feat: add required cache-key input for v2

Replace the hardcoded GITHUB_REPO_NAME sticky disk key with a required
cache-key input. Users must explicitly declare which cache entity their
build targets, preventing cache thrashing in multi-target repos.

The cache-key is saved to action state and passed through to the commit
phase so the same key is used for both expose and commit RPCs.

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: piob-io

action.yml

@@ -5,6 +5,13 @@ branding:
   icon: layers
   color: black
 inputs:
+  cache-key:
+    description: >-
+      Unique identifier for this build's Docker layer cache. Builds with the
+      same cache-key share cached layers across runs. Set this to the Dockerfile
+      being built (e.g., services/api/Dockerfile). Jobs building different
+      Dockerfiles should use different cache-keys to avoid cache thrashing.
+    required: true
   buildx-version:
     description: Buildx version. (e.g., v0.23.0, latest)
     required: false

dist/index.js

@@ -506,6 +506,7 @@ async function startBlacksmithBuilder(
     );
 
     // Save state for post action
+    stateHelper.setCacheKey(core.getInput("cache-key"));
     stateHelper.setExposeId(stickyDiskSetup.exposeId);
 
     return { addr: buildkitdAddr, exposeId: stickyDiskSetup.exposeId };
@@ -959,7 +960,11 @@ void actionsToolkit.run(
                 "No previous step failures detected, committing sticky disk after successful cleanup",
               );
 
-              await reporter.commitStickyDisk(exposeId, fsDiskUsageBytes);
+              await reporter.commitStickyDisk(
+                exposeId,
+                fsDiskUsageBytes,
+                stateHelper.getCacheKey(),
+              );
             } catch (error) {
               core.error(
                 `Failed to commit sticky disk: ${(error as Error).message}`,

dist/index.js.map

@@ -207,13 +207,14 @@ export async function reportIntegrityCheckFailure(
 export async function commitStickyDisk(
   exposeId: string,
   fsDiskUsageBytes: number | null,
+  cacheKey?: string,
 ): Promise<void> {
   try {
     const agentClient = createBlacksmithAgentClient();
 
     const commitRequest: Record<string, unknown> = {
       exposeId: exposeId,
-      stickyDiskKey: process.env.GITHUB_REPO_NAME || "",
+      stickyDiskKey: cacheKey || process.env.GITHUB_REPO_NAME || "",
       vmId: process.env.BLACKSMITH_VM_ID || "",
       shouldCommit: true,
       repoName: process.env.GITHUB_REPO_NAME || "",

src/main.ts

@@ -377,11 +377,12 @@ export async function getStickyDisk(options?: {
     throw new Error(`grpc connection test failed: ${(error as Error).message}`);
   }
 
-  const stickyDiskKey = process.env.GITHUB_REPO_NAME || "";
-  if (stickyDiskKey === "") {
-    throw new Error("GITHUB_REPO_NAME is not set");
+  const cacheKey = core.getInput("cache-key", { required: true });
+  if (cacheKey === "") {
+    throw new Error("cache-key input is required but was empty");
   }
-  core.info(`Getting sticky disk for ${stickyDiskKey}`);
+  const stickyDiskKey = cacheKey;
+  core.info(`Getting sticky disk for cache-key: ${stickyDiskKey}`);
 
   const response = await client.getStickyDisk(
     {

src/reporter.ts

@@ -38,6 +38,14 @@ export function getBuilderName(): string {
   return core.getState("builderName");
 }
 
+export function setCacheKey(key: string) {
+  core.saveState("cacheKey", key);
+}
+
+export function getCacheKey(): string {
+  return core.getState("cacheKey");
+}
+
 let _sigkillUsed = false;
 
 export function setSigkillUsed(used: boolean) {