feat: add streaming option to provider config to support non-streaming backends

[75ACOL]

Issue for this PR

Closes #785
Supersedes #14786

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

• Adds a streaming boolean option to provider configuration (provider.<id>.options.streaming)
• When streaming: false, uses AI SDK simulateStreamingMiddleware() so non-streaming backends can still work with OpenCode's streaming pipeline
• Keeps default behavior unchanged (streaming defaults to enabled)

How did you verify your code works?

• Verified with local typecheck for packages/opencode

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

Usage

{
  "provider": {
    "my-backend": {
      "options": {
        "streaming": false
      }
    }
  }
}

Notes

• This is a clean re-submission of the disable streaming feature on top of latest dev.
• PR feat: add streaming option to provider config to support non-streamin… #14786 had the same feature intent but is superseded by this rebased version.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Duplicate Found

PR #14786 - "feat: add streaming option to provider config to support non-streaming backends"
#14786

Why it's related: This appears to be a previous attempt at the exact same feature. According to the current PR description, PR #15931 is "a clean re-submission of the disable streaming feature on top of latest dev" that supersedes earlier attempts. PR #14786 has a nearly identical title and addresses the same functionality.

Recommendation: Verify that PR #14786 is closed/superseded and that PR #15931 is the current/correct implementation to proceed with.

[75ACOL]

Thanks for flagging. This PR is intentionally a re-submission of the same feature and supersedes #14786.

Reason: the previous PR was based on an older head and hit flaky CI; this one is rebased on latest dev and contains the same scoped change.

For review/merge, please use #15931 as the active PR.

[75ACOL]

Friendly bump for review 🙏
This PR is the active re-submission that supersedes #14786 and is now rebased on latest dev.
Current status:

• mergeable: CLEAN
• checks: all green\n- scope: small (2 files, +11/-0)
• Why this matters: it enables provider.<name>.options.streaming=false so OpenCode can work with OpenAI-compatible backends that do not support SSE reliably.
• If you prefer this landed differently (behind a flag/default/shape), I can adjust quickly.

[KingingWang]

When can this PR be merged?

[poelzi]

One line with usage of an upstream middleware. How long can this take ?

[zanellig]

Shouldn't docs be updated in order for this to be merged or are they not in this repo?

[KingingWang]

I applied this PR, and it can indeed send requests in non-streaming mode, but after receiving several messages, the following error occurs and terminates the conversation

Invalid JSON response

[rekram1-node]

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