diff --git a/actions/setup/js/update_project.cjs b/actions/setup/js/update_project.cjs
index ea71b0a3e52..2fc17bcdcc5 100644
--- a/actions/setup/js/update_project.cjs
+++ b/actions/setup/js/update_project.cjs
@@ -1227,10 +1227,11 @@ async function main(config = {}, githubClient = null) {
         const projectStr = effectiveProjectUrl.trim();
         const projectWithoutHash = projectStr.startsWith("#") ? projectStr.substring(1) : projectStr;
 
-        // Check if it's a temporary ID (aw_XXXXXXXXXXXX)
-        if (/^aw_[0-9a-f]{12}$/i.test(projectWithoutHash)) {
-          // Look up in the unified temporaryIdMap
-          const resolved = tempIdMap.get(projectWithoutHash.toLowerCase());
+        // Check if it's a temporary ID using the canonical pattern (aw_XXX to aw_XXXXXXXX)
+        if (isTemporaryId(projectWithoutHash)) {
+          // Look up in the unified temporaryIdMap using normalized (lowercase) ID
+          const normalizedId = normalizeTemporaryId(projectWithoutHash);
+          const resolved = tempIdMap.get(normalizedId);
           if (resolved && typeof resolved === "object" && "projectUrl" in resolved && resolved.projectUrl) {
             core.info(`Resolved temporary project ID ${projectStr} to ${resolved.projectUrl}`);
             effectiveProjectUrl = resolved.projectUrl;
diff --git a/actions/setup/js/update_project.test.cjs b/actions/setup/js/update_project.test.cjs
index 01fe99d8c95..52b071eda7c 100644
--- a/actions/setup/js/update_project.test.cjs
+++ b/actions/setup/js/update_project.test.cjs
@@ -1795,3 +1795,145 @@ describe("updateProject", () => {
     expect(result.error).toContain("transient GitHub API error");
   });
 });
+
+describe("update_project temporary project ID resolution", () => {
+  let mockSetup;
+  let messageHandler;
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+
+    // Reset mock implementation
+    mockGithub.graphql.mockReset();
+
+    // Create a minimal mock setup for the handler
+    mockSetup = {
+      core: mockCore,
+      github: mockGithub,
+      context: mockContext,
+      updateProjectHandlerFactory,
+    };
+  });
+
+  afterEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("resolves temporary project ID with 8 alphanumeric characters (generated format)", async () => {
+    const temporaryId = "aw_AbC12345"; // 8 chars, mixed case
+    const projectUrl = "https://github.com/orgs/testowner/projects/99";
+    const tempIdMap = new Map();
+    tempIdMap.set("aw_abc12345", { projectUrl }); // Stored in lowercase
+
+    queueResponses([repoResponse(), viewerResponse(), orgProjectV2Response(projectUrl, 99, "project-resolved"), issueResponse("issue-id-1"), existingItemResponse("issue-id-1", "item-resolved"), fieldsResponse([])]);
+
+    // Create handler with config
+    const config = { max: 100 };
+    messageHandler = await updateProjectHandlerFactory(config);
+
+    const message = {
+      type: "update_project",
+      project: temporaryId, // Using temporary ID
+      content_type: "issue",
+      content_number: 42,
+    };
+
+    const result = await messageHandler(message, {}, tempIdMap);
+
+    expect(result.success).toBe(true);
+    expect(mockCore.info).toHaveBeenCalledWith(`Resolved temporary project ID ${temporaryId} to ${projectUrl}`);
+  });
+
+  it("resolves temporary project ID with # prefix", async () => {
+    const temporaryId = "#aw_Test99"; // With hash prefix
+    const projectUrl = "https://github.com/orgs/testowner/projects/88";
+    const tempIdMap = new Map();
+    tempIdMap.set("aw_test99", { projectUrl }); // Stored without hash, lowercase
+
+    queueResponses([repoResponse(), viewerResponse(), orgProjectV2Response(projectUrl, 88, "project-hash"), issueResponse("issue-id-2"), existingItemResponse("issue-id-2", "item-hash"), fieldsResponse([])]);
+
+    const config = { max: 100 };
+    messageHandler = await updateProjectHandlerFactory(config);
+
+    const message = {
+      type: "update_project",
+      project: temporaryId,
+      content_type: "issue",
+      content_number: 43,
+    };
+
+    const result = await messageHandler(message, {}, tempIdMap);
+
+    expect(result.success).toBe(true);
+    expect(mockCore.info).toHaveBeenCalledWith(`Resolved temporary project ID ${temporaryId} to ${projectUrl}`);
+  });
+
+  it("resolves temporary project ID with 3 characters (minimum)", async () => {
+    const temporaryId = "aw_abc"; // 3 chars minimum
+    const projectUrl = "https://github.com/orgs/testowner/projects/77";
+    const tempIdMap = new Map();
+    tempIdMap.set("aw_abc", { projectUrl });
+
+    queueResponses([repoResponse(), viewerResponse(), orgProjectV2Response(projectUrl, 77, "project-min"), issueResponse("issue-id-3"), existingItemResponse("issue-id-3", "item-min"), fieldsResponse([])]);
+
+    const config = { max: 100 };
+    messageHandler = await updateProjectHandlerFactory(config);
+
+    const message = {
+      type: "update_project",
+      project: temporaryId,
+      content_type: "issue",
+      content_number: 44,
+    };
+
+    const result = await messageHandler(message, {}, tempIdMap);
+
+    expect(result.success).toBe(true);
+    expect(mockCore.info).toHaveBeenCalledWith(`Resolved temporary project ID ${temporaryId} to ${projectUrl}`);
+  });
+
+  it("throws error when temporary project ID is not found in map", async () => {
+    const temporaryId = "aw_NotFound";
+    const tempIdMap = new Map(); // Empty map
+
+    const config = { max: 100 };
+    messageHandler = await updateProjectHandlerFactory(config);
+
+    const message = {
+      type: "update_project",
+      project: temporaryId,
+      content_type: "issue",
+      content_number: 45,
+    };
+
+    const result = await messageHandler(message, {}, tempIdMap);
+
+    expect(result.success).toBe(false);
+    expect(result.error).toMatch(/Temporary project ID 'aw_NotFound' not found.*Ensure create_project was called before update_project/);
+  });
+
+  it("handles full project URL normally (not treated as temporary ID)", async () => {
+    const projectUrl = "https://github.com/orgs/testowner/projects/66";
+    const tempIdMap = new Map();
+    // Map has an entry, but it shouldn't be used since we're passing full URL
+    tempIdMap.set("aw_other", { projectUrl: "https://github.com/orgs/other/projects/1" });
+
+    queueResponses([repoResponse(), viewerResponse(), orgProjectV2Response(projectUrl, 66, "project-full"), issueResponse("issue-id-4"), existingItemResponse("issue-id-4", "item-full"), fieldsResponse([])]);
+
+    const config = { max: 100 };
+    messageHandler = await updateProjectHandlerFactory(config);
+
+    const message = {
+      type: "update_project",
+      project: projectUrl, // Full URL, not temporary ID
+      content_type: "issue",
+      content_number: 46,
+    };
+
+    const result = await messageHandler(message, {}, tempIdMap);
+
+    expect(result.success).toBe(true);
+    // Should NOT log temporary ID resolution
+    expect(mockCore.info).not.toHaveBeenCalledWith(expect.stringContaining("Resolved temporary project ID"));
+  });
+});