fix(invocation): preserve opaque JSON and integer precision in backwards requests #827

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Versions

1. dify-plugin-daemon: reproduced on main c798168e4c77890f8f605238718dd64a4cfb9939.
2. dify-api: not required for the reproduction; the failure occurs inside the daemon before it calls the host API.

Describe the bug

A plugin submitting an assistant message with object-valued opaque_body through a backwards LLM invocation fails before reaching the host.
InvokeDify first decodes wire JSON into map[string]any, then genericDispatchTask uses mapstructure to populate a request whose opaque fields are json.RawMessage.
That conversion does not implement JSON decoding:

unmarshal backwards invoke request failed: error decoding map:
'prompt_messages[0].opaque_body': source data must be an array or slice, got map

Other JSON values are also affected: [] is omitted and [49] becomes the JSON number 1.
The initial map decode separately rounds integers such as 9007199254740993 to 9007199254740992 in model parameters, tool parameters, app inputs and content-level opaque data.
Both LLM stream settings are affected.

To Reproduce

1. Use a plugin session with permission to invoke LLMs.
2. Submit the following backwards invocation to the real InvokeDify entry point, or construct the equivalent session.model.llm.invoke() call in a plugin:

{
  "type": "llm",
  "backwards_request_id": "replay",
  "request": {
    "provider": "example",
    "model": "example",
    "mode": "chat",
    "stream": true,
    "prompt_messages": [
      {
        "role": "assistant",
        "content": "",
        "opaque_body": {"state": {"id": 9007199254740993}}
      }
    ]
  }
}

3. Observe the local decoding error before any model or host request.
4. Remove assistant opaque and put the same integer in completion_params.seed; capture the typed request at the dispatch boundary to observe the rounded value.

The reproduction uses actual wire parsing, permission checks, session identity injection and genericDispatchTask, with only the final host call replaced to capture the payload.

Expected behavior

Preserve every valid JSON value and integer through backwards request dispatch, retain existing authorization and request validation, and return errors/end frames correctly.
JSON decoding must also accept the SDK's valid tool-only assistant messages with null or omitted content, while rejecting invalid content types.

Screenshots

Not applicable; deterministic wire-level reproductions are available.

Additional context

The related null-content behavior was reported in #640, closed as a duplicate of #661.
This issue concerns the shared backwards JSON decoding boundary and its opaque-value/precision loss; it is reproducible without the UI or a paid model API.
Raw typed model responses already preserve opaque JSON, so the backwards map conversion is a separate defect.
These daemon changes are one dependency of the Agent replay work tracked in langgenius/dify#41092, implemented on the host in langgenius/dify#44502.
The implementation merged in #828 on 2026-11-02 and is included in daemon 0.6.14.
Controlled transport/history validation is recorded in that PR.
langgenius/dify-plugin-sdks#390 is merged and SDK 0.11.0 publication is tracked in langgenius/dify-plugin-sdks#413; langgenius/dify-official-plugins#4034 and langgenius/dify-official-plugins#4156 remain rollout dependencies.
This issue was closed by #828.
Target product milestone: Dify 1.19.0.