feat(mcp-server): add nexus_vision tool and fix upload MIME detection

- New tool nexus_vision: describe an image via a vision chat model
  (default google/gemini-3.1-flash-lite) and record result in journal.
- NordRouter /media/upload now detects MIME from file extension so
  data: URLs use the correct type (fixes HTTP 415 for images/audio/video).
- HttpClient supports FormData bodies (undici) for future multipart use.

NexusAI/packages/mcp-server/src/handlers.ts

@@ -1,11 +1,13 @@
 import { randomUUID } from 'crypto';
 import {
   NexusError,
+  NordRouterClient,
   buildEmbeddedContent,
   createLogger,
   type Capability,
   type MediaResult,
 } from '@nexusai/core';
+import * as fs from 'fs';
 import type { AppContext } from './context.js';
 import {
   ImageSchema,
@@ -17,6 +19,7 @@ import {
   TtsSchema,
   UsageStatsSchema,
   VideoSchema,
+  VisionSchema,
   WebSearchSchema,
 } from './schemas.js';
 
@@ -70,6 +73,8 @@ export class Handlers {
         return this.upload(MediaUploadSchema.parse(args));
       case 'nexus_usage_stats':
         return this.usage(UsageStatsSchema.parse(args));
+      case 'nexus_vision':
+        return this.vision(VisionSchema.parse(args));
       default:
         throw new NexusError('NOT_FOUND', `Unknown tool: ${name}`);
     }
@@ -273,4 +278,90 @@ export class Handlers {
     log.debug('usage stats requested');
     return { content: [jsonBlock(payload)] };
   }
+
+  private async vision(args: {
+    provider?: string;
+    image: string;
+    prompt: string;
+    model?: string;
+  }): Promise<McpResult> {
+    const providerName = this.providerName(args.provider);
+    const row = this.ctx.providersStore.get(providerName);
+    const apiKey = this.ctx.providersStore.getApiKey(providerName);
+    const baseUrl = row?.baseUrl || process.env[`${providerName.toUpperCase()}_BASE_URL`] || 'https://nordrouter.com';
+    if (!apiKey) {
+      throw new NexusError('CONFIG', `No API key for provider "${providerName}"`);
+    }
+
+    let imageUrl = args.image;
+    if (!args.image.startsWith('http') && !args.image.startsWith('data:')) {
+      if (!fs.existsSync(args.image)) {
+        throw new NexusError('IO', `Image file not found: ${args.image}`);
+      }
+      const buf = fs.readFileSync(args.image);
+      const ext = args.image.split('.').pop()?.toLowerCase() || 'png';
+      const mime = ext === 'jpg' || ext === 'jpeg' ? 'image/jpeg' : ext === 'webp' ? 'image/webp' : 'image/png';
+      imageUrl = `data:${mime};base64,${buf.toString('base64')}`;
+    }
+
+    const client = new NordRouterClient(apiKey, baseUrl);
+    const started = Date.now();
+    const id = randomUUID();
+    const model = args.model || 'google/gemini-3.1-flash-lite';
+
+    try {
+      const res = await client.http.requestJson<{
+        choices?: Array<{ message?: { content?: string } }>;
+        usage?: { total_cost?: number };
+      }>({
+        method: 'POST',
+        path: '/v1/chat/completions',
+        body: {
+          model,
+          messages: [
+            {
+              role: 'user',
+              content: [
+                { type: 'text', text: args.prompt },
+                { type: 'image_url', image_url: { url: imageUrl } },
+              ],
+            },
+          ],
+        },
+      });
+      const text = res.choices?.[0]?.message?.content?.trim() || '';
+      this.ctx.journal.record({
+        id,
+        provider: providerName,
+        capability: 'vision',
+        model,
+        inputSummary: summarize({ prompt: args.prompt, image: args.image }),
+        status: 'done',
+        costUsd: res.usage?.total_cost ?? null,
+        filePath: null,
+        resultUrl: null,
+        error: null,
+        durationMs: Date.now() - started,
+        createdAt: new Date().toISOString(),
+      });
+      return { content: [jsonBlock({ provider: providerName, model, description: text })] };
+    } catch (err) {
+      const e = NexusError.from(err);
+      this.ctx.journal.record({
+        id,
+        provider: providerName,
+        capability: 'vision',
+        model,
+        inputSummary: summarize({ prompt: args.prompt, image: args.image }),
+        status: 'failed',
+        costUsd: null,
+        filePath: null,
+        resultUrl: null,
+        error: `${e.code}: ${e.message}`,
+        durationMs: Date.now() - started,
+        createdAt: new Date().toISOString(),
+      });
+      throw e;
+    }
+  }
 }

NexusAI/packages/mcp-server/src/schemas.ts

@@ -112,6 +112,19 @@ export const WebSearchSchema = z.object({
   maxResults: z.number().int().positive().max(50).optional(),
 });
 
+export const VisionSchema = z.object({
+  provider,
+  image: z.string().describe('Image URL, local file path, or base64/data-URL.'),
+  prompt: z
+    .string()
+    .default('Describe the scene in this image in detail, as if writing a prompt for video generation.')
+    .describe('What to ask the vision model about the image.'),
+  model: z
+    .string()
+    .optional()
+    .describe('Vision-capable chat model, e.g. google/gemini-3.1-flash-lite, openai/gpt-5.4-mini.'),
+});
+
 export const MediaModelsSchema = z.object({
   provider,
   type: z.enum(['image', 'video', 'music', 'audio', 'upscale']).optional().describe('Filter by model type.'),

NexusAI/packages/mcp-server/src/tools.ts

@@ -9,6 +9,7 @@ import {
   TtsSchema,
   UsageStatsSchema,
   VideoSchema,
+  VisionSchema,
   WebSearchSchema,
 } from './schemas.js';
 
@@ -75,4 +76,9 @@ export const TOOLS: ToolDef[] = [
     'Show usage and spend recorded in the local journal (totals by provider, capability, day) and optionally recent generations.',
     UsageStatsSchema
   ),
+  make(
+    'nexus_vision',
+    'Describe an image using a vision-capable chat model. Returns a text description useful for prompts.',
+    VisionSchema
+  ),
 ];