Expose and forward img-forge params: aspect_ratio, image_size, model

[stackbilt-admin]

Problem

Downstream consumers connecting through stackbilt-mcp-gateway do not see newly exposed img-forge generation params (aspect_ratio, image_size, model) even after reconnects.

img-forge is already updated/deployed, but the consumer-facing tool schema appears stale and/or wrapper forwarding is incomplete at the gateway layer.

Why this matters

Tarot/deck workflows require deterministic portrait generation and model control:

• aspect_ratio: "2:3"
• image_size: "2K"
• model: "gemini-3-pro-image-preview" (or tier ultra_plus)

Without explicit schema + pass-through, clients silently default to square outputs and can’t reliably use the intended Gemini path.

Required Fix (Gateway-side)

1) Tool schema exposure

Update the generate_image (or equivalent proxied img-forge tool) schema in stackbilt-mcp-gateway to expose:

• aspect_ratio: enum
  • 1:1, 3:2, 2:3, 3:4, 4:3, 4:5, 5:4, 9:16, 16:9, 21:9
• image_size: enum
  • 512, 1K, 2K, 4K
• model: enum
  • gemini-3.1-flash-image-preview
  • gemini-3-pro-image-preview

Keep existing fields unchanged (prompt, quality_tier, negative_prompt, seed, etc.).

2) Request forwarding

Ensure all three fields are forwarded unchanged to img-forge /v2/generate:

• aspect_ratio
• image_size
• model

No local remapping that drops/overwrites them.

3) Tier/model quota correctness

If model is set, map it to effective tier for quota/audit consistency:

• gemini-3.1-flash-image-preview -> ultra
• gemini-3-pro-image-preview -> ultra_plus

4) Tool list refresh behavior

If gateway caches upstream tool definitions:

• invalidate/rebuild cache on deploy
• emit notifications/tools/list_changed when schema changes

Acceptance Criteria

• New MCP session to stackbilt-mcp-gateway shows tool args including aspect_ratio, image_size, model.
• Tool call with:
  • quality_tier: "ultra_plus"
  • aspect_ratio: "2:3"
  • image_size: "2K"
  • model: "gemini-3-pro-image-preview"
    succeeds and reaches img-forge unchanged.
• Audit/quota reflects ultra_plus when model=gemini-3-pro-image-preview.
• Reconnect-only and fresh-add client paths both receive updated schema.

Validation Checklist

• tools/list at gateway includes new properties
• one smoke generation call with 2:3 + 2K + gemini-3-pro-image-preview
• verify downstream consumer sees updated schema without manual JSON hacks
• verify no regressions for existing clients using only quality_tier

Context

img-forge MCP + gateway are already deployed with support for these params. The missing link is the Stackbilder-facing MCP gateway schema/forwarding path.