Add feed discovery plugin

plugins/feed-discovery/src/validate-feed.ts

@@ -0,0 +1,27 @@
+import { readFeedDiscoveryConfig } from "./config.js";
+import { parseFeedDocument } from "./feed-parsing.js";
+import { fetchTextWithGuards } from "./http.js";
+import type { FeedDiscoveryConfig, ValidationResult } from "./types.js";
+import { canonicalizeUrl } from "./url-safety.js";
+
+export async function validateFeed(feedUrl: string, config: Partial<FeedDiscoveryConfig> = {}): Promise<ValidationResult> {
+  const resolvedConfig = { ...readFeedDiscoveryConfig(), ...config };
+  try {
+    const response = await fetchTextWithGuards(feedUrl, resolvedConfig);
+    const canonicalFeedUrl = canonicalizeUrl(response.url || feedUrl);
+    const parsed = parseFeedDocument(canonicalFeedUrl, response.body, response.contentType);
+    return {
+      ...parsed,
+      feedUrl,
+      canonicalFeedUrl
+    };
+  } catch (error) {
+    return {
+      ok: false,
+      feedUrl,
+      kind: "unknown",
+      sampleItems: [],
+      error: error instanceof Error ? error.message : String(error)
+    };
+  }
+}