diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8ecf24b..93172af 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -293,6 +293,31 @@ actually cutting it, and this file starts there.
   covers `git ls-files '*.sh'` and fails naming the strays otherwise, so a
   future sweep that quietly narrows is red rather than green over nothing.
 
+- **`cast` no longer leaves a full repo clone in the temp dir on every run**
+  (#117) — `resolveCheckout()` mkdtemps an `infra-checkout-` directory and
+  `git clone`s the infra repo into it, and nothing ever removed it. Every
+  `cast apply`, `diff`, or `capture` invoked *without* `--path` — the normal
+  way to run all three — left a shallow clone behind permanently. This is a
+  runtime leak, not a test one: #117 was filed as test-suite hygiene and
+  explicitly scoped the runtime out ("`cast` itself does not leak"), but the
+  box that found it was also holding 602 `infra-checkout-*` directories,
+  73 MB of real `.git` trees, from the same day. The leak fires on the
+  failure path too, since the directory is created before the clone runs.
+  Ephemeral checkouts are now registered and removed on process exit, which
+  is the lifetime that fits: the tree has to outlive `resolveCheckout`'s
+  return — every caller reads it — so a `finally` would delete the checkout
+  out from under the command that asked for it. A `--path` checkout is the
+  operator's own working tree and is never registered.
+
+- **The test suite reaps its temp directories** (#117) — 68 `mkdtempSync`
+  call sites across 21 files, zero cleanups, accumulating ~6700 directories
+  and 189 MB per machine-day, some holding age keys. All 68 now go through a
+  single `tmp()` helper (`test/helpers/tmp.ts`) that allocates inside a
+  per-run root, which vitest's `globalSetup` teardown removes wholesale. A
+  class-guard test (`test/tmp-guard.test.ts`) fails if `mkdtempSync` appears
+  anywhere under `test/` outside those helpers, so the next raw call is
+  caught at review rather than after a day of accumulation.
+
 ## 0.1.1 — 2026-07-19
 
 ### Fixed
diff --git a/src/resolve.ts b/src/resolve.ts
index da2c059..9a7c738 100644
--- a/src/resolve.ts
+++ b/src/resolve.ts
@@ -1,5 +1,5 @@
 import { execFileSync } from "node:child_process";
-import { existsSync, mkdtempSync, readFileSync } from "node:fs";
+import { existsSync, mkdtempSync, readFileSync, rmSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import type { Desired } from "./diff.js";
@@ -162,6 +162,42 @@ export function refusesPathInProd(opts: {
   return opts.path !== undefined && opts.env === "prod";
 }
 
+// Checkouts this process cloned, to be removed when it exits.
+const ephemeralCheckouts: string[] = [];
+let reaperArmed = false;
+
+// A checkout resolved WITHOUT `--path` is ours: we made the directory, we cloned
+// into it, and nothing outside this process refers to it. It has to outlive
+// resolveCheckout's return — every caller reads the tree afterwards — so the
+// lifetime that actually fits is the process, not the call. Hence an exit hook
+// rather than a `finally`, which would delete the checkout out from under the
+// command that just asked for it.
+//
+// A `--path` checkout is the operator's own working tree and is never registered
+// here; deleting that would be catastrophic and is the reason this wraps the
+// mkdtemp result specifically, not the function's return value.
+//
+// Without this, every `cast apply` / `diff` / `capture` run without `--path`
+// left a full shallow clone in the temp dir forever (#117).
+function reapOnExit(dir: string): string {
+  ephemeralCheckouts.push(dir);
+  if (!reaperArmed) {
+    reaperArmed = true;
+    process.once("exit", () => {
+      for (const d of ephemeralCheckouts) {
+        // Best-effort: failing to clean up must never change a command's exit
+        // status. The work is already done by the time we get here.
+        try {
+          rmSync(d, { recursive: true, force: true });
+        } catch {
+          // ignore
+        }
+      }
+    });
+  }
+  return dir;
+}
+
 export function resolveCheckout(
   orgRepo: string,
   opts: { env: string; path?: string },
@@ -170,7 +206,7 @@ export function resolveCheckout(
     throw new Error(PATH_IN_PROD_REFUSAL);
   }
   if (opts.path) return opts.path;
-  const dir = mkdtempSync(join(tmpdir(), "infra-checkout-"));
+  const dir = reapOnExit(mkdtempSync(join(tmpdir(), "infra-checkout-")));
   const auth = resolveGitAuth();
   try {
     execFileSync(
diff --git a/test/backup-cli.test.ts b/test/backup-cli.test.ts
index c730b96..11ebf88 100644
--- a/test/backup-cli.test.ts
+++ b/test/backup-cli.test.ts
@@ -1,10 +1,10 @@
 import { execFileSync, spawn } from "node:child_process";
-import { mkdirSync, mkdtempSync, writeFileSync } from "node:fs";
+import { mkdirSync, writeFileSync } from "node:fs";
 import { createServer } from "node:http";
 import type { AddressInfo } from "node:net";
-import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, beforeAll, describe, expect, it } from "vitest";
+import { tmp } from "./helpers/tmp.js";
 
 // Backup schedules, end to end: manifest -> `cast diff` -> what it prints and
 // what it exits with. The unit tests prove each half (coolify.ts parses the
@@ -21,7 +21,7 @@ let recipient: string;
 let keyFile: string;
 
 beforeAll(() => {
-  const dir = mkdtempSync(join(tmpdir(), "cast-age-"));
+  const dir = tmp("cast-age-");
   keyFile = join(dir, "age.key");
   execFileSync("age-keygen", ["-o", keyFile], { stdio: "pipe" });
   recipient = execFileSync("age-keygen", ["-y", keyFile], {
@@ -110,11 +110,11 @@ environments:
 `;
 
 function fixture(url: string) {
-  const checkout = mkdtempSync(join(tmpdir(), "cast-co-"));
+  const checkout = tmp("cast-co-");
   mkdirSync(join(checkout, ".infra", "env"), { recursive: true });
   writeFileSync(join(checkout, ".infra", "manifest.yaml"), MANIFEST);
 
-  const state = mkdtempSync(join(tmpdir(), "cast-state-"));
+  const state = tmp("cast-state-");
   mkdirSync(join(state, "secrets"));
   writeFileSync(
     join(state, ".coolify.env"),
diff --git a/test/capture-cli.test.ts b/test/capture-cli.test.ts
index 787d227..2440863 100644
--- a/test/capture-cli.test.ts
+++ b/test/capture-cli.test.ts
@@ -1,17 +1,11 @@
 import { execFileSync, spawn } from "node:child_process";
-import {
-  existsSync,
-  mkdirSync,
-  mkdtempSync,
-  readFileSync,
-  writeFileSync,
-} from "node:fs";
+import { existsSync, mkdirSync, readFileSync, writeFileSync } from "node:fs";
 import { createServer } from "node:http";
 import type { AddressInfo } from "node:net";
-import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, beforeAll, describe, expect, it } from "vitest";
 import { decryptSecrets, encryptSecrets } from "../src/secrets.js";
+import { tmp } from "./helpers/tmp.js";
 
 // End-to-end: the real CLI, a real age identity, a stub Coolify holding real
 // live values. The point is the store that comes out the other side — it is
@@ -34,7 +28,7 @@ let keyFile: string;
 let recipient: string;
 
 beforeAll(() => {
-  const dir = mkdtempSync(join(tmpdir(), "cast-age-"));
+  const dir = tmp("cast-age-");
   keyFile = join(dir, "age-staging.key");
   execFileSync("age-keygen", ["-o", keyFile], { stdio: "pipe" });
   const pub = execFileSync("age-keygen", ["-y", keyFile], { encoding: "utf8" });
@@ -110,7 +104,7 @@ function fixture(
   url: string,
   opts: { template?: string; manifest?: string } = {},
 ) {
-  const checkout = mkdtempSync(join(tmpdir(), "cast-co-"));
+  const checkout = tmp("cast-co-");
   mkdirSync(join(checkout, ".infra", "env"), { recursive: true });
   writeFileSync(
     join(checkout, ".infra", "manifest.yaml"),
@@ -121,7 +115,7 @@ function fixture(
     opts.template ?? TEMPLATE,
   );
 
-  const state = mkdtempSync(join(tmpdir(), "cast-state-"));
+  const state = tmp("cast-state-");
   mkdirSync(join(state, "secrets"));
   writeFileSync(
     join(state, ".coolify.env"),
diff --git a/test/capture.test.ts b/test/capture.test.ts
index 1d18b8d..93b0620 100644
--- a/test/capture.test.ts
+++ b/test/capture.test.ts
@@ -1,5 +1,4 @@
-import { mkdirSync, mkdtempSync, writeFileSync } from "node:fs";
-import { tmpdir } from "node:os";
+import { mkdirSync, writeFileSync } from "node:fs";
 import { join } from "node:path";
 import { describe, expect, it } from "vitest";
 import {
@@ -14,6 +13,7 @@ import {
   resolveGeneratedSources,
 } from "../src/capture.js";
 import { requiredSecrets } from "../src/resolve.js";
+import { tmp } from "./helpers/tmp.js";
 
 const CTX = {
   orgRepo: "heavy-duty/incubator",
@@ -241,7 +241,7 @@ describe("renderCapturePlan", () => {
 // the manifest's own templates, read by the same parser apply uses.
 describe("requiredSecrets", () => {
   function checkout(manifest: string, templates: Record<string, string>) {
-    const dir = mkdtempSync(join(tmpdir(), "cast-cap-"));
+    const dir = tmp("cast-cap-");
     mkdirSync(join(dir, ".infra", "env"), { recursive: true });
     writeFileSync(join(dir, ".infra", "manifest.yaml"), manifest);
     for (const [name, body] of Object.entries(templates)) {
diff --git a/test/cli.test.ts b/test/cli.test.ts
index bdc99b5..9d09e4a 100644
--- a/test/cli.test.ts
+++ b/test/cli.test.ts
@@ -1,10 +1,10 @@
 import { spawn } from "node:child_process";
-import { mkdirSync, mkdtempSync, writeFileSync } from "node:fs";
+import { mkdirSync, writeFileSync } from "node:fs";
 import { createServer } from "node:http";
 import type { AddressInfo } from "node:net";
-import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, describe, expect, it } from "vitest";
+import { tmp } from "./helpers/tmp.js";
 
 // Spawned ASYNCHRONOUSLY, and that is load-bearing: the stub Coolify below
 // runs in THIS process, so a blocking execFileSync would hold the event loop
@@ -74,7 +74,7 @@ function stateWith(opts: {
   named?: Record<string, string>;
   boundInstance?: string;
 }): string {
-  const dir = mkdtempSync(join(tmpdir(), "cast-cli-"));
+  const dir = tmp("cast-cli-");
   if (opts.default) writeFileSync(join(dir, ".coolify.env"), opts.default);
   if (opts.named) {
     mkdirSync(join(dir, ".coolify"));
diff --git a/test/config.test.ts b/test/config.test.ts
index 20ee672..fa47dfd 100644
--- a/test/config.test.ts
+++ b/test/config.test.ts
@@ -1,5 +1,4 @@
-import { mkdirSync, mkdtempSync, writeFileSync } from "node:fs";
-import { tmpdir } from "node:os";
+import { mkdirSync, writeFileSync } from "node:fs";
 import { join } from "node:path";
 import { describe, expect, it } from "vitest";
 import {
@@ -8,13 +7,14 @@ import {
   knownInstances,
   loadInstance,
 } from "../src/config.js";
+import { tmp } from "./helpers/tmp.js";
 
 // A state dir with a default .coolify.env and any number of named instances.
 function stateDir(
   named: Record<string, string> = {},
   defaultEnv?: string,
 ): string {
-  const dir = mkdtempSync(join(tmpdir(), "cast-state-"));
+  const dir = tmp("cast-state-");
   if (defaultEnv !== undefined) {
     writeFileSync(join(dir, ".coolify.env"), defaultEnv);
   }
diff --git a/test/destroy.test.ts b/test/destroy.test.ts
index e931a82..4813093 100644
--- a/test/destroy.test.ts
+++ b/test/destroy.test.ts
@@ -1,8 +1,7 @@
 import { spawn } from "node:child_process";
-import { mkdirSync, mkdtempSync, writeFileSync } from "node:fs";
+import { mkdirSync, writeFileSync } from "node:fs";
 import { createServer } from "node:http";
 import type { AddressInfo } from "node:net";
-import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, describe, expect, it } from "vitest";
 import {
@@ -14,6 +13,7 @@ import {
   readBackupState,
   renderDestroyPlan,
 } from "../src/destroy.js";
+import { tmp } from "./helpers/tmp.js";
 
 // The refusals ARE the product. `destroy` is the only verb in cast that removes
 // something a manifest declared, and the difference between it and a hand
@@ -460,11 +460,11 @@ function fixture(
   url: string,
   opts: { destroyAllowed?: boolean | undefined; readOnly?: boolean } = {},
 ) {
-  const checkout = mkdtempSync(join(tmpdir(), "cast-co-"));
+  const checkout = tmp("cast-co-");
   mkdirSync(join(checkout, ".infra"), { recursive: true });
   writeFileSync(join(checkout, ".infra", "manifest.yaml"), MANIFEST);
 
-  const state = mkdtempSync(join(tmpdir(), "cast-state-"));
+  const state = tmp("cast-state-");
   writeFileSync(
     join(state, ".coolify.env"),
     [
diff --git a/test/draft-cli.test.ts b/test/draft-cli.test.ts
index 6906217..dbf6083 100644
--- a/test/draft-cli.test.ts
+++ b/test/draft-cli.test.ts
@@ -2,20 +2,19 @@ import { execFileSync, spawn } from "node:child_process";
 import {
   existsSync,
   mkdirSync,
-  mkdtempSync,
   readFileSync,
   readdirSync,
   writeFileSync,
 } from "node:fs";
 import { createServer } from "node:http";
 import type { AddressInfo } from "node:net";
-import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, beforeAll, describe, expect, it } from "vitest";
 import { loadBindings } from "../src/bindings.js";
 import { GENERATED_PLACEHOLDER } from "../src/capture.js";
 import { loadManifest } from "../src/manifest.js";
 import { decryptSecrets } from "../src/secrets.js";
+import { tmp } from "./helpers/tmp.js";
 
 // `cast inventory --emit-draft` against a stub shaped like the box that made it
 // necessary: a Coolify nobody declared, holding our stack under names someone
@@ -215,7 +214,7 @@ let KEY_FILE = "";
 let RECIPIENT = "";
 
 beforeAll(() => {
-  const dir = mkdtempSync(join(tmpdir(), "cast-age-"));
+  const dir = tmp("cast-age-");
   KEY_FILE = join(dir, "key.txt");
   execFileSync("age-keygen", ["-o", KEY_FILE], { stdio: "ignore" });
   RECIPIENT = execFileSync("age-keygen", ["-y", KEY_FILE], {
@@ -224,7 +223,7 @@ beforeAll(() => {
 });
 
 function fixture(url: string, opts: { recipient?: string } = {}) {
-  const state = mkdtempSync(join(tmpdir(), "cast-state-"));
+  const state = tmp("cast-state-");
   writeFileSync(
     join(state, ".coolify.env"),
     `COOLIFY_BASE_URL="${url}"\nCOOLIFY_ACCESS_TOKEN="t"\n`,
@@ -242,7 +241,7 @@ function fixture(url: string, opts: { recipient?: string } = {}) {
       "",
     ].join("\n"),
   );
-  const out = join(mkdtempSync(join(tmpdir(), "cast-out-")), "draft");
+  const out = join(tmp("cast-out-"), "draft");
   return { state, out };
 }
 
diff --git a/test/draft.test.ts b/test/draft.test.ts
index 2e468f4..db450f7 100644
--- a/test/draft.test.ts
+++ b/test/draft.test.ts
@@ -1,5 +1,4 @@
-import { mkdirSync, mkdtempSync, writeFileSync } from "node:fs";
-import { tmpdir } from "node:os";
+import { mkdirSync, writeFileSync } from "node:fs";
 import { join } from "node:path";
 import { describe, expect, it } from "vitest";
 import { GENERATED_PLACEHOLDER } from "../src/capture.js";
@@ -14,6 +13,7 @@ import {
 } from "../src/draft.js";
 import { templateKeys, templateRefs } from "../src/envtemplate.js";
 import { loadManifest } from "../src/manifest.js";
+import { tmp } from "./helpers/tmp.js";
 
 const ctx = {
   env: "prod",
@@ -240,7 +240,7 @@ describe("planDraft — the emitted shape", () => {
     expect(manifest?.content).toContain("`apply` does not read this file");
     expect(manifest?.content).toContain("box-b");
 
-    const dir = mkdtempSync(join(tmpdir(), "cast-draft-"));
+    const dir = tmp("cast-draft-");
     const path = join(dir, "manifest.yaml");
     writeFileSync(path, manifest?.content ?? "");
     const loaded = loadManifest(path);
@@ -285,7 +285,7 @@ describe("planDraft — the emitted shape", () => {
     });
     const plan = planDraft([p], ctx);
     const manifest = plan.files.find((f) => f.path.endsWith("manifest.yaml"));
-    const dir = mkdtempSync(join(tmpdir(), "cast-draft-"));
+    const dir = tmp("cast-draft-");
     const path = join(dir, "manifest.yaml");
     writeFileSync(path, manifest?.content ?? "");
     const build =
@@ -325,7 +325,7 @@ describe("planDraft — the emitted shape", () => {
     });
     const plan = planDraft([p], ctx);
     const manifest = plan.files.find((f) => f.path.endsWith("manifest.yaml"));
-    const dir = mkdtempSync(join(tmpdir(), "cast-draft-"));
+    const dir = tmp("cast-draft-");
     const path = join(dir, "manifest.yaml");
     writeFileSync(path, manifest?.content ?? "");
     // The whole point: it loads (does not throw), and simply carries no `static`.
@@ -374,7 +374,7 @@ describe("planDraft — the emitted shape", () => {
     // `static: true` would be exactly the fabrication UNCAPTURED.md exists to
     // prevent.
     const manifest = plan.files.find((f) => f.path.endsWith("manifest.yaml"));
-    const dir = mkdtempSync(join(tmpdir(), "cast-draft-"));
+    const dir = tmp("cast-draft-");
     const path = join(dir, "manifest.yaml");
     writeFileSync(path, manifest?.content ?? "");
     const build =
@@ -598,7 +598,7 @@ describe("backup schedules — read and drafted, not hand-waved (#75)", () => {
   });
   const loadedDb = (plan: ReturnType<typeof planDraft>) => {
     const manifest = plan.files.find((f) => f.path.endsWith("manifest.yaml"));
-    const dir = mkdtempSync(join(tmpdir(), "cast-draft-"));
+    const dir = tmp("cast-draft-");
     const path = join(dir, "manifest.yaml");
     writeFileSync(path, manifest?.content ?? "");
     return loadManifest(path).environments.prod.databases?.[
@@ -690,7 +690,7 @@ describe("service hostnames — read and drafted via the per-service GET (#83)",
     });
   const loadedSvc = (plan: ReturnType<typeof planDraft>) => {
     const manifest = plan.files.find((f) => f.path.endsWith("manifest.yaml"));
-    const dir = mkdtempSync(join(tmpdir(), "cast-draft-"));
+    const dir = tmp("cast-draft-");
     const path = join(dir, "manifest.yaml");
     writeFileSync(path, manifest?.content ?? "");
     return loadManifest(path).environments.prod.services?.["Incubator Umami"];
@@ -739,20 +739,20 @@ describe("service hostnames — read and drafted via the per-service GET (#83)",
 
 describe("the emit refusals — adoption is one-way", () => {
   it("refuses a target directory that is not empty", () => {
-    const dir = mkdtempSync(join(tmpdir(), "cast-draft-"));
+    const dir = tmp("cast-draft-");
     writeFileSync(join(dir, "README.md"), "a repo lives here\n");
     expect(() => assertEmptyTarget(dir)).toThrow(/is not empty/);
     expect(() => assertEmptyTarget(dir)).toThrow(/Adoption is one-way/);
   });
 
   it("allows a directory that does not exist yet, and an empty one", () => {
-    const dir = mkdtempSync(join(tmpdir(), "cast-draft-"));
+    const dir = tmp("cast-draft-");
     expect(() => assertEmptyTarget(dir)).not.toThrow();
     expect(() => assertEmptyTarget(join(dir, "new"))).not.toThrow();
   });
 
   it("refuses to write a manifest over one that already exists", () => {
-    const dir = mkdtempSync(join(tmpdir(), "cast-draft-"));
+    const dir = tmp("cast-draft-");
     mkdirSync(join(dir, ".infra"), { recursive: true });
     const path = join(dir, ".infra", "manifest.yaml");
     writeFileSync(path, "project: incubator\n");
diff --git a/test/fleet-cli.test.ts b/test/fleet-cli.test.ts
index 2f68941..7d5203a 100644
--- a/test/fleet-cli.test.ts
+++ b/test/fleet-cli.test.ts
@@ -1,10 +1,10 @@
 import { execFileSync, spawn } from "node:child_process";
-import { mkdirSync, mkdtempSync, writeFileSync } from "node:fs";
+import { mkdirSync, writeFileSync } from "node:fs";
 import { createServer } from "node:http";
 import type { AddressInfo } from "node:net";
-import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, beforeAll, describe, expect, it } from "vitest";
+import { tmp } from "./helpers/tmp.js";
 
 // `cast diff --all` / `cast apply --all` (#26), end to end against a stub
 // Coolify carrying three projects.
@@ -26,7 +26,7 @@ let recipient: string;
 let keyFile: string;
 
 beforeAll(() => {
-  const dir = mkdtempSync(join(tmpdir(), "cast-age-"));
+  const dir = tmp("cast-age-");
   keyFile = join(dir, "age.key");
   execFileSync("age-keygen", ["-o", keyFile], { stdio: "pipe" });
   recipient = execFileSync("age-keygen", ["-y", keyFile], {
@@ -134,7 +134,7 @@ function fixture(
   url: string,
   opts: { registry?: string[]; registryEnv?: string; refIn?: string } = {},
 ) {
-  const root = mkdtempSync(join(tmpdir(), "cast-fleet-"));
+  const root = tmp("cast-fleet-");
   for (const repo of REPOS) {
     const dir = join(root, "repos", "heavy-duty", `${repo}.git`);
     mkdirSync(join(dir, ".infra"), { recursive: true });
diff --git a/test/github-app-cli.test.ts b/test/github-app-cli.test.ts
index dd8bb75..6f8d86d 100644
--- a/test/github-app-cli.test.ts
+++ b/test/github-app-cli.test.ts
@@ -1,10 +1,10 @@
 import { execFileSync, spawn } from "node:child_process";
-import { mkdirSync, mkdtempSync, writeFileSync } from "node:fs";
+import { mkdirSync, writeFileSync } from "node:fs";
 import { createServer } from "node:http";
 import type { AddressInfo } from "node:net";
-import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, beforeAll, describe, expect, it } from "vitest";
+import { tmp } from "./helpers/tmp.js";
 
 // When does `apply` need a GitHub App at all? (#103, found live in the
 // 2026-07-19 release drill.)
@@ -26,7 +26,7 @@ let recipient: string;
 let keyFile: string;
 
 beforeAll(() => {
-  const dir = mkdtempSync(join(tmpdir(), "cast-age-"));
+  const dir = tmp("cast-age-");
   keyFile = join(dir, "age.key");
   execFileSync("age-keygen", ["-o", keyFile], { stdio: "pipe" });
   recipient = execFileSync("age-keygen", ["-y", keyFile], {
@@ -112,11 +112,11 @@ environments:
 
 // The state file the issue is about: no github_apps entry for this repo at all.
 function fixture(url: string, manifest: string) {
-  const checkout = mkdtempSync(join(tmpdir(), "cast-co-"));
+  const checkout = tmp("cast-co-");
   mkdirSync(join(checkout, ".infra", "env"), { recursive: true });
   writeFileSync(join(checkout, ".infra", "manifest.yaml"), manifest);
 
-  const state = mkdtempSync(join(tmpdir(), "cast-state-"));
+  const state = tmp("cast-state-");
   mkdirSync(join(state, "secrets"));
   writeFileSync(
     join(state, ".coolify.env"),
diff --git a/test/greenfield-cli.test.ts b/test/greenfield-cli.test.ts
index b395fbe..d5afbc2 100644
--- a/test/greenfield-cli.test.ts
+++ b/test/greenfield-cli.test.ts
@@ -1,10 +1,10 @@
 import { execFileSync, spawn } from "node:child_process";
-import { mkdirSync, mkdtempSync, writeFileSync } from "node:fs";
+import { mkdirSync, writeFileSync } from "node:fs";
 import { createServer } from "node:http";
 import type { AddressInfo } from "node:net";
-import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, beforeAll, describe, expect, it } from "vitest";
+import { tmp } from "./helpers/tmp.js";
 
 // The greenfield manifest-first bootstrap (#104), end to end: fresh box,
 // registered project, a manifest that declares databases only and refs no
@@ -23,7 +23,7 @@ let recipient: string;
 let keyFile: string;
 
 beforeAll(() => {
-  const dir = mkdtempSync(join(tmpdir(), "cast-age-"));
+  const dir = tmp("cast-age-");
   keyFile = join(dir, "age.key");
   execFileSync("age-keygen", ["-o", keyFile], { stdio: "pipe" });
   recipient = execFileSync("age-keygen", ["-y", keyFile], {
@@ -100,7 +100,7 @@ function fixture(
     manifest: ZERO_REFS_MANIFEST,
   },
 ) {
-  const checkout = mkdtempSync(join(tmpdir(), "cast-co-"));
+  const checkout = tmp("cast-co-");
   mkdirSync(join(checkout, ".infra", "env"), { recursive: true });
   writeFileSync(join(checkout, ".infra", "manifest.yaml"), opts.manifest);
   writeFileSync(
@@ -108,7 +108,7 @@ function fixture(
     "API_KEY=${API_KEY}\n",
   );
 
-  const state = mkdtempSync(join(tmpdir(), "cast-state-"));
+  const state = tmp("cast-state-");
   mkdirSync(join(state, "secrets"));
   writeFileSync(
     join(state, ".coolify.env"),
@@ -148,7 +148,7 @@ function run(
     const { CAST_AGE_KEY_FILE_STAGING: _dropped, ...inherited } = process.env;
     const env = opts.withKey
       ? { ...inherited, CAST_AGE_KEY_FILE_STAGING: keyFile }
-      : { ...inherited, HOME: mkdtempSync(join(tmpdir(), "cast-home-")) };
+      : { ...inherited, HOME: tmp("cast-home-") };
     const child = spawn("node", ["dist/cli.js", "diff", ...args], {
       stdio: ["pipe", "pipe", "pipe"],
       env,
diff --git a/test/helpers/global-setup.ts b/test/helpers/global-setup.ts
new file mode 100644
index 0000000..5048db9
--- /dev/null
+++ b/test/helpers/global-setup.ts
@@ -0,0 +1,39 @@
+import { mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+// The env var that tells `tmp()` (test/helpers/tmp.ts) where to allocate.
+export const RUN_ROOT_ENV = "CAST_TEST_TMP_ROOT";
+
+// One directory per `vitest run`, holding every temp dir the suite allocates.
+//
+// This is what actually reaps the suite's temp dirs (#117). The obvious design —
+// each worker cleaning up after itself in a `process.once("exit")` hook — does
+// NOT work under vitest, and it fails silently, which is worse: vitest recycles
+// its pool workers by killing them, so `exit` handlers registered inside a test
+// file never run. Measured, not assumed: a probe test that wrote a file from an
+// `exit` hook produced no file, and a full suite run with per-worker exit hooks
+// still left 750 directories behind.
+//
+// globalSetup's teardown runs in vitest's MAIN process, after every worker has
+// finished, and vitest awaits it. That makes it the only hook in the run with
+// both of the properties this needs: it is guaranteed to execute, and it sees
+// the whole run rather than one worker's slice of it.
+//
+// Collapsing the whole run into a single root is what makes that teardown one
+// `rmSync` instead of a list to keep in sync across processes — the workers do
+// not have to report anything back, because the parent already knows the one
+// path that contains everything.
+export function setup(): () => void {
+  const root = mkdtempSync(join(tmpdir(), "cast-testrun-"));
+  process.env[RUN_ROOT_ENV] = root;
+
+  return function teardown(): void {
+    // Best-effort: a failure to clean up must not turn a green run red.
+    try {
+      rmSync(root, { recursive: true, force: true });
+    } catch {
+      // ignore
+    }
+  };
+}
diff --git a/test/helpers/tmp.ts b/test/helpers/tmp.ts
new file mode 100644
index 0000000..8f3b158
--- /dev/null
+++ b/test/helpers/tmp.ts
@@ -0,0 +1,54 @@
+import { mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { RUN_ROOT_ENV } from "./global-setup.js";
+
+// Every temp dir this process has handed out, in creation order.
+const created: string[] = [];
+
+// Where to allocate. Under `vitest run` this is the per-run root that
+// global-setup.ts created and will remove wholesale when the run ends; the
+// fallback keeps `tmp()` usable if a file is ever executed outside that config.
+function base(): string {
+  return process.env[RUN_ROOT_ENV] ?? tmpdir();
+}
+
+// Belt-and-braces reaper for the fallback case only.
+//
+// It is deliberately NOT the primary mechanism. Vitest recycles its pool workers
+// by killing them, so an `exit` handler registered from a test file does not run
+// — verified with a probe test, and by a full suite run that still leaked 750
+// directories with this hook in place. The real cleanup is global-setup.ts's
+// teardown, which runs in the main process where an exit IS orderly. This hook
+// only earns its keep when `tmp()` is called with no run root set, where nothing
+// else would ever remove the directory.
+let armed = false;
+
+function arm(): void {
+  if (armed) return;
+  armed = true;
+  process.once("exit", () => {
+    for (const dir of created) {
+      try {
+        rmSync(dir, { recursive: true, force: true });
+      } catch {
+        // ignore
+      }
+    }
+    created.length = 0;
+  });
+}
+
+/**
+ * Create a temp dir and register it for cleanup. Drop-in replacement for
+ * `mkdtempSync(join(tmpdir(), prefix))` — the prefix survives as the directory's
+ * basename, so paths stay as greppable as they were.
+ *
+ * @param prefix e.g. `"cast-home-"` — mkdtemp appends six random characters.
+ */
+export function tmp(prefix: string): string {
+  arm();
+  const dir = mkdtempSync(join(base(), prefix));
+  created.push(dir);
+  return dir;
+}
diff --git a/test/install-sh.test.ts b/test/install-sh.test.ts
index 54731e3..239cedb 100644
--- a/test/install-sh.test.ts
+++ b/test/install-sh.test.ts
@@ -4,16 +4,15 @@ import {
   copyFileSync,
   existsSync,
   mkdirSync,
-  mkdtempSync,
   readFileSync,
   readlinkSync,
   realpathSync,
   writeFileSync,
 } from "node:fs";
-import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { promisify } from "node:util";
 import { describe, expect, it } from "vitest";
+import { tmp } from "./helpers/tmp.js";
 
 const run = promisify(execFile);
 
@@ -59,7 +58,7 @@ type Sandbox = {
 };
 
 function sandbox(): Sandbox {
-  const root = mkdtempSync(join(tmpdir(), "cast-install-"));
+  const root = tmp("cast-install-");
   const stubs = join(root, "stubs");
   const home = join(root, "home");
   const dest = join(root, "cast-home");
diff --git a/test/layout-cli.test.ts b/test/layout-cli.test.ts
index 35b84cc..22e1c6b 100644
--- a/test/layout-cli.test.ts
+++ b/test/layout-cli.test.ts
@@ -4,15 +4,14 @@ import {
   copyFileSync,
   existsSync,
   mkdirSync,
-  mkdtempSync,
   readFileSync,
   realpathSync,
   writeFileSync,
 } from "node:fs";
-import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { promisify } from "node:util";
 import { describe, expect, it } from "vitest";
+import { tmp } from "./helpers/tmp.js";
 
 const run = promisify(execFile);
 
@@ -50,7 +49,7 @@ type Sandbox = {
 };
 
 async function installedSandbox(versions: string[]): Promise<Sandbox> {
-  const root = mkdtempSync(join(tmpdir(), "cast-layout-"));
+  const root = tmp("cast-layout-");
   const stubs = join(root, "stubs");
   const home = join(root, "home");
   const dest = join(root, "cast-home");
diff --git a/test/placement-cli.test.ts b/test/placement-cli.test.ts
index 15f44af..1d5d1c9 100644
--- a/test/placement-cli.test.ts
+++ b/test/placement-cli.test.ts
@@ -1,10 +1,10 @@
 import { execFileSync, spawn } from "node:child_process";
-import { mkdirSync, mkdtempSync, writeFileSync } from "node:fs";
+import { mkdirSync, writeFileSync } from "node:fs";
 import { createServer } from "node:http";
 import type { AddressInfo } from "node:net";
-import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, beforeAll, describe, expect, it } from "vitest";
+import { tmp } from "./helpers/tmp.js";
 
 // Placement, end to end: `environments.yaml` -> `cast diff` -> what it prints
 // and what it exits with. The unit tests prove each half (bindings resolve a
@@ -20,7 +20,7 @@ let recipient: string;
 let keyFile: string;
 
 beforeAll(() => {
-  const dir = mkdtempSync(join(tmpdir(), "cast-age-"));
+  const dir = tmp("cast-age-");
   keyFile = join(dir, "age.key");
   execFileSync("age-keygen", ["-o", keyFile], { stdio: "pipe" });
   recipient = execFileSync("age-keygen", ["-y", keyFile], {
@@ -103,11 +103,11 @@ environments:
 // `declared` is the destination_uuid the state file names for this project —
 // undefined means the state file says nothing, which is every state file today.
 function fixture(url: string, declared?: string) {
-  const checkout = mkdtempSync(join(tmpdir(), "cast-co-"));
+  const checkout = tmp("cast-co-");
   mkdirSync(join(checkout, ".infra", "env"), { recursive: true });
   writeFileSync(join(checkout, ".infra", "manifest.yaml"), MANIFEST);
 
-  const state = mkdtempSync(join(tmpdir(), "cast-state-"));
+  const state = tmp("cast-state-");
   mkdirSync(join(state, "secrets"));
   writeFileSync(
     join(state, ".coolify.env"),
diff --git a/test/read-side-cli.test.ts b/test/read-side-cli.test.ts
index 6f7facd..63ff1f7 100644
--- a/test/read-side-cli.test.ts
+++ b/test/read-side-cli.test.ts
@@ -1,10 +1,10 @@
 import { execFileSync, spawn } from "node:child_process";
-import { existsSync, mkdirSync, mkdtempSync, writeFileSync } from "node:fs";
+import { existsSync, mkdirSync, writeFileSync } from "node:fs";
 import { createServer } from "node:http";
 import type { AddressInfo } from "node:net";
-import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, beforeAll, describe, expect, it } from "vitest";
+import { tmp } from "./helpers/tmp.js";
 
 // The read side, end to end, against a stub Coolify shaped like a box nobody
 // declared: its project is `Incubator` (capital I), its environment is
@@ -31,7 +31,7 @@ const LIVE_ENV = {
 let recipient: string;
 
 beforeAll(() => {
-  const dir = mkdtempSync(join(tmpdir(), "cast-age-"));
+  const dir = tmp("cast-age-");
   const keyFile = join(dir, "age.key");
   execFileSync("age-keygen", ["-o", keyFile], { stdio: "pipe" });
   recipient = execFileSync("age-keygen", ["-y", keyFile], {
@@ -103,14 +103,14 @@ ADMIN_EMAIL=\${ADMIN_EMAIL}
 `;
 
 function fixture(url: string) {
-  const checkout = mkdtempSync(join(tmpdir(), "cast-co-"));
+  const checkout = tmp("cast-co-");
   mkdirSync(join(checkout, ".infra", "env"), { recursive: true });
   writeFileSync(join(checkout, ".infra", "manifest.yaml"), MANIFEST);
   writeFileSync(
     join(checkout, ".infra", "env", "core.staging.env.template"),
     TEMPLATE,
   );
-  const state = mkdtempSync(join(tmpdir(), "cast-state-"));
+  const state = tmp("cast-state-");
   mkdirSync(join(state, "secrets"));
   writeFileSync(
     join(state, ".coolify.env"),
diff --git a/test/release.test.ts b/test/release.test.ts
index 368d352..7161ef6 100644
--- a/test/release.test.ts
+++ b/test/release.test.ts
@@ -4,16 +4,15 @@ import {
   cpSync,
   existsSync,
   mkdirSync,
-  mkdtempSync,
   readFileSync,
   readlinkSync,
   realpathSync,
   writeFileSync,
 } from "node:fs";
-import { tmpdir } from "node:os";
 import { dirname, join } from "node:path";
 import { fileURLToPath } from "node:url";
 import { describe, expect, it } from "vitest";
+import { tmp } from "./helpers/tmp.js";
 
 // The release flow (#96), proven offline. Two surfaces: the changelog-section
 // extraction release.yml publishes (.github/scripts/release-notes.sh), and
@@ -84,7 +83,7 @@ Intro prose that belongs to no section.
 `;
 
 describe("release-notes.sh", () => {
-  const work = mkdtempSync(join(tmpdir(), "cast-relnotes-"));
+  const work = tmp("cast-relnotes-");
   const fix = join(work, "CHANGELOG.md");
   writeFileSync(fix, FIXTURE);
   const notes = (ver: string, file = fix) => run("bash", [NOTES, ver, file]);
@@ -277,7 +276,7 @@ function disarmedBecause(version: string, changelog: string): string | null {
 }
 
 describe("the changelog is armed for the next entry (rig#66)", () => {
-  const work = mkdtempSync(join(tmpdir(), "cast-arming-"));
+  const work = tmp("cast-arming-");
   const dated = (v: string) => `## ${v} — 2026-07-19`;
   const body = "\n\n- **An entry** — prose.\n";
   const armed = `# Changelog\n\n## Unreleased${body}\n${dated("0.2.0")}${body}`;
@@ -859,7 +858,7 @@ describe("release.yml", () => {
 // test opts into the stub build — so any release-channel install that
 // touches npm fails its assertion by failing the install.
 
-const STUB = mkdtempSync(join(tmpdir(), "cast-stub-"));
+const STUB = tmp("cast-stub-");
 writeFileSync(
   join(STUB, "curl"),
   `#!/usr/bin/env bash
@@ -943,7 +942,7 @@ async function runInstall(
   env: Record<string, string>,
   opts: { preexistingDest?: boolean } = {},
 ): Promise<Install> {
-  const work = mkdtempSync(join(tmpdir(), "cast-inst-"));
+  const work = tmp("cast-inst-");
   const dest = join(work, "dest");
   const bin = join(work, "bin");
   const curlLog = join(work, "curl.log");
@@ -976,7 +975,7 @@ async function runInstall(
 }
 
 describe("install.sh — the three channels", () => {
-  const work = mkdtempSync(join(tmpdir(), "cast-tarballs-"));
+  const work = tmp("cast-tarballs-");
   const asset = makeTarball(work, "9.9.9");
   const mainSrc = makeTarball(work, "main");
   const brokenAsset = makeTarball(join(work, "broken"), "9.9.9", {
diff --git a/test/reserved.test.ts b/test/reserved.test.ts
index 799de8b..4ef0f10 100644
--- a/test/reserved.test.ts
+++ b/test/reserved.test.ts
@@ -1,5 +1,4 @@
-import { mkdirSync, mkdtempSync, writeFileSync } from "node:fs";
-import { tmpdir } from "node:os";
+import { mkdirSync, writeFileSync } from "node:fs";
 import { join } from "node:path";
 import { describe, expect, it } from "vitest";
 import { classify } from "../src/capture.js";
@@ -12,6 +11,7 @@ import {
   requiredSecrets,
 } from "../src/resolve.js";
 import { SMOKE_KEEP_KEY, SMOKE_PROBE_KEY } from "../src/smoke.js";
+import { tmp } from "./helpers/tmp.js";
 
 // #50. Coolify injects SOURCE_COMMIT and the COOLIFY_* family itself, and SKIPS
 // its own injection of a name the resource already carries a var of
@@ -58,7 +58,7 @@ describe("the rule", () => {
 // --- resolve / apply: REFUSE ---------------------------------------------------
 
 function checkout(template: string, envName = "staging"): string {
-  const dir = mkdtempSync(join(tmpdir(), "infra-reserved-"));
+  const dir = tmp("infra-reserved-");
   mkdirSync(join(dir, ".infra", "env"), { recursive: true });
   writeFileSync(
     join(dir, ".infra", "manifest.yaml"),
diff --git a/test/resolve.test.ts b/test/resolve.test.ts
index ebe90dc..ed9b0a4 100644
--- a/test/resolve.test.ts
+++ b/test/resolve.test.ts
@@ -1,6 +1,8 @@
-import { mkdirSync, mkdtempSync, writeFileSync } from "node:fs";
+import { execFileSync } from "node:child_process";
+import { existsSync, mkdirSync, readdirSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
+import { pathToFileURL } from "node:url";
 import { describe, expect, it, vi } from "vitest";
 import { computeDiff } from "../src/diff.js";
 import { DERIVED_UNRESOLVED } from "../src/envtemplate.js";
@@ -12,6 +14,7 @@ import {
   resolveCheckout,
   resolveGitAuth,
 } from "../src/resolve.js";
+import { tmp } from "./helpers/tmp.js";
 
 describe("resolveCheckout", () => {
   it("hard-refuses --path with prod", () => {
@@ -27,6 +30,57 @@ describe("resolveCheckout", () => {
       }),
     ).toBe("/tmp/x");
   });
+
+  // #117: the ephemeral checkout used to survive the process that made it, so
+  // every `cast apply`/`diff`/`capture` without --path left a full clone behind.
+  // This has to run in a real child process — the reaper is an exit hook, and
+  // the thing under test is precisely what happens when the process ends.
+  //
+  // A stub `git` on PATH makes it hermetic and fast: the clone fails, which is
+  // the *harder* case, since the directory is created before the clone runs and
+  // the failure path rethrows. If the dir is gone after a failed clone, the
+  // registration happens early enough to cover the successful one too.
+  it("removes the ephemeral checkout when the process exits", () => {
+    const bin = tmp("cast-fakebin-");
+    writeFileSync(join(bin, "git"), "#!/bin/sh\nexit 1\n", { mode: 0o755 });
+
+    // Other suites (and other machines) have their own checkouts lying around;
+    // only the one this child allocates is ours to assert on.
+    const preexisting = new Set(
+      readdirSync(tmpdir()).filter((d) => d.startsWith("infra-checkout-")),
+    );
+
+    const script = `
+      const { resolveCheckout } = await import(${JSON.stringify(
+        pathToFileURL(join(process.cwd(), "dist/resolve.js")).href,
+      )});
+      try { resolveCheckout("acme/widget", { env: "dev" }); } catch {}
+      // Report what was allocated, then let the process exit normally.
+      const fs = await import("node:fs");
+      const os = await import("node:os");
+      console.log(JSON.stringify(
+        fs.readdirSync(os.tmpdir()).filter((d) => d.startsWith("infra-checkout-")),
+      ));
+    `;
+
+    const out = execFileSync(
+      process.execPath,
+      ["--input-type=module", "-e", script],
+      {
+        env: { ...process.env, PATH: `${bin}:${process.env.PATH}` },
+        encoding: "utf8",
+      },
+    );
+
+    const allocated: string[] = JSON.parse(
+      out.trim().split("\n").pop() ?? "[]",
+    );
+    const mine = allocated.filter((d) => !preexisting.has(d));
+    // It must have allocated exactly one — otherwise this test proves nothing.
+    expect(mine).toHaveLength(1);
+    // ...and that one must be gone now that the child has exited.
+    expect(existsSync(join(tmpdir(), mine[0]))).toBe(false);
+  });
 });
 
 describe("resolveGitAuth", () => {
@@ -119,7 +173,7 @@ describe("cloneFailureMessage", () => {
 
 describe("desiredFromManifest", () => {
   it("maps manifest + templates to Desired[] with resolved env", () => {
-    const dir = mkdtempSync(join(tmpdir(), "infra-co-"));
+    const dir = tmp("infra-co-");
     mkdirSync(join(dir, ".infra", "env"), { recursive: true });
     writeFileSync(
       join(dir, ".infra", "manifest.yaml"),
@@ -171,7 +225,7 @@ environments:
     expect(desired[0].fields).not.toHaveProperty("start_command");
   });
   it("emits is_static:false when static:false is explicitly declared (a guard against a UI flip)", () => {
-    const dir = mkdtempSync(join(tmpdir(), "infra-co-"));
+    const dir = tmp("infra-co-");
     mkdirSync(join(dir, ".infra"), { recursive: true });
     writeFileSync(
       join(dir, ".infra", "manifest.yaml"),
@@ -190,7 +244,7 @@ environments:
   });
   // #63: the static-site build settings a workspace monorepo needs.
   it("emits is_static:true and the three commands for a non-compose app that declares them", () => {
-    const dir = mkdtempSync(join(tmpdir(), "infra-co-"));
+    const dir = tmp("infra-co-");
     mkdirSync(join(dir, ".infra"), { recursive: true });
     writeFileSync(
       join(dir, ".infra", "manifest.yaml"),
@@ -226,7 +280,7 @@ environments:
   // /databases/{uuid}/backups), and the side channel is what made a `backup:`
   // block added to an existing database silently do nothing (#51).
   it("puts a database backup block in fields, so it is diffed like any other", () => {
-    const dir = mkdtempSync(join(tmpdir(), "infra-co-"));
+    const dir = tmp("infra-co-");
     mkdirSync(join(dir, ".infra"), { recursive: true });
     writeFileSync(
       join(dir, ".infra", "manifest.yaml"),
@@ -249,7 +303,7 @@ environments:
     });
   });
   it("leaves `backup` out of fields entirely when none is declared", () => {
-    const dir = mkdtempSync(join(tmpdir(), "infra-co-"));
+    const dir = tmp("infra-co-");
     mkdirSync(join(dir, ".infra"), { recursive: true });
     writeFileSync(
       join(dir, ".infra", "manifest.yaml"),
@@ -271,7 +325,7 @@ environments:
     expect("backup" in desired[0].fields).toBe(false);
   });
   it("emits a service's service_domains into fields, canonicalized (cast#72)", () => {
-    const dir = mkdtempSync(join(tmpdir(), "infra-co-"));
+    const dir = tmp("infra-co-");
     mkdirSync(join(dir, ".infra"), { recursive: true });
     writeFileSync(
       join(dir, ".infra", "manifest.yaml"),
@@ -297,7 +351,7 @@ environments:
     });
   });
   it("is clean for a service whose live per-container hostnames match (cast#72, no perpetual update)", () => {
-    const dir = mkdtempSync(join(tmpdir(), "infra-co-"));
+    const dir = tmp("infra-co-");
     mkdirSync(join(dir, ".infra"), { recursive: true });
     writeFileSync(
       join(dir, ".infra", "manifest.yaml"),
@@ -331,7 +385,7 @@ environments:
     expect(report.clean).toBe(true);
   });
   it("diffs a service whose declared hostname is missing live (apply will set it)", () => {
-    const dir = mkdtempSync(join(tmpdir(), "infra-co-"));
+    const dir = tmp("infra-co-");
     mkdirSync(join(dir, ".infra"), { recursive: true });
     writeFileSync(
       join(dir, ".infra", "manifest.yaml"),
@@ -370,7 +424,7 @@ environments:
     ]);
   });
   it("a service with no service_domains carries only its type", () => {
-    const dir = mkdtempSync(join(tmpdir(), "infra-co-"));
+    const dir = tmp("infra-co-");
     mkdirSync(join(dir, ".infra"), { recursive: true });
     writeFileSync(
       join(dir, ".infra", "manifest.yaml"),
@@ -387,7 +441,7 @@ environments:
     expect(desired[0].fields).toEqual({ type: "plausible" });
   });
   it("resolves a dockercompose app to docker_compose_location/docker_compose_domains and no port/healthcheck/domains keys", () => {
-    const dir = mkdtempSync(join(tmpdir(), "infra-co-"));
+    const dir = tmp("infra-co-");
     mkdirSync(join(dir, ".infra", "env"), { recursive: true });
     writeFileSync(
       join(dir, ".infra", "manifest.yaml"),
@@ -436,7 +490,7 @@ environments:
     expect(desired[0].fields).not.toHaveProperty("start_command");
   });
   it('warns that apply cannot enable "Include Source Commit in Build" on a dockercompose app (unsettable via the Coolify 4.1.2 API)', () => {
-    const dir = mkdtempSync(join(tmpdir(), "infra-co-"));
+    const dir = tmp("infra-co-");
     mkdirSync(join(dir, ".infra"), { recursive: true });
     writeFileSync(
       join(dir, ".infra", "manifest.yaml"),
@@ -466,7 +520,7 @@ environments:
     );
   });
   it("does not warn about the source-commit toggle for a non-dockercompose app (the build arg is a compose concern)", () => {
-    const dir = mkdtempSync(join(tmpdir(), "infra-co-"));
+    const dir = tmp("infra-co-");
     mkdirSync(join(dir, ".infra"), { recursive: true });
     writeFileSync(
       join(dir, ".infra", "manifest.yaml"),
@@ -486,7 +540,7 @@ environments:
     warn.mockRestore();
   });
   it("throws when the env is missing from the manifest", () => {
-    const dir = mkdtempSync(join(tmpdir(), "infra-co-"));
+    const dir = tmp("infra-co-");
     mkdirSync(join(dir, ".infra"), { recursive: true });
     writeFileSync(
       join(dir, ".infra", "manifest.yaml"),
@@ -505,7 +559,7 @@ describe("derived resource refs (#60)", () => {
     ref = "${resource:postgres.url}",
     dbBlock = "    databases:\n      postgres: { type: postgresql }\n",
   ): string => {
-    const dir = mkdtempSync(join(tmpdir(), "infra-co-"));
+    const dir = tmp("infra-co-");
     mkdirSync(join(dir, ".infra", "env"), { recursive: true });
     writeFileSync(
       join(dir, ".infra", "manifest.yaml"),
@@ -580,7 +634,7 @@ describe("derived domain refs (#66)", () => {
   // Assemble a manifest from an applications block plus one env template. The
   // env_template line is appended to whichever app comes last in `apps`.
   const write = (apps: string, tmpl: string): string => {
-    const dir = mkdtempSync(join(tmpdir(), "infra-co-"));
+    const dir = tmp("infra-co-");
     mkdirSync(join(dir, ".infra", "env"), { recursive: true });
     writeFileSync(
       join(dir, ".infra", "manifest.yaml"),
diff --git a/test/secrets.test.ts b/test/secrets.test.ts
index da908f5..3f19fe8 100644
--- a/test/secrets.test.ts
+++ b/test/secrets.test.ts
@@ -1,19 +1,13 @@
 import { execFileSync, spawn } from "node:child_process";
-import {
-  closeSync,
-  mkdirSync,
-  mkdtempSync,
-  openSync,
-  writeFileSync,
-} from "node:fs";
-import { tmpdir } from "node:os";
+import { closeSync, mkdirSync, openSync, writeFileSync } from "node:fs";
 import { join } from "node:path";
 import { describe, expect, it } from "vitest";
 import { decryptSecrets, keyFileFor, secretsFileFor } from "../src/secrets.js";
+import { tmp } from "./helpers/tmp.js";
 
 // A key file and a store encrypted to it, for the decrypt tests.
 function ageFixture(): { keyFile: string; enc: string } {
-  const dir = mkdtempSync(join(tmpdir(), "infra-age-"));
+  const dir = tmp("infra-age-");
   const keyFile = join(dir, "key.txt");
   execFileSync("age-keygen", ["-o", keyFile]);
   const recipient = execFileSync("age-keygen", ["-y", keyFile], {
@@ -70,7 +64,7 @@ describe("secretsFileFor", () => {
 describe("decryptSecrets identity caching", () => {
   it("a read-once pipe key survives two decrypts — the --all loop shape", () => {
     const { keyFile, enc } = ageFixture();
-    const dir = mkdtempSync(join(tmpdir(), "infra-fifo-"));
+    const dir = tmp("infra-fifo-");
     const fifo = join(dir, "key.fifo");
     execFileSync("mkfifo", [fifo]);
     // One writer, one serving of the key: exactly what a process substitution
@@ -124,7 +118,7 @@ describe("keyFileFor", () => {
     // Isolate $HOME: a standing age-drill-b.key on the dev machine must not
     // turn the refusal into a hit (os.homedir() reads $HOME on POSIX).
     const home = process.env.HOME;
-    process.env.HOME = mkdtempSync(join(tmpdir(), "cast-home-"));
+    process.env.HOME = tmp("cast-home-");
     try {
       expect(() => keyFileFor("drill-b")).toThrow(
         /no age key for drill-b.*CAST_AGE_KEY_FILE_DRILL_B.*age-drill-b\.key/s,
@@ -135,7 +129,7 @@ describe("keyFileFor", () => {
   });
   it("falls back to a standing key on disk when one exists", () => {
     const home = process.env.HOME;
-    const dir = mkdtempSync(join(tmpdir(), "cast-home-"));
+    const dir = tmp("cast-home-");
     const cfg = join(dir, ".config", "cast");
     mkdirSync(cfg, { recursive: true });
     writeFileSync(join(cfg, "age-staging.key"), "AGE-SECRET-KEY-1\n");
diff --git a/test/smoke-cli.test.ts b/test/smoke-cli.test.ts
index abcc068..79fca9d 100644
--- a/test/smoke-cli.test.ts
+++ b/test/smoke-cli.test.ts
@@ -1,10 +1,10 @@
 import { spawn } from "node:child_process";
-import { mkdtempSync, writeFileSync } from "node:fs";
+import { writeFileSync } from "node:fs";
 import { createServer } from "node:http";
 import type { AddressInfo } from "node:net";
-import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, describe, expect, it } from "vitest";
+import { tmp } from "./helpers/tmp.js";
 
 // `cast smoke`, end to end, against the instance shape #29 is actually about.
 //
@@ -167,7 +167,7 @@ function state(
     "acme/client-site": "core",
   },
 ): string {
-  const dir = mkdtempSync(join(tmpdir(), "cast-smoke-"));
+  const dir = tmp("cast-smoke-");
   writeFileSync(
     join(dir, ".coolify.env"),
     `COOLIFY_BASE_URL="${url}"\nCOOLIFY_ACCESS_TOKEN="t"\n`,
diff --git a/test/sweep-cli.test.ts b/test/sweep-cli.test.ts
index abd004e..826c7f8 100644
--- a/test/sweep-cli.test.ts
+++ b/test/sweep-cli.test.ts
@@ -1,10 +1,10 @@
 import { spawn } from "node:child_process";
-import { mkdirSync, mkdtempSync, writeFileSync } from "node:fs";
+import { mkdirSync, writeFileSync } from "node:fs";
 import { createServer } from "node:http";
 import type { AddressInfo } from "node:net";
-import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, describe, expect, it } from "vitest";
+import { tmp } from "./helpers/tmp.js";
 
 // The sweep, against a stub shaped like the box that made it necessary.
 //
@@ -91,10 +91,10 @@ environments:
 `;
 
 function fixture(url: string) {
-  const checkout = mkdtempSync(join(tmpdir(), "cast-co-"));
+  const checkout = tmp("cast-co-");
   mkdirSync(join(checkout, ".infra", "env"), { recursive: true });
   writeFileSync(join(checkout, ".infra", "manifest.yaml"), MANIFEST);
-  const state = mkdtempSync(join(tmpdir(), "cast-state-"));
+  const state = tmp("cast-state-");
   mkdirSync(join(state, "secrets"));
   writeFileSync(
     join(state, ".coolify.env"),
diff --git a/test/tmp-guard.test.ts b/test/tmp-guard.test.ts
new file mode 100644
index 0000000..a667a3c
--- /dev/null
+++ b/test/tmp-guard.test.ts
@@ -0,0 +1,52 @@
+import { readFileSync, readdirSync, statSync } from "node:fs";
+import { join, relative } from "node:path";
+import { fileURLToPath } from "node:url";
+import { describe, expect, it } from "vitest";
+
+const TEST_DIR = fileURLToPath(new URL(".", import.meta.url));
+
+// The only files allowed to call the raw API: the allocator and the per-run
+// root that global setup reaps. Everything else goes through `tmp()`.
+const HELPER = "helpers/tmp.ts";
+const ALLOWED = new Set([HELPER, "helpers/global-setup.ts"]);
+
+// Assembled at runtime rather than written out, so THIS file is not itself a
+// hit. Exempting the guard by path instead would punch a permanent hole in the
+// very check it performs.
+const NEEDLE = ["mkdtemp", "Sync"].join("");
+
+function walk(dir: string, acc: string[] = []): string[] {
+  for (const entry of readdirSync(dir)) {
+    if (entry === "node_modules") continue;
+    const full = join(dir, entry);
+    if (statSync(full).isDirectory()) walk(full, acc);
+    else acc.push(full);
+  }
+  return acc;
+}
+
+// The class guard the issue asks for (#117): the suite leaked 6731 temp dirs
+// because cleanup was opt-in and 68 sites opted out. Making `tmp()` the only
+// way to allocate is what keeps the next site clean by default — and this test
+// is what stops the next raw call surviving review, the same shape as box#112's
+// eof_guard_sweep. It is a source-text check on purpose: it fails at the point
+// the habit returns, not after a machine-day of accumulation.
+describe("temp dir allocation", () => {
+  it(`uses the tmp() helper everywhere — no raw ${NEEDLE} under test/`, () => {
+    const offenders = walk(TEST_DIR)
+      .filter((f) => /\.(ts|js|mjs|sh)$/.test(f))
+      .filter((f) => !ALLOWED.has(relative(TEST_DIR, f)))
+      .filter((f) => readFileSync(f, "utf8").includes(NEEDLE))
+      .map((f) => relative(TEST_DIR, f))
+      .sort();
+
+    expect(offenders).toEqual([]);
+  });
+
+  it("keeps the helper as the single allocation point", () => {
+    const helper = readFileSync(join(TEST_DIR, HELPER), "utf8");
+    expect(helper).toContain(NEEDLE);
+    // and it must actually reap
+    expect(helper).toContain("rmSync");
+  });
+});
diff --git a/vitest.config.ts b/vitest.config.ts
index 808ec69..91ae773 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -1,2 +1,8 @@
 import { defineConfig } from "vitest/config";
-export default defineConfig({ test: { include: ["test/**/*.test.ts"] } });
+export default defineConfig({
+  test: {
+    include: ["test/**/*.test.ts"],
+    // Creates the per-run temp root and removes it when the run ends (#117).
+    globalSetup: ["./test/helpers/global-setup.ts"],
+  },
+});