feat(upload): add pause and cancel controls for active uploads

- Add CSS grid layout for upload-active-actions and hidden state
- Implement JavaScript logic for pausing and cancelling uploads with confirmation
- Add test to verify home page includes upload control elements

backend/static/js/40-upload.js

@@ -15,6 +15,11 @@
   const manageLink = document.querySelector("#manage-link");
   const newUpload = document.querySelector("#new-upload");
   const folderPicker = document.querySelector("[data-folder-picker]");
+  const submitButton = form && form.querySelector("button[type='submit']");
+  const idleUploadActions = form ? Array.from(form.querySelectorAll(".upload-idle-action")) : [];
+  const activeUploadActions = document.querySelector("#upload-active-actions");
+  const cancelUpload = document.querySelector("#cancel-upload");
+  const pauseUpload = document.querySelector("#pause-upload");
   const RESUMABLE_SESSIONS_KEY = "warpbox-resumable-sessions";
   const SHARE_CACHE = "warpbox-share-target-v1";
   const SHARE_LATEST_KEY = "/__warpbox_share_target__/latest";
@@ -52,6 +57,12 @@
   let recoveredDraft = null;
   let resumeMode = false;
   let sharedTargetDraft = null;
+  let activeUploadRequest = null;
+  let activeUploadSession = null;
+  let uploadPaused = false;
+  let uploadCancelled = false;
+  let uploadFinalizing = false;
+  let pauseWaiters = [];
   const maxUploadBytes = parseInt(form.dataset.maxUploadBytes || "-1", 10);
   const maxUploadLabel = form.dataset.maxUploadLabel || (maxUploadBytes > 0 && window.Warpbox.formatBytes ? window.Warpbox.formatBytes(maxUploadBytes) : "the configured limit");
 
@@ -145,7 +156,6 @@
       }
     }
 
-    const submit = form.querySelector("button[type='submit']");
     const formData = uploadFormData();
     await maybeRequestUploadNotificationPermission(selectedFiles);
     if (resumeMode && recoveredDraft) {
@@ -153,7 +163,7 @@
     } else {
       renderQueue(selectedFiles, "queued");
     }
-    setLoading(true, submit);
+    beginUpload();
 
     try {
       const payload = await uploadResumable(form.action, formData, selectedFiles);
@@ -175,14 +185,55 @@
         fileSummary.textContent = "Upload complete.";
       }
     } catch (error) {
+      if (isUploadCancelledError(error)) {
+        await discardActiveUploadSession();
+        await clearSharedTargetPayload();
+        form.reset();
+        resetFreshUploadState();
+        return;
+      }
       updateStatus(error.message || "Upload failed");
       notifyUploadError(error);
       showUploadNotification("Warpbox upload failed", error.message || "Upload failed");
     } finally {
-      setLoading(false, submit);
+      finishUpload();
     }
   });
 
+  if (pauseUpload) {
+    pauseUpload.addEventListener("click", () => {
+      if (!uploadLocked || uploadCancelled) {
+        return;
+      }
+      if (uploadPaused) {
+        resumeActiveUpload();
+      } else {
+        pauseActiveUpload();
+      }
+    });
+  }
+
+  if (cancelUpload) {
+    cancelUpload.addEventListener("click", async () => {
+      if (!uploadLocked || uploadCancelled) {
+        return;
+      }
+      const confirmed = await window.Warpbox.confirmDialog(
+        "Cancel this upload? Uploaded chunks will be deleted and the form will be reset for a new upload.",
+        {
+          title: "Cancel upload?",
+          variant: "warning",
+          confirmLabel: "Cancel Upload",
+          cancelLabel: "Keep Uploading",
+        },
+      );
+      if (!confirmed || !uploadLocked || uploadFinalizing) {
+        return;
+      }
+      requestUploadCancellation();
+    });
+  }
+
   if (copyURL) {
     copyURL.addEventListener("click", () => {
       window.Warpbox.copyText(latestBoxURL, copyURL, "Copied");
@@ -622,20 +673,147 @@
     newUpload.style.display = visible ? "" : "none";
   }
 
-  function setLoading(isLoading, submit) {
+  function beginUpload() {
+    uploadPaused = false;
+    uploadCancelled = false;
+    uploadFinalizing = false;
+    activeUploadRequest = null;
+    activeUploadSession = null;
+    setLoading(true);
+  }
+
+  function finishUpload() {
+    activeUploadRequest = null;
+    activeUploadSession = null;
+    uploadPaused = false;
+    uploadCancelled = false;
+    uploadFinalizing = false;
+    releasePauseWaiters();
+    setLoading(false);
+  }
+
+  function setLoading(isLoading) {
     uploadLocked = isLoading;
     if (progress) {
       progress.hidden = !isLoading;
     }
-    if (submit) {
-      submit.disabled = isLoading;
-      submit.textContent = isLoading ? "Uploading..." : "Upload files";
+    idleUploadActions.forEach((button) => {
+      button.style.display = isLoading ? "none" : "";
+    });
+    if (activeUploadActions) {
+      activeUploadActions.hidden = !isLoading;
+    }
+    if (submitButton) {
+      submitButton.disabled = isLoading;
+      submitButton.textContent = "Upload files";
     }
     if (newUpload) {
       newUpload.disabled = isLoading;
     }
+    if (cancelUpload) {
+      cancelUpload.disabled = !isLoading;
+      cancelUpload.textContent = "Cancel Upload";
+    }
+    updatePauseButton();
     updateStatus(isLoading ? "Transferring files..." : "");
     setTotalProgress(isLoading ? 0 : 100);
+    if (!isLoading) {
+      updateNewUploadVisibility();
+    }
+  }
+
+  function pauseActiveUpload() {
+    uploadPaused = true;
+    updatePauseButton();
+    updateStatus("Upload paused.");
+    if (activeUploadRequest) {
+      activeUploadRequest.abort();
+    }
+  }
+
+  function resumeActiveUpload() {
+    uploadPaused = false;
+    updatePauseButton();
+    updateStatus("Resuming upload...");
+    releasePauseWaiters();
+  }
+
+  function requestUploadCancellation() {
+    if (uploadFinalizing) {
+      return;
+    }
+    uploadCancelled = true;
+    uploadPaused = false;
+    updateStatus("Cancelling upload...");
+    if (cancelUpload) {
+      cancelUpload.disabled = true;
+      cancelUpload.textContent = "Cancelling...";
+    }
+    if (pauseUpload) {
+      pauseUpload.disabled = true;
+    }
+    releasePauseWaiters();
+    if (activeUploadRequest) {
+      activeUploadRequest.abort();
+    }
+  }
+
+  function updatePauseButton() {
+    if (!pauseUpload) {
+      return;
+    }
+    pauseUpload.disabled = !uploadLocked || uploadCancelled || uploadFinalizing;
+    pauseUpload.textContent = uploadPaused ? "Resume Upload" : "Pause Upload";
+    pauseUpload.classList.toggle("button-primary", uploadPaused);
+    pauseUpload.classList.toggle("button-outline", !uploadPaused);
+  }
+
+  function releasePauseWaiters() {
+    const waiters = pauseWaiters;
+    pauseWaiters = [];
+    waiters.forEach((resolve) => resolve());
+  }
+
+  async function waitForUploadReady() {
+    while (uploadPaused && !uploadCancelled) {
+      await new Promise((resolve) => pauseWaiters.push(resolve));
+    }
+    if (uploadCancelled) {
+      throw uploadControlError("UploadCancelledError", "Upload cancelled");
+    }
+  }
+
+  function uploadControlError(name, message) {
+    const error = new Error(message);
+    error.name = name;
+    return error;
+  }
+
+  function isUploadPausedError(error) {
+    return Boolean(error && error.name === "UploadPausedError");
+  }
+
+  function isUploadCancelledError(error) {
+    return Boolean(error && error.name === "UploadCancelledError");
+  }
+
+  async function discardActiveUploadSession() {
+    const session = activeUploadSession;
+    activeUploadSession = null;
+    if (!session || !session.sessionId) {
+      return;
+    }
+    await cancelResumableSession(session.sessionId, session.resumeToken).catch(() => {});
+    removeResumableSession(session.sessionId);
+  }
+
+  function beginUploadFinalization() {
+    uploadFinalizing = true;
+    updateStatus("Finalizing upload...");
+    if (cancelUpload) {
+      cancelUpload.disabled = true;
+    }
+    updatePauseButton();
   }
 
   function updateStatus(message) {
@@ -709,8 +887,20 @@
   }
 
   function uploadWithProgress(url, formData, files) {
+    return uploadWithProgressAttempt(url, formData, files).catch(async (error) => {
+      if (isUploadPausedError(error)) {
+        await waitForUploadReady();
+        return uploadWithProgress(url, formData, files);
+      }
+      throw error;
+    });
+  }
+
+  async function uploadWithProgressAttempt(url, formData, files) {
+    await waitForUploadReady();
     return new Promise((resolve, reject) => {
       const request = new XMLHttpRequest();
+      activeUploadRequest = request;
       const rateTracker = createTransferRateTracker(0);
       request.open("POST", url);
       request.setRequestHeader("Accept", "application/json");
@@ -728,6 +918,9 @@
       });
 
       request.addEventListener("load", () => {
+        if (activeUploadRequest === request) {
+          activeUploadRequest = null;
+        }
         let payload = {};
         try {
           payload = JSON.parse(request.responseText || "{}");
@@ -744,19 +937,37 @@
         resolve(payload);
       });
 
-      request.addEventListener("error", () => reject(new Error("Network error during upload")));
-      request.addEventListener("abort", () => reject(new Error("Upload aborted")));
+      request.addEventListener("error", () => {
+        if (activeUploadRequest === request) {
+          activeUploadRequest = null;
+        }
+        reject(new Error("Network error during upload"));
+      });
+      request.addEventListener("abort", () => {
+        if (activeUploadRequest === request) {
+          activeUploadRequest = null;
+        }
+        if (uploadCancelled) {
+          reject(uploadControlError("UploadCancelledError", "Upload cancelled"));
+        } else if (uploadPaused) {
+          reject(uploadControlError("UploadPausedError", "Upload paused"));
+        } else {
+          reject(new Error("Upload aborted"));
+        }
+      });
       request.send(formData);
     });
   }
 
   async function uploadResumable(fallbackUrl, formData, files) {
+    await waitForUploadReady();
     if (!window.fetch || typeof Blob === "undefined") {
       return uploadWithProgress(fallbackUrl, formData, files);
     }
 
     updateStatus("Fingerprinting files...");
     const fingerprints = await Promise.all(files.map((file) => fileFingerprint(file)));
+    await waitForUploadReady();
     const createPayload = {
       files: files.map((file, index) => ({
         name: uploadName(file),
@@ -779,6 +990,7 @@
       session = await findResumableSession(createPayload);
     }
     if (session) {
+      activeUploadSession = session;
       validateResumeSelection(session, createPayload);
       session = await addMissingResumableFiles(session, createPayload);
       if (resumeMode && recoveredDraft && recoveredDraft.session.sessionId === session.sessionId) {
@@ -787,6 +999,7 @@
       if (persistable) {
         saveResumableSession(session, createPayload);
       }
+      activeUploadSession = session;
     }
     if (!session || session.status !== "uploading") {
       try {
@@ -800,7 +1013,9 @@
       if (persistable) {
         saveResumableSession(session, createPayload);
       }
+      activeUploadSession = session;
     }
+    await waitForUploadReady();
     const sessionFiles = files.map((file, index) => matchSessionFile(session, createPayload.files[index]));
     if (sessionFiles.some((file) => !file)) {
       throw new Error("Upload session could not match the selected files");
@@ -822,6 +1037,7 @@
       const sessionFile = sessionFiles[fileIndex];
       const uploaded = new Set(sessionFile.uploadedChunks || []);
       for (let chunkIndex = 0; chunkIndex < sessionFile.chunkCount; chunkIndex++) {
+        await waitForUploadReady();
         if (uploaded.has(chunkIndex)) {
           continue;
         }
@@ -845,12 +1061,14 @@
       setSingleFileProgress(fileIndex, file, 100);
     }
 
-    updateStatus("Finalizing upload...");
+    await waitForUploadReady();
+    beginUploadFinalization();
     const resultPayload = await completeResumableSession(session.sessionId, session.resumeToken);
     const wasResumeMode = resumeMode;
     if (persistable) {
       removeResumableSession(session.sessionId);
     }
+    activeUploadSession = null;
     if (resumeMode && recoveredDraft && recoveredDraft.session.sessionId === session.sessionId) {
       resumeMode = false;
       recoveredDraft = null;
@@ -897,6 +1115,7 @@
   function uploadChunk(sessionID, resumeToken, fileID, chunkIndex, chunk, onProgress) {
     return new Promise((resolve, reject) => {
       const request = new XMLHttpRequest();
+      activeUploadRequest = request;
       request.open("PUT", `/api/v1/uploads/resumable/${encodeURIComponent(sessionID)}/files/${encodeURIComponent(fileID)}/chunks/${chunkIndex}`);
       request.setRequestHeader("Accept", "application/json");
       request.setRequestHeader("X-Warpbox-Resume-Token", resumeToken || "");
@@ -906,6 +1125,9 @@
         }
       });
       request.addEventListener("load", () => {
+        if (activeUploadRequest === request) {
+          activeUploadRequest = null;
+        }
         if (request.status < 200 || request.status >= 300) {
           let payload = {};
           try {
@@ -918,8 +1140,24 @@
         }
         resolve();
       });
-      request.addEventListener("error", () => reject(new Error("Network error during chunk upload")));
-      request.addEventListener("abort", () => reject(new Error("Chunk upload aborted")));
+      request.addEventListener("error", () => {
+        if (activeUploadRequest === request) {
+          activeUploadRequest = null;
+        }
+        reject(new Error("Network error during chunk upload"));
+      });
+      request.addEventListener("abort", () => {
+        if (activeUploadRequest === request) {
+          activeUploadRequest = null;
+        }
+        if (uploadCancelled) {
+          reject(uploadControlError("UploadCancelledError", "Upload cancelled"));
+        } else if (uploadPaused) {
+          reject(uploadControlError("UploadPausedError", "Upload paused"));
+        } else {
+          reject(new Error("Chunk upload aborted"));
+        }
+      });
       request.send(chunk);
     });
   }
@@ -928,16 +1166,26 @@
     const delays = [1000, 2000, 5000, 10000, 20000];
     let lastError = null;
     for (let attempt = 0; attempt <= delays.length; attempt++) {
+      await waitForUploadReady();
       try {
         return await uploadChunk(session.sessionId, session.resumeToken, sessionFile.id, chunkIndex, chunk, onProgress);
       } catch (error) {
+        if (isUploadCancelledError(error)) {
+          throw error;
+        }
+        if (isUploadPausedError(error)) {
+          await waitForUploadReady();
+          await wait(150);
+          attempt -= 1;
+          continue;
+        }
         lastError = error;
         if (attempt >= delays.length) {
           break;
         }
         const seconds = Math.round(delays[attempt] / 1000);
         updateStatus(`Connection interrupted, retrying chunk ${chunkIndex + 1} in ${seconds}s`);
-        await wait(delays[attempt]);
+        await waitForUploadDelay(delays[attempt]);
       }
     }
     throw lastError || new Error("Chunk upload failed");
@@ -972,6 +1220,14 @@
     return new Promise((resolve) => window.setTimeout(resolve, ms));
   }
 
+  async function waitForUploadDelay(ms) {
+    const deadline = performance.now() + ms;
+    while (performance.now() < deadline) {
+      await wait(Math.min(100, Math.max(0, deadline - performance.now())));
+      await waitForUploadReady();
+    }
+  }
+
   async function readUploadJSON(response, fallback) {
     let payload = {};
     try {