fix(e2e): fix SSE chunk splitting and URL normalization in cassette conversion

Two issues in the legacy cassette converter:

1. SSE chunks were stored as raw HTTP DATA frame fragments in the old format,
   not as complete SSE events. The converter was mapping each old fragment to
   a new seinfeld chunk, causing mid-event splits. The AI SDK then saw truncated
   JSON fragments as SSE event bodies and failed to parse them.
   Fix: concatenate all fragment bytes first, then split on \n\n to produce
   complete SSE events as seinfeld's format requires.

2. The huggingface cassette stored URLs with percent-encoded brackets
   (%5B%5D) but the HuggingFace SDK sends them unencoded ([]). Seinfeld's
   default matcher uses strict string comparison on the full URL, so the
   encoding difference caused spurious misses.
   Fix: add URL normalization through the WHATWG URL parser to seinfeld's
   default filter preset, applied to both cassette candidates and incoming
   requests before comparison.

All 25 cassettes re-converted from the original legacy format with the
corrected SSE splitting logic.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: Qard

dev-packages/seinfeld/scripts/migrate-from-legacy.mjs

@@ -205,24 +205,30 @@ function convertBody(encoding, body, chunks) {
       return { kind: "base64", value: String(body ?? "") };
     }
     case "sse-chunks": {
-      // Legacy SSE: chunks is an array of { data: base64, encoding: 'base64' }.
-      // Seinfeld SSE: chunks is an array of raw UTF-8 strings.
+      // Legacy SSE: arbitrary byte-stream fragments, each base64-encoded.
+      // The fragments may NOT align with SSE event boundaries — a single SSE
+      // event can span multiple chunks. Seinfeld's chunk array must contain
+      // complete SSE events (one entry per \n\n-terminated event).
+      // Fix: concatenate all decoded fragment bytes first, then split on \n\n.
       const rawChunks = Array.isArray(chunks)
         ? chunks
         : Array.isArray(body)
           ? body
           : [];
-      return {
-        kind: "sse",
-        chunks: rawChunks.map((c) => {
+      const fullText = rawChunks
+        .map((c) => {
           if (typeof c === "string") return c;
           const obj = /** @type {Record<string, unknown>} */ (c);
           if (obj["encoding"] === "base64" && typeof obj["data"] === "string") {
             return Buffer.from(String(obj["data"]), "base64").toString("utf8");
           }
           return String(obj["data"] ?? c);
-        }),
-      };
+        })
+        .join("");
+      // Split on \n\n (SSE event separator) and drop trailing empty entry.
+      const parts = fullText.replace(/\r\n/g, "\n").split("\n\n");
+      if (parts.length > 0 && parts[parts.length - 1] === "") parts.pop();
+      return { kind: "sse", chunks: parts };
     }
     default:
       // Unknown encoding — fall back to empty

dev-packages/seinfeld/src/normalizer/presets.ts

@@ -21,6 +21,15 @@ const DEFAULT_FILTER: FilterConfig = {
     ...RATE_LIMIT_HEADERS,
     ...FINGERPRINT_HEADERS,
   ],
+  // Normalize the URL through the WHATWG URL parser so that percent-encoding
+  // differences (e.g. `%5B%5D` vs `[]`) don't produce spurious misses.
+  normalizeRequest: (req) => {
+    try {
+      return { ...req, url: new URL(req.url).href };
+    } catch {
+      return req;
+    }
+  },
 };
 
 /**

e2e/scenarios/ai-sdk-instrumentation/__cassettes__/ai-sdk-v3.cassette.json

@@ -328,13 +328,13 @@
         "body": {
           "kind": "sse",
           "chunks": [
-            "event: message_start\ndata: {\"type\":\"message_start\",\"message\":{\"model\":\"claude-haiku-4-5-20251001\",\"id\":\"msg_01YPdGeF3zFRM14L8B2cC6TL\",\"type\":\"message\",\"role\":\"assistant\",\"content\":[],\"stop_reason\":null,\"stop_sequence\":null,\"stop_details\":null,\"usage\":{\"input_tokens\":24,\"cache_creation_input_tokens\":0,\"cache_read_input_tokens\":0,\"cache_creation\":{\"ephemeral_5m_input_tokens\":0,\"ephemeral_1h_input_tokens\":0},\"output_tokens\":1,\"service_tier\":\"standard\",\"inference_geo\":\"not_available\"}}     }\n\n",
-            "event: content_block_start\ndata: {\"type\":\"content_block_start\",\"index\":0,\"content_block\":{\"type\":\"text\",\"text\":\"\"}  }\n\n",
-            "event: ping\ndata: {\"type\": \"ping\"}\n\n",
-            "event: content_block_delta\ndata: {\"type\":\"content_block_delta\",\"index\":0,\"delta\":{\"type\":\"text_delta\",\"text\":\"1 one\\n2 two\\n3 three\"}          }\n\n",
-            "event: content_block_stop\ndata: {\"type\":\"content_block_stop\",\"index\":0            }\n\n",
-            "event: message_delta\ndata: {\"type\":\"message_delta\",\"delta\":{\"stop_reason\":\"end_turn\",\"stop_sequence\":null,\"stop_details\":null},\"usage\":{\"input_tokens\":24,\"cache_creation_input_tokens\":0,\"cache_read_input_tokens\":0,\"output_tokens\":15} }\n\n",
-            "event: message_stop\ndata: {\"type\":\"message_stop\"        }\n\n"
+            "event: message_start\ndata: {\"type\":\"message_start\",\"message\":{\"model\":\"claude-haiku-4-5-20251001\",\"id\":\"msg_01YPdGeF3zFRM14L8B2cC6TL\",\"type\":\"message\",\"role\":\"assistant\",\"content\":[],\"stop_reason\":null,\"stop_sequence\":null,\"stop_details\":null,\"usage\":{\"input_tokens\":24,\"cache_creation_input_tokens\":0,\"cache_read_input_tokens\":0,\"cache_creation\":{\"ephemeral_5m_input_tokens\":0,\"ephemeral_1h_input_tokens\":0},\"output_tokens\":1,\"service_tier\":\"standard\",\"inference_geo\":\"not_available\"}}     }",
+            "event: content_block_start\ndata: {\"type\":\"content_block_start\",\"index\":0,\"content_block\":{\"type\":\"text\",\"text\":\"\"}  }",
+            "event: ping\ndata: {\"type\": \"ping\"}",
+            "event: content_block_delta\ndata: {\"type\":\"content_block_delta\",\"index\":0,\"delta\":{\"type\":\"text_delta\",\"text\":\"1 one\\n2 two\\n3 three\"}          }",
+            "event: content_block_stop\ndata: {\"type\":\"content_block_stop\",\"index\":0            }",
+            "event: message_delta\ndata: {\"type\":\"message_delta\",\"delta\":{\"stop_reason\":\"end_turn\",\"stop_sequence\":null,\"stop_details\":null},\"usage\":{\"input_tokens\":24,\"cache_creation_input_tokens\":0,\"cache_read_input_tokens\":0,\"output_tokens\":15} }",
+            "event: message_stop\ndata: {\"type\":\"message_stop\"        }"
           ]
         }
       }
@@ -398,12 +398,13 @@
         "body": {
           "kind": "sse",
           "chunks": [
-            "event: message_start\ndata: {\"type\":\"message_start\",\"message\":{\"model\":\"claude-haiku-4-5-20251001\",\"id\":\"msg_012EbUGmLfEc7GsCBMZAKpSK\",\"type\":\"message\",\"role\":\"assistant\",\"content\":[],\"stop_reason\":null,\"stop_sequence\":null,\"stop_details\":null,\"usage\":{\"input_tokens\":24,\"cache_creation_input_tokens\":0,\"cache_read_input_tokens\":0,\"cache_creation\":{\"ephemeral_5m_input_tokens\":0,\"ephemeral_1h_input_tokens\":0},\"output_tokens\":1,\"service_tier\":\"standard\",\"inference_geo\":\"not_available\"}}  }\n\n",
-            "event: content_block_start\ndata: {\"type\":\"content_block_start\",\"index\":0,\"content_block\":{\"type\":\"text\",\"text\":\"\"}}\n\n",
-            "event: ping\ndata: {\"type\": \"ping\"}\n\nevent: content_block_delta\ndata: {\"type\":\"content_block_delta\",\"index\":0,\"delta\":{\"type\":\"text_delta\",\"text\":\"1 one\\n2 two\\n3 three\"}       }\n\n",
-            "event: content_block_stop\ndata: {\"type\":\"content_block_stop\",\"index\":0        }\n\n",
-            "event: message_delta\ndata: {\"type\":\"message_delta\",\"delta\":{\"stop_reason\":\"end_turn\",\"stop_sequence\":null,\"stop_details\":null},\"usage\":{\"input_tokens\":24,\"cache_creation_input_tokens\":0,\"cache_read_input_tokens\":0,\"output_tokens\":15}             }\n\n",
-            "event: message_stop\ndata: {\"type\":\"message_stop\"       }\n\n"
+            "event: message_start\ndata: {\"type\":\"message_start\",\"message\":{\"model\":\"claude-haiku-4-5-20251001\",\"id\":\"msg_012EbUGmLfEc7GsCBMZAKpSK\",\"type\":\"message\",\"role\":\"assistant\",\"content\":[],\"stop_reason\":null,\"stop_sequence\":null,\"stop_details\":null,\"usage\":{\"input_tokens\":24,\"cache_creation_input_tokens\":0,\"cache_read_input_tokens\":0,\"cache_creation\":{\"ephemeral_5m_input_tokens\":0,\"ephemeral_1h_input_tokens\":0},\"output_tokens\":1,\"service_tier\":\"standard\",\"inference_geo\":\"not_available\"}}  }",
+            "event: content_block_start\ndata: {\"type\":\"content_block_start\",\"index\":0,\"content_block\":{\"type\":\"text\",\"text\":\"\"}}",
+            "event: ping\ndata: {\"type\": \"ping\"}",
+            "event: content_block_delta\ndata: {\"type\":\"content_block_delta\",\"index\":0,\"delta\":{\"type\":\"text_delta\",\"text\":\"1 one\\n2 two\\n3 three\"}       }",
+            "event: content_block_stop\ndata: {\"type\":\"content_block_stop\",\"index\":0        }",
+            "event: message_delta\ndata: {\"type\":\"message_delta\",\"delta\":{\"stop_reason\":\"end_turn\",\"stop_sequence\":null,\"stop_details\":null},\"usage\":{\"input_tokens\":24,\"cache_creation_input_tokens\":0,\"cache_read_input_tokens\":0,\"output_tokens\":15}             }",
+            "event: message_stop\ndata: {\"type\":\"message_stop\"       }"
           ]
         }
       }
@@ -450,7 +451,9 @@
                       "type": "string"
                     }
                   },
-                  "required": ["location"],
+                  "required": [
+                    "location"
+                  ],
                   "type": "object"
                 },
                 "name": "get_weather"
@@ -486,16 +489,16 @@
         "body": {
           "kind": "sse",
           "chunks": [
-            "event: message_start\ndata: {\"type\":\"message_start\",\"message\":{\"model\":\"claude-haiku-4-5-20251001\",\"id\":\"msg_01V3odUVvBp7MxCnzqZFrW1u\",\"type\":\"message\",\"role\":\"assistant\",\"content\":[],\"stop_reason\":null,\"stop_sequence\":null,\"stop_details\":null,\"usage\":{\"input_tokens\":687,\"cache_creation_input_tokens\":0,\"cache_read_input_tokens\":0,\"cache_creation\":{\"ephemeral_5m_input_tokens\":0,\"ephemeral_1h_input_tokens\":0},\"output_tokens\":13,\"service_tier\":\"standard\",\"inference_geo\":\"not_available\"}}             }\n\n",
-            "event: content_block_start\ndata: {\"type\":\"content_block_start\",\"index\":0,\"content_block\":{\"type\":\"tool_use\",\"id\":\"toolu_016LWtxJSJr8E91HsktMeniw\",\"name\":\"get_weather\",\"input\":{},\"caller\":{\"type\":\"direct\"}}        }\n\n",
-            "event: ping\ndata: {\"type\": \"ping\"}\n\n",
-            "event: content_block_delta\ndata: {\"type\":\"content_block_delta\",\"index\":0,\"delta\":{\"type\":\"input_json_delta\",\"partial_json\":\"\"}              }\n\n",
-            "event: content_block_delta\ndata: {\"type\":\"content_block_delta\",\"index\":0,\"delta\":{\"type\":\"input_json_delta\",\"partial_json\":\"{\\\"location\\\":\"}          }\n\n",
-            "event: content_block_delta\ndata: {\"type\":\"content_block_delta\",\"index\":0,\"delta\":{\"type\":\"input_json_delta\",\"partial_json\":\" \\\"Paris, F\"}              }\n\n",
-            "event: content_block_delta\ndata: {\"type\":\"content_block_delta\",\"index\":0,\"delta\":{\"type\":\"input_json_delta\",\"partial_json\":\"rance\\\"}\"}     }\n\n",
-            "event: content_block_stop\ndata: {\"type\":\"content_block_stop\",\"index\":0          }\n\n",
-            "event: message_delta\ndata: {\"type\":\"message_delta\",\"delta\":{\"stop_reason\":\"tool_use\",\"stop_sequence\":null,\"stop_details\":null},\"usage\":{\"input_tokens\":687,\"cache_creation_input_tokens\":0,\"cache_read_input_tokens\":0,\"output_tokens\":26}      }\n\n",
-            "event: message_stop\ndata: {\"type\":\"message_stop\" }\n\n"
+            "event: message_start\ndata: {\"type\":\"message_start\",\"message\":{\"model\":\"claude-haiku-4-5-20251001\",\"id\":\"msg_01V3odUVvBp7MxCnzqZFrW1u\",\"type\":\"message\",\"role\":\"assistant\",\"content\":[],\"stop_reason\":null,\"stop_sequence\":null,\"stop_details\":null,\"usage\":{\"input_tokens\":687,\"cache_creation_input_tokens\":0,\"cache_read_input_tokens\":0,\"cache_creation\":{\"ephemeral_5m_input_tokens\":0,\"ephemeral_1h_input_tokens\":0},\"output_tokens\":13,\"service_tier\":\"standard\",\"inference_geo\":\"not_available\"}}             }",
+            "event: content_block_start\ndata: {\"type\":\"content_block_start\",\"index\":0,\"content_block\":{\"type\":\"tool_use\",\"id\":\"toolu_016LWtxJSJr8E91HsktMeniw\",\"name\":\"get_weather\",\"input\":{},\"caller\":{\"type\":\"direct\"}}        }",
+            "event: ping\ndata: {\"type\": \"ping\"}",
+            "event: content_block_delta\ndata: {\"type\":\"content_block_delta\",\"index\":0,\"delta\":{\"type\":\"input_json_delta\",\"partial_json\":\"\"}              }",
+            "event: content_block_delta\ndata: {\"type\":\"content_block_delta\",\"index\":0,\"delta\":{\"type\":\"input_json_delta\",\"partial_json\":\"{\\\"location\\\":\"}          }",
+            "event: content_block_delta\ndata: {\"type\":\"content_block_delta\",\"index\":0,\"delta\":{\"type\":\"input_json_delta\",\"partial_json\":\" \\\"Paris, F\"}              }",
+            "event: content_block_delta\ndata: {\"type\":\"content_block_delta\",\"index\":0,\"delta\":{\"type\":\"input_json_delta\",\"partial_json\":\"rance\\\"}\"}     }",
+            "event: content_block_stop\ndata: {\"type\":\"content_block_stop\",\"index\":0          }",
+            "event: message_delta\ndata: {\"type\":\"message_delta\",\"delta\":{\"stop_reason\":\"tool_use\",\"stop_sequence\":null,\"stop_details\":null},\"usage\":{\"input_tokens\":687,\"cache_creation_input_tokens\":0,\"cache_read_input_tokens\":0,\"output_tokens\":26}      }",
+            "event: message_stop\ndata: {\"type\":\"message_stop\" }"
           ]
         }
       }
@@ -536,7 +539,9 @@
                       "type": "string"
                     }
                   },
-                  "required": ["location"],
+                  "required": [
+                    "location"
+                  ],
                   "type": "object"
                 },
                 "name": "get_weather"