diff --git a/README.md b/README.md
index 58ba78c..20afbeb 100644
--- a/README.md
+++ b/README.md
@@ -218,7 +218,9 @@ development workflow, and the Makefile targets are thin shims that call them. We
 provide:
 
 - `script/bootstrap` — install all dependencies (pinned node via nvm if needed,
-  yarn via corepack, `yarn install --frozen-lockfile`)
+  yarn via corepack, `yarn install --frozen-lockfile`), then fail, naming the
+  package, if node cannot find a package listed in `dependencies` or
+  `devDependencies` of `package.json`
 - `script/setup` — make a fresh clone ready for development: bootstrap plus the
   git pre-commit hook
 - `script/projectname` — print the project name (used for the Docker image tag)
diff --git a/TODO.md b/TODO.md
index 225c833..a3db404 100644
--- a/TODO.md
+++ b/TODO.md
@@ -45,6 +45,15 @@ but the review is broader than any of them.
 
 # Completed Steps
 
+- 2026-10-06: `script/bootstrap` no longer reports success while node cannot
+  find a package listed in `dependencies` or `devDependencies` of `package.json`
+  ([#263](https://git.eeqj.de/sneak/AutistMask/issues/263)). After the install
+  it asks node for each one's `package.json`, and fails naming the missing
+  package and the fix. yarn skips the install whenever
+  `node_modules/.yarn-integrity` matches `yarn.lock`, so a package deleted from
+  `node_modules` stayed deleted while bootstrap said it was complete. The
+  fresh-clone failure the issue reports did not reproduce.
+
 - 2026-10-06: A token symbol or name read off a contract is no longer stored cut
   between the two halves of an emoji
   ([#458](https://git.eeqj.de/sneak/AutistMask/issues/458)). `lookupTokenInfo()`
diff --git a/script/bootstrap b/script/bootstrap
index 4df1d8c..a0a19ef 100755
--- a/script/bootstrap
+++ b/script/bootstrap
@@ -127,6 +127,40 @@ install_js_deps() {
     fi
 }
 
+# run_node: run node from the repo root, through nvm when node is not on PATH;
+# the script comes on stdin
+run_node() {
+    if missing node && [ -s "$HOME/.nvm/nvm.sh" ]; then
+        nvm_sh "nvm use $NODE_VERSION >/dev/null && cd \"$ROOT\" && node"
+    else
+        node
+    fi
+}
+
+# yarn install exits 0 without touching node_modules once
+# node_modules/.yarn-integrity matches yarn.lock, so a package deleted from
+# node_modules stays deleted. Fail unless node finds every package listed in
+# dependencies and devDependencies of package.json, by its package.json. When a
+# package's exports does not list that file, node throws
+# ERR_PACKAGE_PATH_NOT_EXPORTED, which it can only do once it has found the
+# package, so that error counts as found.
+check_js_deps() {
+    run_node <<'EOF'
+const { dependencies, devDependencies } = require("./package.json");
+for (const name of Object.keys({ ...dependencies, ...devDependencies })) {
+    try {
+        require.resolve(name + "/package.json");
+    } catch (e) {
+        if (e.code !== "ERR_PACKAGE_PATH_NOT_EXPORTED") {
+            console.error(`bootstrap: node cannot find ${name} after yarn install`);
+            console.error("  fix: rm -rf node_modules && make bootstrap");
+            process.exit(1);
+        }
+    }
+}
+EOF
+}
+
 main() {
     cd "$ROOT"
 
@@ -136,6 +170,7 @@ main() {
     ensure_node
     ensure_yarn
     install_js_deps
+    check_js_deps
 
     echo "bootstrap complete"
 }