[ProfSynapse]

Summary

Makes Nano Banana 2.1 (gemini-nano-banana-2.1) the default image model on Google direct and OpenRouter. Google recommends it over Nano Banana 2 (gemini-3.1-flash-image, now deprecated with no shutdown date) at half the price.

• The default was repeated as a literal in a dozen places (settings defaults, both adapters, chat settings, defaults resolver, generateImage fallbacks). It is now a single constant, DEFAULT_IMAGE_MODEL.
• Nano Banana 2.1 is first in the Google and OpenRouter image catalogs, which is what the generateImage tool and the chat picker fall back to. Google's first entry was Nano Banana 2 Lite, so the tool's no-model fallback silently used Lite.
• Saved image choices are unchanged; only fresh installs and unset fallbacks move.
• Adds a gated paid smoke lane, tests/debug/image-generation-live-smoke.test.ts, that generates with the default and no model override through the shipped adapters.

Test plan

• Live (paid, one image each): Google direct POST …/models/gemini-nano-banana-2.1:generateContent 200 → 1K JPEG; OpenRouter POST /api/v1/images 200 → 1K JPEG. This also settles that Nano Banana 2.1 still works over generateContent.
• New DefaultImageModel.test.ts: shipped settings, both catalogs' first entry and the constant agree
• Tests that pinned the old default updated deliberately (Gemini and OpenRouter adapter request shape and fallback)
• npm run build (schemas regenerated), full Jest 6,628 passing, registry gate google/openrouter

🤖 Generated with Claude Code