fix(desktop): bound exported task array-index conversion (#9139)

src/domain/desktop/appTaskPython.ts

@@ -61,7 +61,11 @@ def _selects(member, conditions) -> bool:
 def _step(items: list, token: str, last: bool):
     """One step into an array, by index or by a selector that must match one member, or none when it is the last."""
     if INDEX.fullmatch(token):
-        return ("member", items[int(token)]) if int(token) < len(items) else ("none", None)
+        # A canonical decimal longer than the array length cannot name a member.
+        if len(token) > len(str(len(items))):
+            return "none", None
+        index = int(token)
+        return ("member", items[index]) if index < len(items) else ("none", None)
     conditions = _selector(token)
     if conditions is None:
         return ("unresolved", f"{token} is not a selector of the form [KEY=VALUE]") if _bracketed(token) else (

tests/boundary/providers/desktopTaskArrayIndex.test.ts

@@ -0,0 +1,52 @@
+import { execFileSync } from "node:child_process";
+import { writeFile } from "node:fs/promises";
+import { join } from "node:path";
+import { expect, it } from "vitest";
+import { PYTHON_TASK_EVALUATOR } from "../../../src/domain/desktop/appTaskPython.js";
+import { locatePointer } from "../../../src/domain/desktop/viewPointer.js";
+import { createTestTempDirectory } from "../../fixtures/temporaryDirectory.js";
+
+it("keeps oversized array indices absent without crashing exported task checks", async () => {
+  const huge = "9".repeat(5000);
+  const cases = [
+    { items: [1], pointer: `/${huge}` },
+    { items: [], pointer: `/${huge}` },
+    { items: [1], pointer: "/0" },
+    { items: [1], pointer: "/1" },
+    { items: Array.from({ length: 12 }, (_, index) => index), pointer: "/11" },
+    { items: Array.from({ length: 12 }, (_, index) => index), pointer: "/12" },
+    { items: [1], pointer: "/01" },
+  ];
+  const folder = await createTestTempDirectory("task-array-index-");
+  const script = join(folder, "fixture.py");
+  await writeFile(
+    script,
+    `import json, re, math, sys
+${PYTHON_TASK_EVALUATOR}
+results = []
+for case in json.load(sys.stdin):
+    items, pointer = case["items"], case["pointer"]
+    located = _locate(items, pointer)
+    check = {"id": "absent", "kind": "value_absent", "file": "state.json", "pointer": pointer}
+    verdict = evaluate([check], {"state.json": {"format": "json", "view": items, "truncated": False}})[0]
+    results.append([located[0], located[1], verdict["result"]])
+print(json.dumps(results))
+`,
+  );
+  const results = JSON.parse(
+    execFileSync("python3", ["-I", "-B", script], {
+      input: JSON.stringify(cases),
+      encoding: "utf8",
+    }),
+  );
+  expect(results).toEqual(
+    cases.map(({ items, pointer }) => {
+      const located = locatePointer(items, pointer);
+      return [
+        located.kind,
+        located.kind === "value" ? located.value : null,
+        located.kind === "none",
+      ];
+    }),
+  );
+});