Responses multi-turn fails on strict gateways: replayed reasoning items drop provider id (input.N.id: expected a value)

Description

Fresh session, first turn works (reasoning summary streams back); any second turn fails with 400 — but only against Responses gateways that strictly validate input items. Same two turns succeed against lenient upstreams.

Root cause (verified below): on turn 2, opencode replays the previous turn's typed items (type: reasoning / type: message) without the provider-side ids (rs_* / msg_*). Gateways requiring id on typed items reject the request:

Opencode failed to send message with error: Invalid value for 'input.2.id': expected a value.

Minimal repros against the gateway (POST /v1/responses, stream: true):

# reasoning item WITHOUT id -> 400, same error template as the client
{"input":[
  {"role":"user","content":"hi"},
  {"type":"reasoning","summary":[{"type":"summary_text","text":"..."}]},
  {"type":"message","id":"msg_real123","role":"assistant","status":"completed",
   "content":[{"type":"output_text","text":"hi!"}]},
  {"role":"user","content":"what can you do?"}]}
# -> {"param":"input.1.id","message":"Invalid value for 'input.1.id': expected a value."}

# message item WITHOUT id -> 400 as well
{"input":[
  {"role":"user","content":"hi"},
  {"type":"message","role":"assistant","status":"completed",
   "content":[{"type":"output_text","text":"hi!"}]},
  {"role":"user","content":"why?"}]}
# -> {"message":"Invalid value for 'input.1': Responses output message status requires an item id."}

Control cases (all 200): role-based messages, typed items with id, function_call_output replays.

Related but distinct from #5104: in Dec 2025 (v1.0.133) the replay carried id + encrypted_content and died on crypto verification; now it carries no id and dies on id validation. Lenient upstreams accept the id-less replay, which is likely why this went unnoticed.

Possible fixes (maintainer's call): preserve provider item ids when round-tripping typed items, skip replaying id-less/empty reasoning items, or put it behind an option.

Provider/model config (keys redacted; same failure via two different baseURLs with identical model options, so it's not gateway-specific):

"experientiallabs": {
  "npm": "@ai-sdk/openai",
  "name": "ExperientialLabs Direct",
  "options": {
    "baseURL": "https://api.experientiallabs.ai/v1",
    "apiKey": "<redacted>"
  },
  "models": {
    "gpt-5.6-luna": {
      "name": "GPT-5.6 Luna",
      "modalities": { "input": ["text", "image"], "output": ["text"] },
      "options": {
        "reasoningEffort": "max",
        "reasoningSummary": "detailed",
        "include": ["reasoning.encrypted_content"],
        "maxTokens": 32000
      },
      "variants": {
        "max": { "reasoningEffort": "max", "reasoningSummary": "detailed", "include": ["reasoning.encrypted_content"] },
        "xhigh": { "reasoningEffort": "xhigh", "reasoningSummary": "detailed", "include": ["reasoning.encrypted_content"] },
        "high": { "reasoningEffort": "high", "reasoningSummary": "detailed", "include": ["reasoning.encrypted_content"] },
        "medium": { "reasoningEffort": "medium", "reasoningSummary": "detailed", "include": ["reasoning.encrypted_content"] },
        "low": { "reasoningEffort": "low", "reasoningSummary": "detailed", "include": ["reasoning.encrypted_content"] }
      },
      "limit": { "context": 256000, "input": 224000, "output": 32000 }
    }
  }
}

Plugins

opencode-mem

OpenCode version

1.18.30 (running inside OpenChamber)

Steps to reproduce

1. Point @ai-sdk/openai at any strict Responses gateway (reasoningSummary: detailed so turn 1 yields a reasoning item).
2. New session, send hi → works.
3. Send a second message → Invalid value for 'input.2.id': expected a value. (see screenshot).
4. Same two turns against a lenient upstream → both succeed.

Screenshot and/or share link

Screenshot attached below (turn 1 streams reasoning summary + answer; turn 2 errors; bottom bar shows the direct-gateway model in use).

Operating System

Windows 11 (WSL backend)

Terminal

OpenChamber desktop v1.22.2 (hosting opencode web UI)