Streaming validator aborts run on injected non-standard SSE frame from OpenAI-compatible provider (invalid_union) #54330

Description

The chat-completion stream validator hard-fails when an OpenAI-compatible provider injects a non-standard metadata SSE frame into the stream body. The frame is a valid JSON object, so it is not dropped by SSE framing, and it has neither choices nor error — so it fails the invalid_union validation and aborts the entire run.

This is not provider-specific. Vireonix emits routing/classification metadata; SiliconFlow emits billing metadata (see #39087); other relays emit tool-progress or keep-alive events. All of them hit the same validator.

The response is a perfectly valid OpenAI chat completion after the metadata frame. Only the injected frame is rejected.

Actual error

Type validation failed: Value: {"vireonix":{"request_id":"5121e30b-57ce-49c3-a516-c9439b26667c","route":"auto","route_host":"http://127.0.0.1:50728/v1","route_reason":"custom_router","selected_model":"auto","classification":{"complexity":"complex","political":false,"agent":true,"safety_score":0,"safety_review":"sentinel","safety_profile":"cloud","classifier_model":"vireonix-sentinel-v1","classifier_category":"hard","classifier_confidence":0.6696,"classifier_latency_ms":132.58},"reasoning_limit_tokens":null,"effective_model":"auto","user_notice":null,"generation_host":"http://127.0.0.1:50728/v1","failover":false,"upstream_model":"auto"}}.
Error message: [
  {
    "code": "invalid_union",
    "errors": [
      [
        {
          "expected": "array",
          "code": "invalid_type",
          "path": ["choices"],
          "message": "Invalid input: expected array, received undefined"
        }
      ],
      [
        {
          "expected": "object",
          "code": "invalid_type",
          "path": ["error"],
          "message": "Invalid input: expected object, received undefined"
        }
      ]
    ],
    "path": [],
    "message": "Invalid input"
  }
]

Note the shape: the rejected value is the metadata envelope. The validator demands choices: array OR error: object; the envelope is neither, so both union branches fail.

Raw wire evidence

This is the literal SSE stream from POST https://vireonix.ai/v1/chat/completions, no credentials required:

content-type: text/event-stream; charset=utf-8

data: {"vireonix":{"request_id":"a2bb2241-2930-46df-9bdf-dc42e4a89888","route":"local","route_host":null,"route_reason":"exact_reply","selected_model":"auto","classification":{"complexity":"simple","political":false,"agent":false,"safety_score":0,"safety_review":"local_exact_reply","automation_review":"skipped","reason":"local_exact_reply"},"upstream_model":"auto"}}

data: {"id":"chatcmpl_local_a2...","object":"chat.completion.chunk","created":...,"model":"auto","choices":[...]}

• Exactly 1 metadata frame per stream, always first.
• Every subsequent frame is a valid chat.completion.chunk.
• The metadata frame carries no event: name — it is a bare data: payload, which is why the event: field is not usable to route it.

Steps to reproduce

The endpoint is keyless, so this needs no credentials:

curl -s -N -X POST https://vireonix.ai/v1/chat/completions \
  -H 'Content-Type: application/json' \
  -d '{"model":"auto","stream":true,"messages":[{"role":"user","content":"Say hello in one word."}]}'

1. Add a keyless OpenAI-compatible provider to opencode.json:

   "provider": {
     "vireonix": {
       "npm": "@ai-sdk/openai-compatible",
       "name": "Vireonix (keyless)",
       "options": { "apiKey": "not-required", "baseURL": "https://vireonix.ai/v1" },
       "models": { "auto": { "name": "Vireonix Auto (keyless)" } }
     }
   }

2. Restart OpenCode, select vireonix/auto, send any message.

3. Every request fails with the invalid_union error above. 100% reproducible, not intermittent.

Key detail: this is NOT the bug #50508 fixes

PR #50508 (ignore non-object SSE keep-alive frames) targets frames that are valid JSON but not an object — e.g. data: null. It states explicitly:

The framing now drops a payload that is valid JSON but not a plain object, beside the empty and [DONE] cases. Invalid JSON, and object payloads that fail the event schema, still reach the decoder.

The frame in this report is a plain object ({"vireonix":{...}}), so #50508 would not drop it. The still-rejected case is exactly the one the PR description carves out as still reaching the decoder.

That PR is also merged=false and was noted as targeting the wrong branch (base=dev, author reply: "your pr wasnt for the correct branch").

Requested behavior

Silently skip SSE frames that do not match the expected event schema and are not the last frame, rather than aborting the whole run. The stream that follows is well-formed, so a strict-but-non-fatal parse is safe.

For diagnostics, it would help to preserve the offending frame's index and first ~200 chars in the error when all frames fail, so a genuinely broken provider is still surfaced clearly rather than silently truncated.

Why this keeps recurring

This root cause has been reported at least five times, and every one was closed by the stale-bot (60 days of no activity) rather than resolved:

• SSE named events from custom providers cause type validation failure and break streaming #28833 — SSE event: field ignored; every data: validated (original)
• Tool progress messages rejected by streaming validator due to invalid union type #36428 — tool progress messages rejected by the streaming validator
• [Bug]: AI SDK ignores SSE event: field — custom server events crash Chat Completions stream with TypeValidationError #38106 — custom server events crash the Chat Completions stream
• [BUG]: Type validation failed for billing.summary SSE event from SiliconFlow-compatible providers #39087 — SiliconFlow billing.summary SSE event (closest match)
• provider: openai-compatible stream aborts the whole run on non-object SSE payloads (data: null) #50314 — data: null aborts the whole run (→ fix(opencode): ignore non-object SSE keep-alive frames #50508, unmerged)

The provider varies each time; the root cause does not.

Environment

• OpenCode version: 1.18.35 (latest release as of 2026-10-06)
• Plugins: none involved
• Operating System: macOS 27.0.1 (arm64)
• Terminal: Ghostty
• Provider: @ai-sdk/openai-compatible