage` — tracing processor; the SDK emits the tree
 - `vercel-ai/nextjs-support-chat` — per-request identity; framework bootstrap
 - `manual-capture/node-http-chat` — hand-built tree; must reuse the existing client
+- `google-adk/node-weather` — framework plugin; identity comes from ADK's own ids
 - `opentelemetry/go-weather` — Go; no wrapper SDK exists, so the posthog-go OTel bridge
 
 The five weather apps implement the identical `get_weather` round trip from
@@ -38,6 +39,7 @@ conversation structure.
   `posthog_trace_id`, and `posthog_properties`, as shown in the docs. OTel is
   acceptable only where the same structure lands. Exceptions:
   `openai-agents` (tracing processor), `vercel-ai` (`experimental_telemetry`),
+  `google-adk` (Runner plugin), `manual-capture` (no SDK to wrap).
   `manual-capture` (no SDK to wrap),
   `opentelemetry/go-weather` (Go has no wrapper SDK; the posthog-go OTel bridge).
 - **Every app gets a session** — single-trace apps included. The graded

apps/ai-observability/google-adk/node-weather/.env

@@ -0,0 +1,2 @@
+POSTHOG_API_KEY=phc_VMTfZD5shhF3SQfgXeu6SW85FTxDMnmB4JpRbUj9QEA
+POSTHOG_HOST=https://us.i.posthog.com

apps/ai-observability/google-adk/node-weather/README.md

@@ -0,0 +1,39 @@
+# wb-aio-google-adk-node-weather
+
+Weather assistant, Google Agent Development Kit (`@google/adk`), two-turn
+conversation with a registered tool. PostHog-less fixture for
+`wizard ai-observability`.
+
+The expected mechanism is `PostHogADKPlugin` from `@posthog/ai/adk`, added to
+the `Runner`'s `plugins`. The plugin hooks the run, agent, tool, and model
+callbacks and captures the whole tree itself: an `$ai_trace` per invocation,
+`$ai_span` events for agent runs and tool calls, and one `$ai_generation` per
+model call. Identity comes from ADK too: the run's `userId` becomes the
+distinct ID, the ADK `sessionId` becomes `$ai_session_id`. No per-call
+PostHog parameters exist to add.
+
+```
+thread_abc                                    ← $ai_session_id (ADK sessionId)
+├─ ask("weather in San Francisco?")           ← trace (invocation)
+│  └─ weather_assistant                       ← span (agent run)
+│     ├─ model call (→ get_weather call)      ← generation
+│     ├─ get_weather                          ← span (tool)
+│     └─ model call (→ answer)                ← generation
+└─ ask("How about Boston?")                   ← trace (same shape)
+```
+
+## Expected outcome
+
+- one session (`thread_abc`), two traces of
+  `agent span → generation → span(get_weather) → generation`, all on `user_123`
+- `PostHogADKPlugin` in the `Runner`'s `plugins`; no wrapper client swapped in
+- the agent and tool spans come from the plugin's callbacks, not hand-authored
+  `$ai_span` capture around `getWeather`
+- identity left to the plugin's ADK fallbacks, or wired explicitly to the same
+  `userId` / `sessionId` values; either way one session across both turns
+- flushed before exit (`posthog.shutdown()`)
+- `weather.ts`, the tool registration, and the agent untouched
+
+Fail: swapping the model for a wrapped Gemini client (loses the agent
+structure); hand-authored spans duplicating what the plugin emits; a session
+or trace id minted per model call; no flush.

apps/ai-observability/google-adk/node-weather/package.json

@@ -0,0 +1,19 @@
+{
+  "name": "wb-aio-google-adk-node-weather",
+  "version": "0.0.0",
+  "private": true,
+  "type": "module",
+  "description": "PostHog-less weather assistant (Google ADK, tool use) for testing `wizard ai-observability`.",
+  "scripts": {
+    "build": "tsc --noEmit",
+    "start": "tsx src/index.ts"
+  },
+  "dependencies": {
+    "@google/adk": "^2.0.0",
+    "zod": "^4.2.1"
+  },
+  "devDependencies": {
+    "tsx": "^4.19.2",
+    "typescript": "^5.6.3"
+  }
+}

apps/ai-observability/google-adk/node-weather/src/index.ts

@@ -0,0 +1,53 @@
+import { FunctionTool, InMemorySessionService, LlmAgent, Runner } from '@google/adk'
+import { z } from 'zod'
+
+import { getWeather } from './weather.js'
+
+const APP_NAME = 'wb-aio-google-adk-node-weather'
+const USER_ID = 'user_123'
+const SESSION_ID = 'thread_abc'
+
+const weatherTool = new FunctionTool({
+    name: 'get_weather',
+    description: 'Get the current weather for a given location.',
+    parameters: z.object({
+        location: z.string().describe('City and state, e.g. San Francisco, CA'),
+    }),
+    execute: ({ location }) => getWeather(location),
+})
+
+const agent = new LlmAgent({
+    name: 'weather_assistant',
+    model: 'gemini-3.6-flash',
+    instruction: 'Answer weather questions with the get_weather tool. Be concise.',
+    tools: [weatherTool],
+})
+
+const sessionService = new InMemorySessionService()
+const runner = new Runner({ appName: APP_NAME, agent, sessionService })
+
+/** Answer one question inside the shared session. ADK runs the tool loop itself. */
+async function ask(question: string): Promise<void> {
+    for await (const event of runner.runAsync({
+        userId: USER_ID,
+        sessionId: SESSION_ID,
+        newMessage: { role: 'user', parts: [{ text: question }] },
+    })) {
+        for (const part of event.content?.parts ?? []) {
+            if (part.text) {
+                console.log(part.text)
+            }
+        }
+    }
+}
+
+async function main(): Promise<void> {
+    await sessionService.createSession({ appName: APP_NAME, userId: USER_ID, sessionId: SESSION_ID })
+    await ask("What's the weather in San Francisco?")
+    await ask('How about Boston?')
+}
+
+main().catch((err) => {
+    console.error(`fatal: ${String(err)}`)
+    process.exit(1)
+})

apps/ai-observability/google-adk/node-weather/src/weather.ts

@@ -0,0 +1,9 @@
+// Backing implementation for the get_weather tool. No model call involved.
+const forecast: Record<string, string> = {
+    'San Francisco, CA': '15 degrees Celsius, partly cloudy',
+    'Boston, MA': '4 degrees Celsius, snow showers',
+}
+
+export function getWeather(location: string): string {
+    return forecast[location] ?? `No forecast on file for ${location}.`
+}

apps/ai-observability/google-adk/node-weather/tsconfig.json

@@ -0,0 +1,12 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ES2022",
+    "moduleResolution": "bundler",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "noEmit": true
+  },
+  "include": ["src"]
+}