feat(core): jobs, scheduler, plugin registry, connections

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

packages/core/test/fixtures/plugins/broken/index.ts

@@ -0,0 +1 @@
+export default { nope: true };

packages/core/test/fixtures/plugins/echo/index.ts

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+import { definePlugin, type SourceRecord } from "@sttracker/plugin-sdk/types";
+
+export default definePlugin({
+  manifest: {
+    id: "echo",
+    name: "Echo",
+    version: "0.0.1",
+    sdkVersion: 1,
+    mediaTypes: ["book"],
+    capabilities: ["pull", "pullChanges"],
+    config: [
+      { key: "label", label: "Label", type: "string" },
+      { key: "token", label: "Token", type: "secret" },
+    ],
+    rateLimit: { perMinute: 30, burst: 2 },
+  },
+  async *pull(ctx) {
+    const cfg = ctx.config;
+    if (cfg.label === "explode") {
+      await ctx.credentials.save({ refresh: "new-refresh" });
+      throw new Error("boom after save");
+    }
+    const rec: SourceRecord = {
+      kind: "entry",
+      key: "echo-1",
+      raw: { label: cfg.label ?? null },
+      work: { title: String(cfg.label ?? "Echo"), mediaType: "book", externalIds: { isbn13: "9780000000002" } },
+      entry: { status: "completed" },
+    };
+    yield rec;
+  },
+  async *pullChanges(ctx) {
+    yield* this.pull!(ctx);
+  },
+});