diff --git a/CHANGES.md b/CHANGES.md
index 6d87518a..e1018beb 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -5,6 +5,8 @@ This port applies the Cursor → Claude Code substitutions in skill bodies. Earl
 
 ## Unreleased
 
+The shipped `pstack-runner` no longer loads the caller project's environment files or `bunfig.toml` at startup. Its POSIX shell launcher clears inherited `BUN_OPTIONS` and `NODE_OPTIONS`, then executes Bun with env-file loading disabled and project Bun configuration ignored while preserving ordinary parent-provided environment variables. It needs no `env -S` or directory-resolution helpers. The TypeScript entry keeps the first-statement deadline capture, and `exec` preserves signal behavior. Direct-executable regressions cover startup isolation, inherited environment, and preflight cancellation.
+
 - Document Linux Landlock and bubblewrap prerequisites for bounded Grok lanes, including affected Claude Code cloud hosts, and link setup failures to the shared host and parent prerequisites without changing runner behavior (#56).
 
 ## 1.5.0 syncs to Cursor pstack 0.15.5
diff --git a/plugins/pstack/skills/poteto-mode/scripts/runner/entry.ts b/plugins/pstack/skills/poteto-mode/scripts/runner/entry.ts
new file mode 100644
index 00000000..65cb38a4
--- /dev/null
+++ b/plugins/pstack/skills/poteto-mode/scripts/runner/entry.ts
@@ -0,0 +1,4 @@
+const startedAt = Date.now();
+const { main } = await import("./cli.ts");
+process.exitCode = await main(process.argv.slice(2), startedAt);
+export {};
diff --git a/plugins/pstack/skills/poteto-mode/scripts/runner/pstack-runner b/plugins/pstack/skills/poteto-mode/scripts/runner/pstack-runner
index 7cd5a6e9..55e3c8b8 100755
--- a/plugins/pstack/skills/poteto-mode/scripts/runner/pstack-runner
+++ b/plugins/pstack/skills/poteto-mode/scripts/runner/pstack-runner
@@ -1,4 +1,4 @@
-#!/usr/bin/env bun
-const startedAt = Date.now();
-const { main } = await import("./cli.ts");
-process.exitCode = await main(process.argv.slice(2), startedAt);
+#!/bin/sh
+unset BUN_OPTIONS NODE_OPTIONS
+case $0 in */*) dir=${0%/*} ;; *) dir=. ;; esac
+exec bun --no-env-file --config=/dev/null "$dir/entry.ts" "$@"
diff --git a/plugins/pstack/skills/poteto-mode/scripts/runner/run.test.ts b/plugins/pstack/skills/poteto-mode/scripts/runner/run.test.ts
index 7a4b0008..56ed5944 100644
--- a/plugins/pstack/skills/poteto-mode/scripts/runner/run.test.ts
+++ b/plugins/pstack/skills/poteto-mode/scripts/runner/run.test.ts
@@ -501,6 +501,83 @@ process.exit(${scenario.endsWith("nonzero") ? 1 : 0});
 });
 
 describe("runLane", () => {
+  for (const startup of ["dotenv", "bunfig", "bun-options", "node-options", "combined", "hostile-path", "bare-name"]) {
+    it(`shipped launcher startup isolation: ${startup}`, async () => {
+      const input = options("codex", startup);
+      // Exceed pipe capacity so the fake provider must consume stdin before exiting.
+      writeFileSync(input.promptPath, "Return the marker.\n".repeat(100_000));
+      const captured = join(scratch, "provider-env.txt");
+      const capturedPrompt = join(scratch, "provider-prompt.txt");
+      const bunPreload = join(scratch, "bun-preload.ran");
+      const nodePreload = join(scratch, "node-preload.ran");
+      const env: Record<string, string> = {
+        PATH: process.env.PATH!,
+        PSTACK_ENV_CAPTURE: captured,
+        PSTACK_PROMPT_CAPTURE: capturedPrompt,
+        PSTACK_INHERITED_ENV_SENTINEL: "inherited-from-parent",
+      };
+      if (startup === "dotenv" || startup === "combined") {
+        writeFileSync(join(scratch, ".env"), "PSTACK_PROJECT_ENV_SENTINEL=loaded-from-project-dotenv\n");
+        writeFileSync(join(scratch, ".env.local"), "PSTACK_LOCAL_ENV_SENTINEL=loaded-from-project-local-dotenv\n");
+      }
+      if (startup === "bunfig" || startup === "combined") {
+        writeFileSync(join(scratch, "bunfig.toml"), 'preload = ["./project-preload.ts"]\n');
+        writeFileSync(join(scratch, "project-preload.ts"),
+          `await Bun.write(${JSON.stringify(bunPreload)}, "project preload ran");\n`);
+      }
+      if (startup === "bun-options" || startup === "combined") {
+        writeFileSync(join(scratch, "startup.env"), "PSTACK_PROJECT_ENV_SENTINEL=loaded-from-bun-options\n");
+        env.BUN_OPTIONS = "--env-file=./startup.env";
+      }
+      if (startup === "node-options" || startup === "combined") {
+        writeFileSync(join(scratch, "project-preload.cjs"),
+          `require("node:fs").writeFileSync(${JSON.stringify(nodePreload)}, "node preload ran");\n`);
+        env.NODE_OPTIONS = "--require=./project-preload.cjs";
+      }
+      writeFileSync(join(bin, "codex"), `#!/bin/sh
+if [ "$1" = "login" ]; then
+  printf '%s\\n' 'Logged in using ChatGPT'
+  exit 0
+fi
+cat > "$PSTACK_PROMPT_CAPTURE"
+printf '%s\\n' "\${PSTACK_PROJECT_ENV_SENTINEL-unset}" "\${PSTACK_LOCAL_ENV_SENTINEL-unset}" "\${PSTACK_INHERITED_ENV_SENTINEL-unset}" "\${BUN_OPTIONS-unset}" "\${NODE_OPTIONS-unset}" > "$PSTACK_ENV_CAPTURE"
+printf '%s\\n' '{"type":"thread.started","thread_id":"isolated"}' '{"type":"item.completed","item":{"type":"agent_message","text":"CODEX_OK"}}' '{"type":"turn.completed","usage":{"input_tokens":1,"output_tokens":1}}'
+`);
+      chmodSync(join(bin, "codex"), 0o755);
+      const helperSentinel = join(scratch, "helper.ran");
+      if (startup === "hostile-path") {
+        for (const name of ["env", "dirname", "readlink"]) {
+          writeFileSync(join(bin, name), `#!/bin/sh\nprintf '%s\\n' '${name}' > "${helperSentinel}"\nexit 1\n`);
+          chmodSync(join(bin, name), 0o755);
+        }
+      }
+      const runner = Bun.spawn(startup === "bare-name"
+        ? ["/bin/sh", "pstack-runner", ...runnerArgs(input).slice(1)]
+        : runnerArgs(input), {
+        cwd: startup === "bare-name" ? import.meta.dir : scratch,
+        env,
+        stdout: "pipe",
+        stderr: "pipe",
+      });
+      const stdout = new Response(runner.stdout).text();
+      const stderr = new Response(runner.stderr).text();
+      const exitCode = await exitWithin(runner, 3_000);
+      const [stdoutText, stderrText] = await Promise.all([stdout, stderr]);
+      expect(exitCode, JSON.stringify({
+        stdout: stdoutText,
+        stderr: stderrText,
+        receipt: existsSync(input.receiptPath) ? receipt(input.receiptPath) : null,
+      })).toBe(0);
+      expect(readFileSync(capturedPrompt, "utf8")).toBe(readFileSync(input.promptPath, "utf8"));
+      expect(readFileSync(captured, "utf8")).toBe("unset\nunset\ninherited-from-parent\nunset\nunset\n");
+      expect(existsSync(bunPreload)).toBe(false);
+      expect(existsSync(nodePreload)).toBe(false);
+      expect(existsSync(helperSentinel)).toBe(false);
+      expect(readFileSync(input.outputPath, "utf8")).toContain("CODEX_OK");
+      expect(receipt(input.receiptPath)).toMatchObject({ status: "complete" });
+    });
+  }
+
   for (const provider of ["claude", "codex", "grok"] as const) {
     it(`executes and receipts the ${provider} external lane`, async () => {
       const input = options(provider);
@@ -648,7 +725,7 @@ describe("runLane", () => {
     const transientMarker = join(scratch, "grok-cancel-unauth.pid");
     const preflightLog = join(scratch, "grok-cancel-unauth.log");
     const input = options("grok", "grok-preflight-retry-cancelled");
-    const runner = Bun.spawn([process.execPath, ...runnerArgs(input)], {
+    const runner = Bun.spawn(runnerArgs(input), {
       cwd: scratch,
       env: {
         ...process.env,
@@ -707,7 +784,7 @@ describe("runLane", () => {
   it("does not spawn the model when preflight exhausts the wrapper deadline", async () => {
     const modelStarted = join(scratch, "deadline-model.started");
     const input = { ...options("claude", "preflight-deadline"), timeoutMs: 300 };
-    const runner = Bun.spawn([process.execPath, ...runnerArgs(input)], {
+    const runner = Bun.spawn(runnerArgs(input), {
       cwd: scratch,
       env: {
         ...process.env,
@@ -732,7 +809,7 @@ describe("runLane", () => {
 
   it("lets a delayed wrapper lane finish when timeout is omitted", async () => {
     const input = options("claude", "unbounded-default");
-    const runner = Bun.spawn([process.execPath, ...runnerArgs(input)], {
+    const runner = Bun.spawn(runnerArgs(input), {
       cwd: scratch,
       env: { ...process.env, FAKE_MODEL_DELAY_MS: "400" },
       stdout: "pipe",
@@ -755,7 +832,7 @@ describe("runLane", () => {
       ...options("claude", "long-runtime-deadline"),
       timeoutMs: 2_147_483_648,
     };
-    const runner = Bun.spawn([process.execPath, ...runnerArgs(input)], {
+    const runner = Bun.spawn(runnerArgs(input), {
       cwd: scratch,
       env: { ...process.env, FAKE_MODEL_DELAY_MS: "100" },
       stdout: "pipe",
@@ -818,7 +895,7 @@ describe("runLane", () => {
   it("bounds a descendant-held pipe by the explicit deadline without fabricating a signal", async () => {
     const descendantPidPath = join(scratch, "deadline-descendant.pid");
     const input = { ...options("claude", "deadline-drain"), timeoutMs: 700 };
-    const runner = Bun.spawn([process.execPath, ...runnerArgs(input)], {
+    const runner = Bun.spawn(runnerArgs(input), {
       cwd: scratch,
       env: {
         ...process.env,
@@ -849,7 +926,7 @@ describe("runLane", () => {
   it("does not claim a signal was sent to an already signal-reaped child", async () => {
     const descendantPidPath = join(scratch, "signalled-descendant.pid");
     const input = { ...options("claude", "signalled-drain"), timeoutMs: 700 };
-    const runner = Bun.spawn([process.execPath, ...runnerArgs(input)], {
+    const runner = Bun.spawn(runnerArgs(input), {
       cwd: scratch,
       env: {
         ...process.env,
@@ -880,7 +957,7 @@ describe("runLane", () => {
     const descendantPidPath = join(scratch, "cancel-descendant.pid");
     const modelExiting = join(scratch, "cancel-model.exiting");
     const input = options("claude", "cancel-drain");
-    const runner = Bun.spawn([process.execPath, ...runnerArgs(input)], {
+    const runner = Bun.spawn(runnerArgs(input), {
       cwd: scratch,
       env: {
         ...process.env,
@@ -913,7 +990,7 @@ describe("runLane", () => {
 
   it("clears a losing long-deadline timer when the shipped wrapper succeeds", async () => {
     const input = { ...options("claude", "long-deadline"), timeoutMs: 60_000 };
-    const runner = Bun.spawn([process.execPath, ...runnerArgs(input)], {
+    const runner = Bun.spawn(runnerArgs(input), {
       cwd: scratch,
       env: { ...process.env },
       stdout: "pipe",
@@ -934,7 +1011,6 @@ describe("runLane", () => {
     const isolatedRunner = join(scratch, "isolated-runner");
     cpSync(import.meta.dir, isolatedRunner, { recursive: true });
     const runner = Bun.spawn([
-      process.execPath,
       join(isolatedRunner, "pstack-runner"),
       ...runnerArgs(input).slice(1),
     ], {
@@ -968,7 +1044,7 @@ describe("runLane", () => {
     const input = { ...options("codex", "repeated-cancel"), timeoutMs: 60_000 };
     const started = join(scratch, "repeated-child.started");
     const terminated = join(scratch, "repeated-child.terminated");
-    const runner = Bun.spawn([process.execPath, ...runnerArgs(input)], {
+    const runner = Bun.spawn(runnerArgs(input), {
       cwd: scratch,
       env: {
         ...process.env,
@@ -1009,7 +1085,7 @@ describe("runLane", () => {
       FAKE_STARTED_PATH: started,
       FAKE_TERMINATED_PATH: terminated,
     };
-    const runner = Bun.spawn([process.execPath, ...runnerArgs(input)], {
+    const runner = Bun.spawn(runnerArgs(input), {
       cwd: scratch,
       env,
       stdout: "pipe",
@@ -1031,7 +1107,7 @@ describe("runLane", () => {
       error: { message: "launcher received SIGTERM; signal was sent to child" },
     });
 
-    const samePaths = Bun.spawn([process.execPath, ...runnerArgs(input)], {
+    const samePaths = Bun.spawn(runnerArgs(input), {
       cwd: scratch,
       env: { ...process.env },
       stdout: "pipe",
@@ -1080,7 +1156,7 @@ describe("runLane", () => {
   it("terminalizes catchable failures after reserving output paths", async () => {
     const unreadable = options("claude", "unreadable-prompt");
     chmodSync(unreadable.promptPath, 0o000);
-    const unreadableRunner = Bun.spawn([process.execPath, ...runnerArgs(unreadable)], {
+    const unreadableRunner = Bun.spawn(runnerArgs(unreadable), {
       cwd: scratch,
       env: { ...process.env },
       stdout: "pipe",
@@ -1101,7 +1177,7 @@ describe("runLane", () => {
       error: { message: "launcher failed after reserving output paths" },
     });
 
-    const samePaths = Bun.spawn([process.execPath, ...runnerArgs(unreadable)], {
+    const samePaths = Bun.spawn(runnerArgs(unreadable), {
       cwd: scratch,
       env: { ...process.env },
       stdout: "pipe",
@@ -1115,7 +1191,7 @@ describe("runLane", () => {
 
     const spawnFailure = options("claude", "spawn-failure");
     const modelStarted = join(scratch, "spawn-failure-model.started");
-    const spawnRunner = Bun.spawn([process.execPath, ...runnerArgs(spawnFailure)], {
+    const spawnRunner = Bun.spawn(runnerArgs(spawnFailure), {
       cwd: scratch,
       env: {
         ...process.env,