Add current-generation Gemini models to AIModel and deprecate the 2.x members (#366)

Google has withdrawn most of the Gemini 2.x generation. A `hint` naming one of
those models made `ai.prompt()` fail outright, and the speed/cost tiers that
resolve without a hint pointed at several of them too, so `{ speed: "capable",
cost: "high" }` and neighbouring tiers stopped working.

Adds `GEMINI_31_PRO`, `GEMINI_35_FLASH`, and `GEMINI_35_FLASH_LITE`, and marks
the `GEMINI_25_*` and `GEMINI_20_*` members deprecated. The deprecated members
are kept so twists built against an earlier SDK version still compile, and a
hint naming a withdrawn model is now served by its current equivalent instead
of erroring.

`GEMINI_25_FLASH` is deprecated but not remapped: it still works, and silently
substituting a model an author deliberately asked for would be worse than
letting it run until it is actually withdrawn.


Claude-Session: https://claude.ai/code/session_01Y9GNwKEBkEAoLYzkTngfGk

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

Author: KrisBraun

.changeset/gemini-3-model-refresh.md

@@ -0,0 +1,16 @@
+---
+"@plotday/twister": minor
+---
+
+Added: `AIModel.GEMINI_31_PRO`, `AIModel.GEMINI_35_FLASH`, and
+`AIModel.GEMINI_35_FLASH_LITE` for the current generation of Gemini models.
+
+Deprecated: the `GEMINI_25_*` and `GEMINI_20_*` members. Google has withdrawn
+most of that generation, so a `hint` naming one of them previously failed the
+whole `ai.prompt()` call. The members still exist and still compile, and a hint
+naming a withdrawn model is now served by its current equivalent instead of
+erroring — but new code should name a 3.x member.
+
+The speed/cost tiers that `ai.prompt()` resolves without a hint have also moved
+onto current models, so `{ speed: "capable", cost: "high" }` and the other tiers
+that previously mapped to withdrawn Gemini models work again.

twister/src/tools/ai.ts

@@ -188,13 +188,13 @@ export type AICapabilities = {
  *   prompt: "Summarize this in one sentence: ..."
  * });
  *
- * // Balanced performance - uses GPT-5 Mini or Gemini 2.5 Flash
+ * // Balanced performance - uses GPT-5 Mini or Gemini 3.5 Flash
  * const response = await ai.prompt({
  *   model: { speed: "balanced", cost: "medium" },
  *   prompt: "Analyze this data..."
  * });
  *
- * // Most capable - uses models like GPT-5, Claude Sonnet 4.6, or Gemini 2.5 Pro
+ * // Most capable - uses models like GPT-5, Claude Sonnet 4.6, or Gemini 3.1 Pro
  * const response = await ai.prompt({
  *   model: { speed: "capable", cost: "high" },
  *   prompt: "Solve this complex reasoning problem..."
@@ -256,11 +256,26 @@ export enum AIModel {
   CLAUDE_SONNET_46 = "anthropic/claude-sonnet-4-6",
   CLAUDE_HAIKU_45 = "anthropic/claude-haiku-4-5",
 
-  // Google models - Gemini 2.x series
+  // Google models - Gemini 3.x series
+  GEMINI_31_PRO = "google/gemini-3.1-pro-preview",
+  GEMINI_35_FLASH = "google/gemini-3.5-flash",
+  GEMINI_35_FLASH_LITE = "google/gemini-3.5-flash-lite",
+
+  // Google models - Gemini 2.x series (superseded)
+  //
+  // Google has withdrawn most of this generation. The members are kept so that
+  // twists built against an earlier SDK version still compile, and a hint
+  // naming a withdrawn model is transparently served by its 3.x equivalent
+  // rather than failing — but new code should name a 3.x member directly.
+  /** @deprecated Withdrawn by Google. Use {@link AIModel.GEMINI_31_PRO}. */
   GEMINI_25_PRO = "google/gemini-2.5-pro",
+  /** @deprecated Superseded. Use {@link AIModel.GEMINI_35_FLASH}. */
   GEMINI_25_FLASH = "google/gemini-2.5-flash",
+  /** @deprecated Withdrawn by Google. Use {@link AIModel.GEMINI_35_FLASH_LITE}. */
   GEMINI_25_FLASH_LITE = "google/gemini-2.5-flash-lite",
+  /** @deprecated Withdrawn by Google. Use {@link AIModel.GEMINI_35_FLASH}. */
   GEMINI_20_FLASH = "google/gemini-2.0-flash",
+  /** @deprecated Withdrawn by Google. Use {@link AIModel.GEMINI_35_FLASH_LITE}. */
   GEMINI_20_FLASH_LITE = "google/gemini-2.0-flash-lite",
 
   // Cloudflare Workers AI models - Free/low-cost models running on Cloudflare's network