diff --git a/src/agents/workers/android.ts b/src/agents/workers/android.ts
index 9dbd503..a0c5949 100644
--- a/src/agents/workers/android.ts
+++ b/src/agents/workers/android.ts
@@ -16,6 +16,7 @@ type RenameStats = {
 
 const SKIP_SEGMENTS = new Set([
   ".git",
+  ".claude",
   "build",
   ".gradle",
   ".idea",
diff --git a/src/agents/workers/ios.ts b/src/agents/workers/ios.ts
index da3affd..079865e 100644
--- a/src/agents/workers/ios.ts
+++ b/src/agents/workers/ios.ts
@@ -14,7 +14,7 @@ type RenameStats = {
   files_renamed: number;
 };
 
-const SKIP_RELATIVE_PATHS = ["/.git", "/DerivedData", "/.build", "/Pods", "/Carthage"];
+const SKIP_RELATIVE_PATHS = ["/.git", "/.claude", "/DerivedData", "/.build", "/Pods", "/Carthage"];
 
 export async function runIosWorker(domain: DomainSpec): Promise<WorkerResult> {
   if (isStub("ios")) {
diff --git a/src/agents/workers/rails.ts b/src/agents/workers/rails.ts
index d6363d6..9930a26 100644
--- a/src/agents/workers/rails.ts
+++ b/src/agents/workers/rails.ts
@@ -14,7 +14,7 @@ type RenameStats = {
   files_renamed: number;
 };
 
-const SKIP_RELATIVE_PATHS = ["/.git", "/node_modules", "/tmp", "/log", "/vendor/bundle"];
+const SKIP_RELATIVE_PATHS = ["/.git", "/.claude", "/node_modules", "/tmp", "/log", "/vendor/bundle"];
 
 export async function runRailsWorker(domain: DomainSpec): Promise<WorkerResult> {
   if (isStub("rails")) {
diff --git a/src/validation/layer1.ts b/src/validation/layer1.ts
index 7b8f5af..c31e58d 100644
--- a/src/validation/layer1.ts
+++ b/src/validation/layer1.ts
@@ -1,3 +1,6 @@
+import { readdir, readFile, stat } from "node:fs/promises";
+import { extname, join, relative, basename } from "node:path";
+
 export type Layer1Input = {
   projectDir: string;
   forbiddenTokens: readonly string[];
@@ -15,7 +18,104 @@ export type Layer1Result = {
   findings: Layer1Finding[];
 };
 
+const TEXT_EXTS = new Set([
+  ".rb", ".erb", ".yml", ".yaml", ".json", ".md", ".gemspec", ".rake", ".ru",
+  ".txt", ".sample", ".example", ".conf", ".html", ".css", ".scss", ".js", ".mjs",
+  ".tt", ".lock",
+  ".swift", ".plist", ".strings", ".xcconfig", ".entitlements", ".pbxproj",
+  ".xcworkspacedata", ".modulemap",
+  ".kt", ".kts", ".xml", ".gradle", ".pro", ".toml", ".properties", ".cfg",
+]);
+
+const TEXT_BASENAMES = new Set([
+  "Gemfile", "Gemfile.lock", "Rakefile", "Procfile", "Procfile.dev",
+  "config.ru", "Dockerfile",
+  "Podfile", "Podfile.lock", "Package.swift", "Cartfile", "Makefile",
+  "gradlew", "gradlew.bat", "gradle.properties", "local.properties",
+]);
+
+const SKIP_SEGMENTS = new Set([
+  ".git", "node_modules", "tmp", "log", "vendor",
+  "DerivedData", "Pods", "Carthage", "xcuserdata", ".build",
+  "build", ".gradle", ".idea", ".kotlin", "captures",
+]);
+
 export async function runLayer1(input: Layer1Input): Promise<Layer1Result> {
-  void input;
-  throw new Error("runLayer1 not implemented: shell out to rg --json, collect matches, pass=true iff findings is empty");
+  if (input.forbiddenTokens.length === 0) {
+    return { pass: true, findings: [] };
+  }
+
+  const root = await realRoot(input.projectDir);
+  if (!root) {
+    return { pass: false, findings: [] };
+  }
+
+  const regex = buildRegex(input.forbiddenTokens);
+  const findings: Layer1Finding[] = [];
+
+  for await (const filePath of walk(root)) {
+    const content = await safeRead(filePath);
+    if (!content) continue;
+    const lines = content.split("\n");
+    for (let i = 0; i < lines.length; i++) {
+      const line = lines[i]!;
+      regex.lastIndex = 0;
+      let m: RegExpExecArray | null;
+      while ((m = regex.exec(line)) !== null) {
+        findings.push({
+          token: m[0],
+          file: relative(root, filePath),
+          line: i + 1,
+          text: line,
+        });
+      }
+    }
+  }
+
+  return { pass: findings.length === 0, findings };
+}
+
+async function realRoot(dir: string): Promise<string | null> {
+  try {
+    const s = await stat(dir);
+    return s.isDirectory() ? dir : null;
+  } catch {
+    return null;
+  }
+}
+
+function buildRegex(tokens: readonly string[]): RegExp {
+  const escaped = tokens.map(escapeRegex).join("|");
+  return new RegExp(`(?:${escaped})`, "g");
+}
+
+function escapeRegex(s: string): string {
+  return s.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
+}
+
+async function* walk(dir: string): AsyncGenerator<string> {
+  const entries = await readdir(dir, { withFileTypes: true });
+  for (const entry of entries) {
+    if (SKIP_SEGMENTS.has(entry.name)) continue;
+    const full = join(dir, entry.name);
+    if (entry.isDirectory()) {
+      yield* walk(full);
+    } else if (entry.isFile() && isTextFile(full)) {
+      yield full;
+    }
+  }
+}
+
+function isTextFile(path: string): boolean {
+  const base = basename(path);
+  if (TEXT_BASENAMES.has(base)) return true;
+  return TEXT_EXTS.has(extname(path));
+}
+
+async function safeRead(path: string): Promise<string | null> {
+  try {
+    return await readFile(path, "utf8");
+  } catch {
+    return null;
+  }
 }
diff --git a/tests/smoke.test.ts b/tests/smoke.test.ts
index 363b3c4..69e1b3b 100644
--- a/tests/smoke.test.ts
+++ b/tests/smoke.test.ts
@@ -9,11 +9,10 @@ test("validation layers are exported as functions", () => {
   assert.equal(typeof runLayer3, "function");
 });
 
-test("runLayer1 rejects until implemented", async () => {
-  await assert.rejects(
-    runLayer1({ projectDir: "/tmp", forbiddenTokens: [] }),
-    /not implemented/i,
-  );
+test("runLayer1 returns pass when forbiddenTokens is empty", async () => {
+  const result = await runLayer1({ projectDir: "/tmp", forbiddenTokens: [] });
+  assert.equal(result.pass, true);
+  assert.deepEqual(result.findings, []);
 });
 
 test("runLayer2 returns a failed result for a non-Rails directory", async () => {