diff --git a/src/index.ts b/src/index.ts
index 2a92092..86bfa81 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -417,13 +417,25 @@ function getFlag(args: string[], flag: string): string | undefined {
 }
 
 function createVisionModel(config: VisionConfig) {
-  const headers: Record<string, string> = {
-    'x-langfuse-tags': 'skill:video-product-snapshot',
+  const sessionId = config.sessionId || '';
+  const originFetch = globalThis.fetch;
+  // Inject metadata.session_id into request body so LiteLLM → Langfuse creates sessions
+  const wrapped = async (input: RequestInfo | URL, init?: RequestInit) => {
+    if (init?.body && typeof init.body === 'string') {
+      try {
+        const body = JSON.parse(init.body);
+        if (!body.metadata) body.metadata = {};
+        if (!body.metadata.session_id) body.metadata.session_id = sessionId;
+        body.metadata.tags = ['skill:video-product-snapshot'];
+        init = { ...init, body: JSON.stringify(body) };
+      } catch {}
+    }
+    return originFetch(input, init);
   };
-  if (config.sessionId) {
-    headers['x-langfuse-session-id'] = config.sessionId;
-  }
-  const openai = createOpenAI({ apiKey: config.apiKey, baseURL: config.baseURL, headers });
+  const openai = createOpenAI({
+    apiKey: config.apiKey, baseURL: config.baseURL,
+    fetch: wrapped as typeof globalThis.fetch,
+  });
   return openai(config.model);
 }
 
diff --git a/src/post-filter.ts b/src/post-filter.ts
index b87e8b0..f667fab 100644
--- a/src/post-filter.ts
+++ b/src/post-filter.ts
@@ -34,13 +34,24 @@ const FILTER_PROMPT = (count: number, description?: string) => {
 };
 
 function createModel(config: VisionConfig) {
-  const headers: Record<string, string> = {
-    'x-langfuse-tags': 'skill:video-product-snapshot',
+  const sessionId = config.sessionId || '';
+  const originFetch = globalThis.fetch;
+  const wrapped = async (input: RequestInfo | URL, init?: RequestInit) => {
+    if (init?.body && typeof init.body === 'string') {
+      try {
+        const body = JSON.parse(init.body);
+        if (!body.metadata) body.metadata = {};
+        if (!body.metadata.session_id) body.metadata.session_id = sessionId;
+        body.metadata.tags = ['skill:video-product-snapshot'];
+        init = { ...init, body: JSON.stringify(body) };
+      } catch {}
+    }
+    return originFetch(input, init);
   };
-  if (config.sessionId) {
-    headers['x-langfuse-session-id'] = config.sessionId;
-  }
-  const provider = createOpenAI({ apiKey: config.apiKey, baseURL: config.baseURL, headers });
+  const provider = createOpenAI({
+    apiKey: config.apiKey, baseURL: config.baseURL,
+    fetch: wrapped as typeof globalThis.fetch,
+  });
   return provider(config.model);
 }
 
diff --git a/src/product-detector.ts b/src/product-detector.ts
index 1e971aa..68d3eeb 100644
--- a/src/product-detector.ts
+++ b/src/product-detector.ts
@@ -78,13 +78,24 @@ Return:
 - boundingBox: tight box of the PRODUCT ONLY as [x1, y1, x2, y2] normalized 0.0–1.0, top-left origin. Exclude hands, background, and unrelated objects. The product is near the center of the frame.`;
 
 function createVisionModel(config: VisionConfig) {
-  const headers: Record<string, string> = {
-    'x-langfuse-tags': 'skill:video-product-snapshot',
+  const sessionId = config.sessionId || '';
+  const originFetch = globalThis.fetch;
+  const wrapped = async (input: RequestInfo | URL, init?: RequestInit) => {
+    if (init?.body && typeof init.body === 'string') {
+      try {
+        const body = JSON.parse(init.body);
+        if (!body.metadata) body.metadata = {};
+        if (!body.metadata.session_id) body.metadata.session_id = sessionId;
+        body.metadata.tags = ['skill:video-product-snapshot'];
+        init = { ...init, body: JSON.stringify(body) };
+      } catch {}
+    }
+    return originFetch(input, init);
   };
-  if (config.sessionId) {
-    headers['x-langfuse-session-id'] = config.sessionId;
-  }
-  const provider = createOpenAI({ apiKey: config.apiKey, baseURL: config.baseURL, headers });
+  const provider = createOpenAI({
+    apiKey: config.apiKey, baseURL: config.baseURL,
+    fetch: wrapped as typeof globalThis.fetch,
+  });
   return provider(config.model);
 }