feat: add MiniMax image generation provider

[ejimenezc93]

Summary

Adds an image_gen backend for the MiniMax Token Plan / Subscription API
(POST https://api.minimax.io/v1/image_generation, model image-01).

Hermes ships with fal, krea, openai, openai-codex, openrouter,
and xai for image generation, but MiniMax Plus subscribers don't have
a backend that consumes their bundled Token Plan credits.

Changes

• New plugin: plugins/image_gen/minimax/ (__init__.py, plugin.yaml)
• New tests: tests/plugins/image_gen/test_minimax_provider.py (38 tests)

Features

• text-to-image
• image-to-image via subject_reference (single reference image)
• Signed response URLs cached locally via save_url_image
• Aspect ratio mapping (landscape/square/portrait → 16:9/1:1/9:16)
• MiniMax business-error handling (base_resp.status_code)
• HTTP non-2xx error mapping
• Empty-prompt validation
• Model override via MINIMAX_IMAGE_MODEL or image_gen.minimax.model
• Base URL override via MINIMAX_BASE_URL (env-only, for tests)

Auth

MINIMAX_API_KEY env var (Subscription Key, sk-cp-...). Falls back to
MINIMAX_SUBSCRIPTION_KEY / MINIMAX_SUBS_KEY.

Verification

• python -m pytest tests/plugins/image_gen/test_minimax_provider.py -v → 38 passed
• python -m py_compile plugins/image_gen/minimax/__init__.py tests/plugins/image_gen/test_minimax_provider.py → OK
• Live end-to-end: provider.generate(...) returns success with a cached local JPEG
  on Windows 11 / Python 3.11 / real MiniMax API.

[alt-glitch]

This was generated by AI during triage.

Duplicate of #25451 (the earliest open MiniMax image_gen plugin at the same plugins/image_gen/minimax/ path). Same feature and same dedicated ImageGenProvider approach; #47660 is also tracked against #25451. Related: #44167 (Chinese image-gen provider feature request). Leaving open for the maintainer to pick the canonical PR from the cluster.

[teknium1]

Thanks for the MiniMax image-generation implementation and the dedicated provider tests.

This automated hermes-sweeper review is closing the PR under the standing in-tree-provider-integration policy: third-party vendor integrations must be published as standalone plugins rather than as new directories in the repository's plugins/ tree.

• This PR adds the MiniMax-specific backend at plugins/image_gen/minimax/__init__.py and its bundled manifest at plugins/image_gen/minimax/plugin.yaml (PR head 2f236afe3727).
• Hermes supports the intended extension path: image providers register through ImageGenProvider / ctx.register_image_gen_provider(...), with user-installed backends at ~/.hermes/plugins/image_gen/<name>/ or pip entry points (website/docs/developer-guide/image-gen-provider-plugin.md:17-25).
• The duplicate discussion is useful context: the earlier MiniMax implementation, feat(image-gen): add MiniMax image-01 backend plugin #25451, was resolved under this same maintenance-boundary policy.

Please publish or continue this as a standalone MiniMax image-generation plugin repository and share it in #plugins-skills-and-skins.

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Automated hermes-sweeper review; closed as not planned under standing policy in-tree-provider-integration. This is a maintenance-boundary decision, not a judgment of the implementation's quality.

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Closed as not-planned per standing maintainer policy (in-tree-provider-integration). This is a design-direction decision, not a code-quality judgment — see the Contribution Rubric in AGENTS.md for what the project is looking for. If you believe this policy was misapplied to your change, comment here and a maintainer will take a look.