ACP: fable missing from Claude Code model picker suggestions

Is there an existing feature request for this?

• I have searched existing issues and feature requests, and this is not a duplicate.

Problem or Use Case

The static Claude Code model suggestion list _CLAUDE_MODELS in acp_providers.py does not include fable, so it never appears in the ACP model picker suggestions, even for accounts that can use it (setting acp_model: "fable" explicitly works fine).

This is the SDK-side tracking issue for OpenHands/OpenHands#16440, which has the full report and environment details.

Desired Behavior

fable is offered in the ACP Claude Code model suggestions.

This covers only the SDK part: adding ACPModelOption(id="fable", label="Claude Fable") to _CLAUDE_MODELS, as was done for claude-opus-5 in #4326.

Acceptance Criteria

• fable appears in the ACP Claude Code model picker suggestions list.

Alternatives Considered

Setting acp_model: "fable" explicitly already works, but the model isn't discoverable through the picker suggestions without this change.

Priority / Severity

Medium - Would improve experience

Estimated Scope

Small - API addition, config option, or minor change

Feature Area

• Other

Technical Implementation Ideas (Optional)

PR #4437 already implements this; it was blocked by PR description validation because it linked only the cross-repo OpenHands/OpenHands issue.

Additional Context

Feature area: ACP (Agent Client Protocol) integration, specifically acp_providers.py.

Start in acp_providers.py and inspect the static _CLAUDE_MODELS list, then compare the addition made for claude-opus-5 in #4326. Add the fable model option with the requested label; the work is done when fable appears in the ACP Claude Code model picker suggestions.