diff --git a/docs/NPM_DISTRIBUTION.md b/docs/NPM_DISTRIBUTION.md
index 0cdc162..53c54a8 100644
--- a/docs/NPM_DISTRIBUTION.md
+++ b/docs/NPM_DISTRIBUTION.md
@@ -54,8 +54,9 @@ its own npm 12, which is how 0.3.1 broke there (issue #41).
 
 The binary goes in the package's `bin/`, or, when that is not writable (a
 root-owned `sudo npm install -g` whose postinstall npm 12 skipped), in a
-per-user cache: `$XDG_CACHE_HOME`, else `~/.cache` (`~/Library/Caches` on
-macOS), under `<package>/<version>/`. The launcher looks in both. A
+per-user cache: `$XDG_CACHE_HOME` (if absolute), else `~/.cache`
+(`~/Library/Caches` on macOS), under `<package>/<version>/<platform>-<arch>/`.
+The launcher looks in both. A
 termination signal during that first-run download stops the installer too,
 and it removes its partial file.
 
diff --git a/scripts/idx.js b/scripts/idx.js
index ea9dde0..b743544 100755
--- a/scripts/idx.js
+++ b/scripts/idx.js
@@ -20,6 +20,7 @@ let child = null;
 // A termination signal received while installing; the installer cleans up
 // and exits, and the launcher then stops the same way.
 let stopping = null;
+let installing = false;
 
 // Pass termination signals from a supervisor (kill, docker stop) to the child.
 for (const signal of ["SIGTERM", "SIGHUP"]) {
@@ -32,8 +33,15 @@ for (const signal of ["SIGTERM", "SIGHUP"]) {
     }
   });
 }
-// Ctrl+C already reaches the child through the terminal's process group.
-process.on("SIGINT", () => {});
+// Ctrl+C already reaches the binary through the terminal's process group, so
+// the launcher ignores SIGINT then. During the first-run install, forward it
+// too: a supervisor may signal only the launcher's PID.
+process.on("SIGINT", () => {
+  if (installing) {
+    stopping = "SIGINT";
+    child.kill("SIGINT");
+  }
+});
 
 function exitLike(code, signal) {
   if (signal) {
@@ -61,6 +69,7 @@ if (installed) {
   // or its download failed: install now. Its log goes to stderr, since stdout
   // is the MCP channel for idx-mcp.
   console.error(`${packageName}: binary not installed; running the installer`);
+  installing = true;
   child = spawn(process.execPath, [installer], { stdio: ["ignore", 2, 2] });
   child.once("error", (error) => {
     console.error(`${packageName}: failed to run the installer: ${error.message}`);
@@ -68,6 +77,7 @@ if (installed) {
   });
   child.once("exit", (code, signal) => {
     child = null;
+    installing = false;
     if (signal || stopping) {
       exitLike(code, signal || stopping);
       return;
diff --git a/scripts/install.js b/scripts/install.js
index b19c604..126e985 100755
--- a/scripts/install.js
+++ b/scripts/install.js
@@ -23,13 +23,19 @@ const binaryName = process.platform === "win32" ? `${nativeBinary}.exe` : native
 // (a root-owned global install whose postinstall npm 12 skipped), in a
 // per-user cache. scripts/idx.js looks in both, in this order.
 const packageBinaryPath = path.join(packageRoot, "bin", binaryName);
+// A relative XDG_CACHE_HOME is invalid per the XDG spec, and would make the
+// launcher run a binary from the current directory: ignore it.
+const xdgCacheHome = process.env.XDG_CACHE_HOME;
 const cacheBinaryPath = path.join(
-  process.env.XDG_CACHE_HOME ||
-    (process.platform === "darwin"
+  xdgCacheHome && path.isAbsolute(xdgCacheHome)
+    ? xdgCacheHome
+    : process.platform === "darwin"
       ? path.join(os.homedir(), "Library", "Caches")
-      : path.join(os.homedir(), ".cache")),
+      : path.join(os.homedir(), ".cache"),
   packageName,
   packageManifest.version,
+  // A home directory shared across machines must not mix architectures.
+  `${process.platform}-${process.arch}`,
   binaryName,
 );
 const binaryLocations = [packageBinaryPath, cacheBinaryPath];
diff --git a/scripts/npm-smoke.sh b/scripts/npm-smoke.sh
index 81c82db..69c5161 100755
--- a/scripts/npm-smoke.sh
+++ b/scripts/npm-smoke.sh
@@ -88,9 +88,12 @@ echo "npm smoke: installing idx-mcp with --ignore-scripts"
 no_scripts_dir="${smoke_dir}/idx-mcp-no-scripts"
 npm_config_cache="$npm_cache" npm install --prefix "$no_scripts_dir" "${smoke_dir}"/idx-mcp/idx-mcp-*.tgz \
   --no-save --no-package-lock --no-audit --no-fund --ignore-scripts
-IDX_BINARY_URL="${repo_root}/target/release/idx-mcp" \
+# An empty user cache, so a binary cached by an earlier run cannot stand in
+# for the first-run install.
+XDG_CACHE_HOME="${smoke_dir}/no-scripts-cache" IDX_BINARY_URL="${repo_root}/target/release/idx-mcp" \
   "${no_scripts_dir}/node_modules/.bin/idx-mcp" --help > "${smoke_dir}/no-scripts-help.txt"
-if ! head -n 1 "${smoke_dir}/no-scripts-help.txt" | grep -q "MCP server"; then
+if ! head -n 1 "${smoke_dir}/no-scripts-help.txt" | grep -q "MCP server" \
+  || [[ ! -x "${no_scripts_dir}/node_modules/idx-mcp/bin/idx-mcp" ]]; then
   echo "npm smoke: idx-mcp without postinstall did not start cleanly:" >&2
   cat "${smoke_dir}/no-scripts-help.txt" >&2
   exit 1
@@ -104,7 +107,7 @@ chmod -R a-w "${read_only_dir}/node_modules/idx-mcp"
 XDG_CACHE_HOME="${smoke_dir}/user-cache" IDX_BINARY_URL="${repo_root}/target/release/idx-mcp" \
   "${read_only_dir}/node_modules/.bin/idx-mcp" --help > "${smoke_dir}/read-only-help.txt"
 chmod -R u+w "${read_only_dir}/node_modules/idx-mcp"
-cached=("${smoke_dir}"/user-cache/idx-mcp/*/idx-mcp)
+cached=("${smoke_dir}"/user-cache/idx-mcp/*/*/idx-mcp)
 if ! head -n 1 "${smoke_dir}/read-only-help.txt" | grep -q "MCP server" || [[ ! -x "${cached[0]}" ]]; then
   echo "npm smoke: idx-mcp with a read-only package did not install to the user cache:" >&2
   cat "${smoke_dir}/read-only-help.txt" >&2