fix: strip markdown code fences from structured output before decoding

[vaishnavyogesh]

Strip markdown code fences from structured output before decoding

Problem

Some models return structured output JSON wrapped in a markdown fence (e.g. json\n{...}\n). Every gateway decoded with a bare json_decode($text, true) ?? [], so the wrapped payload silently became [].

Fix

• New trait Laravel\Ai\Gateway\Concerns\DecodesStructuredOutput exposes decodeStructuredOutput(?string $text): array, which strips a wrapping ```json / ``` fence (entire-payload match only, with optional whitespace/newlines) and then decodes.
• Trait is wired into every gateway parser that produces structured output: Xai, OpenAi, OpenRouter, Ollama, Mistral, Groq, Gemini, DeepSeek, Anthropic (fallback branch), and replacing Bedrock's private decodeStructuredOutput.

Safety

• Regex is anchored to the start/end of the trimmed payload, so JSON strings containing triple-backtick substrings are not mangled.
• Non-array decode results (scalars/strings) still return [], matching prior semantics.
• Streaming structured output is already unsupported, so no streaming paths touched.

Tests

tests/Unit/Gateway/Concerns/DecodesStructuredOutputTest.php — 9 cases covering:

• plain JSON, ```json fence, bare ``` fence, uppercase JSON
• leading/trailing whitespace and newlines around the fence
• invalid JSON, null/empty input
• partial-fence safety (triple-backticks inside string values)
• non-array scalar decodes

[pushpak1300]

can you send me curl request to reproduce this with any provider ?

[vaishnavyogesh]

can you send me curl request to reproduce this with any provider ?

curl --location 'https://api.fastrouter.ai/api/v1/chat/completions' \
--header 'Content-Type: application/json' \
--header 'Authorization: Bearer API_KEY' \
--data '{
    "model": "anthropic/claude-haiku-4.5",
    "messages": [
      {
        "role": "system",
        "content": "You are a helpful assistant that responds in JSON format. The weather in london is 20 degree celsius."
      },
      {
        "role": "user",
        "content": "What is the weather like in London?"
      }
    ],
    "response_format": {
      "type": "json_schema",
      "json_schema": {
        "name": "weather",
        "strict": true,
        "schema": {
          "type": "object",
          "properties": {
            "location": {
              "type": "string",
              "description": "City or location name"
            },
            "temperature": {
              "type": "number",
              "description": "Temperature in Celsius"
            },
            "conditions": {
              "type": "string",
              "description": "Weather conditions description"
            }
          },
          "required": ["location", "temperature", "conditions"],
          "additionalProperties": false
        }
      }
    }
}'

Response:

{
    "choices": [
        {
            "message": {
                "role": "assistant",
                "content": "```json\n{\n  \"location\": \"London\",\n  \"temperature\": 20,\n  \"conditions\": \"Clear\"\n}\n```",
                "annotations": null
            },
            "finish_reason": "stop",
            "index": 0
        }
    ],
    ...
 }

I'm using fastrouter provider behind openrouter gateway, if possible can you check if it's getting reproduced when prompting claude's haiku model directly through Anthropic gateway?

[vaishnavyogesh]

Hey @pushpak1300, were you able to reproduce it consistently?