src: add some idempotent cleanup safeguard in post action

src/main.ts

@@ -788,6 +788,43 @@ actionsToolkit.run(
         fs.rmSync(stateHelper.tmpDir, {recursive: true});
       });
     }
+    // Check for any lingering buildkitd processes as a safeguard.
+    // TODO(adityamaru): Let's add an endpoint to sentry alert on this cause this
+    // means we've not handled some error throws in the main action.
+    try {
+      const {stdout} = await execAsync('pgrep buildkitd');
+      if (stdout) {
+        core.info('Found lingering buildkitd processes, cleaning up...');
+        await shutdownBuildkitd();
+        core.info('Shutdown buildkitd');
+
+        // Try to unmount if mounted
+        try {
+          const {stdout: mountOutput} = await execAsync(`mount | grep ${mountPoint}`);
+          if (mountOutput) {
+            for (let attempt = 1; attempt <= 3; attempt++) {
+              try {
+                await execAsync(`sudo umount ${mountPoint}`);
+                core.debug(`${mountPoint} has been unmounted`);
+                break;
+              } catch (error) {
+                if (attempt === 3) {
+                  throw error;
+                }
+                core.warning(`Unmount failed, retrying (${attempt}/3)...`);
+                await new Promise(resolve => setTimeout(resolve, 100));
+              }
+            }
+            core.info('Unmounted device');
+          }
+        } catch (error) {
+          core.warning(`Error during cleanup: ${error.message}`);
+        }
+      }
+    } catch (error) {
+      // pgrep returns non-zero if no processes found, which is fine.
+      core.debug('No lingering buildkitd processes found');
+    }
   }
 );