diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index edb2b5731..e949339fc 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -539,6 +539,8 @@ jobs:
     if: ${{ needs.validation_scope.outputs.full == 'true' && needs.lanes.outputs.linux == 'true' }}
     name: test (tsgo and tsc-ts give the same IR)
     runs-on: ubuntu-24.04
+    # The two corpus compiles run back to back and take close to 30 minutes on a
+    # slow hosted runner, so a 30-minute limit cancels otherwise healthy runs.
     timeout-minutes: 60
     steps:
       - uses: actions/checkout@v4
@@ -633,8 +635,9 @@ jobs:
     # Shard 1 additionally runs package/install and link-parity contracts
     # before its LLVM differential slice. The slice itself can take ~10
     # minutes on a cold hosted runner, so 20 minutes cancels an otherwise
-    # healthy job before the differential completes.
-    timeout-minutes: 35
+    # healthy job before the differential completes. Slow runners need more
+    # headroom than that, so the limit is 50 minutes.
+    timeout-minutes: 50
     strategy:
       fail-fast: false
       matrix:
diff --git a/.github/workflows/prune-caches.yml b/.github/workflows/prune-caches.yml
new file mode 100644
index 000000000..1509d56ce
--- /dev/null
+++ b/.github/workflows/prune-caches.yml
@@ -0,0 +1,41 @@
+name: Prune caches
+
+# Pull request caches are scoped to that pull request, so once it is closed no
+# run can use them again. Deleting them keeps the repository under its cache
+# size limit, so caches that main and open pull requests use are not evicted.
+on:
+  pull_request:
+    types: [closed]
+  schedule:
+    - cron: "17 6 * * *"
+  workflow_dispatch:
+
+permissions:
+  actions: write
+  pull-requests: read
+
+jobs:
+  prune:
+    runs-on: ubuntu-24.04
+    timeout-minutes: 10
+    steps:
+      - name: Delete caches of closed pull requests
+        env:
+          GH_TOKEN: ${{ github.token }}
+          REPO: ${{ github.repository }}
+        run: |
+          set -euo pipefail
+          # Read both lists in full before deleting anything: deleting while the cache
+          # listing pages shifts later pages, and a failed request must stop the job
+          # instead of leaving open pull requests out of the list.
+          open=$(gh api --paginate "repos/$REPO/pulls?state=open&per_page=100" --jq '.[].number')
+          caches=$(gh api --paginate "repos/$REPO/actions/caches?per_page=100" \
+            --jq '.actions_caches[] | select(.ref | startswith("refs/pull/")) | "\(.id) \(.ref)"')
+          while read -r id ref; do
+            [ -n "$id" ] || continue
+            number=$(echo "$ref" | cut -d/ -f3)
+            if ! grep -qx "$number" <<<"$open"; then
+              gh api --method DELETE "repos/$REPO/actions/caches/$id" >/dev/null
+              echo "deleted cache $id ($ref)"
+            fi
+          done <<<"$caches"
diff --git a/tests/corpus/6611-child-properties-across-modules/definer.cjs b/tests/corpus/6611-child-properties-across-modules/definer.cjs
index 8b1c8f1a3..ea58bc046 100644
--- a/tests/corpus/6611-child-properties-across-modules/definer.cjs
+++ b/tests/corpus/6611-child-properties-across-modules/definer.cjs
@@ -21,5 +21,5 @@ module.exports = function run() {
     console.log(e instanceof TypeError, e.message.length, e.message.slice(0, 30), e.message.slice(-40));
   }
   child.on("close", (code) => console.log("close", code, child.killedBy));
-  child.kill("SIGTERM");
+  child.stdout.once("data", () => child.kill("SIGTERM"));
 };
diff --git a/tests/corpus/6611-child-properties-across-modules/main.cjs b/tests/corpus/6611-child-properties-across-modules/main.cjs
index a3f422c64..3dfb6756a 100644
--- a/tests/corpus/6611-child-properties-across-modules/main.cjs
+++ b/tests/corpus/6611-child-properties-across-modules/main.cjs
@@ -5,17 +5,24 @@
 // and writes a getter-only property with a long name.
 const patched = require("./patcher.cjs");
 const definer = require("./definer.cjs");
-const child = patched();
-console.log(child.label);
-child.label = "x";
-console.log(child.stored, child.same);
-try {
-  child.same = 1;
-} catch (e) {
-  console.log(e instanceof TypeError, e.message);
+if (process.argv.at(2) === "child") {
+  // The child reports that it started, then waits for the parent's SIGTERM.
+  // It exits after 30 seconds without one.
+  process.stdout.write("ready");
+  setTimeout(() => {}, 30000);
+} else {
+  const child = patched();
+  console.log(child.label);
+  child.label = "x";
+  console.log(child.stored, child.same);
+  try {
+    child.same = 1;
+  } catch (e) {
+    console.log(e instanceof TypeError, e.message);
+  }
+  child.on("close", (code) => {
+    console.log("close", code, child.killedBy);
+  });
+  child.stdout.once("data", () => child.kill("SIGTERM"));
+  child.on("close", () => definer());
 }
-child.on("close", (code) => {
-  console.log("close", code, child.killedBy);
-});
-child.kill("SIGTERM");
-child.on("exit", () => definer());
diff --git a/tests/corpus/6611-child-properties-across-modules/spawner.cjs b/tests/corpus/6611-child-properties-across-modules/spawner.cjs
index d0c52d9b7..5701145a8 100644
--- a/tests/corpus/6611-child-properties-across-modules/spawner.cjs
+++ b/tests/corpus/6611-child-properties-across-modules/spawner.cjs
@@ -1,5 +1,5 @@
 "use strict";
 const { spawn } = require("child_process");
 module.exports = function start() {
-  return spawn(process.execPath, ["-e", "process.stdout.write('ok')"]);
+  return spawn(process.execPath, [process.argv[1], "child"]);
 };