diff --git a/package.json b/package.json
index 4573508..4ad0b13 100644
--- a/package.json
+++ b/package.json
@@ -83,6 +83,7 @@
     "stylelint-config-recommended-scss": "^16.0.0",
     "tiktoken": "^1.0.22",
     "tinyglobby": "^0.2.14",
+    "tree-kill": "^1.2.2",
     "tsx": "^4.20.3",
     "typescript": "^5.8.3",
     "yargs": "^18.0.0",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 785b57a..ab2e5b7 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -104,6 +104,9 @@ importers:
       tinyglobby:
         specifier: ^0.2.14
         version: 0.2.15
+      tree-kill:
+        specifier: ^1.2.2
+        version: 1.2.2
       tsx:
         specifier: ^4.20.3
         version: 4.20.5
@@ -6033,6 +6036,10 @@ packages:
   tr46@0.0.3:
     resolution: {integrity: sha512-N3WMsuqV66lT30CrXNbEjx4GEwlow3v6rr4mCcv6prnfwhS01rkgyFdjPNBYd9br7LpXV1+Emh01fHnq2Gdgrw==}
 
+  tree-kill@1.2.2:
+    resolution: {integrity: sha512-L0Orpi8qGpRG//Nd+H90vFB+3iHnue1zSSGmNOOCh1GLJ7rUKVwV2HvijphGQS2UmhUZewS9VgvxYIdgr+fG1A==}
+    hasBin: true
+
   trim-lines@3.0.1:
     resolution: {integrity: sha512-kRj8B+YHZCc9kQYdWfJB2/oUl9rA99qbowYYBtr4ui4mZyAQ2JpvVBd/6U2YloATfqBhBTSMhTpgBHtU0Mf3Rg==}
 
@@ -13567,6 +13574,8 @@ snapshots:
 
   tr46@0.0.3: {}
 
+  tree-kill@1.2.2: {}
+
   trim-lines@3.0.1: {}
 
   triple-beam@1.4.1: {}
diff --git a/runner/orchestration/generate.ts b/runner/orchestration/generate.ts
index 2322aa3..90104db 100644
--- a/runner/orchestration/generate.ts
+++ b/runner/orchestration/generate.ts
@@ -158,7 +158,7 @@ export async function generateCodeAndAssess(options: {
           ? // Building can be really expensive. We likely should add support for "CPU hints" per environment.
             // E.g. CLI building is really CPU intensive with ESBuild being multi-core.
             // TODO: Follow-up on this and add CPU hints.
-            Math.floor(availableParallelism() * 0.4 * 0.5)
+            Math.floor(appConcurrency * 0.5)
           : Infinity,
     });
 
diff --git a/runner/utils/kill-gracefully.ts b/runner/utils/kill-gracefully.ts
index 195b707..b922c11 100644
--- a/runner/utils/kill-gracefully.ts
+++ b/runner/utils/kill-gracefully.ts
@@ -1,13 +1,31 @@
 import { ChildProcess } from 'child_process';
+import treeKill from 'tree-kill';
+
+function treeKillPromise(pid: number, signal: string): Promise<void> {
+  return new Promise((resolve, reject) => {
+    treeKill(pid, signal, (err) => {
+      if (err !== undefined) {
+        reject(err);
+      } else {
+        resolve(err);
+      }
+    });
+  });
+}
 
 export function killChildProcessGracefully(
   child: ChildProcess,
   timeoutInMs = 1000 * 10 // 10s
 ): Promise<void> {
-  return new Promise((resolve, reject) => {
+  return new Promise(async (resolve, reject) => {
     // Process already exited.
     if (child.exitCode !== null) {
       resolve();
+      return;
+    }
+    const pid = child.pid;
+    if (pid === undefined) {
+      throw new Error(`No process ID for processed that should be killed.`);
     }
 
     // Watch for exiting, so that we can cancel the timeout(s) then.
@@ -18,10 +36,17 @@ export function killChildProcessGracefully(
     });
 
     // Send SIGTERM
-    child.kill('SIGTERM');
+    try {
+      await treeKillPromise(pid, 'SIGTERM');
+    } catch (e) {
+      console.error(
+        `Could not send "SIGTERM" for killing process. Trying "SIGKILL".`
+      );
+    }
+
     // Start a timeout for the SIGKILL fallback
     const sigkillTimeoutId = setTimeout(
-      () => child.kill('SIGKILL'),
+      () => treeKill(pid, 'SIGKILL'),
       timeoutInMs
     );
     // Start another timeout to reject the promise if the child process never fires `exit` for some reasons.