diff --git a/packages/aws-lambda/src/sdk/deploySite.test.ts b/packages/aws-lambda/src/sdk/deploySite.test.ts
index 9863b051878..c89bdaa38fb 100644
--- a/packages/aws-lambda/src/sdk/deploySite.test.ts
+++ b/packages/aws-lambda/src/sdk/deploySite.test.ts
@@ -94,6 +94,18 @@ describe("deploySite", () => {
     expect(s3.ops.filter((op) => op.kind === "head")).toHaveLength(2);
   });
 
+  it("uploads a distinct tree when its contents resemble another file record", async () => {
+    const s3 = new FakeS3();
+    writeFileSync(join(projectDir, "a"), "ab\0def");
+    const first = await deploySite({ projectDir, bucketName: "test-bucket", s3: asS3Client(s3) });
+    writeFileSync(join(projectDir, "a"), "");
+    writeFileSync(join(projectDir, "ab"), "def");
+    const second = await deploySite({ projectDir, bucketName: "test-bucket", s3: asS3Client(s3) });
+    expect(second.siteId).not.toBe(first.siteId);
+    expect(second.uploaded).toBe(true);
+    expect(s3.ops.filter((op) => op.kind === "put")).toHaveLength(2);
+  });
+
   it("honours a caller-supplied siteId", async () => {
     const s3 = new FakeS3();
     const result = await deploySite({
diff --git a/packages/gcp-cloud-run/src/sdk/deploySite.test.ts b/packages/gcp-cloud-run/src/sdk/deploySite.test.ts
index 6c631ef6c9b..b6a1e6637eb 100644
--- a/packages/gcp-cloud-run/src/sdk/deploySite.test.ts
+++ b/packages/gcp-cloud-run/src/sdk/deploySite.test.ts
@@ -72,6 +72,27 @@ describe("deploySite", () => {
     expect(gcs.ops.filter((o) => o.kind === "upload").length).toBe(1);
   });
 
+  it("uploads a distinct tree when its contents resemble another file record", async () => {
+    const gcs = new FakeGcs();
+    const directory = mkProject("<html>same</html>");
+    writeFileSync(join(directory, "a"), "bc\0def");
+    const first = await deploySite({
+      projectDir: directory,
+      bucketName: "b",
+      storage: asStorage(gcs),
+    });
+    writeFileSync(join(directory, "a"), "");
+    writeFileSync(join(directory, "bc"), "def");
+    const second = await deploySite({
+      projectDir: directory,
+      bucketName: "b",
+      storage: asStorage(gcs),
+    });
+    expect(second.siteId).not.toBe(first.siteId);
+    expect(second.uploaded).toBe(true);
+    expect(gcs.ops.filter((op) => op.kind === "upload")).toHaveLength(2);
+  });
+
   it("honours an explicit siteId override", async () => {
     const gcs = new FakeGcs();
     const handle = await deploySite({
diff --git a/packages/producer/src/services/distributed/projectHash.test.ts b/packages/producer/src/services/distributed/projectHash.test.ts
new file mode 100644
index 00000000000..13416f91b7a
--- /dev/null
+++ b/packages/producer/src/services/distributed/projectHash.test.ts
@@ -0,0 +1,60 @@
+import { afterEach, describe, expect, it } from "bun:test";
+import { mkdirSync, mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { dirname, join } from "node:path";
+import { hashProjectDir } from "./projectHash.js";
+
+const projects: string[] = [];
+function project(files: Record<string, string | Buffer>): string {
+  const directory = mkdtempSync(join(tmpdir(), "hf-project-hash-"));
+  projects.push(directory);
+  for (const [name, content] of Object.entries(files)) {
+    const path = join(directory, name);
+    mkdirSync(dirname(path), { recursive: true });
+    writeFileSync(path, content);
+  }
+  return directory;
+}
+afterEach(() => {
+  for (const directory of projects.splice(0)) rmSync(directory, { recursive: true, force: true });
+});
+
+describe("hashProjectDir", () => {
+  it("distinguishes file content from another file path", () => {
+    const combined = project({ a: "bc\0def" });
+    const split = project({ a: "", bc: "def" });
+    expect(hashProjectDir(combined)).not.toBe(hashProjectDir(split));
+  });
+
+  it("distinguishes binary content from multiple file records", () => {
+    const content = Buffer.from([0, 255, 128, 1]);
+    const combined = project({ a: Buffer.concat([Buffer.from("asset\0"), content]) });
+    const split = project({ a: "", asset: content });
+    expect(hashProjectDir(combined)).not.toBe(hashProjectDir(split));
+  });
+
+  it("is stable across directory locations and file creation order", () => {
+    const first = project({ "nested/b": "雪😀", a: "" });
+    const second = project({ a: "", "nested/b": "雪😀" });
+    expect(hashProjectDir(first)).toMatch(/^[a-f0-9]{16}$/);
+    expect(hashProjectDir(first)).toBe(hashProjectDir(second));
+  });
+
+  it("includes paths and empty files", () => {
+    expect(hashProjectDir(project({ a: "same" }))).not.toBe(hashProjectDir(project({ b: "same" })));
+    expect(hashProjectDir(project({}))).not.toBe(hashProjectDir(project({ a: "" })));
+  });
+
+  it("ignores skipped top-level directories", () => {
+    const base = { "index.html": "same" };
+    const first = project(base);
+    const second = project({ ...base, "node_modules/package/ignored": "different" });
+    expect(hashProjectDir(first)).toBe(hashProjectDir(second));
+  });
+
+  it("includes nested directories with a skipped top-level name", () => {
+    const first = project({ "assets/node_modules/content": "first" });
+    const second = project({ "assets/node_modules/content": "second" });
+    expect(hashProjectDir(first)).not.toBe(hashProjectDir(second));
+  });
+});
diff --git a/packages/producer/src/services/distributed/projectHash.ts b/packages/producer/src/services/distributed/projectHash.ts
index bc64c031574..286bf01516f 100644
--- a/packages/producer/src/services/distributed/projectHash.ts
+++ b/packages/producer/src/services/distributed/projectHash.ts
@@ -18,7 +18,7 @@ import { PLAN_PROJECT_DIR_SKIP_SEGMENTS } from "./plan.js";
  * SHA-256 over every regular file under `projectDir` (sorted by relative
  * path) → 16-character hex prefix. The prefix is the `siteId`.
  *
- * The hash includes the relative path plus every byte of each file, so a
+ * The hash includes the relative path, byte length, and contents of each file, so a
  * same-bytes rename still yields a fresh id. We trim to 16 chars because the
  * full 64 isn't useful in an object key for legibility. Top-level segments in
  * {@link PLAN_PROJECT_DIR_SKIP_SEGMENTS} (e.g. `node_modules`) are skipped to
@@ -44,9 +44,12 @@ export function hashProjectDir(projectDir: string): string {
   walk(projectDir, true);
   for (const file of files) {
     const rel = relative(projectDir, file).replaceAll("\\", "/");
+    const content = readFileSync(file);
     hash.update(rel);
     hash.update("\0");
-    hash.update(readFileSync(file));
+    hash.update(String(content.length));
+    hash.update("\0");
+    hash.update(content);
   }
   return hash.digest("hex").slice(0, 16);
 }