diff --git a/.changeset/idempotent-action-builds.md b/.changeset/idempotent-action-builds.md
new file mode 100644
index 0000000..73bd942
--- /dev/null
+++ b/.changeset/idempotent-action-builds.md
@@ -0,0 +1,8 @@
+---
+"@savvy-web/github-action-builder": patch
+---
+
+## Bug Fixes
+
+- Action builds are now reproducible. When `build.ignore` was set, the ignore stub was written to a random `mkdtemp` directory whose absolute path rspack embedded in the bundle as a module id, so building the same source twice produced byte-different output and noisy diffs in committed action code. The stub now lives at a deterministic path under `node_modules/.cache`, so repeated builds are byte-identical.
+- Bundled third-party license banners are kept inline instead of being extracted to `*.LICENSE.txt` sidecar files, removing the extra committed file from action output while preserving license attribution.
diff --git a/.gitignore b/.gitignore
index 602fb6a..f0a3440 100644
--- a/.gitignore
+++ b/.gitignore
@@ -31,6 +31,8 @@ pnpm-release.json
 
 # Claude AI files
 .claude/settings.local.json
+.claude/scheduled_tasks.lock
+.claude/cache
 .claude/plans/
 .claude/plugins-debug.log
 .playwright-mcp
diff --git a/__test__/integration/fixtures/license-comments/action.yml b/__test__/integration/fixtures/license-comments/action.yml
new file mode 100644
index 0000000..f6284cb
--- /dev/null
+++ b/__test__/integration/fixtures/license-comments/action.yml
@@ -0,0 +1,5 @@
+name: license-comments fixture
+description: Fixture for issue #94 — license-comment handling in bundled output.
+runs:
+  using: node24
+  main: dist/main.js
diff --git a/__test__/integration/fixtures/license-comments/src/main.ts b/__test__/integration/fixtures/license-comments/src/main.ts
new file mode 100644
index 0000000..b667e23
--- /dev/null
+++ b/__test__/integration/fixtures/license-comments/src/main.ts
@@ -0,0 +1,6 @@
+// Imports a bundled dependency that carries a license banner. Minifiers extract
+// such `/*! */` banners to `main.js.LICENSE.txt` by default — noise for a
+// committed action (issue #94). See vendor/banner-dep.cjs.
+import { greeting } from "../vendor/banner-dep.cjs";
+
+process.stdout.write(`${greeting}\n`);
diff --git a/__test__/integration/fixtures/license-comments/vendor/banner-dep.cjs b/__test__/integration/fixtures/license-comments/vendor/banner-dep.cjs
new file mode 100644
index 0000000..d85af73
--- /dev/null
+++ b/__test__/integration/fixtures/license-comments/vendor/banner-dep.cjs
@@ -0,0 +1,5 @@
+/*! @license MIT | example-licensed-dep v1.2.3 | (c) 2026 Example Corp */
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.greeting = void 0;
+exports.greeting = "licensed-bundle-ok";
diff --git a/__test__/integration/fixtures/license-comments/vendor/banner-dep.d.cts b/__test__/integration/fixtures/license-comments/vendor/banner-dep.d.cts
new file mode 100644
index 0000000..58ffe05
--- /dev/null
+++ b/__test__/integration/fixtures/license-comments/vendor/banner-dep.d.cts
@@ -0,0 +1 @@
+export declare const greeting: string;
diff --git a/__test__/integration/idempotent-build.int.test.ts b/__test__/integration/idempotent-build.int.test.ts
new file mode 100644
index 0000000..7165ee3
--- /dev/null
+++ b/__test__/integration/idempotent-build.int.test.ts
@@ -0,0 +1,88 @@
+/**
+ * Integration regression test for issue #94.
+ *
+ * Building the same source with the same config twice must produce byte-identical
+ * output. The compiled action is committed to git, so a changing identifier in the
+ * bundle creates pure diff noise. The build must also not emit `*.LICENSE.txt`
+ * sidecar files, which are npm-publishing niceties that are noise for committed
+ * action code.
+ *
+ * `build.ignore` is the trigger: the builder aliases ignored modules to a stub
+ * file whose path rspack embeds as the module id. A per-build `mkdtemp` directory
+ * made that path — and therefore the bundle — change on every run.
+ */
+import { createHash } from "node:crypto";
+import { cpSync, mkdtempSync, readFileSync, readdirSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { dirname, join, resolve } from "node:path";
+import { fileURLToPath } from "node:url";
+import { beforeAll, describe, expect, it } from "vitest";
+
+import { GitHubAction } from "../../src/index.js";
+
+const sourceFixture = resolve(dirname(fileURLToPath(import.meta.url)), "fixtures/ignore-modules");
+
+function buildOnce(cwd: string) {
+	const action = GitHubAction.create({
+		cwd,
+		skipValidation: true,
+		config: {
+			// minify is off so a diff is readable; the embedded stub path is
+			// non-deterministic regardless of minification.
+			build: { minify: false, ignore: ["excluded-native-dep"] },
+			persistLocal: { enabled: false },
+		},
+	});
+	return action.build();
+}
+
+function firstDiffingLines(a: string, b: string, max = 6): string {
+	const la = a.split("\n");
+	const lb = b.split("\n");
+	const out: string[] = [];
+	for (let i = 0; i < Math.max(la.length, lb.length) && out.length < max; i++) {
+		if (la[i] !== lb[i]) {
+			out.push(`L${i + 1}:\n  - ${la[i] ?? "<eof>"}\n  + ${lb[i] ?? "<eof>"}`);
+		}
+	}
+	return out.join("\n");
+}
+
+describe("issue #94: idempotent builds", () => {
+	let first: string;
+	let second: string;
+	let licenseFiles: string[];
+
+	beforeAll(async () => {
+		// Build inside an isolated copy of the fixture so this never races the #81
+		// ignore-modules test, which shares the same fixture's dist/.
+		const work = mkdtempSync(join(tmpdir(), "gha-idempotent-"));
+		cpSync(sourceFixture, work, { recursive: true });
+		const mainJs = join(work, "dist", "main.js");
+
+		const r1 = await buildOnce(work);
+		if (!r1.success) {
+			throw new Error(`build 1 failed: ${r1.error ?? "unknown error"}`);
+		}
+		first = readFileSync(mainJs, "utf8");
+		licenseFiles = readdirSync(join(work, "dist")).filter((f) => f.endsWith(".LICENSE.txt"));
+
+		const r2 = await buildOnce(work);
+		if (!r2.success) {
+			throw new Error(`build 2 failed: ${r2.error ?? "unknown error"}`);
+		}
+		second = readFileSync(mainJs, "utf8");
+	}, 240_000);
+
+	it("produces byte-identical output across builds", () => {
+		if (first !== second) {
+			expect.fail(`main.js differs between builds:\n${firstDiffingLines(first, second)}`);
+		}
+		const hash = (s: string) => createHash("sha256").update(s).digest("hex");
+		expect(hash(second)).toBe(hash(first));
+	});
+
+	it("does not emit *.LICENSE.txt sidecar files", () => {
+		expect(licenseFiles).toEqual([]);
+	});
+});
diff --git a/__test__/integration/license-comments.int.test.ts b/__test__/integration/license-comments.int.test.ts
new file mode 100644
index 0000000..2b5f3d3
--- /dev/null
+++ b/__test__/integration/license-comments.int.test.ts
@@ -0,0 +1,51 @@
+/**
+ * Integration regression test for issue #94 (license sidecars).
+ *
+ * A minified action bundle must not emit `*.LICENSE.txt` sidecar files — they are
+ * an npm-publishing nicety and pure noise for a committed action. License notices
+ * from bundled code must instead stay inline so attribution is still preserved.
+ */
+import { cpSync, mkdtempSync, readFileSync, readdirSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { dirname, join, resolve } from "node:path";
+import { fileURLToPath } from "node:url";
+import { beforeAll, describe, expect, it } from "vitest";
+
+import { GitHubAction } from "../../src/index.js";
+
+const sourceFixture = resolve(dirname(fileURLToPath(import.meta.url)), "fixtures/license-comments");
+
+describe("issue #94: no license sidecar files", () => {
+	let distFiles: string[];
+	let bundle: string;
+
+	beforeAll(async () => {
+		const work = mkdtempSync(join(tmpdir(), "gha-license-"));
+		cpSync(sourceFixture, work, { recursive: true });
+
+		const action = GitHubAction.create({
+			cwd: work,
+			skipValidation: true,
+			config: {
+				build: { minify: true },
+				persistLocal: { enabled: false },
+			},
+		});
+		const result = await action.build();
+		if (!result.success) {
+			throw new Error(`build failed: ${result.error ?? "unknown error"}`);
+		}
+
+		const distDir = join(work, "dist");
+		distFiles = readdirSync(distDir);
+		bundle = readFileSync(join(distDir, "main.js"), "utf8");
+	}, 240_000);
+
+	it("emits no *.LICENSE.txt sidecar", () => {
+		expect(distFiles.filter((f) => f.endsWith(".LICENSE.txt"))).toEqual([]);
+	});
+
+	it("keeps the license notice inline in the bundle", () => {
+		expect(bundle).toContain("@license MIT | example-licensed-dep");
+	});
+});
diff --git a/src/services/build-live.ts b/src/services/build-live.ts
index f6a4669..b828950 100644
--- a/src/services/build-live.ts
+++ b/src/services/build-live.ts
@@ -3,9 +3,8 @@
  * BuildService Layer implementation.
  *
  */
-import { existsSync, mkdirSync, mkdtempSync, rmSync, statSync, writeFileSync } from "node:fs";
-import { tmpdir } from "node:os";
-import { join, resolve } from "node:path";
+import { existsSync, mkdirSync, rmSync, statSync, writeFileSync } from "node:fs";
+import { resolve } from "node:path";
 import { createRsbuild } from "@rsbuild/core";
 import { Effect, Layer } from "effect";
 
@@ -124,21 +123,19 @@ function bundleEntry(
 		const outputDir = resolve(cwd, "dist");
 
 		// Modules listed in `build.ignore` are aliased to a throwing stub so
-		// they are neither bundled nor resolved against node_modules. The stub
-		// lives in a private per-build temp directory created with mkdtemp, so
-		// a predictable shared path cannot be pre-created or symlinked by
-		// another process. See
+		// they are neither bundled nor resolved against node_modules. See
 		// docs/superpowers/specs/2026-05-15-build-ignore-option-design.md.
 		const externalsSet = new Set(config.build.externals);
 		const ignoreSet = new Set(config.build.ignore);
 		const ignoreAlias: Record<string, string> = {};
-		let stubDir: string | undefined;
 		if (config.build.ignore.length > 0) {
-			stubDir = yield* Effect.try({
-				try: () => mkdtempSync(join(tmpdir(), "github-action-builder-")),
-				catch: (error) => new WriteError({ path: tmpdir(), cause: error }),
-			});
-			const stubPath = resolve(stubDir, "ignore-stub.mjs");
+			// rspack embeds the stub's path verbatim as the ignored modules' module
+			// id, so the path must be deterministic — a per-build `mkdtemp` directory
+			// made the committed bundle change on every run (#94). This cache path is
+			// project-local (under node_modules, not a world-writable shared tmp), so
+			// a fixed name keeps the symlink-safety property the original design (#81)
+			// relied on while making the output reproducible.
+			const stubPath = resolve(cwd, "node_modules", ".cache", "github-action-builder", "ignore-stub.mjs");
 			yield* writeFile(stubPath, IGNORE_STUB_SOURCE);
 			for (const moduleName of config.build.ignore) {
 				ignoreAlias[`${moduleName}$`] = stubPath;
@@ -187,6 +184,10 @@ function bundleEntry(
 								return false;
 							},
 							cleanDistPath: false,
+							// Keep third-party license banners inline instead of extracting them
+							// to `*.LICENSE.txt` sidecars (rspack's "linked" behavior), which are
+							// committed-action noise — while still preserving attribution (#94).
+							legalComments: "inline",
 							minify: config.build.minify,
 							sourceMap: config.build.sourceMap ? { js: "source-map" as const } : false,
 						},
@@ -237,12 +238,6 @@ function bundleEntry(
 				}),
 		});
 
-		// Remove the private stub directory now the bundle has been written.
-		if (stubDir !== undefined) {
-			const dir = stubDir;
-			yield* Effect.ignore(Effect.try(() => rmSync(dir, { recursive: true, force: true })));
-		}
-
 		const outputPath = resolve(outputDir, `${entry.type}.js`);
 		const size = yield* Effect.try({
 			try: () => statSync(outputPath).size,