diff --git a/packages/core-eslint/rules/_manifest-source.js b/packages/core-eslint/rules/_manifest-source.js
new file mode 100644
index 0000000..dba87ba
--- /dev/null
+++ b/packages/core-eslint/rules/_manifest-source.js
@@ -0,0 +1,57 @@
+import fs from "node:fs";
+import path from "node:path";
+
+/**
+ * Reads a feature.manifest.ts file and extracts the manifest's `name` field
+ * and `requiredCores` array via regex. Returns null if the file does not
+ * exist or does not match the expected literal `as const` manifest shape.
+ *
+ * The repo's convention is that every feature.manifest.ts uses defineFeature
+ * with literal `as const` syntax — this is enforced by the type-system
+ * design (defineFeature has `<const M>` to preserve literal types). The
+ * regex extraction is therefore safe; the AST path is overkill.
+ *
+ * Returns: { name: string, requiredCores: string[] } | null
+ */
+export function readManifestSource(manifestPath) {
+  let src;
+  try {
+    src = fs.readFileSync(manifestPath, "utf8");
+  } catch {
+    return null;
+  }
+  const nameMatch = src.match(/name:\s*"([^"]+)"/);
+  if (!nameMatch) return null;
+  const coresMatch = src.match(/requiredCores:\s*\[([^\]]*)\]/);
+  const cores = coresMatch
+    ? coresMatch[1]
+        .split(",")
+        .map((s) => s.trim().replace(/^"/, "").replace(/"$/, ""))
+        .filter((s) => s.length > 0)
+    : [];
+  return { name: nameMatch[1], requiredCores: cores };
+}
+
+/**
+ * Canonical manifest path for a given feature package root.
+ */
+export function manifestPathForFeature(featureRoot) {
+  return path.join(featureRoot, "src", "feature.manifest.ts");
+}
+
+/**
+ * Given an absolute file path and the monorepo root, returns the feature
+ * package root that contains the file (e.g. /repo/packages/auth). Returns
+ * null when the file lives outside the packages/ tree.
+ *
+ * Assumes the conventional layout `packages/<feature>/src/...`.
+ */
+export function featureRootForFile(filepath, repoRoot) {
+  const packagesDir = path.join(repoRoot, "packages");
+  if (!filepath.startsWith(packagesDir + path.sep)) return null;
+  const rel = filepath.slice(packagesDir.length + 1); // e.g. "auth/src/..."
+  const slash = rel.indexOf(path.sep);
+  if (slash === -1) return null;
+  const featureName = rel.slice(0, slash);
+  return path.join(packagesDir, featureName);
+}
diff --git a/packages/core-eslint/rules/_manifest-source.test.js b/packages/core-eslint/rules/_manifest-source.test.js
new file mode 100644
index 0000000..bbab369
--- /dev/null
+++ b/packages/core-eslint/rules/_manifest-source.test.js
@@ -0,0 +1,74 @@
+import { describe, it, expect } from "vitest";
+import path from "node:path";
+import os from "node:os";
+import fs from "node:fs";
+import { readManifestSource, manifestPathForFeature, featureRootForFile } from "./_manifest-source.js";
+
+function writeTempFile(filename, contents) {
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), "manifest-source-"));
+  const filepath = path.join(dir, filename);
+  fs.writeFileSync(filepath, contents);
+  return { dir, filepath };
+}
+
+describe("_manifest-source", () => {
+  describe("readManifestSource", () => {
+    it("returns { name, requiredCores: [] } for a minimal manifest", () => {
+      const { filepath } = writeTempFile(
+        "feature.manifest.ts",
+        `import { defineFeature } from "@repo/core-shared/conformance";
+export const xManifest = defineFeature({
+  name: "test",
+  requiredCores: [],
+  useCases: {},
+  realtimeChannels: [],
+  jobs: [],
+} as const);`
+      );
+      expect(readManifestSource(filepath)).toEqual({ name: "test", requiredCores: [] });
+    });
+
+    it("extracts multi-element requiredCores", () => {
+      const { filepath } = writeTempFile(
+        "feature.manifest.ts",
+        `export const xManifest = defineFeature({
+  name: "auth",
+  requiredCores: ["audit", "events"],
+  useCases: {},
+  realtimeChannels: [],
+  jobs: [],
+} as const);`
+      );
+      expect(readManifestSource(filepath)).toEqual({ name: "auth", requiredCores: ["audit", "events"] });
+    });
+
+    it("returns null when the file does not exist", () => {
+      expect(readManifestSource("/nonexistent/path/feature.manifest.ts")).toBeNull();
+    });
+
+    it("returns null when the file is unreadable as a manifest (no name field)", () => {
+      const { filepath } = writeTempFile("feature.manifest.ts", `export const x = 1;`);
+      expect(readManifestSource(filepath)).toBeNull();
+    });
+  });
+
+  describe("manifestPathForFeature", () => {
+    it("returns the canonical manifest path for a feature root", () => {
+      expect(manifestPathForFeature("/repo/packages/auth")).toBe(
+        path.join("/repo/packages/auth", "src", "feature.manifest.ts"),
+      );
+    });
+  });
+
+  describe("featureRootForFile", () => {
+    it("returns the package root containing a use-case file", () => {
+      const file = "/repo/packages/auth/src/application/use-cases/sign-in.use-case.ts";
+      expect(featureRootForFile(file, "/repo")).toBe("/repo/packages/auth");
+    });
+
+    it("returns null for files outside the packages tree", () => {
+      const file = "/repo/apps/web-next/src/app/page.tsx";
+      expect(featureRootForFile(file, "/repo")).toBeNull();
+    });
+  });
+});