feat(open-sse): streamErrorPatterns matching util (text + regex)

open-sse/utils/streamErrorPatterns.js

@@ -0,0 +1,47 @@
+/**
+ * Config-driven in-stream error pattern matching.
+ * See docs/2026-08-04-stream-error-patterns-design.md.
+ *
+ * Settings shape: streamErrorPatterns: { [provider]: string[] }
+ * Pattern syntax per entry:
+ *   - "plain text"   → case-insensitive substring match
+ *   - "/regex/flags" → RegExp match (flags after the last "/")
+ */
+
+export function parsePatterns(patterns) {
+  if (!Array.isArray(patterns)) return [];
+  const out = [];
+  for (const entry of patterns) {
+    if (typeof entry !== "string" || !entry.trim()) continue;
+    const raw = entry.trim();
+    const m = raw.match(/^\/(.*)\/([a-z]*)$/s);
+    if (m) {
+      try {
+        out.push({ regex: new RegExp(m[1], m[2]), raw });
+      } catch {
+        // invalid regex → skip; config errors must never break requests
+      }
+      continue;
+    }
+    out.push({ text: raw.toLowerCase(), raw });
+  }
+  return out;
+}
+
+export function matchStreamErrorPatterns(patterns, text) {
+  if (!Array.isArray(patterns) || patterns.length === 0) return null;
+  if (typeof text !== "string" || !text) return null;
+  const lower = text.toLowerCase();
+  for (const p of parsePatterns(patterns)) {
+    if (p.text && lower.includes(p.text)) return p.raw;
+    if (p.regex) {
+      p.regex.lastIndex = 0; // stateless even with /g
+      if (p.regex.test(text)) return p.raw;
+    }
+  }
+  return null;
+}
+
+export function streamStatusForContent(patterns, content) {
+  return matchStreamErrorPatterns(patterns, content) ? "error" : "success";
+}