Add example fixture files

Greeting, tool call, multi-turn, and error response examples
used by integration tests and as documentation for fixture format.

Author: jpr5

fixtures/example-greeting.json

@@ -0,0 +1,12 @@
+{
+  "fixtures": [
+    {
+      "match": { "userMessage": "hello" },
+      "response": { "content": "Hello! How can I help you today?" }
+    },
+    {
+      "match": { "userMessage": "goodbye" },
+      "response": { "content": "Goodbye! Have a great day!" }
+    }
+  ]
+}

fixtures/example-multi-turn.json

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+{
+  "fixtures": [
+    {
+      "match": { "userMessage": "change background to blue" },
+      "response": {
+        "toolCalls": [{ "name": "change_background", "arguments": "{\"background\":\"blue\"}" }]
+      }
+    },
+    {
+      "match": { "toolCallId": "call_background" },
+      "response": { "content": "Done! I've changed the background." }
+    }
+  ]
+}

fixtures/example-tool-call.json

@@ -0,0 +1,15 @@
+{
+  "fixtures": [
+    {
+      "match": { "toolName": "get_weather" },
+      "response": {
+        "toolCalls": [
+          {
+            "name": "get_weather",
+            "arguments": "{\"location\":\"San Francisco\",\"unit\":\"fahrenheit\"}"
+          }
+        ]
+      }
+    }
+  ]
+}