feat: add image generation support (gemini-3.1-flash-image)

README.md

@@ -122,6 +122,7 @@ opencode run "Hello" --model=google/antigravity-claude-opus-4-6-thinking --varia
 | `antigravity-gemini-3-flash` | minimal, low, medium, high | Gemini 3 Flash with thinking |
 | `antigravity-claude-sonnet-4-6` | — | Claude Sonnet 4.6 |
 | `antigravity-claude-opus-4-6-thinking` | low, max | Claude Opus 4.6 with extended thinking |
+| `antigravity-gemini-3.1-flash-image` | minimal, high | Gemini 3.1 Flash image generation |
 
 **Gemini CLI quota** (separate from Antigravity; used when `cli_first` is true or as fallback):
 
@@ -148,6 +149,30 @@ opencode run "Hello" --model=google/antigravity-claude-opus-4-6-thinking --varia
 
 For details on variant configuration and thinking levels, see [docs/MODEL-VARIANTS.md](docs/MODEL-VARIANTS.md).
 
+**Image generation:**
+
+Select an image model and include your prompt. Images are saved to `./nanobanana/` in your project directory.
+
+```bash
+opencode run "a realistic animal sitting by a window, soft streetlight, bokeh" --model=google/antigravity-gemini-3.1-flash-image
+```
+
+Use `--resolution` and `--aspect-ratio` flags inline to override defaults:
+
+```bash
+# 4K resolution with 16:9 aspect ratio
+opencode run "mountain landscape --resolution=4K --aspect-ratio=16:9" --model=google/antigravity-gemini-3.1-flash-image
+```
+
+Flags are stripped from the prompt before sending to Gemini. Defaults can also be set via environment variables:
+
+| Flag / Env Var | Values | Default |
+|----------------|--------|---------|
+| `--resolution` / `OPENCODE_IMAGE_SIZE` | `0.5K`\*, `1K`, `2K`, `4K` | `1K` |
+| `--aspect-ratio` / `OPENCODE_IMAGE_ASPECT_RATIO` | `1:1`, `2:3`, `3:2`, `3:4`, `4:3`, `4:5`, `5:4`, `9:16`, `16:9`, `21:9`, `4:1`\*, `8:1`\* | `1:1` |
+
+\* `0.5K` and extended aspect ratios (`4:1`, `8:1`) are only supported by `gemini-3.1-flash-image`.
+
 <details>
 <summary><b>Full models configuration (copy-paste ready)</b></summary>
 
@@ -203,6 +228,15 @@ Add this to your `~/.config/opencode/opencode.json`:
             "max": { "thinkingConfig": { "thinkingBudget": 32768 } }
           }
         },
+        "antigravity-gemini-3.1-flash-image": {
+          "name": "Gemini 3.1 Flash Image (Antigravity)",
+          "limit": { "context": 131072, "output": 32768 },
+          "modalities": { "input": ["text", "image", "pdf"], "output": ["text", "image"] },
+          "variants": {
+            "minimal": { "thinkingLevel": "minimal" },
+            "high": { "thinkingLevel": "high" }
+          }
+        },
         "gemini-2.5-flash": {
           "name": "Gemini 2.5 Flash (Gemini CLI)",
           "limit": { "context": 1048576, "output": 65536 },

src/plugin/accounts.test.ts

@@ -1163,18 +1163,18 @@ describe("AccountManager", () => {
       const manager = new AccountManager(undefined, stored);
       const account = manager.getCurrentOrNextForFamily("gemini");
 
-      manager.markRateLimited(account!, 30000, "gemini", "antigravity", "gemini-3-pro-image");
+      manager.markRateLimited(account!, 30000, "gemini", "antigravity", "gemini-3.1-flash-image");
 
       expect(
         manager.getMinWaitTimeForFamily(
           "gemini",
-          "gemini-3-pro-image",
+          "gemini-3.1-flash-image",
           "antigravity",
           true,
         ),
       ).toBe(30000);
 
-      expect(manager.getMinWaitTimeForFamily("gemini", "gemini-3-pro-image")).toBe(0);
+      expect(manager.getMinWaitTimeForFamily("gemini", "gemini-3.1-flash-image")).toBe(0);
     });
 
     describe("parseRateLimitReason", () => {

src/plugin/config/models.test.ts

@@ -19,6 +19,7 @@ describe("OPENCODE_MODEL_DEFINITIONS", () => {
       "antigravity-claude-sonnet-4-6",
       "antigravity-gemini-3-flash",
       "antigravity-gemini-3-pro",
+      "antigravity-gemini-3.1-flash-image",
       "antigravity-gemini-3.1-pro",
       "gemini-2.5-flash",
       "gemini-2.5-pro",

src/plugin/config/models.ts

@@ -67,6 +67,18 @@ export const OPENCODE_MODEL_DEFINITIONS: OpencodeModelDefinitions = {
       high: { thinkingLevel: "high" },
     },
   },
+  "antigravity-gemini-3.1-flash-image": {
+    name: "Gemini 3.1 Flash Image (Antigravity)",
+    limit: { context: 131072, output: 32768 },
+    modalities: {
+      input: ["text", "image", "pdf"],
+      output: ["text", "image"],
+    },
+    variants: {
+      minimal: { thinkingLevel: "minimal" },
+      high: { thinkingLevel: "high" },
+    },
+  },
   "antigravity-claude-sonnet-4-6": {
     name: "Claude Sonnet 4.6 (Antigravity)",
     limit: { context: 200000, output: 64000 },

src/plugin/image-saver.ts

@@ -2,19 +2,18 @@
  * Image Saving Utility
  * 
  * Handles saving generated images to disk and returning file paths.
+ * Images are saved to ./nanobanana/ relative to the current working directory.
  */
 
 import * as fs from 'fs';
 import * as path from 'path';
-import * as os from 'os';
 
 /**
  * Default directory for saving generated images.
- * Uses ~/.opencode/generated-images/
+ * Uses ./nanobanana/ relative to the current working directory (process.cwd()).
  */
 function getImageOutputDir(): string {
-  const homeDir = os.homedir();
-  const outputDir = path.join(homeDir, '.opencode', 'generated-images');
+  const outputDir = path.join(process.cwd(), 'nanobanana');
 
   // Create directory if it doesn't exist
   if (!fs.existsSync(outputDir)) {

src/plugin/request.ts

@@ -58,7 +58,8 @@ import {
   needsThinkingRecovery,
 } from "./thinking-recovery";
 import { sanitizeCrossModelPayloadInPlace } from "./transform/cross-model-sanitizer";
-import { isGemini3Model, isImageGenerationModel, buildImageGenerationConfig, applyGeminiTransforms } from "./transform";
+import { isGemini3Model, isImageGenerationModel, isFlashImageModel, buildImageGenerationConfig, applyGeminiTransforms } from "./transform";
+import { parsePromptFlags, extractLastUserPrompt } from "./transform/prompt-flags";
 import {
   resolveModelWithTier,
   resolveModelWithVariant,
@@ -956,25 +957,58 @@ export function prepareAntigravityRequest(
         }
 
         // Resolve thinking configuration based on user settings and model capabilities
-        // Image generation models don't support thinking - skip thinking config entirely
+        // Pro image models don't support thinking. Flash image models support minimal/high.
         const isImageModel = isImageGenerationModel(effectiveModel);
-        const userThinkingConfig = isImageModel ? undefined : extractThinkingConfig(requestPayload, rawGenerationConfig, extraBody);
+        const isFlashImage = isImageModel && isFlashImageModel(effectiveModel);
+        const skipThinkingForImage = isImageModel && !isFlashImage;
+        const userThinkingConfig = skipThinkingForImage ? undefined : extractThinkingConfig(requestPayload, rawGenerationConfig, extraBody);
         const hasAssistantHistory = Array.isArray(requestPayload.contents) &&
           requestPayload.contents.some((c: any) => c?.role === "model" || c?.role === "assistant");
 
         // Claude Sonnet 4.6 is non-thinking only.
         // Ignore any client-provided thinkingConfig for this model.
         const lowerEffective = effectiveModel.toLowerCase();
         const isClaudeSonnetNonThinking = lowerEffective === "claude-sonnet-4-6";
-        const effectiveUserThinkingConfig = (isClaudeSonnetNonThinking || isImageModel) ? undefined : userThinkingConfig;
+        const effectiveUserThinkingConfig = (isClaudeSonnetNonThinking || skipThinkingForImage) ? undefined : userThinkingConfig;
 
-        // For image models, add imageConfig instead of thinkingConfig
+        // For image models, add imageConfig (and optionally thinkingConfig for flash-image)
         if (isImageModel) {
-          const imageConfig = buildImageGenerationConfig();
+          // Parse --resolution and --aspect-ratio flags from the last user prompt
+          let imageConfigOverrides: { aspectRatio?: string; imageSize?: string } | undefined;
+          if (Array.isArray(requestPayload.contents)) {
+            const lastPrompt = extractLastUserPrompt(requestPayload.contents as unknown[]);
+            if (lastPrompt) {
+              const parsed = parsePromptFlags(lastPrompt.text);
+              if (parsed.resolution || parsed.aspectRatio) {
+                imageConfigOverrides = {
+                  imageSize: parsed.resolution,
+                  aspectRatio: parsed.aspectRatio,
+                };
+                // Replace prompt text with flags stripped out
+                const content = (requestPayload.contents as any[])[lastPrompt.contentIndex];
+                if (content?.parts?.[lastPrompt.partIndex]) {
+                  content.parts[lastPrompt.partIndex].text = parsed.cleanedPrompt;
+                }
+                log.debug(`[image] Parsed prompt flags: resolution=${parsed.resolution ?? "default"}, aspectRatio=${parsed.aspectRatio ?? "default"}`);
+              }
+            }
+          }
+
+          const imageConfig = buildImageGenerationConfig(effectiveModel, imageConfigOverrides);
           const generationConfig = (rawGenerationConfig ?? {}) as Record<string, unknown>;
           generationConfig.imageConfig = imageConfig;
-          // Remove any thinkingConfig that might have been set
-          delete generationConfig.thinkingConfig;
+
+          // Flash image models support thinking (minimal/high)
+          if (isFlashImage && resolved.isThinkingModel && resolved.thinkingLevel) {
+            generationConfig.thinkingConfig = {
+              includeThoughts: true,
+              thinkingLevel: resolved.thinkingLevel,
+            };
+          } else {
+            // Remove any thinkingConfig for non-thinking image models
+            delete generationConfig.thinkingConfig;
+          }
+
           // Set reasonable defaults for image generation
           if (!generationConfig.candidateCount) {
             generationConfig.candidateCount = 1;
@@ -1750,6 +1784,22 @@ export async function transformAntigravityResponse(
           headers.set("x-antigravity-context-error", "tool_pairing");
         }
 
+        // Detect imageSize / imageConfig errors from Antigravity API
+        // If the endpoint doesn't support imageSize, strip it and let the user know
+        if (
+          response.status === 400 &&
+          (errorMessage.includes("imagesize") ||
+           errorMessage.includes("image_size") ||
+           (errorMessage.includes("imageconfig") && errorMessage.includes("invalid")))
+        ) {
+          headers.set("x-antigravity-image-error", "imagesize_unsupported");
+          console.warn(
+            `[image] imageSize rejected by API (model: ${effectiveModel || "unknown"}). ` +
+            `The Antigravity endpoint may not support imageSize for this model. ` +
+            `Unset OPENCODE_IMAGE_SIZE to use the default 1K resolution.`
+          );
+        }
+
         return new Response(JSON.stringify(errorBody), {
           status: response.status,
           statusText: response.statusText,