Merge pull request #66 from SteelDynamite/claude/gracious-cray-yN12q

docs(api): clarify thread-safety bounds and multi-process limits

Audit.md

@@ -1,5 +1,38 @@
 # Audit Log
 
+## 2026-04-27
+
+Found and fixed 3 issues:
+
+1. **Perf: needless clone of upload payload** (sync.rs:733) — the `SyncAction::Upload` arm read the file into `data`, computed `compute_checksum(&data)`, then called `client.put_file(path, data.clone())`. The clone existed only because the next statement needed `data.len()` for the sync-state record. Captured `data.len() as u64` into `len` first, moved `data` into `put_file`, and used `len` afterwards — one full byte copy avoided per uploaded file.
+2. **Bug: Google Tasks sync silently drops metadata-write failures** (google_tasks.rs:361, 377) — both `.listdata.json` and `.onyx-workspace.json` were written via `if let Ok(meta_content) = serde_json::to_string_pretty(...) { let _ = atomic_write(...); }`, so a serialization or atomic-write error returned `Ok(GoogleSyncResult { downloaded: N, errors: [] })` even though list/workspace ordering was never persisted. Both writes now push their errors into the `errors` vec already returned in `GoogleSyncResult`.
+3. **Code quality: unreachable dead-error path in storage dedup** (storage.rs:447) — the dedup loop computed `Option<Task>` from each `by_id` group and then `ok_or_else(|| Error::InvalidData("Empty dedup entries for task"))?`. `by_id` is only populated by `entry(uuid).or_default().push(entry)`, so every group has ≥1 element and the `None` branch is unreachable. Replaced the `Option`+`?` with direct `expect` calls (one per branch) that document the non-empty invariant; the loop now yields `Task` directly.
+
+## 2026-04-25
+
+Found and fixed 3 issues:
+
+1. **Perf: O(n²) deletion-detection in `get_sync_status`** (sync.rs:918) — for every path tracked in `sync_state.files`, the loop scanned `local_files` linearly via `.any(|f| f.path == *path)` to decide whether to count it as a deleted-locally pending change. The earlier "modified or new" loop already used the inverse direction with `sync_state.files.get(...)` (O(1)), so the second loop was the inconsistent one. Built a `HashSet<&str>` of local paths once and used `contains` for the membership check.
+2. **Perf: cascade delete walks all_tasks per frontier pop** (tauri/lib.rs:460) — `delete_task`'s descendant BFS scanned the full task list on every parent popped from the frontier, making the work O(n × depth). Built a `parent_id -> [child_id]` `HashMap` once, then the BFS visits each descendant in O(1) amortised, dropping total cost to O(n).
+3. **Code quality: duplicate atomic-write in `AppConfig::save_to_file`** (config.rs:114) — the function had its own copy of the temp-file + rename + cleanup-on-failure dance even though `storage::atomic_write` is `pub(crate)` and was already shared by `google_tasks.rs`. Replaced the inline implementation with a call to `crate::storage::atomic_write` so the crate has one canonical atomic write path.
+
+## 2026-04-24
+
+Found and fixed 3 issues:
+
+1. **Bug: orphan base entries never cleaned from sync state** (sync.rs) — when a file was deleted both locally and remotely, `compute_sync_actions` emitted no action (the `(None, None, Some(_))` arm), so the base entry in `.syncstate.json` persisted forever. On each subsequent sync the same no-op case fired and the state file grew. Added `prune_orphan_bases` pass in `sync_workspace_inner` that drops base entries not present in either scan.
+2. **Code quality: redundant is_some_and on already-matched Option** (sync.rs:208) — the `(None, Some(_), Some(b))` arm re-checked `remote` via `remote.is_some_and(|r| ...)` even though the pattern had just proven `remote` is `Some(_)`. Bound the inner value with `Some(r)` in the pattern and used `r` directly.
+3. **Code quality: single-caller sanitize_filename wrapper** (storage.rs) — `FileSystemStorage::sanitize_filename` was a one-line forwarder to `crate::sanitize_filename` with one call site. Inlined the crate call and removed the method.
+
+## 2026-04-20
+
+Found and fixed 4 issues:
+
+1. **Dead code in conflict recovery** (sync.rs:756) — `parts[1] != ".listdata.json"` was unreachable because the branch is already gated on `parts[1].ends_with(".md")`, which `.listdata.json` cannot satisfy. Removed the redundant check.
+2. **O(n²) cascade delete** (tauri/lib.rs) — descendant traversal in `delete_task` used `Vec::contains` inside the inner loop, making it quadratic in the number of tasks per list. Swapped the visited set to `HashSet`; `HashSet::insert` folds the contains+push into one call.
+3. **Silent cascade failure in toggle_task** (tauri/lib.rs) — subtask `update_task` errors were discarded with `let _ = ...`, leaving subtasks stuck at the old status with no UI feedback. Propagate the error so the frontend can surface it.
+4. **Duplicated UUID-parse boilerplate** (tauri/lib.rs) — 17 commands repeated `Uuid::parse_str(&x).map_err(|e| e.to_string())?`. Extracted a `parse_uuid` helper so callers read as `let id = parse_uuid(&list_id)?;`.
+
 ## 2026-04-15
 
 Found and fixed 4 issues:

CLAUDE.md

@@ -30,7 +30,7 @@ The Tauri dev server runs on port 1422 (`vite.config.ts` and `tauri.conf.json`).
 Two-crate workspace (`resolver = "2"`, edition 2021) plus a Tauri app:
 
 - **onyx-core** — Pure Rust library. Storage trait with `FileSystemStorage` implementation, `TaskRepository` (main API), data models, config, error types. No CLI/UI dependencies. `keyring` feature-gated behind `keyring-storage` (default on) for Android compatibility.
-- **onyx-cli** — CLI frontend using clap. Commands are in `src/commands/` (init, workspace, list, task, group). Output formatting in `src/output.rs`.
+- **onyx-cli** — CLI frontend using clap. Commands are in `src/commands/` (init, workspace, list, task, group, sync). Output formatting in `src/output.rs`.
 - **apps/tauri/** — Tauri v2 GUI. Svelte 5 frontend in `src/`, Rust backend in `src-tauri/` with Tauri commands that call into `onyx-core`. `notify` crate feature-gated for Android. `tauri-plugin-credentials/` provides cross-platform credential storage (Android Keystore via EncryptedSharedPreferences, desktop via keyring crate).
 
 ### Key patterns
@@ -64,7 +64,7 @@ The GUI uses Svelte 5 runes mode (`$state`, `$derived`, `$effect`, `$props()`).
 
 Pre-alpha. No users, no released builds, no data to migrate. Breaking changes to on-disk formats, config structure, or sync conventions are free — do not add migration logic.
 
-### Current state (2026-04-15)
+### Current state (2026-04-27)
 
 - **Phase 1** (Core + CLI): Complete
 - **Phase 2** (WebDAV sync): Complete — remote folder browsing, checksum-based conflict resolution, auto-sync lifecycle, per-workspace sync interval
@@ -106,7 +106,7 @@ Pre-alpha. No users, no released builds, no data to migrate. Breaking changes to
 - Task deduplication on load (handles sync conflict duplicates)
 - Subtask hierarchy: subtask count shown on parent tasks in list, subtask detail via three-panel slide navigation, inline add at top of subtask list (new subtasks prepend), collapsible completed subtasks section, cascade delete (parent deletion removes all subtasks with confirmation warning)
 - Custom confirmation dialogs (ConfirmDialog component replaces native confirm())
-- Workspace path validation (rejects system directories)
+- Workspace path validation (rejects filesystem root `/` and system directories: `/etc`, `/usr`, `/bin`, `/sbin`, `/var`, `/proc`, `/sys`, `/dev`)
 - Task detail auto-cleanup (taskStack clears when viewed task is deleted or list switches)
 - Swipe gestures on mobile: swipe left/right on a task to toggle completion (swipe direction depends on current status)
 - Accessibility: ARIA labels/roles on interactive components, keyboard handlers, `prefers-reduced-motion` CSS support

PLAN.md

@@ -671,7 +671,6 @@ apps/tauri/
 │       │   ├── TaskItem.svelte
 │       │   ├── NewTaskInput.svelte
 │       │   ├── TaskDetailView.svelte
-│       │   ├── BottomSheet.svelte
 │       │   ├── ConfirmDialog.svelte
 │       │   └── DateTimePicker.svelte
 │       └── stores/
@@ -766,7 +765,7 @@ WorkspaceConfig {
 - [x] List rename (inline input via list kebab menu in drawer)
 - [x] Keyboard shortcuts (Escape closes settings → detail → drawer → menus in priority order)
 - [x] Sync status indicators (last-sync time + upload/download counts chip in TasksScreen)
-- [x] Push/pull sync mode selection (session-only sync direction selector in SettingsScreen)
+- [ ] Push/pull sync mode selection (session-only sync direction selector in SettingsScreen)
 - [x] Group-by-date toggle per list (checkmark toggle in list kebab menu)
 - [x] Subtask hierarchy (expand/collapse, inline add, cascade toggle/delete)
 - [ ] Search/filter tasks
@@ -1059,6 +1058,6 @@ This project is free and open-source software licensed under GPL v3.
 
 ---
 
-**Last Updated**: 2026-04-17
-**Document Version**: 4.3
+**Last Updated**: 2026-04-27
+**Document Version**: 4.5
 **Status**: Ready to Implement - Milestone-Driven Plan

apps/tauri/src-tauri/src/lib.rs

@@ -60,6 +60,11 @@ fn lock_state(state: &Mutex<AppState>) -> Result<std::sync::MutexGuard<'_, AppSt
     state.lock().map_err(|e| format!("State lock poisoned: {}", e))
 }
 
+/// Parse a UUID from a string, converting errors to the String format Tauri commands use.
+fn parse_uuid(s: &str) -> Result<Uuid, String> {
+    Uuid::parse_str(s).map_err(|e| e.to_string())
+}
+
 impl AppState {
     /// Persist config to disk, converting errors to String for Tauri commands.
     fn save_config(&self) -> Result<(), String> {
@@ -67,6 +72,25 @@ impl AppState {
     }
 }
 
+/// Extract the hostname from a URL (scheme://host/...), used as the credential key.
+/// Returns an empty string if the URL has no scheme or host.
+fn credential_domain(url: &str) -> String {
+    url.split("://")
+        .nth(1)
+        .and_then(|rest| rest.split('/').next())
+        .unwrap_or("")
+        .to_string()
+}
+
+/// Join a remote base directory with a child path, handling empty base and trailing slashes.
+fn join_remote_path(base: &str, child: &str) -> String {
+    if base.is_empty() {
+        child.to_string()
+    } else {
+        format!("{}/{}", base.trim_end_matches('/'), child)
+    }
+}
+
 /// Validate that a workspace path is a reasonable directory and not a system path.
 fn validate_workspace_path(path: &str) -> Result<(), String> {
     let p = PathBuf::from(path);
@@ -79,7 +103,10 @@ fn validate_workspace_path(path: &str) -> Result<(), String> {
     #[cfg(unix)]
     {
         let forbidden = ["/", "/etc", "/usr", "/bin", "/sbin", "/var", "/proc", "/sys", "/dev"];
+        // Strip trailing slashes, but keep "/" itself — trim_end_matches would
+        // collapse it to "" and slip past the forbidden check.
         let canonical = normalized.trim_end_matches('/');
+        let canonical = if canonical.is_empty() { "/" } else { canonical };
         if forbidden.contains(&canonical) {
             return Err(format!("Cannot use system directory as workspace: {}", path));
         }
@@ -263,10 +290,7 @@ async fn rename_workspace(
             let base_url = webdav_url.as_deref().ok_or("No WebDAV URL configured")?;
             let remote_path = webdav_path.as_deref().unwrap_or("");
 
-            let domain = base_url
-                .split("://").nth(1)
-                .and_then(|rest| rest.split('/').next())
-                .unwrap_or("").to_string();
+            let domain = credential_domain(base_url);
             let creds = app_handle.state::<Credentials<tauri::Wry>>();
             let (username, password) = creds.load(&domain)?;
 
@@ -347,7 +371,7 @@ fn delete_list(
     let mut s = lock_state(&state)?;
     ensure_repo(&mut s)?;
     mute_watcher(&mut s);
-    let id = Uuid::parse_str(&list_id).map_err(|e| e.to_string())?;
+    let id = parse_uuid(&list_id)?;
     repo_mut(&mut s)?
         .delete_list(id)
         .map_err(|e| e.to_string())
@@ -362,7 +386,7 @@ fn list_tasks(
 ) -> Result<Vec<Task>, String> {
     let mut s = lock_state(&state)?;
     ensure_repo(&mut s)?;
-    let id = Uuid::parse_str(&list_id).map_err(|e| e.to_string())?;
+    let id = parse_uuid(&list_id)?;
     repo_ref(&s)?
         .list_tasks(id)
         .map_err(|e| e.to_string())
@@ -381,13 +405,13 @@ fn create_task(
     let mut s = lock_state(&state)?;
     ensure_repo(&mut s)?;
     mute_watcher(&mut s);
-    let id = Uuid::parse_str(&list_id).map_err(|e| e.to_string())?;
+    let id = parse_uuid(&list_id)?;
     let mut task = Task::new(title);
     if let Some(desc) = description.filter(|d| !d.is_empty()) {
         task.description = desc;
     }
     if let Some(pid) = parent_id {
-        let parent_uuid = Uuid::parse_str(&pid).map_err(|e| e.to_string())?;
+        let parent_uuid = parse_uuid(&pid)?;
         task.parent_id = Some(parent_uuid);
     }
     // Accept the date fields at creation time so callers don't have to do a
@@ -409,7 +433,7 @@ fn update_task(
     let mut s = lock_state(&state)?;
     ensure_repo(&mut s)?;
     mute_watcher(&mut s);
-    let id = Uuid::parse_str(&list_id).map_err(|e| e.to_string())?;
+    let id = parse_uuid(&list_id)?;
     repo_mut(&mut s)?
         .update_task(id, task)
         .map_err(|e| e.to_string())
@@ -424,20 +448,30 @@ fn delete_task(
     let mut s = lock_state(&state)?;
     ensure_repo(&mut s)?;
     mute_watcher(&mut s);
-    let lid = Uuid::parse_str(&list_id).map_err(|e| e.to_string())?;
-    let tid = Uuid::parse_str(&task_id).map_err(|e| e.to_string())?;
+    let lid = parse_uuid(&list_id)?;
+    let tid = parse_uuid(&task_id)?;
     let repo = repo_mut(&mut s)?;
     // Cascade-delete the full descendant subtree (not just direct children)
     // so deleting a parent can't leave grandchildren orphaned with a
     // parent_id pointing at a deleted task.
     let all_tasks = repo.list_tasks(lid).map_err(|e| e.to_string())?;
-    let mut to_delete: Vec<Uuid> = Vec::new();
+    // Build a parent -> children index in one pass so the BFS below is O(n)
+    // instead of O(n * depth) scanning all tasks for each frontier pop.
+    let mut children_by_parent: std::collections::HashMap<Uuid, Vec<Uuid>> =
+        std::collections::HashMap::new();
+    for t in &all_tasks {
+        if let Some(pid) = t.parent_id {
+            children_by_parent.entry(pid).or_default().push(t.id);
+        }
+    }
+    let mut to_delete: std::collections::HashSet<Uuid> = std::collections::HashSet::new();
     let mut frontier: Vec<Uuid> = vec![tid];
     while let Some(parent) = frontier.pop() {
-        for t in &all_tasks {
-            if t.parent_id == Some(parent) && !to_delete.contains(&t.id) {
-                to_delete.push(t.id);
-                frontier.push(t.id);
+        if let Some(children) = children_by_parent.get(&parent) {
+            for &child_id in children {
+                if to_delete.insert(child_id) {
+                    frontier.push(child_id);
+                }
             }
         }
     }
@@ -459,8 +493,8 @@ fn toggle_task(
     let mut s = lock_state(&state)?;
     ensure_repo(&mut s)?;
     mute_watcher(&mut s);
-    let lid = Uuid::parse_str(&list_id).map_err(|e| e.to_string())?;
-    let tid = Uuid::parse_str(&task_id).map_err(|e| e.to_string())?;
+    let lid = parse_uuid(&list_id)?;
+    let tid = parse_uuid(&task_id)?;
     let repo = repo_mut(&mut s)?;
     let mut task = repo.get_task(lid, tid).map_err(|e| e.to_string())?;
     match task.status {
@@ -477,7 +511,9 @@ fn toggle_task(
                 TaskStatus::Backlog => child.uncomplete(),
                 TaskStatus::Completed => child.complete(),
             }
-            let _ = repo.update_task(lid, child);
+            let child_id = child.id;
+            repo.update_task(lid, child)
+                .map_err(|e| format!("Failed to cascade to subtask {}: {}", child_id, e))?;
         }
     }
     Ok(task)
@@ -493,8 +529,8 @@ fn reorder_task(
     let mut s = lock_state(&state)?;
     ensure_repo(&mut s)?;
     mute_watcher(&mut s);
-    let lid = Uuid::parse_str(&list_id).map_err(|e| e.to_string())?;
-    let tid = Uuid::parse_str(&task_id).map_err(|e| e.to_string())?;
+    let lid = parse_uuid(&list_id)?;
+    let tid = parse_uuid(&task_id)?;
     repo_mut(&mut s)?
         .reorder_task(lid, tid, new_position)
         .map_err(|e| e.to_string())
@@ -512,9 +548,9 @@ fn move_task(
     let mut s = lock_state(&state)?;
     ensure_repo(&mut s)?;
     mute_watcher(&mut s);
-    let from = Uuid::parse_str(&from_list_id).map_err(|e| e.to_string())?;
-    let to = Uuid::parse_str(&to_list_id).map_err(|e| e.to_string())?;
-    let tid = Uuid::parse_str(&task_id).map_err(|e| e.to_string())?;
+    let from = parse_uuid(&from_list_id)?;
+    let to = parse_uuid(&to_list_id)?;
+    let tid = parse_uuid(&task_id)?;
     repo_mut(&mut s)?
         .move_task(from, to, tid)
         .map_err(|e| e.to_string())
@@ -529,7 +565,7 @@ fn rename_list(
     let mut s = lock_state(&state)?;
     ensure_repo(&mut s)?;
     mute_watcher(&mut s);
-    let id = Uuid::parse_str(&list_id).map_err(|e| e.to_string())?;
+    let id = parse_uuid(&list_id)?;
     repo_mut(&mut s)?
         .rename_list(id, new_name)
         .map_err(|e| e.to_string())
@@ -544,7 +580,7 @@ fn set_group_by_date(
     let mut s = lock_state(&state)?;
     ensure_repo(&mut s)?;
     mute_watcher(&mut s);
-    let id = Uuid::parse_str(&list_id).map_err(|e| e.to_string())?;
+    let id = parse_uuid(&list_id)?;
     repo_mut(&mut s)?
         .set_group_by_date(id, enabled)
         .map_err(|e| e.to_string())
@@ -557,7 +593,7 @@ fn get_group_by_date(
 ) -> Result<bool, String> {
     let mut s = lock_state(&state)?;
     ensure_repo(&mut s)?;
-    let id = Uuid::parse_str(&list_id).map_err(|e| e.to_string())?;
+    let id = parse_uuid(&list_id)?;
     repo_ref(&s)?
         .get_group_by_date(id)
         .map_err(|e| e.to_string())
@@ -645,10 +681,9 @@ async fn list_remote_folder(
     let dir_entries: Vec<_> = entries.into_iter().filter(|e| e.is_dir).collect();
 
     // Check all subfolders for .onyx-workspace.json in parallel
-    let sub_paths: Vec<_> = dir_entries.iter().map(|entry| {
-        if path.is_empty() { entry.path.clone() }
-        else { format!("{}/{}", path.trim_end_matches('/'), entry.path) }
-    }).collect();
+    let sub_paths: Vec<_> = dir_entries.iter()
+        .map(|entry| join_remote_path(&path, &entry.path))
+        .collect();
     let checks: Vec<_> = sub_paths.iter().map(|sp| {
         client.list_files(sp)
     }).collect();
@@ -680,11 +715,7 @@ async fn inspect_remote_workspace(
     let mut lists = Vec::new();
     for entry in entries {
         if !entry.is_dir { continue; }
-        let list_path = if path.is_empty() {
-            entry.path.clone()
-        } else {
-            format!("{}/{}", path.trim_end_matches('/'), entry.path)
-        };
+        let list_path = join_remote_path(&path, &entry.path);
         let files = client.list_files(&list_path).await.unwrap_or_else(|e| {
             eprintln!("Warning: failed to list remote folder '{}': {}", list_path, e);
             Vec::new()
@@ -720,11 +751,7 @@ async fn create_remote_workspace(
         "list_order": [],
         "last_opened_list": null,
     });
-    let file_path = if path.is_empty() {
-        ".onyx-workspace.json".to_string()
-    } else {
-        format!("{}/{}", path.trim_end_matches('/'), ".onyx-workspace.json")
-    };
+    let file_path = join_remote_path(&path, ".onyx-workspace.json");
     client.put_file(&file_path, serde_json::to_string_pretty(&metadata).map_err(|e| e.to_string())?.into_bytes())
         .await
         .map_err(|e| e.to_string())?;
@@ -758,12 +785,7 @@ fn add_webdav_workspace(
     s.repo = None;
 
     // Store credentials keyed by hostname
-    let domain = webdav_url
-        .split("://")
-        .nth(1)
-        .and_then(|rest| rest.split('/').next())
-        .unwrap_or("")
-        .to_string();
+    let domain = credential_domain(&webdav_url);
     s.save_config()?;
     drop(s);
     let creds = app_handle.state::<Credentials<tauri::Wry>>();
@@ -826,12 +848,7 @@ async fn sync_workspace(
     };
 
     // Step 2: load credentials
-    let domain = webdav_url
-        .split("://")
-        .nth(1)
-        .and_then(|rest| rest.split('/').next())
-        .unwrap_or("")
-        .to_string();
+    let domain = credential_domain(&webdav_url);
     let creds = app_handle.state::<Credentials<tauri::Wry>>();
     let (username, password) = creds.load(&domain)?;
 

apps/tauri/src/lib/components/DateTimePicker.svelte

@@ -13,6 +13,8 @@
   let viewYear = $state(existing ? existing.getFullYear() : now.getFullYear());
   let viewMonth = $state(existing ? existing.getMonth() : now.getMonth());
   let selectedDay = $state(existing ? existing.getDate() : now.getDate());
+  let selectedYear = $state(existing ? existing.getFullYear() : now.getFullYear());
+  let selectedMonth = $state(existing ? existing.getMonth() : now.getMonth());
   let includeTime = $state(has_time);
   let selectedHour = $state(existing ? existing.getHours() : now.getHours());
   let selectedMinute = $state(existing ? existing.getMinutes() : 0);
@@ -58,9 +60,6 @@
     return `${viewYear}-${viewMonth + 1}-${day}` === todayStr;
   }
 
-  let selectedYear = $state(existing ? existing.getFullYear() : now.getFullYear());
-  let selectedMonth = $state(existing ? existing.getMonth() : now.getMonth());
-
   function isSelected(day: number): boolean {
     return selectedDay === day && selectedYear === viewYear && selectedMonth === viewMonth;
   }

apps/tauri/src/lib/stores/app.svelte.ts

@@ -418,7 +418,7 @@ function debouncedSync() {
 
 function restartSyncInterval() {
   if (_syncInterval) clearInterval(_syncInterval);
-  var secs = _appFocused ? syncIntervalSecs : syncIntervalUnfocusedSecs;
+  const secs = _appFocused ? syncIntervalSecs : syncIntervalUnfocusedSecs;
   _syncInterval = setInterval(triggerSync, secs * 1000);
 }
 

crates/onyx-core/src/config.rs

@@ -116,13 +116,7 @@ impl AppConfig {
             std::fs::create_dir_all(parent)?;
         }
         let content = serde_json::to_string_pretty(&self)?;
-        // Atomic write: write to temp file then rename to prevent corruption on crash
-        let temp = path.with_extension("tmp");
-        std::fs::write(&temp, &content)?;
-        if let Err(e) = std::fs::rename(&temp, path) {
-            let _ = std::fs::remove_file(&temp);
-            return Err(e.into());
-        }
+        crate::storage::atomic_write(path, content.as_bytes())?;
         Ok(())
     }
 

crates/onyx-core/src/google_tasks.rs

@@ -358,8 +358,15 @@ pub async fn sync_google_tasks(
         list_meta.task_order = task_order;
         list_meta.updated_at = Utc::now();
 
-        if let Ok(meta_content) = serde_json::to_string_pretty(&list_meta) {
-            let _ = atomic_write(&listdata_path, meta_content.as_bytes());
+        match serde_json::to_string_pretty(&list_meta) {
+            Ok(meta_content) => {
+                if let Err(e) = atomic_write(&listdata_path, meta_content.as_bytes()) {
+                    errors.push(format!("Failed to write metadata for list '{}': {}", gt_list.title, e));
+                }
+            }
+            Err(e) => {
+                errors.push(format!("Failed to serialize metadata for list '{}': {}", gt_list.title, e));
+            }
         }
     }
 
@@ -374,8 +381,15 @@ pub async fn sync_google_tasks(
         RootMetadata::default()
     };
     root_meta.list_order = new_list_order;
-    if let Ok(meta_content) = serde_json::to_string_pretty(&root_meta) {
-        let _ = atomic_write(&root_meta_path, meta_content.as_bytes());
+    match serde_json::to_string_pretty(&root_meta) {
+        Ok(meta_content) => {
+            if let Err(e) = atomic_write(&root_meta_path, meta_content.as_bytes()) {
+                errors.push(format!("Failed to write workspace metadata: {}", e));
+            }
+        }
+        Err(e) => {
+            errors.push(format!("Failed to serialize workspace metadata: {}", e));
+        }
     }
 
     Ok(GoogleSyncResult { downloaded, errors })

crates/onyx-core/src/storage.rs

@@ -236,12 +236,8 @@ impl FileSystemStorage {
         Ok(path)
     }
 
-    fn sanitize_filename(name: &str) -> String {
-        crate::sanitize_filename(name)
-    }
-
     fn task_file_path(&self, list_dir: &Path, task: &Task) -> PathBuf {
-        let safe_title = Self::sanitize_filename(&task.title);
+        let safe_title = crate::sanitize_filename(&task.title);
         let filename = if safe_title.is_empty() {
             task.id.to_string()
         } else {
@@ -457,27 +453,42 @@ impl Storage for FileSystemStorage {
         }
 
         let mut tasks = Vec::new();
-        for (_id, mut entries) in by_id {
-            if entries.len() > 1 {
-                entries.sort_by(|a, b| {
+        for (_id, entries) in by_id {
+            // `by_id` only inserts non-empty groups, so each `entries` has at
+            // least one element.
+            let task = if entries.len() > 1 {
+                // Read mtime once per file so sort_by doesn't hit the filesystem
+                // O(n log n) times and can't produce inconsistent orderings if a
+                // file is touched mid-sort.
+                let mut with_mtime: Vec<(PathBuf, Task, Option<std::time::SystemTime>)> = entries
+                    .into_iter()
+                    .map(|(p, t)| {
+                        let mtime = fs::metadata(&p).and_then(|m| m.modified()).ok();
+                        (p, t, mtime)
+                    })
+                    .collect();
+                with_mtime.sort_by(|a, b| {
                     // Primary: highest version first
                     let version_cmp = b.1.version.cmp(&a.1.version);
                     if version_cmp != std::cmp::Ordering::Equal {
                         return version_cmp;
                     }
                     // Tiebreaker: most recently modified file first
-                    let mtime_a = fs::metadata(&a.0).and_then(|m| m.modified()).ok();
-                    let mtime_b = fs::metadata(&b.0).and_then(|m| m.modified()).ok();
-                    mtime_b.cmp(&mtime_a)
+                    b.2.cmp(&a.2)
                 });
-                for (stale_path, _) in entries.drain(1..) {
+                for (stale_path, _, _) in with_mtime.drain(1..) {
                     if let Err(e) = fs::remove_file(&stale_path) {
                         eprintln!("Warning: failed to remove stale duplicate task file {:?}: {}", stale_path, e);
                     }
                 }
-            }
-            let (_, task) = entries.into_iter().next()
-                .ok_or_else(|| Error::InvalidData("Empty dedup entries for task".to_string()))?;
+                let (_, t, _) = with_mtime.into_iter().next()
+                    .expect("dedup group is non-empty after drain(1..)");
+                t
+            } else {
+                let (_, t) = entries.into_iter().next()
+                    .expect("dedup group is non-empty");
+                t
+            };
             tasks.push(task);
         }
 

crates/onyx-core/src/sync.rs

@@ -204,8 +204,9 @@ pub fn compute_sync_actions(
             }
 
             // Remote present, local gone, base known: local was deleted
-            (None, Some(_), Some(b)) => {
-                let remote_changed = remote.is_some_and(|r| r.size != b.size || !timestamps_equal(r.last_modified.as_deref(), b.modified_at.as_deref()));
+            (None, Some(r), Some(b)) => {
+                let remote_changed = r.size != b.size
+                    || !timestamps_equal(r.last_modified.as_deref(), b.modified_at.as_deref());
                 if remote_changed {
                     // deleted locally + modified remotely -> download (remote wins)
                     actions.push(SyncAction::Download { path: path.to_string() });
@@ -229,6 +230,22 @@ pub fn compute_sync_actions(
     actions
 }
 
+/// Remove base entries for files that are gone from both local and remote.
+/// `compute_sync_actions` emits no action for the both-deleted case, so without
+/// this pass those entries would persist in `.syncstate.json` indefinitely.
+fn prune_orphan_bases(
+    sync_state: &mut SyncState,
+    local_files: &[LocalFileInfo],
+    remote_files: &[RemoteFileSnapshot],
+) {
+    let live_paths: std::collections::HashSet<&str> = local_files
+        .iter()
+        .map(|f| f.path.as_str())
+        .chain(remote_files.iter().map(|f| f.path.as_str()))
+        .collect();
+    sync_state.files.retain(|p, _| live_paths.contains(p.as_str()));
+}
+
 /// Compare two timestamps for equality by parsing both, tolerating format differences.
 fn timestamps_equal(a: Option<&str>, b: Option<&str>) -> bool {
     match (a, b) {
@@ -604,6 +621,12 @@ async fn sync_workspace_inner(
         }
     };
 
+    // Purge orphan base entries: files we previously tracked that are now gone
+    // from both local and remote. Without this, `.syncstate.json` accumulates
+    // ghost entries forever because the both-deleted diff case emits no action
+    // and so nothing else would clean them.
+    prune_orphan_bases(&mut sync_state, &local_files, &remote_files);
+
     // Compute actions from three-way diff
     let fresh_actions = compute_sync_actions(&local_files, &remote_files, &sync_state);
 
@@ -701,19 +724,20 @@ async fn execute_action(
                 Err(e) => return Err(e.into()),
             };
             let checksum = compute_checksum(&data);
+            let len = data.len() as u64;
 
             if let Some(parent) = path_parent(path) {
                 client.ensure_dir(parent).await?;
             }
 
             report(&format!("  ^ Uploading {}", path));
-            client.put_file(path, data.clone()).await?;
+            client.put_file(path, data).await?;
 
             // Record in sync state using local file metadata
             let modified = std::fs::metadata(&local_path).ok()
                 .and_then(|m| m.modified().ok())
                 .map(|t| { let dt: DateTime<Utc> = t.into(); dt.to_rfc3339() });
-            sync_state.record_file(path, &checksum, modified.as_deref(), data.len() as u64);
+            sync_state.record_file(path, &checksum, modified.as_deref(), len);
         }
 
         SyncAction::Conflict { path } => {
@@ -753,7 +777,7 @@ async fn execute_action(
 
                 // For .md task files inside a list dir, create a duplicate of the local version
                 let parts: Vec<&str> = path.split('/').collect();
-                if parts.len() == 2 && parts[1].ends_with(".md") && parts[1] != ".listdata.json" {
+                if parts.len() == 2 && parts[1].ends_with(".md") {
                     let local_content = String::from_utf8_lossy(&local_data);
                     if let Ok((frontmatter, description)) = parse_frontmatter_for_conflict(&local_content) {
                         let original_id = frontmatter.id;
@@ -891,9 +915,15 @@ pub fn get_sync_status(workspace_path: &Path) -> Result<SyncStatusInfo> {
         }
     }
 
-    // Count files in base that are now missing locally (deleted)
+    // Count files in base that are now missing locally (deleted).
+    // Build a set of local paths once so the membership check is O(1) per
+    // tracked file instead of scanning local_files linearly each time.
+    let local_paths: std::collections::HashSet<&str> = local_files
+        .iter()
+        .map(|f| f.path.as_str())
+        .collect();
     for path in sync_state.files.keys() {
-        if !local_files.iter().any(|f| f.path == *path) {
+        if !local_paths.contains(path.as_str()) {
             pending_changes += 1;
         }
     }
@@ -1106,6 +1136,22 @@ mod tests {
         assert!(actions.is_empty());
     }
 
+    #[test]
+    fn test_prune_orphan_bases() {
+        let mut state = SyncState::default();
+        state.files.insert("kept_local.md".to_string(), make_base("a"));
+        state.files.insert("kept_remote.md".to_string(), make_base("b"));
+        state.files.insert("orphan.md".to_string(), make_base("c"));
+
+        let local = vec![make_local("kept_local.md", "a")];
+        let remote = vec![make_remote("kept_remote.md")];
+        prune_orphan_bases(&mut state, &local, &remote);
+
+        assert!(state.files.contains_key("kept_local.md"));
+        assert!(state.files.contains_key("kept_remote.md"));
+        assert!(!state.files.contains_key("orphan.md"));
+    }
+
     #[test]
     fn test_multiple_files_mixed() {
         let local = vec![

docs/API.md

@@ -353,12 +353,14 @@ Credentials are stored in the platform keychain (Windows Credential Manager, mac
 
 ```rust
 use onyx_core::webdav::{store_credentials, load_credentials, delete_credentials};
+use zeroize::Zeroizing;
 
 // Store credentials
 store_credentials("nextcloud.example.com", "username", "password")?;
 
-// Load credentials (returns Zeroizing<String> wrappers that wipe memory on drop)
-let (username, password) = load_credentials("nextcloud.example.com")?;
+// Load credentials — returns Zeroizing<String> wrappers that wipe memory on drop
+let (username, password): (Zeroizing<String>, Zeroizing<String>) =
+    load_credentials("nextcloud.example.com")?;
 
 // Delete credentials
 delete_credentials("nextcloud.example.com")?;
@@ -454,7 +456,7 @@ All metadata and state files use an atomic write pattern (write to `.tmp` then r
 
 - **List names**: Rejected if they contain `/`, `\`, or `..` components. Canonicalized and verified to stay within workspace root.
 - **Sync paths**: Validated to reject `..` components and backslashes anywhere in the path before any file system operation.
-- **Workspace paths** (Tauri): Rejected if they point to system directories (`/etc`, `/usr`, `/bin`, etc.).
+- **Workspace paths** (Tauri): Rejected if they point to the filesystem root (`/`) or system directories (`/etc`, `/usr`, `/bin`, `/sbin`, `/var`, `/proc`, `/sys`, `/dev`).
 - **Filenames**: Sanitized to replace `/ \ : * ? " < > |` and control characters with `_`.
 
 ## Example: Complete Workflow
@@ -521,9 +523,9 @@ Key test areas:
 
 ## Thread Safety
 
-The `Storage` trait requires `Send + Sync`, and `TaskRepository` wraps `Box<dyn Storage + Send + Sync>`, so repository instances can be shared across threads behind a `Mutex`. The Tauri GUI uses `Mutex<AppState>` for this purpose.
+`TaskRepository` holds its storage as `Box<dyn Storage + Send + Sync>`, so any concrete storage implementation passed in must be `Send + Sync`. Repository instances can be shared across threads behind a `Mutex` — the Tauri GUI uses `Mutex<AppState>` for this purpose.
 
 For concurrent access:
 
 1. Wrap `TaskRepository` in `Mutex` or `RwLock` (the Tauri app does this)
-2. Or create separate repository instances per thread (file system handles locking)
+2. Or create separate repository instances per thread. Note that `FileSystemStorage` does not coordinate writes between processes — concurrent multi-process writes to the same workspace are not supported outside the WebDAV sync flow, which uses a `.sync.lock` file.

docs/DEVELOPMENT.md

@@ -72,11 +72,15 @@ onyx/
 │       │   ├── main.ts
 │       │   ├── app.css                 # Tailwind CSS 4 + theme
 │       │   ├── App.svelte
+│       │   ├── test/
+│       │   │   └── setup.ts
 │       │   └── lib/
 │       │       ├── screens/            # Full-page views
 │       │       ├── components/         # Reusable UI components
 │       │       ├── stores/             # Svelte state (app.svelte.ts)
 │       │       ├── dateFormat.ts       # Date formatting utilities
+│       │       ├── grouping.ts         # Task grouping logic
+│       │       ├── paths.ts            # Path utilities
 │       │       └── types.ts           # TypeScript type definitions
 │       ├── tauri-plugin-credentials/   # Cross-platform credential storage plugin
 │       │   ├── Cargo.toml