@@ -153,6 +153,10 @@ export function scriptChainRuns(scripts, entry, target) {
       .map((part) => unwrapGateLease(part.trim()))) {
       if (segment === `npm run ${target}`) return true;
       const tokens = segment.split(/\s+/);
+      // An intermediate hop must be as unmasked as the target itself: in
+      // `npm run stage || true` (or `| tee`) the stage's failure is swallowed,
+      // so a target reached through it gates nothing (Copilot, #4895).
+      if (segment.includes("|")) continue;
       if (tokens[0] === "npm" && tokens[1] === "run" && tokens[2]) {
         queue.push(tokens[2]);
       }
 
@@ -786,6 +786,15 @@ async function pool(items, n, fn) {
   return out;
 }
 
+/**
+ * Whether an env-supplied count is usable as a run, turn or worker count.
+ *
+ * @param {number} value
+ */
+export function isPositiveInteger(value) {
+  return Number.isInteger(value) && value > 0;
+}
+
 /**
  * Whether a measured rate clears its bar.
  *
@@ -906,6 +915,22 @@ async function main() {
     );
     process.exit(1);
   }
+  // The turn budget is also Copilot's external stop condition, so a non-numeric
+  // value would silently remove the cap on metered calls (`turnOffset >= NaN`
+  // is never true); RUNS and CONCURRENCY fail the same quiet way (Copilot,
+  // #4895).
+  for (const [name, value] of [
+    ["CHAIN_MAX_TURNS", CHAIN_MAX_TURNS],
+    ["RUNS", RUNS],
+    ["CONCURRENCY", CONCURRENCY],
+  ]) {
+    if (!isPositiveInteger(value)) {
+      console.error(
+        `skills:eval — ${name} must be a positive integer (got ${process.env[name] ?? value}).`,
+      );
+      process.exit(1);
+    }
+  }
   if (!AGENTS.includes(AGENT)) {
     console.error(
       `skills:eval — AGENT must be one of ${AGENTS.join(", ")} (got \`${AGENT}\`).`,
 
@@ -1053,3 +1053,11 @@ test("a rejected Copilot run leaves the in-flight set", async () => {
   );
   assert.equal(stopLiveCopilotRuns(), 0);
 });
+
+test("isPositiveInteger accepts only usable counts (#4895)", async () => {
+  const { isPositiveInteger } = await import("./skill-eval.mjs");
+  for (const ok of [1, 3, 14]) assert.equal(isPositiveInteger(ok), true, ok);
+  for (const bad of [0, -1, 1.5, Number.NaN, Number("abc"), Infinity]) {
+    assert.equal(isPositiveInteger(bad), false, String(bad));
+  }
+});
@@ -746,3 +746,27 @@ test("scriptChainRuns follows npm's implicit pre/post hooks", () => {
     true,
   );
 });
+
+test("scriptChainRuns does not follow a masked intermediate hop (#4895)", () => {
+  const T = "verify:skills:cli";
+  for (const gate of ["npm run stage || true", "npm run stage | tee log"]) {
+    assert.equal(
+      scriptChainRuns(
+        { "local:gate": gate, stage: `npm run ${T}` },
+        "local:gate",
+        T,
+      ),
+      false,
+      gate,
+    );
+  }
+  // The unmasked hop is still followed.
+  assert.equal(
+    scriptChainRuns(
+      { "local:gate": "npm run stage", stage: `npm run ${T}` },
+      "local:gate",
+      T,
+    ),
+    true,
+  );
+});