Agents/Tools: preflight exec script files for shell var injection (#18457)

* fix(agents): don't force store=true for codex responses

* test: stabilize respawn + subagent usage assertions

* Agents/Tools: preflight exec to detect shell variable injection in scripts

* Changelog: fix merge marker formatting

src/agents/bash-tools.exec.ts

@@ -1,5 +1,7 @@
 import type { AgentTool, AgentToolResult } from "@mariozechner/pi-agent-core";
 import crypto from "node:crypto";
+import fs from "node:fs/promises";
+import path from "node:path";
 import type { BashSandboxConfig } from "./bash-tools.shared.js";
 import {
   type ExecAsk,
@@ -118,6 +120,97 @@ export type ExecToolDetails =
       nodeId?: string;
     };
 
+function extractScriptTargetFromCommand(
+  command: string,
+): { kind: "python"; relOrAbsPath: string } | { kind: "node"; relOrAbsPath: string } | null {
+  const raw = command.trim();
+  if (!raw) {
+    return null;
+  }
+
+  // Intentionally simple parsing: we only support common forms like
+  //   python file.py
+  //   python3 -u file.py
+  //   node --experimental-something file.js
+  // If the command is more complex (pipes, heredocs, quoted paths with spaces), skip preflight.
+  const pythonMatch = raw.match(/^\s*(python3?|python)\s+(?:-[^\s]+\s+)*([^\s]+\.py)\b/i);
+  if (pythonMatch?.[2]) {
+    return { kind: "python", relOrAbsPath: pythonMatch[2] };
+  }
+  const nodeMatch = raw.match(/^\s*(node)\s+(?:--[^\s]+\s+)*([^\s]+\.js)\b/i);
+  if (nodeMatch?.[2]) {
+    return { kind: "node", relOrAbsPath: nodeMatch[2] };
+  }
+
+  return null;
+}
+
+async function validateScriptFileForShellBleed(params: {
+  command: string;
+  workdir: string;
+}): Promise<void> {
+  const target = extractScriptTargetFromCommand(params.command);
+  if (!target) {
+    return;
+  }
+
+  const absPath = path.isAbsolute(target.relOrAbsPath)
+    ? path.resolve(target.relOrAbsPath)
+    : path.resolve(params.workdir, target.relOrAbsPath);
+
+  // Best-effort: only validate if file exists and is reasonably small.
+  let stat: { isFile(): boolean; size: number };
+  try {
+    stat = await fs.stat(absPath);
+  } catch {
+    return;
+  }
+  if (!stat.isFile()) {
+    return;
+  }
+  if (stat.size > 512 * 1024) {
+    return;
+  }
+
+  const content = await fs.readFile(absPath, "utf-8");
+
+  // Common failure mode: shell env var syntax leaking into Python/JS.
+  // We deliberately match all-caps/underscore vars to avoid false positives with `$` as a JS identifier.
+  const envVarRegex = /\$[A-Z_][A-Z0-9_]{1,}/g;
+  const first = envVarRegex.exec(content);
+  if (first) {
+    const idx = first.index;
+    const before = content.slice(0, idx);
+    const line = before.split("\n").length;
+    const token = first[0];
+    throw new Error(
+      [
+        `exec preflight: detected likely shell variable injection (${token}) in ${target.kind} script: ${path.basename(
+          absPath,
+        )}:${line}.`,
+        target.kind === "python"
+          ? `In Python, use os.environ.get(${JSON.stringify(token.slice(1))}) instead of raw ${token}.`
+          : `In Node.js, use process.env[${JSON.stringify(token.slice(1))}] instead of raw ${token}.`,
+        "(If this is inside a string literal on purpose, escape it or restructure the code.)",
+      ].join("\n"),
+    );
+  }
+
+  // Another recurring pattern from the issue: shell commands accidentally emitted as JS.
+  if (target.kind === "node") {
+    const firstNonEmpty = content
+      .split(/\r?\n/)
+      .map((l) => l.trim())
+      .find((l) => l.length > 0);
+    if (firstNonEmpty && /^NODE\b/.test(firstNonEmpty)) {
+      throw new Error(
+        `exec preflight: JS file starts with shell syntax (${firstNonEmpty}). ` +
+          `This looks like a shell command, not JavaScript.`,
+      );
+    }
+  }
+}
+
 export function createExecTool(
   defaults?: ExecToolDefaults,
   // oxlint-disable-next-line typescript/no-explicit-any
@@ -874,6 +967,11 @@ export function createExecTool(
         typeof params.timeout === "number" ? params.timeout : defaultTimeoutSec;
       const getWarningText = () => (warnings.length ? `${warnings.join("\n")}\n\n` : "");
       const usePty = params.pty === true && !sandbox;
+
+      // Preflight: catch a common model failure mode (shell syntax leaking into Python/JS sources)
+      // before we execute and burn tokens in cron loops.
+      await validateScriptFileForShellBleed({ command: params.command, workdir });
+
       const run = await runExecProcess({
         command: params.command,
         execCommand: execCommandOverride,