Per-agent model configuration has no effect when using ACP #46311

Description

Expected behavior
ACP prompt routing should match CLI behavior in terms of per-agent models taking precedence over the session default.

Actural behavior

1. The ACP prompt handler always passes the session-level model as input.model to session.prompt(). This short-circuits the fallback chain in prompt.ts, so ag.model is never reached.
2. loadDirectorySnapshot in service.ts strips agent models when building the mode list, mapping other agent fields but omitting model. Meanwhile the CLI path in directory.ts correctly includes the model spread.

Plugins

None

OpenCode version

1.18.25 (dc4449d)

Steps to reproduce

1. Configure per-agent models in opencode.jsonc:

{
  "agent": {
    "plan": { "model": "provider/large-model" },
    "build": { "model": "provider/fast-model" }
  }
}

2. Connect an ACP client (e.g., Xcode) and create a new session
3. Switch to the "plan" agent via session/set_mode or session/set_config_option
4. Send a prompt
5. Observe the provider logs; the prompt is routed to the session-level default model, not provider/large-model
6. For comparison, run the same agent via the CLI: opencode run --agent plan "hello", where the CLI correctly routes to provider/large-model

Screenshot and/or share link

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Operating System

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Terminal

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