fix(core): job failure semantics, stale-lock reaper, run-scoped context, reload

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

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

@@ -20,6 +20,7 @@ export default definePlugin({
       await ctx.credentials.save({ refresh: "new-refresh" });
       throw new Error("boom after save");
     }
+    ctx.log("echo pulled");
     const rec: SourceRecord = {
       kind: "entry",
       key: "echo-1",