diff --git a/docs/packages/cli.mdx b/docs/packages/cli.mdx
index bee7781ea7..9aa0edfc56 100644
--- a/docs/packages/cli.mdx
+++ b/docs/packages/cli.mdx
@@ -1920,6 +1920,9 @@ default 3); `--json` prints the results as JSON.
 
 ## Keep the environment healthy
 
+HyperFrames keeps what it downloads and builds (the headless browser, models, optional packages, fonts and project
+history) under `~/.cache/hyperframes`. Set `HYPERFRAMES_CACHE_DIR` to an absolute path to keep it somewhere else.
+
 ### `doctor`
 
 Check the machine for everything a render needs.
diff --git a/packages/cli/src/audio/analysis/providers/apple.ts b/packages/cli/src/audio/analysis/providers/apple.ts
index 36e24a6348..ce3147147b 100644
--- a/packages/cli/src/audio/analysis/providers/apple.ts
+++ b/packages/cli/src/audio/analysis/providers/apple.ts
@@ -1,10 +1,10 @@
 import { createHash } from "node:crypto";
 import { existsSync } from "node:fs";
 import { mkdir, rename, writeFile } from "node:fs/promises";
-import { homedir } from "node:os";
 import { join } from "node:path";
 import type { AudioAnalysisProvider, AudioSignal } from "@hyperframes/core/audio-analysis";
 import { AVAILABLE, runFile, unavailable, withWavFile } from "./shared.js";
+import { hyperframesCacheDir } from "@hyperframes/core/cache-dir";
 
 const SOUND_ANALYSIS = "/System/Library/Frameworks/SoundAnalysis.framework";
 const MUSIC_UNDERSTANDING_MACOS = 27;
@@ -62,7 +62,7 @@ function atLeastOneWindow(signal: AudioSignal): AudioSignal {
   };
 }
 
-const helperDir = () => join(homedir(), ".cache", "hyperframes", "audio-helpers");
+const helperDir = () => hyperframesCacheDir("audio-helpers");
 
 function helperPath(name: string, source: string): string {
   const hash = createHash("sha256").update(source).digest("hex").slice(0, 12);
diff --git a/packages/cli/src/background-removal/coremlTemp.ts b/packages/cli/src/background-removal/coremlTemp.ts
index 1b92779995..3d1fb33f5f 100644
--- a/packages/cli/src/background-removal/coremlTemp.ts
+++ b/packages/cli/src/background-removal/coremlTemp.ts
@@ -1,17 +1,12 @@
 import { mkdirSync, readdirSync, readFileSync, rmSync, writeFileSync } from "node:fs";
-import { homedir, tmpdir } from "node:os";
+import { tmpdir } from "node:os";
+import { hyperframesCacheDir } from "@hyperframes/core/cache-dir";
 import { basename, join } from "node:path";
 import { processIsAlive } from "../utils/processTree.js";
 
 const COMPILED_MODEL = /^onnxruntime-.*\.mlmodelc?$/;
 
-const COREML_TEMP_MANIFESTS = join(
-  homedir(),
-  ".cache",
-  "hyperframes",
-  "background-removal",
-  "coreml-temp",
-);
+const COREML_TEMP_MANIFESTS = hyperframesCacheDir("background-removal", "coreml-temp");
 
 interface Manifest {
   pid: number;
diff --git a/packages/cli/src/background-removal/manager.ts b/packages/cli/src/background-removal/manager.ts
index d149c0e2ea..3a37b40dd2 100644
--- a/packages/cli/src/background-removal/manager.ts
+++ b/packages/cli/src/background-removal/manager.ts
@@ -1,9 +1,10 @@
 import { existsSync, mkdirSync } from "node:fs";
-import { homedir, platform, arch } from "node:os";
+import { platform, arch } from "node:os";
 import { join } from "node:path";
 import { downloadFile } from "../utils/download.js";
+import { hyperframesCacheDir } from "@hyperframes/core/cache-dir";
 
-export const MODELS_DIR = join(homedir(), ".cache", "hyperframes", "background-removal", "models");
+export const MODELS_DIR = hyperframesCacheDir("background-removal", "models");
 
 export const DEFAULT_MODEL = "u2net_human_seg" as const;
 export type ModelId = typeof DEFAULT_MODEL;
diff --git a/packages/cli/src/browser/manager.ts b/packages/cli/src/browser/manager.ts
index 380e4b53a4..831b18ebaf 100644
--- a/packages/cli/src/browser/manager.ts
+++ b/packages/cli/src/browser/manager.ts
@@ -24,6 +24,7 @@ import { BrowserDownloadStalledError, installInChild } from "./installInChild.js
 import { normalizeErrorMessage } from "../utils/errorMessage.js";
 import { runRenderSetupWorker } from "../utils/cancellableProcess.js";
 import { unzipArchive } from "./unzipArchive.js";
+import { hyperframesCacheDir } from "@hyperframes/core/cache-dir";
 
 type PuppeteerBrowsers = typeof import("@puppeteer/browsers");
 
@@ -39,8 +40,8 @@ async function loadPuppeteerBrowsers(): Promise<PuppeteerBrowsers> {
   }
 }
 
-const CACHE_ROOT_DIR = join(homedir(), ".cache", "hyperframes");
-const CACHE_DIR = join(homedir(), ".cache", "hyperframes", "chrome");
+const CACHE_ROOT_DIR = hyperframesCacheDir();
+const CACHE_DIR = hyperframesCacheDir("chrome");
 const ARCHIVE_PLUS_UNPACKED_SHELL_MB = 512;
 // Puppeteer's managed cache — where `@puppeteer/browsers install
 // chrome-headless-shell` (and `puppeteer install`) drop binaries. The engine's
diff --git a/packages/cli/src/cloud/offload.ts b/packages/cli/src/cloud/offload.ts
index 11516c0110..459bfee2ba 100644
--- a/packages/cli/src/cloud/offload.ts
+++ b/packages/cli/src/cloud/offload.ts
@@ -15,7 +15,7 @@ import {
   rmSync,
   writeFileSync,
 } from "node:fs";
-import { homedir, tmpdir } from "node:os";
+import { tmpdir } from "node:os";
 import { basename, dirname, extname, join, posix, relative, resolve } from "node:path";
 import { promisify } from "node:util";
 import { parseHTML } from "linkedom";
@@ -41,6 +41,7 @@ import {
   stagedSize,
   TEXT_FILE_EXTS,
 } from "../utils/publishProject.js";
+import { hyperframesCacheDir } from "@hyperframes/core/cache-dir";
 
 const execFileAsync = promisify(execFile);
 
@@ -202,7 +203,7 @@ interface CacheEntry {
 }
 
 function defaultOffloadCachePath(): string {
-  return join(homedir(), ".cache", "hyperframes", "cloud-assets.json");
+  return hyperframesCacheDir("cloud-assets.json");
 }
 
 function readCache(path: string): Record<string, CacheEntry> {
@@ -652,7 +653,7 @@ async function prepareEntryGifs(
     downloadDir: outputDir,
     outputDir,
     outputSrcPrefix: posix.relative(posix.dirname(entryPath), GIF_PREFIX),
-    cacheDir: join(homedir(), ".cache", "hyperframes", "animated-gif"),
+    cacheDir: hyperframesCacheDir("animated-gif"),
     sourceAssets,
   });
   if (result.preparedGifs.length === 0) return;
diff --git a/packages/cli/src/commands/lambda/prebuiltHandler.ts b/packages/cli/src/commands/lambda/prebuiltHandler.ts
index 81d0f72fa4..2a6df0fae6 100644
--- a/packages/cli/src/commands/lambda/prebuiltHandler.ts
+++ b/packages/cli/src/commands/lambda/prebuiltHandler.ts
@@ -11,14 +11,14 @@ import {
   renameSync,
   unlinkSync,
 } from "node:fs";
-import { homedir } from "node:os";
 import { dirname, join } from "node:path";
 import { downloadFile } from "../../utils/download.js";
 import { isMissingPackageError } from "../../utils/missingPackage.js";
 import { VERSION } from "../../version.js";
+import { hyperframesCacheDir } from "@hyperframes/core/cache-dir";
 
 const DOCS_URL = "https://hyperframes.heygen.com/deploy/aws-lambda";
-const HANDLER_CACHE_DIR = join(homedir(), ".cache", "hyperframes", "lambda-handler");
+const HANDLER_CACHE_DIR = hyperframesCacheDir("lambda-handler");
 
 type AdapterSdk = typeof import("@hyperframes/aws-lambda/sdk");
 
diff --git a/packages/cli/src/measure/opencv.ts b/packages/cli/src/measure/opencv.ts
index 6cdcb4f541..654571e136 100644
--- a/packages/cli/src/measure/opencv.ts
+++ b/packages/cli/src/measure/opencv.ts
@@ -3,14 +3,14 @@
 // Haar face models, pinned by size and sha256, into ~/.cache/hyperframes/opencv/<version>/.
 import { mkdirSync, readFileSync, renameSync, rmSync } from "node:fs";
 import { createRequire } from "node:module";
-import { homedir } from "node:os";
 import { join } from "node:path";
+import { hyperframesCacheDir } from "@hyperframes/core/cache-dir";
 import { downloadToFile } from "../cloud/download.js";
 import { verifies, type ModelFile } from "../whisper/modelFile.js";
 import { Fix } from "./media.js";
 
 const VERSION = "4.10.0";
-export const OPENCV_DIR = join(homedir(), ".cache", "hyperframes", "opencv", VERSION);
+export const OPENCV_DIR = hyperframesCacheDir("opencv", VERSION);
 
 interface Pinned extends ModelFile {
   url: string;
diff --git a/packages/cli/src/tts/manager.ts b/packages/cli/src/tts/manager.ts
index 317f8d307b..6181aedf43 100644
--- a/packages/cli/src/tts/manager.ts
+++ b/packages/cli/src/tts/manager.ts
@@ -1,9 +1,9 @@
 import { existsSync, mkdirSync } from "node:fs";
-import { homedir } from "node:os";
 import { join } from "node:path";
 import { downloadFile } from "../utils/download.js";
+import { hyperframesCacheDir } from "@hyperframes/core/cache-dir";
 
-const CACHE_DIR = join(homedir(), ".cache", "hyperframes", "tts");
+const CACHE_DIR = hyperframesCacheDir("tts");
 const MODELS_DIR = join(CACHE_DIR, "models");
 const VOICES_DIR = join(CACHE_DIR, "voices");
 
diff --git a/packages/cli/src/tts/synthesize.ts b/packages/cli/src/tts/synthesize.ts
index 4ec225a248..c1b0390605 100644
--- a/packages/cli/src/tts/synthesize.ts
+++ b/packages/cli/src/tts/synthesize.ts
@@ -2,7 +2,6 @@
 import { execFileSync } from "node:child_process";
 import { existsSync, mkdirSync, readdirSync, unlinkSync } from "node:fs";
 import { join, dirname, basename } from "node:path";
-import { homedir } from "node:os";
 import {
   ensureModel,
   ensureVoices,
@@ -12,6 +11,7 @@ import {
 } from "./manager.js";
 import { findPython, hasPythonPackage, workingPythonEnv } from "./python.js";
 import { writeNewFileSync } from "../utils/writeNewFile.js";
+import { hyperframesCacheDir } from "@hyperframes/core/cache-dir";
 
 // ---------------------------------------------------------------------------
 // Inline Python script for Kokoro synthesis
@@ -115,7 +115,7 @@ const ESPEAK_LANG_OVERRIDES: Partial<Record<SupportedLang, string>> = {
 // Cache the script to avoid rewriting it on every invocation.
 // The filename carries a version suffix so older installs automatically
 // upgrade when the script body changes (e.g., adding the `lang` kwarg).
-const SCRIPT_DIR = join(homedir(), ".cache", "hyperframes", "tts");
+const SCRIPT_DIR = hyperframesCacheDir("tts");
 const SCRIPT_PATH = join(SCRIPT_DIR, "synth-v4.py");
 
 function ensureSynthScript(): string {
diff --git a/packages/cli/src/utils/optionalPackages.test.ts b/packages/cli/src/utils/optionalPackages.test.ts
index a93974dc64..c98bfcdd2f 100644
--- a/packages/cli/src/utils/optionalPackages.test.ts
+++ b/packages/cli/src/utils/optionalPackages.test.ts
@@ -611,9 +611,8 @@ describe("install", () => {
   function setup() {
     const cache = mkdtempSync(join(tmpdir(), "hf-optional-"));
     const dir = join(cache, "pkg@1.0.0");
-    const stubNpm = async (args: string[]) => {
+    const stubNpm = async (_args: string[], prefix: string) => {
       await new Promise((r) => setTimeout(r, 50));
-      const prefix = args[args.indexOf("--prefix") + 1] as string;
       if (!existsSync(prefix)) throw new Error("ENOENT: staging dir vanished mid-install");
       mkdirSync(join(prefix, "node_modules", name), { recursive: true });
       writeFileSync(join(prefix, "node_modules", name, "package.json"), "{}");
@@ -621,6 +620,22 @@ describe("install", () => {
     return { cache, dir, stubNpm };
   }
 
+  it("runs npm inside the staging dir, with no path on its command line", async () => {
+    const { cache, dir } = setup();
+    const seen: { args: string[]; cwd: string }[] = [];
+    try {
+      await install(dir, name, version, async (args, cwd) => {
+        seen.push({ args, cwd });
+      });
+      expect(seen).toHaveLength(1);
+      expect(seen[0]!.args).not.toContain("--prefix");
+      expect(seen[0]!.args.some((arg) => arg.includes(cache))).toBe(false);
+      expect(seen[0]!.cwd.startsWith(`${dir}.tmp-`)).toBe(true);
+    } finally {
+      rmSync(cache, { recursive: true, force: true });
+    }
+  });
+
   it("gives each overlapping install in one process its own staging dir", async () => {
     const { cache, dir, stubNpm } = setup();
     try {
diff --git a/packages/cli/src/utils/optionalPackages.ts b/packages/cli/src/utils/optionalPackages.ts
index 81ae64fc76..5126ddc5a3 100644
--- a/packages/cli/src/utils/optionalPackages.ts
+++ b/packages/cli/src/utils/optionalPackages.ts
@@ -12,9 +12,9 @@ import {
   writeFileSync,
 } from "node:fs";
 import { createRequire } from "node:module";
-import { homedir } from "node:os";
 import { basename, dirname, join, sep } from "node:path";
 import { buildNpmCommand } from "./npxCommand.js";
+import { hyperframesCacheDir } from "@hyperframes/core/cache-dir";
 
 /** Module type of each optional package; the keys are the only names the loader accepts. */
 export interface OptionalPackageModules {
@@ -37,7 +37,7 @@ export const PINNED_PACKAGES = {
 
 type PinnedPackage = keyof typeof PINNED_PACKAGES;
 
-export const CACHE_DIR = join(homedir(), ".cache", "hyperframes", "optional");
+export const CACHE_DIR = hyperframesCacheDir("optional");
 
 /** Installed on first use only when a host bundled the CLI without its sharp dependency. */
 export const SHARP_VERSION = "0.35.3";
@@ -286,9 +286,9 @@ export function loadBesideCli(name: PinnedPackage, cliUrl = import.meta.url): un
   return copy?.resolution === "entry" ? createRequire(cliUrl)(copy.path) : null;
 }
 
-export function runNpm(args: string[], signal?: AbortSignal): Promise<void> {
+export function runNpm(args: string[], signal?: AbortSignal, cwd?: string): Promise<void> {
   const npm = buildNpmCommand(args);
-  const child = spawn(npm.command, npm.args, { stdio: ["ignore", "pipe", "pipe"], signal });
+  const child = spawn(npm.command, npm.args, { stdio: ["ignore", "pipe", "pipe"], signal, cwd });
   return new Promise((resolve, reject) => {
     let output = "";
     child.stdout.on("data", (chunk) => (output += chunk));
@@ -340,26 +340,27 @@ export async function install(
   dir: string,
   name: string,
   version: string,
-  run: (args: string[]) => Promise<void> = runNpm,
+  run: (args: string[], cwd: string) => Promise<void> = (args, cwd) => runNpm(args, undefined, cwd),
 ): Promise<void> {
   sweepStaleStaging(dir);
   const staging = `${dir}.tmp-${process.pid}-${randomUUID().slice(0, 8)}`;
   mkdirSync(staging, { recursive: true });
   writeFileSync(join(staging, "package.json"), "{}");
   try {
-    await run([
-      "install",
-      `${name}@${version}`,
-      "--prefix",
+    await run(
+      [
+        "install",
+        `${name}@${version}`,
+        "--no-audit",
+        "--no-fund",
+        "--loglevel=error",
+        // A first-use install is interactive, not a CI resolve: fail fast and name the
+        // manual command instead of sitting through npm's default multi-minute backoff.
+        "--fetch-retries=0",
+        "--fetch-timeout=20000",
+      ],
       staging,
-      "--no-audit",
-      "--no-fund",
-      "--loglevel=error",
-      // A first-use install is interactive, not a CI resolve: fail fast and name the
-      // manual command instead of sitting through npm's default multi-minute backoff.
-      "--fetch-retries=0",
-      "--fetch-timeout=20000",
-    ]);
+    );
     if (isInstalled(dir, name)) return;
     rmSync(dir, { recursive: true, force: true });
     renameSync(staging, dir);
diff --git a/packages/cli/src/warmCheckProtocol.ts b/packages/cli/src/warmCheckProtocol.ts
index 1c46924a59..b0fcef0ec4 100644
--- a/packages/cli/src/warmCheckProtocol.ts
+++ b/packages/cli/src/warmCheckProtocol.ts
@@ -4,6 +4,7 @@ import { homedir } from "node:os";
 import { join } from "node:path";
 import { Writable } from "node:stream";
 import { fileURLToPath } from "node:url";
+import { hyperframesCacheDir } from "@hyperframes/core/cache-dir";
 
 export const WARM_IDLE_MS = 5 * 60_000;
 export const HANDSHAKE_TIMEOUT_MS = 2_000;
@@ -50,7 +51,7 @@ export function warmCheckDirectory(env = process.env): string | undefined {
       ? join(env.LOCALAPPDATA ?? join(homedir(), "AppData", "Local"), "hyperframes", "warm")
       : env.XDG_RUNTIME_DIR
         ? join(env.XDG_RUNTIME_DIR, "hyperframes-warm")
-        : join(homedir(), ".cache", "hyperframes", "warm");
+        : hyperframesCacheDir("warm");
   try {
     mkdirSync(dir, { recursive: true, mode: 0o700 });
   } catch {
diff --git a/packages/cli/src/whisper/manager.install.test.ts b/packages/cli/src/whisper/manager.install.test.ts
index f959e98450..3a2acf4e28 100644
--- a/packages/cli/src/whisper/manager.install.test.ts
+++ b/packages/cli/src/whisper/manager.install.test.ts
@@ -38,3 +38,28 @@ it("never installs when the runtime vanishes after discovery and installation is
     rmSync(dir, { recursive: true, force: true });
   }
 });
+
+it("clones whisper.cpp inside its build dir, with no cache path on the command line", async () => {
+  const cache = mkdtempSync(join(tmpdir(), "hf-whisper-cache-"));
+  vi.stubEnv("HYPERFRAMES_CACHE_DIR", cache);
+  vi.resetModules();
+  const { ensureWhisper: ensure, WhisperUnavailableError: Unavailable } =
+    await import("./manager.js");
+  calls.exec.mockImplementation((command: string, args: string[]) => {
+    const lookup = command === "which" || command === "where";
+    if (lookup && (args[0] === "brew" || args[0] === "whisper-cli"))
+      throw new Error("not available");
+    if (lookup) return `/bin/${args[0]}\n`;
+    if (command === "git" && args[0] === "clone") throw new Error("stop after the clone");
+    return "";
+  });
+  try {
+    await expect(ensure()).rejects.toBeInstanceOf(Unavailable);
+    const clone = calls.exec.mock.calls.find(([c, a]) => c === "git" && a[0] === "clone");
+    const [, args, options] = clone as [string, string[], { cwd?: string }];
+    expect(args.some((arg) => arg.includes(cache))).toBe(false);
+    expect(options.cwd).toBe(join(cache, "whisper", "whisper.cpp"));
+  } finally {
+    rmSync(cache, { recursive: true, force: true });
+  }
+});
diff --git a/packages/cli/src/whisper/manager.ts b/packages/cli/src/whisper/manager.ts
index 97aa68cb57..f1a69bc4be 100644
--- a/packages/cli/src/whisper/manager.ts
+++ b/packages/cli/src/whisper/manager.ts
@@ -1,14 +1,15 @@
 // fallow-ignore-file code-duplication complexity
 import { execFileSync } from "node:child_process";
 import { existsSync, mkdirSync, readdirSync, rmSync, statSync } from "node:fs";
-import { homedir, platform } from "node:os";
+import { platform } from "node:os";
 import { join } from "node:path";
 import { findFFmpeg } from "../browser/ffmpeg.js";
 import { downloadFile } from "../utils/download.js";
 import { stoppableExecFile } from "../utils/stoppableExecFile.js";
 import { verifies, type ModelFile } from "./modelFile.js";
+import { hyperframesCacheDir } from "@hyperframes/core/cache-dir";
 
-const MODELS_DIR = join(homedir(), ".cache", "hyperframes", "whisper", "models");
+const MODELS_DIR = hyperframesCacheDir("whisper", "models");
 const DEFAULT_MODEL = "small.en";
 
 export type WhisperSource = "env" | "system" | "brew" | "build";
@@ -144,7 +145,7 @@ function findFromSystem(): WhisperResult | undefined {
 
 // --- Build from source ------------------------------------------------------
 
-const BUILD_DIR = join(homedir(), ".cache", "hyperframes", "whisper", "whisper.cpp");
+const BUILD_DIR = hyperframesCacheDir("whisper", "whisper.cpp");
 const WHISPER_REPO = "https://github.com/ggml-org/whisper.cpp.git";
 
 function findBuiltBinary(): WhisperResult | undefined {
@@ -168,10 +169,9 @@ async function buildFromSource(
 
   if (!existsSync(BUILD_DIR)) {
     onProgress?.("Downloading whisper.cpp...");
-    mkdirSync(join(homedir(), ".cache", "hyperframes", "whisper"), {
-      recursive: true,
-    });
-    await stoppableExecFile("git", ["clone", "--depth", "1", WHISPER_REPO, BUILD_DIR], {
+    mkdirSync(BUILD_DIR, { recursive: true });
+    await stoppableExecFile("git", ["clone", "--depth", "1", WHISPER_REPO, "."], {
+      cwd: BUILD_DIR,
       stdio: "ignore",
       timeout: 60_000,
       env: { ...process.env, GIT_TERMINAL_PROMPT: "0" },
diff --git a/packages/cli/src/whisper/sherpa.test.ts b/packages/cli/src/whisper/sherpa.test.ts
index 32342c35c9..428166df6d 100644
--- a/packages/cli/src/whisper/sherpa.test.ts
+++ b/packages/cli/src/whisper/sherpa.test.ts
@@ -92,8 +92,8 @@ describe("installSherpaRuntime", () => {
       expect(await sherpaRuntimeLoadError(dir)).toBe(
         "libonnxruntime.so: cannot open shared object",
       );
-      const run = vi.fn(async (args: string[]) =>
-        fakeRuntime(args[args.indexOf("--prefix") + 1]!, LOADS),
+      const run = vi.fn(async (_args: string[], _signal?: AbortSignal, cwd?: string) =>
+        fakeRuntime(cwd!, LOADS),
       );
 
       expect(await installSherpaRuntime({ run, dir })).toEqual({
@@ -125,8 +125,8 @@ describe("installSherpaRuntime", () => {
   it("fails with the loader's error when the reinstalled runtime still does not load", async () => {
     const dir = mkdtempSync(join(tmpdir(), "hf-sherpa-runtime-"));
     try {
-      const run = vi.fn(async (args: string[]) =>
-        fakeRuntime(args[args.indexOf("--prefix") + 1]!, BROKEN),
+      const run = vi.fn(async (_args: string[], _signal?: AbortSignal, cwd?: string) =>
+        fakeRuntime(cwd!, BROKEN),
       );
       await expect(installSherpaRuntime({ run, dir })).rejects.toThrow(
         "The sherpa-onnx runtime was reinstalled but still does not load (libonnxruntime.so: cannot open shared object). Use --engine whisper for now.",
diff --git a/packages/cli/src/whisper/sherpa.ts b/packages/cli/src/whisper/sherpa.ts
index f18a6c0937..2940db8c15 100644
--- a/packages/cli/src/whisper/sherpa.ts
+++ b/packages/cli/src/whisper/sherpa.ts
@@ -1,7 +1,7 @@
 import { execFile, spawn, type ExecFileException } from "node:child_process";
 import { randomUUID } from "node:crypto";
 import { mkdirSync, renameSync, rmSync, statSync } from "node:fs";
-import { homedir } from "node:os";
+import { hyperframesCacheDir } from "@hyperframes/core/cache-dir";
 import { join } from "node:path";
 import { createInterface } from "node:readline";
 import { fileURLToPath } from "node:url";
@@ -45,13 +45,7 @@ export const SHERPA_RUNTIME_DIR = join(
 
 const MODEL_REPO = "csukuangfj/sherpa-onnx-nemo-parakeet-tdt-0.6b-v3-int8";
 const MODEL_REVISION = "2bda32ec70b097a55adaa07d9a7173915b43cc78";
-export const PARAKEET_MODEL_DIR = join(
-  homedir(),
-  ".cache",
-  "hyperframes",
-  "parakeet",
-  "parakeet-tdt-0.6b-v3-int8",
-);
+export const PARAKEET_MODEL_DIR = hyperframesCacheDir("parakeet", "parakeet-tdt-0.6b-v3-int8");
 
 export type { ModelFile };
 
@@ -252,7 +246,7 @@ export async function installSherpaRuntime({
   // install() keeps any dir holding the runtime manifest, so a broken one goes first.
   rmSync(dir, { recursive: true, force: true });
   const native = sherpaPlatformPackage();
-  await install(dir, RUNTIME, RUNTIME_VERSION, (args) => run([...args, native], signal));
+  await install(dir, RUNTIME, RUNTIME_VERSION, (args, cwd) => run([...args, native], signal, cwd));
   const selected = await cachedRuntime(dir, 60_000, signal);
   if (selected.status === "unavailable") {
     throw new Error(
diff --git a/packages/core/package-subpaths.json b/packages/core/package-subpaths.json
index d901470b2a..d1aca87de1 100644
--- a/packages/core/package-subpaths.json
+++ b/packages/core/package-subpaths.json
@@ -68,6 +68,12 @@
       "types": "./dist/atomicFile.d.ts",
       "environments": ["bun", "node"]
     },
+    "./cache-dir": {
+      "source": "./src/cacheDir.ts",
+      "runtime": "./dist/cacheDir.js",
+      "types": "./dist/cacheDir.d.ts",
+      "environments": ["bun", "node"]
+    },
     "./remove-tree": {
       "source": "./src/removeTree.ts",
       "runtime": "./dist/removeTree.js",
diff --git a/packages/core/package.json b/packages/core/package.json
index 94c8953dea..194eb67ab8 100644
--- a/packages/core/package.json
+++ b/packages/core/package.json
@@ -80,6 +80,12 @@
       "import": "./src/atomicFile.ts",
       "types": "./src/atomicFile.ts"
     },
+    "./cache-dir": {
+      "bun": "./src/cacheDir.ts",
+      "node": "./dist/cacheDir.js",
+      "import": "./src/cacheDir.ts",
+      "types": "./src/cacheDir.ts"
+    },
     "./remove-tree": {
       "bun": "./src/removeTree.ts",
       "node": "./dist/removeTree.js",
@@ -662,6 +668,10 @@
         "import": "./dist/atomicFile.js",
         "types": "./dist/atomicFile.d.ts"
       },
+      "./cache-dir": {
+        "import": "./dist/cacheDir.js",
+        "types": "./dist/cacheDir.d.ts"
+      },
       "./remove-tree": {
         "import": "./dist/removeTree.js",
         "types": "./dist/removeTree.d.ts"
diff --git a/packages/core/src/cacheDir.test.ts b/packages/core/src/cacheDir.test.ts
new file mode 100644
index 0000000000..0edded2d1e
--- /dev/null
+++ b/packages/core/src/cacheDir.test.ts
@@ -0,0 +1,59 @@
+import { readdirSync, readFileSync } from "node:fs";
+import { homedir, tmpdir } from "node:os";
+import { join, resolve } from "node:path";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { hyperframesCacheDir } from "./cacheDir.js";
+
+afterEach(() => vi.unstubAllEnvs());
+
+describe("hyperframesCacheDir", () => {
+  it("defaults to ~/.cache/hyperframes", () => {
+    vi.stubEnv("HYPERFRAMES_CACHE_DIR", "");
+    expect(hyperframesCacheDir()).toBe(join(homedir(), ".cache", "hyperframes"));
+    expect(hyperframesCacheDir("chrome")).toBe(join(homedir(), ".cache", "hyperframes", "chrome"));
+  });
+
+  it("follows HYPERFRAMES_CACHE_DIR, read on each call, a relative one resolved", () => {
+    const elsewhere = join(tmpdir(), "elsewhere-cache");
+    vi.stubEnv("HYPERFRAMES_CACHE_DIR", elsewhere);
+    expect(hyperframesCacheDir("whisper", "models")).toBe(join(elsewhere, "whisper", "models"));
+    vi.stubEnv("HYPERFRAMES_CACHE_DIR", "rel/cache");
+    expect(hyperframesCacheDir("tts")).toBe(join(resolve("rel/cache"), "tts"));
+  });
+});
+
+/** Source files under every package's src, tests and test helpers left out. */
+function sources(dir: string): string[] {
+  return readdirSync(dir, { recursive: true, withFileTypes: true })
+    .filter((entry) => entry.isFile() && /\.(m?[jt]sx?)$/.test(entry.name))
+    .filter((entry) => !/\.test[.-]|__tests__/.test(join(entry.parentPath, entry.name)))
+    .map((entry) => join(entry.parentPath, entry.name));
+}
+
+it("every cache path in every package goes through hyperframesCacheDir", () => {
+  const packages = resolve(__dirname, "..", "..");
+  const built: string[] = [];
+  for (const name of readdirSync(packages)) {
+    let files: string[];
+    try {
+      files = sources(join(packages, name, "src"));
+    } catch {
+      continue; // a package without src
+    }
+    for (const file of files) {
+      if (file.endsWith(join("core", "src", "cacheDir.ts"))) continue;
+      // Prose about the default path is fine; code that builds it is not.
+      const code = readFileSync(file, "utf8")
+        .split("\n")
+        .filter((line) => !/^\s*(\/\/|\*|\/\*)/.test(line))
+        .join("\n");
+      if (
+        /["'`]\.cache["'`]\s*,\s*["'`]hyperframes["'`]|["'`][^"'`\n]*\.cache\/hyperframes/.test(
+          code,
+        )
+      )
+        built.push(file.slice(packages.length + 1));
+    }
+  }
+  expect(built).toEqual([]);
+});
diff --git a/packages/core/src/cacheDir.ts b/packages/core/src/cacheDir.ts
new file mode 100644
index 0000000000..6d364613a2
--- /dev/null
+++ b/packages/core/src/cacheDir.ts
@@ -0,0 +1,7 @@
+import { homedir } from "node:os";
+import { join, resolve } from "node:path";
+
+export function hyperframesCacheDir(...parts: string[]): string {
+  const named = process.env["HYPERFRAMES_CACHE_DIR"];
+  return join(named ? resolve(named) : join(homedir(), ".cache", "hyperframes"), ...parts);
+}
diff --git a/packages/core/src/fonts/deterministicFonts.ts b/packages/core/src/fonts/deterministicFonts.ts
index 2bb382872f..1eb00e0904 100644
--- a/packages/core/src/fonts/deterministicFonts.ts
+++ b/packages/core/src/fonts/deterministicFonts.ts
@@ -8,7 +8,7 @@ import {
   rmSync,
   writeFileSync,
 } from "node:fs";
-import { homedir, tmpdir } from "node:os";
+import { tmpdir } from "node:os";
 import { join } from "node:path";
 
 import { FONT_ALIAS_MAP, resolveAliasDisplayName } from "./aliases.js";
@@ -25,6 +25,7 @@ import {
   type FontDiagnostics,
   type FontDiagPath,
 } from "./fontDiagnostics.js";
+import { hyperframesCacheDir } from "../cacheDir.js";
 
 export type { FontDiagnostics };
 
@@ -1123,7 +1124,7 @@ function resolveFontCacheRoot(): string {
     lambdaFontCacheRoot ??= mkdtempSync(join(tmpdir(), "hyperframes-fonts-"));
     return lambdaFontCacheRoot;
   }
-  return join(homedir(), ".cache", "hyperframes", "fonts");
+  return hyperframesCacheDir("fonts");
 }
 
 // Chrome UA triggers woff2 responses from Google Fonts CSS API
diff --git a/packages/core/src/fonts/fontCompression.ts b/packages/core/src/fonts/fontCompression.ts
index bbeee94455..8bf56309fd 100644
--- a/packages/core/src/fonts/fontCompression.ts
+++ b/packages/core/src/fonts/fontCompression.ts
@@ -10,8 +10,9 @@ import {
   rmSync,
   writeFileSync,
 } from "node:fs";
-import { homedir, tmpdir } from "node:os";
+import { tmpdir } from "node:os";
 import { dirname, join } from "node:path";
+import { hyperframesCacheDir } from "../cacheDir.js";
 
 const { compress } = wawoff2 as {
   compress: (input: Buffer | Uint8Array) => Promise<Uint8Array>;
@@ -41,7 +42,7 @@ function defaultCacheDir(): string {
     process.env.HYPERFRAMES_FONT_CACHE_DIR ??
     (process.env.AWS_LAMBDA_FUNCTION_NAME
       ? join(tmpdir(), "hyperframes", "fonts")
-      : join(homedir(), ".cache", "hyperframes", "fonts"));
+      : hyperframesCacheDir("fonts"));
   return join(root, "local-compression-v1");
 }
 
diff --git a/packages/engine/src/services/browserManager.ts b/packages/engine/src/services/browserManager.ts
index d26bfc048c..9d91a29998 100644
--- a/packages/engine/src/services/browserManager.ts
+++ b/packages/engine/src/services/browserManager.ts
@@ -46,6 +46,7 @@ export type {
   BrowserPoolState,
   CaptureMode,
 } from "./browserLeasePool.js";
+import { hyperframesCacheDir } from "@hyperframes/core/cache-dir";
 
 let _puppeteer: PuppeteerNode | undefined;
 
@@ -271,7 +272,7 @@ export function resolveHeadlessShellPath(
     }
     return fromEnv.path;
   }
-  const ours = join(homedir(), ".cache", "hyperframes", "chrome", "chrome-headless-shell");
+  const ours = hyperframesCacheDir("chrome", "chrome-headless-shell");
   const shared = join(homedir(), ".cache", "puppeteer", "chrome-headless-shell");
   return (
     findManagedHeadlessShell(ours) ??
diff --git a/packages/inspector/src/service.ts b/packages/inspector/src/service.ts
index ab09b1a39f..8c96383fff 100644
--- a/packages/inspector/src/service.ts
+++ b/packages/inspector/src/service.ts
@@ -22,7 +22,6 @@ import {
   readdirSync,
 } from "node:fs";
 import { resolve, join, extname, sep } from "node:path";
-import { homedir } from "node:os";
 import { getHyperframeRuntimeScript } from "../../core/src/generated/runtime-inline";
 import puppeteer, { type Browser, type Page } from "puppeteer-core";
 import {
@@ -32,6 +31,7 @@ import {
 import { closeServer } from "./pageServer";
 import { Sources, fingerprint } from "./sources";
 import type { InspectRequest, Snippet } from "./types";
+import { hyperframesCacheDir } from "../../core/src/cacheDir";
 
 const pageRunner = (page: Page): PageRunner => ({
   run: <A, R>(fn: (arg: A) => R, arg: A) =>
@@ -59,7 +59,7 @@ function chromePath() {
       "Set HF_INSPECT_CHROME to an installed Chrome executable; inspection does not download a browser.",
     );
   }
-  const root = join(homedir(), ".cache/hyperframes/chrome/chrome-headless-shell");
+  const root = hyperframesCacheDir("chrome", "chrome-headless-shell");
   if (existsSync(root))
     for (const version of readdirSync(root).sort().reverse()) {
       const dir = join(root, version);
diff --git a/packages/studio-server/src/history/projectHistory.ts b/packages/studio-server/src/history/projectHistory.ts
index d1e22d2cae..87d8ea3e1f 100644
--- a/packages/studio-server/src/history/projectHistory.ts
+++ b/packages/studio-server/src/history/projectHistory.ts
@@ -12,7 +12,6 @@ import {
   realpathSync,
   rmSync,
 } from "node:fs";
-import { homedir } from "node:os";
 import { dirname, isAbsolute, join, relative, resolve, sep } from "node:path";
 import { replaceFileAtomically } from "@hyperframes/core/atomic-file";
 import {
@@ -64,9 +63,10 @@ import {
   type LogRecord,
   type Manifest,
 } from "./historyLog.js";
+import { hyperframesCacheDir } from "@hyperframes/core/cache-dir";
 
 /** Where hosts keep project histories unless told otherwise: outside every project, so no tidy-up takes one away. */
-export const DEFAULT_HISTORY_ROOT = join(homedir(), ".cache", "hyperframes", "history");
+export const DEFAULT_HISTORY_ROOT = hyperframesCacheDir("history");
 
 export interface ProjectHistoryOptions {
   projectDir: string;