Agent V2 and the legacy version shouldn't be an either-or choice

[arcsun]

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1. Is this request related to a challenge you're experiencing? Tell me about your story.

V2 has a noticeably higher configuration complexity， and v2 is not a complete functional replacement for the legacy Agent. In practice, the two versions share some overlapping features while also offering distinct functionalities.
Making them an either-or proposition also introduces compatibility issues with existing workflows， like #39209

I put together a quick compatibility fix on my custom branch and it's working pretty well (cost me $2). The main branch really should have similar compatibility built-in.

2. Additional context or comments

No response

3. Can you help us with this feature?

• I am interested in contributing to this feature.

[sdkrre]

@arcsun Hi, may I ask how you implemented it so that both versions can be used?

[arcsun]

see #39209