src: move buildkit prune to cleanup stage and invoke it inline

Previously, we were firing off an async buildkit prune to clean
up layers unused in 14 days. This changes that to cleanup layers
unused in 7 days and fires it off inline on cleanup. It just seems
easier to reason about that way.

src/main.ts

@@ -20,7 +20,7 @@ import * as context from './context';
 import {promisify} from 'util';
 import {exec} from 'child_process';
 import * as reporter from './reporter';
-import {setupStickyDisk, startAndConfigureBuildkitd, getNumCPUs, leaveTailnet} from './setup_builder';
+import {setupStickyDisk, startAndConfigureBuildkitd, getNumCPUs, leaveTailnet, pruneBuildkitCache} from './setup_builder';
 import {Metric_MetricType} from '@buf/blacksmith_vm-agent.bufbuild_es/stickydisk/v1/stickydisk_pb';
 
 const buildxVersion = 'v0.17.0';
@@ -74,9 +74,9 @@ export async function startBlacksmithBuilder(inputs: context.Inputs): Promise<{a
     // If setup-only is true, we don't want to report the build to our control plane
     // since we are only setting up the builder and therefore cannot expose any analytics
     // about the build.
-    const dockerfilePath = inputs.setupOnly ? "" : context.getDockerfilePath(inputs);
+    const dockerfilePath = inputs.setupOnly ? '' : context.getDockerfilePath(inputs);
     if (!inputs.setupOnly && !dockerfilePath) {
-        throw new Error('Failed to resolve dockerfile path');
+      throw new Error('Failed to resolve dockerfile path');
     }
     const stickyDiskStartTime = Date.now();
     const stickyDiskSetup = await setupStickyDisk(dockerfilePath || '', inputs.setupOnly);
@@ -217,7 +217,6 @@ actionsToolkit.run(
         core.warning(`Failed to create builder setup sentinel file: ${error.message}`);
       }
 
-
       let builder: BuilderInfo;
       await core.group(`Builder info`, async () => {
         builder = await toolkit.builder.inspect();
@@ -231,7 +230,6 @@ actionsToolkit.run(
         process.exit(0);
       }
 
-
       await core.group(`Proxy configuration`, async () => {
         let dockerConfig: ConfigFile | undefined;
         let dockerConfigMalformed = false;
@@ -362,6 +360,16 @@ actionsToolkit.run(
           });
         }
 
+        // Prune buildkit cache to clean up unused layers before shutting down buildkitd.
+        try {
+          core.info('Pruning BuildKit cache');
+          await pruneBuildkitCache();
+          core.info('BuildKit cache pruned');
+        } catch (error) {
+          // Log warning but don't fail the cleanup
+          core.warning(`Error pruning BuildKit cache: ${error.message}`);
+        }
+
         await leaveTailnet();
 
         try {
@@ -448,6 +456,16 @@ actionsToolkit.run(
         try {
           const {stdout} = await execAsync('pgrep buildkitd');
           if (stdout.trim()) {
+            // Prune buildkit cache to clean up unused layers before shutting down buildkitd.
+            try {
+              core.info('Pruning BuildKit cache');
+              await pruneBuildkitCache();
+              core.info('BuildKit cache pruned');
+            } catch (error) {
+              // Log warning but don't fail the cleanup
+              core.warning(`Error pruning BuildKit cache: ${error.message}`);
+            }
+
             await shutdownBuildkitd();
             core.info('Shutdown buildkitd');
           }

src/setup_builder.ts

@@ -300,16 +300,11 @@ export async function startAndConfigureBuildkitd(parallelism: number, setupOnly:
     throw error;
   }
 
-  // Start cache pruning in the background without blocking.
-  pruneBuildkitCache().catch(error => {
-    core.warning(`Background cache pruning failed: ${error.message}`);
-  });
-
   return addr;
 }
 
 /**
- * Prunes buildkit cache data older than 14 days.
+ * Prunes buildkit cache data older than 7 days.
  * We don't specify any keep bytes here since we are
  * handling the ceph volume size limits ourselves in
  * the VM Agent.
@@ -317,8 +312,8 @@ export async function startAndConfigureBuildkitd(parallelism: number, setupOnly:
  */
 export async function pruneBuildkitCache(): Promise<void> {
   try {
-    const fourteenDaysInHours = 14 * 24;
+    const sevenDaysInHours = 7 * 24;
-    await execAsync(`sudo buildctl --addr ${BUILDKIT_DAEMON_ADDR} prune --keep-duration ${fourteenDaysInHours}h --all`);
+    await execAsync(`sudo buildctl --addr ${BUILDKIT_DAEMON_ADDR} prune --keep-duration ${sevenDaysInHours}h --all`);
     core.debug('Successfully pruned buildkit cache');
   } catch (error) {
     core.warning(`Error pruning buildkit cache: ${error.message}`);