feat: implement usage tracking for AI requests

Adds local token usage tracking for all AI providers. Usage data is
captured during stream processing and stored in a local database.
Includes a new Usage tab in the Providers dashboard to visualize
historical token consumption.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

open-sse/handlers/chatCore.js

@@ -8,6 +8,46 @@ import { createRequestLogger } from "../utils/requestLogger.js";
 import { getModelTargetFormat, PROVIDER_ID_TO_ALIAS } from "../config/providerModels.js";
 import { createErrorResult, parseUpstreamError, formatProviderError } from "../utils/error.js";
 import { handleBypassRequest } from "../utils/bypassHandler.js";
+import { saveRequestUsage } from "@/lib/usageDb.js";
+
+/**
+ * Extract usage from non-streaming response body
+ * Handles different provider response formats
+ */
+function extractUsageFromResponse(responseBody, provider) {
+  if (!responseBody) return null;
+
+  // OpenAI format
+  if (responseBody.usage) {
+    return {
+      prompt_tokens: responseBody.usage.prompt_tokens || 0,
+      completion_tokens: responseBody.usage.completion_tokens || 0,
+      cached_tokens: responseBody.usage.prompt_tokens_details?.cached_tokens,
+      reasoning_tokens: responseBody.usage.completion_tokens_details?.reasoning_tokens
+    };
+  }
+
+  // Claude format
+  if (responseBody.usage?.input_tokens !== undefined || responseBody.usage?.output_tokens !== undefined) {
+    return {
+      prompt_tokens: responseBody.usage.input_tokens || 0,
+      completion_tokens: responseBody.usage.output_tokens || 0,
+      cache_read_input_tokens: responseBody.usage.cache_read_input_tokens,
+      cache_creation_input_tokens: responseBody.usage.cache_creation_input_tokens
+    };
+  }
+
+  // Gemini format
+  if (responseBody.usageMetadata) {
+    return {
+      prompt_tokens: responseBody.usageMetadata.promptTokenCount || 0,
+      completion_tokens: responseBody.usageMetadata.candidatesTokenCount || 0,
+      reasoning_tokens: responseBody.usageMetadata.thoughtsTokenCount
+    };
+  }
+
+  return null;
+}
 
 /**
  * Core chat handler - shared between SSE and Worker
@@ -20,8 +60,9 @@ import { handleBypassRequest } from "../utils/bypassHandler.js";
  * @param {function} options.onCredentialsRefreshed - Callback when credentials are refreshed
  * @param {function} options.onRequestSuccess - Callback when request succeeds (to clear error status)
  * @param {function} options.onDisconnect - Callback when client disconnects
+ * @param {string} options.connectionId - Connection ID for usage tracking
  */
-export async function handleChatCore({ body, modelInfo, credentials, log, onCredentialsRefreshed, onRequestSuccess, onDisconnect, clientRawRequest }) {
+export async function handleChatCore({ body, modelInfo, credentials, log, onCredentialsRefreshed, onRequestSuccess, onDisconnect, clientRawRequest, connectionId }) {
   const { provider, model } = modelInfo;
 
   const sourceFormat = detectFormat(body);
@@ -220,12 +261,29 @@ export async function handleChatCore({ body, modelInfo, credentials, log, onCred
   // Non-streaming response
   if (!stream) {
     const responseBody = await providerResponse.json();
-    
+
     // Notify success - caller can clear error status if needed
     if (onRequestSuccess) {
       await onRequestSuccess();
     }
-    
+
+    // Log usage for non-streaming responses
+    const usage = extractUsageFromResponse(responseBody, provider);
+    if (usage) {
+      const msg = `[${new Date().toLocaleTimeString("en-US", { hour12: false, hour: "2-digit", minute: "2-digit" })}] 📊 [USAGE] ${provider.toUpperCase()} | in=${usage.prompt_tokens || 0} | out=${usage.completion_tokens || 0}${connectionId ? ` | account=${connectionId.slice(0, 8)}...` : ""}`;
+      console.log(`${COLORS.green}${msg}${COLORS.reset}`);
+
+      saveRequestUsage({
+        provider: provider || "unknown",
+        model: model || "unknown",
+        tokens: usage,
+        timestamp: new Date().toISOString(),
+        connectionId: connectionId || undefined
+      }).catch(err => {
+        console.error("Failed to save usage stats:", err.message);
+      });
+    }
+
     return {
       success: true,
       response: new Response(JSON.stringify(responseBody), {
@@ -254,9 +312,9 @@ export async function handleChatCore({ body, modelInfo, credentials, log, onCred
   // Create transform stream with logger for streaming response
   let transformStream;
   if (needsTranslation(targetFormat, sourceFormat)) {
-    transformStream = createSSETransformStreamWithLogger(targetFormat, sourceFormat, provider, reqLogger, toolNameMap);
+    transformStream = createSSETransformStreamWithLogger(targetFormat, sourceFormat, provider, reqLogger, toolNameMap, model, connectionId);
   } else {
-    transformStream = createPassthroughStreamWithLogger(provider, reqLogger);
+    transformStream = createPassthroughStreamWithLogger(provider, reqLogger, model, connectionId);
   }
 
   // Pipe response through transform with disconnect detection