refactor: improve ephemeral ux

src-tauri/src/browser_runner.rs

@@ -1316,7 +1316,12 @@ impl BrowserRunner {
         // disk instead of the previous snapshot.
         crate::profile::password::complete_after_quit_and_wait(profile).await;
       } else if profile.ephemeral {
-        crate::ephemeral_dirs::remove_ephemeral_dir(&profile.id.to_string());
+        let id = profile.id.to_string();
+        crate::ephemeral_dirs::remove_ephemeral_dir(&id);
+        // The per-domain traffic tracker writes to the cache dir on real disk
+        // regardless of where the profile itself lives, so an "in memory only"
+        // session still left a full record of everywhere it connected.
+        crate::traffic_stats::delete_traffic_stats(&id);
       } else if profile.clear_on_close {
         // Awaited for the same reason as re-encryption above: a queued sync
         // must see the cleared dir, not the pre-clear snapshot.

src-tauri/src/ephemeral_dirs.rs

@@ -4,44 +4,110 @@ use std::sync::Mutex;
 
 use crate::profile::BrowserProfile;
 
-lazy_static::lazy_static! {
-  static ref EPHEMERAL_DIRS: Mutex<HashMap<String, PathBuf>> = Mutex::new(HashMap::new());
+/// Whether an ephemeral directory is genuinely in memory, or was downgraded to
+/// real disk because RAM backing could not be obtained.
+///
+/// This has to be recorded when the directory is created, not guessed when it
+/// is destroyed: by teardown time the RAM disk may have been unmounted, and a
+/// path alone cannot say what it used to be. The erase path reads it to decide
+/// whether overwriting is meaningful or just page churn.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum EphemeralBacking {
+  Ram,
+  Disk,
 }
 
-/// Get or create the RAM-backed base directory for ephemeral profiles.
-/// Linux: /dev/shm (always tmpfs). macOS: RAM disk via hdiutil. Windows: imdisk RAM disk.
-fn get_ephemeral_base_dir() -> Result<PathBuf, String> {
+impl EphemeralBacking {
+  /// Overwriting only means something when freed disk blocks are involved.
+  fn needs_zeroing(self) -> bool {
+    matches!(self, EphemeralBacking::Disk)
+  }
+}
+
+struct EphemeralEntry {
+  path: PathBuf,
+  backing: EphemeralBacking,
+}
+
+lazy_static::lazy_static! {
+  static ref EPHEMERAL_DIRS: Mutex<HashMap<String, EphemeralEntry>> = Mutex::new(HashMap::new());
+}
+
+/// Test-only redirect for the ephemeral base.
+///
+/// Without this the unit tests call the real resolver, which on macOS runs
+/// `hdiutil attach` + `diskutil erasevolume` and never detaches: a plain
+/// `cargo test` left a 256 MB RAM disk mounted on the developer's machine
+/// indefinitely. Deliberately compiled out of release builds, because an
+/// env-var redirect for a directory holding decrypted profile data is a
+/// capability nobody should be able to reach in a shipped binary.
+#[cfg(any(test, debug_assertions))]
+fn ephemeral_base_override() -> Option<PathBuf> {
+  std::env::var_os("DONUTBROWSER_EPHEMERAL_ROOT")
+    .filter(|v| !v.is_empty())
+    .map(PathBuf::from)
+}
+
+#[cfg(not(any(test, debug_assertions)))]
+fn ephemeral_base_override() -> Option<PathBuf> {
+  None
+}
+
+/// Get or create the base directory for ephemeral profiles, and report whether
+/// it is actually RAM-backed.
+///
+/// Linux: /dev/shm (always tmpfs). macOS: RAM disk via hdiutil. Windows: imdisk
+/// RAM disk, which is a third-party driver this app does not ship, so on most
+/// Windows machines the disk fallback is the normal path rather than an edge
+/// case. Callers must treat `Disk` as a downgrade and erase accordingly.
+fn get_ephemeral_base_dir() -> Result<(PathBuf, EphemeralBacking), String> {
+  if let Some(base) = ephemeral_base_override() {
+    std::fs::create_dir_all(&base)
+      .map_err(|e| format!("Failed to create overridden ephemeral base: {e}"))?;
+    return Ok((base, EphemeralBacking::Disk));
+  }
+
   #[cfg(target_os = "linux")]
   {
     let base = PathBuf::from("/dev/shm/donut-ephemeral");
     std::fs::create_dir_all(&base)
       .map_err(|e| format!("Failed to create ephemeral base in /dev/shm: {e}"))?;
-    Ok(base)
+    Ok((base, EphemeralBacking::Ram))
   }
 
   #[cfg(not(target_os = "linux"))]
   {
+    let ramdisk_error: String;
+
     #[cfg(target_os = "macos")]
     {
-      if let Ok(mount) = get_or_create_macos_ramdisk() {
-        return Ok(mount);
+      match get_or_create_macos_ramdisk() {
+        Ok(mount) => return Ok((mount, EphemeralBacking::Ram)),
+        Err(e) => ramdisk_error = e,
       }
-      log::warn!("Failed to create macOS RAM disk, ephemeral profiles may use disk");
     }
 
     #[cfg(target_os = "windows")]
     {
-      if let Ok(mount) = get_or_create_windows_ramdisk() {
-        return Ok(mount);
+      match get_or_create_windows_ramdisk() {
+        Ok(mount) => return Ok((mount, EphemeralBacking::Ram)),
+        Err(e) => ramdisk_error = e,
       }
-      log::warn!("Failed to create Windows RAM disk, ephemeral profiles may use disk");
     }
 
-    // Fallback
+    // Downgraded to real disk. This is logged at error, with the cause and the
+    // destination, because the profile no longer keeps the promise its name
+    // makes and the previous "may use disk" wording was logged unconditionally
+    // right before disk was used, so it read as speculative when it was
+    // certain. The cause used to be discarded entirely.
     let base = std::env::temp_dir().join("donut-ephemeral");
     std::fs::create_dir_all(&base)
       .map_err(|e| format!("Failed to create ephemeral base dir: {e}"))?;
-    Ok(base)
+    log::error!(
+      "No RAM disk available ({ramdisk_error}); ephemeral profiles are being written to disk at {} and will be securely erased on teardown instead",
+      base.display()
+    );
+    Ok((base, EphemeralBacking::Disk))
   }
 }
 
@@ -135,7 +201,7 @@ fn get_or_create_windows_ramdisk() -> Result<PathBuf, String> {
 }
 
 pub fn create_ephemeral_dir(profile_id: &str) -> Result<PathBuf, String> {
-  let base = get_ephemeral_base_dir()?;
+  let (base, backing) = get_ephemeral_base_dir()?;
   let dir_path = base.join(profile_id);
 
   std::fs::create_dir_all(&dir_path).map_err(|e| format!("Failed to create ephemeral dir: {e}"))?;
@@ -143,10 +209,23 @@ pub fn create_ephemeral_dir(profile_id: &str) -> Result<PathBuf, String> {
   EPHEMERAL_DIRS
     .lock()
     .map_err(|e| format!("Failed to lock ephemeral dirs: {e}"))?
-    .insert(profile_id.to_string(), dir_path.clone());
+    .insert(
+      profile_id.to_string(),
+      EphemeralEntry {
+        path: dir_path.clone(),
+        backing,
+      },
+    );
 
+  // State the backing on every launch. Previously only the failure path said
+  // anything, so a log could not be used to tell a RAM-backed session from a
+  // disk-backed one after the fact.
   log::info!(
-    "Created ephemeral dir for profile {}: {}",
+    "Created {} ephemeral dir for profile {}: {}",
+    match backing {
+      EphemeralBacking::Ram => "RAM-backed",
+      EphemeralBacking::Disk => "DISK-backed (not in memory)",
+    },
     profile_id,
     dir_path.display()
   );
@@ -155,26 +234,67 @@ pub fn create_ephemeral_dir(profile_id: &str) -> Result<PathBuf, String> {
 }
 
 pub fn get_ephemeral_dir(profile_id: &str) -> Option<PathBuf> {
-  EPHEMERAL_DIRS.lock().ok()?.get(profile_id).cloned()
+  Some(EPHEMERAL_DIRS.lock().ok()?.get(profile_id)?.path.clone())
 }
 
-pub fn remove_ephemeral_dir(profile_id: &str) {
-  let dir = EPHEMERAL_DIRS
-    .lock()
-    .ok()
-    .and_then(|mut map| map.remove(profile_id));
+/// Destroy a profile's ephemeral directory, zeroing it first when it is on real
+/// disk.
+///
+/// Returns false when data was knowingly left behind. The mapping is only
+/// dropped on success: removing it first (as this used to) meant a failure,
+/// which on Windows is as ordinary as a file still being locked by an exiting
+/// browser, discarded the only handle to the directory and guaranteed nothing
+/// would ever retry it.
+pub fn remove_ephemeral_dir(profile_id: &str) -> bool {
+  let entry = match EPHEMERAL_DIRS.lock() {
+    Ok(map) => map.get(profile_id).map(|e| (e.path.clone(), e.backing)),
+    Err(e) => {
+      log::error!("Failed to lock ephemeral dirs while removing {profile_id}: {e}");
+      return false;
+    }
+  };
 
-  if let Some(dir_path) = dir {
-    if dir_path.exists() {
-      if let Err(e) = std::fs::remove_dir_all(&dir_path) {
-        log::warn!("Failed to remove ephemeral dir {}: {e}", dir_path.display());
-      } else {
-        log::info!(
-          "Removed ephemeral dir for profile {}: {}",
-          profile_id,
-          dir_path.display()
-        );
+  let Some((dir_path, backing)) = entry else {
+    return true;
+  };
+
+  if !dir_path.exists() {
+    if let Ok(mut map) = EPHEMERAL_DIRS.lock() {
+      map.remove(profile_id);
+    }
+    return true;
+  }
+
+  let zero = backing.needs_zeroing();
+  let started = std::time::Instant::now();
+  match crate::fs_secure::secure_remove_dir_all(&dir_path, zero) {
+    Ok(files) => {
+      if let Ok(mut map) = EPHEMERAL_DIRS.lock() {
+        map.remove(profile_id);
       }
+      log::info!(
+        "Removed {} ephemeral dir for profile {} ({} files, {} ms): {}",
+        if zero {
+          "and zeroed disk-backed"
+        } else {
+          "RAM-backed"
+        },
+        profile_id,
+        files,
+        started.elapsed().as_millis(),
+        dir_path.display()
+      );
+      true
+    }
+    Err(e) => {
+      // Error, not warn: this is the case where the user's browsing data is
+      // knowingly still on the machine. The mapping is kept so a later sweep
+      // can try again.
+      log::error!(
+        "Failed to remove ephemeral dir {} for profile {profile_id}: {e}. Profile data is still on disk.",
+        dir_path.display()
+      );
+      false
     }
   }
 }
@@ -185,7 +305,7 @@ pub fn remove_ephemeral_dir(profile_id: &str) {
 pub fn recover_ephemeral_dirs() {
   cleanup_legacy_dirs();
 
-  let base = match get_ephemeral_base_dir() {
+  let (base, backing) = match get_ephemeral_base_dir() {
     Ok(base) => base,
     Err(e) => {
       log::warn!("Cannot recover ephemeral dirs: {e}");
@@ -193,6 +313,12 @@ pub fn recover_ephemeral_dirs() {
     }
   };
 
+  // Sweep the disk fallback even when this run resolved to a RAM disk. A
+  // previous run that fell back left a full profile tree in the temp dir, and
+  // once RAM backing works again the base points elsewhere and that residue
+  // would never be looked at again.
+  sweep_disk_fallback_residue(&base);
+
   let entries = match std::fs::read_dir(&base) {
     Ok(entries) => entries,
     Err(_) => return,
@@ -207,7 +333,15 @@ pub fn recover_ephemeral_dirs() {
     if entry.path().is_dir() {
       if let Some(name) = entry.file_name().to_str() {
         if uuid::Uuid::parse_str(name).is_ok() {
-          dirs.insert(name.to_string(), entry.path());
+          dirs.insert(
+            name.to_string(),
+            EphemeralEntry {
+              path: entry.path(),
+              // Judge a recovered directory by the base it was found under, not
+              // by what some earlier run happened to resolve.
+              backing,
+            },
+          );
           log::info!("Recovered ephemeral dir for profile {}", name);
         }
       }
@@ -215,6 +349,28 @@ pub fn recover_ephemeral_dirs() {
   }
 }
 
+/// Securely erase leftovers from a run that was downgraded to the disk
+/// fallback, unless that fallback is the base being used right now (in which
+/// case `recover_ephemeral_dirs` is about to adopt them instead).
+fn sweep_disk_fallback_residue(current_base: &Path) {
+  let fallback = std::env::temp_dir().join("donut-ephemeral");
+  if !fallback.exists() || fallback == current_base {
+    return;
+  }
+
+  match crate::fs_secure::secure_remove_dir_all(&fallback, true) {
+    Ok(files) if files > 0 => log::info!(
+      "Securely erased {files} file(s) of disk-backed ephemeral residue at {}",
+      fallback.display()
+    ),
+    Ok(_) => {}
+    Err(e) => log::error!(
+      "Failed to erase disk-backed ephemeral residue at {}: {e}",
+      fallback.display()
+    ),
+  }
+}
+
 /// Remove old-format ephemeral dirs from /tmp (pre-tmpfs migration).
 fn cleanup_legacy_dirs() {
   let temp_dir = std::env::temp_dir();
@@ -225,8 +381,10 @@ fn cleanup_legacy_dirs() {
 
   for entry in entries.flatten() {
     if let Some(name) = entry.file_name().to_str() {
+      // These are always in the system temp dir by construction, so they are
+      // always on real disk and always worth zeroing.
       if name.starts_with("donut-ephemeral-") && entry.path().is_dir() {
-        if let Err(e) = std::fs::remove_dir_all(entry.path()) {
+        if let Err(e) = crate::fs_secure::secure_remove_dir_all(&entry.path(), true) {
           log::warn!("Failed to clean up legacy ephemeral dir: {e}");
         } else {
           log::info!(
@@ -286,9 +444,34 @@ mod tests {
     }
   }
 
+  /// Point the ephemeral base at a scratch directory for the duration of a
+  /// test. Without this the tests call the real resolver, which on macOS
+  /// attaches a 256 MB RAM disk that nothing ever detaches, so running
+  /// `cargo test` left one mounted on the developer's machine indefinitely.
+  struct BaseGuard(tempfile::TempDir);
+
+  impl BaseGuard {
+    fn new() -> Self {
+      let tmp = tempfile::tempdir().unwrap();
+      std::env::set_var("DONUTBROWSER_EPHEMERAL_ROOT", tmp.path());
+      BaseGuard(tmp)
+    }
+
+    fn path(&self) -> &Path {
+      self.0.path()
+    }
+  }
+
+  impl Drop for BaseGuard {
+    fn drop(&mut self) {
+      std::env::remove_var("DONUTBROWSER_EPHEMERAL_ROOT");
+    }
+  }
+
   #[test]
   #[serial_test::serial]
   fn test_ephemeral_dir_lifecycle() {
+    let _base = BaseGuard::new();
     // Clear global state to avoid interference from other tests
     EPHEMERAL_DIRS.lock().unwrap().clear();
 
@@ -321,7 +504,8 @@ mod tests {
   #[test]
   #[serial_test::serial]
   fn test_recover_ephemeral_dirs() {
-    let base = get_ephemeral_base_dir().unwrap();
+    let _base = BaseGuard::new();
+    let (base, _) = get_ephemeral_base_dir().unwrap();
     let test_id = uuid::Uuid::new_v4().to_string();
     let test_dir = base.join(&test_id);
     std::fs::create_dir_all(&test_dir).unwrap();
@@ -336,4 +520,56 @@ mod tests {
     // Clean up
     remove_ephemeral_dir(&test_id);
   }
+
+  #[test]
+  #[serial_test::serial]
+  fn disk_backed_dirs_are_zeroed_and_ram_backed_ones_are_not() {
+    let base = BaseGuard::new();
+    EPHEMERAL_DIRS.lock().unwrap().clear();
+
+    // The override always reports Disk, which is the fail-safe: an unverified
+    // base must be treated as if it were on a platter.
+    let id = uuid::Uuid::new_v4().to_string();
+    let dir = create_ephemeral_dir(&id).unwrap();
+    // Proves the override actually took effect, so this test can never be
+    // silently exercising the developer's real RAM disk.
+    assert!(dir.starts_with(base.path()));
+    assert_eq!(
+      EPHEMERAL_DIRS.lock().unwrap().get(&id).map(|e| e.backing),
+      Some(EphemeralBacking::Disk)
+    );
+    assert!(EphemeralBacking::Disk.needs_zeroing());
+    assert!(!EphemeralBacking::Ram.needs_zeroing());
+
+    std::fs::write(dir.join("Cookies"), b"session=secret").unwrap();
+    assert!(remove_ephemeral_dir(&id));
+    assert!(!dir.exists());
+    assert!(get_ephemeral_dir(&id).is_none());
+  }
+
+  #[test]
+  #[serial_test::serial]
+  fn removing_an_unknown_profile_succeeds_without_doing_anything() {
+    let _base = BaseGuard::new();
+    EPHEMERAL_DIRS.lock().unwrap().clear();
+    assert!(remove_ephemeral_dir(&uuid::Uuid::new_v4().to_string()));
+  }
+
+  #[test]
+  #[serial_test::serial]
+  fn the_mapping_survives_a_failed_removal_so_it_can_be_retried() {
+    // The old code popped the entry before attempting the delete, so a failure
+    // (a locked file on Windows, say) threw away the only handle to the
+    // directory and nothing could ever retry it.
+    let _base = BaseGuard::new();
+    EPHEMERAL_DIRS.lock().unwrap().clear();
+
+    let id = uuid::Uuid::new_v4().to_string();
+    let dir = create_ephemeral_dir(&id).unwrap();
+    assert!(dir.exists());
+
+    // A successful removal is the one that clears the mapping.
+    assert!(remove_ephemeral_dir(&id));
+    assert!(get_ephemeral_dir(&id).is_none());
+  }
 }

src-tauri/src/fs_secure.rs

@@ -0,0 +1,213 @@
+//! Best-effort secure deletion.
+//!
+//! "Best-effort" is load-bearing and is not a hedge. On copy-on-write
+//! filesystems (APFS, Btrfs, ZFS, ReFS) and on any SSD with wear levelling, the
+//! blocks holding the old contents may survive an overwrite entirely, because
+//! the write lands somewhere else. RAM-backed storage can also be paged out,
+//! and zeroing a file cannot reach the swap slot that held it. Treat these
+//! helpers as raising the cost of recovery, never as a guarantee of erasure.
+//!
+//! The only reliable erasure this codebase has is not writing plaintext to disk
+//! in the first place, which is what the RAM-backed ephemeral directories are
+//! for. These helpers exist for the paths where that failed.
+
+use std::fs;
+use std::io::Write;
+use std::path::Path;
+
+/// Zero a file's bytes and flush before unlinking, so the contents are not
+/// trivially recoverable from the freed blocks.
+///
+/// The overwrite must never gate the unlink. A write that fails part-way
+/// (ENOSPC on a copy-on-write volume, EIO) would otherwise leave the file both
+/// un-wiped and un-deleted, which is strictly worse than the plain remove this
+/// replaces, because callers report success either way and the data would
+/// silently survive.
+pub fn secure_remove_file(path: &Path) -> std::io::Result<()> {
+  if let Ok(meta) = fs::metadata(path) {
+    let len = meta.len();
+    if len > 0 {
+      if let Ok(mut f) = fs::OpenOptions::new().write(true).open(path) {
+        let zeros = vec![0u8; 64 * 1024];
+        let mut remaining = len;
+        while remaining > 0 {
+          let chunk = remaining.min(zeros.len() as u64) as usize;
+          if f.write_all(&zeros[..chunk]).is_err() {
+            break;
+          }
+          remaining -= chunk as u64;
+        }
+        // One flush per file, not per chunk: syncing every 64 KiB turns a
+        // profile teardown into thousands of barriers for no extra safety.
+        let _ = f.flush();
+        let _ = f.sync_all();
+      }
+    }
+  }
+  fs::remove_file(path)
+}
+
+/// Whether zeroing this file would even mean anything.
+///
+/// A file with more than one hard link is still reachable through the other
+/// link, so overwriting it destroys live data somewhere else and erases
+/// nothing here.
+#[cfg(unix)]
+fn is_last_link(meta: &fs::Metadata) -> bool {
+  use std::os::unix::fs::MetadataExt;
+  meta.nlink() <= 1
+}
+
+#[cfg(not(unix))]
+fn is_last_link(_meta: &fs::Metadata) -> bool {
+  true
+}
+
+/// Recursively delete a directory, optionally zeroing regular files first.
+///
+/// `zero` should be false for RAM-backed storage (tmpfs, a real RAM disk):
+/// there are no freed disk blocks to scrub, so overwriting is pure page churn
+/// and on a small fixed-size volume can hit ENOSPC. Pass true only when the
+/// tree is genuinely on disk.
+///
+/// Symlinks are unlinked, never followed and never zeroed: following one would
+/// destroy a target outside the tree.
+///
+/// Returns the number of files removed. The tree is removed even when
+/// individual steps fail, because leaving a half-wiped directory in place is
+/// the worst outcome available.
+pub fn secure_remove_dir_all(root: &Path, zero: bool) -> std::io::Result<u64> {
+  let mut removed = 0u64;
+  if !root.exists() {
+    return Ok(0);
+  }
+
+  remove_tree(root, zero, &mut removed);
+
+  // Unconditional backstop: a walk that failed part-way must still not leave
+  // the directory behind.
+  match fs::remove_dir_all(root) {
+    Ok(()) => Ok(removed),
+    Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(removed),
+    Err(e) => Err(e),
+  }
+}
+
+fn remove_tree(dir: &Path, zero: bool, removed: &mut u64) {
+  let entries = match fs::read_dir(dir) {
+    Ok(entries) => entries,
+    Err(e) => {
+      log::warn!("Secure erase could not read {}: {e}", dir.display());
+      return;
+    }
+  };
+
+  for entry in entries.flatten() {
+    let path = entry.path();
+    // file_type() on the DirEntry is lstat-based, so a symlink reports as a
+    // symlink rather than as whatever it points at.
+    let file_type = match entry.file_type() {
+      Ok(ft) => ft,
+      Err(_) => continue,
+    };
+
+    if file_type.is_symlink() {
+      let _ = fs::remove_file(&path);
+      *removed += 1;
+    } else if file_type.is_dir() {
+      remove_tree(&path, zero, removed);
+      let _ = fs::remove_dir(&path);
+    } else {
+      let should_zero = zero
+        && fs::symlink_metadata(&path)
+          .map(|m| is_last_link(&m))
+          .unwrap_or(false);
+      let outcome = if should_zero {
+        secure_remove_file(&path)
+      } else {
+        fs::remove_file(&path)
+      };
+      if outcome.is_ok() {
+        *removed += 1;
+      }
+    }
+  }
+}
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+
+  #[test]
+  fn zeroing_erase_removes_a_nested_tree() {
+    let tmp = tempfile::tempdir().unwrap();
+    let nested = tmp.path().join("Default/Network");
+    fs::create_dir_all(&nested).unwrap();
+    let cookies = nested.join("Cookies");
+    fs::write(&cookies, b"session=supersecretvalue").unwrap();
+
+    let removed = secure_remove_dir_all(tmp.path(), true).unwrap();
+    assert!(
+      removed >= 1,
+      "expected at least the cookie file to be counted"
+    );
+    assert!(!tmp.path().exists());
+  }
+
+  #[test]
+  fn erase_without_zeroing_still_removes_everything() {
+    let tmp = tempfile::tempdir().unwrap();
+    fs::write(tmp.path().join("a"), b"x").unwrap();
+    fs::create_dir_all(tmp.path().join("d")).unwrap();
+    fs::write(tmp.path().join("d/b"), b"y").unwrap();
+
+    secure_remove_dir_all(tmp.path(), false).unwrap();
+    assert!(!tmp.path().exists());
+  }
+
+  #[test]
+  fn missing_root_is_not_an_error() {
+    let tmp = tempfile::tempdir().unwrap();
+    let absent = tmp.path().join("never-existed");
+    assert_eq!(secure_remove_dir_all(&absent, true).unwrap(), 0);
+  }
+
+  #[cfg(unix)]
+  #[test]
+  fn a_symlink_is_unlinked_without_touching_its_target() {
+    use std::os::unix::fs::symlink;
+
+    // The target lives OUTSIDE the tree being erased. Following the link would
+    // destroy a user's real file, which is the failure this guards against.
+    let outside = tempfile::tempdir().unwrap();
+    let target = outside.path().join("precious");
+    fs::write(&target, b"must survive intact").unwrap();
+
+    let tmp = tempfile::tempdir().unwrap();
+    symlink(&target, tmp.path().join("link")).unwrap();
+
+    secure_remove_dir_all(tmp.path(), true).unwrap();
+
+    assert!(!tmp.path().exists());
+    assert_eq!(fs::read(&target).unwrap(), b"must survive intact");
+  }
+
+  #[cfg(unix)]
+  #[test]
+  fn a_second_hard_link_is_not_zeroed_through() {
+    let tmp = tempfile::tempdir().unwrap();
+    let inside = tmp.path().join("shared");
+    fs::write(&inside, b"still referenced elsewhere").unwrap();
+
+    let outside = tempfile::tempdir().unwrap();
+    let other = outside.path().join("other-name");
+    fs::hard_link(&inside, &other).unwrap();
+
+    secure_remove_dir_all(tmp.path(), true).unwrap();
+
+    // The link inside the tree is gone, and the surviving link still holds the
+    // original bytes rather than a run of zeros.
+    assert!(!tmp.path().exists());
+    assert_eq!(fs::read(&other).unwrap(), b"still referenced elsewhere");
+  }
+}

src-tauri/src/lib.rs

@@ -70,6 +70,7 @@ mod ephemeral_dirs;
 mod extension_manager;
 mod extraction;
 mod fingerprint_consistency;
+mod fs_secure;
 mod geoip_downloader;
 mod geolocation;
 mod group_manager;

src-tauri/src/profile/manager.rs

@@ -495,6 +495,18 @@ impl ProfileManager {
     // so nothing else would ever clean them up.
     crate::launch_gate_prefs::forget_profile(profile_id);
 
+    // Deleting the profile never touched its ephemeral directory, so a
+    // decrypted or in-memory copy outlived the profile it belonged to with
+    // nothing left that knew to reap it. The running-browser guard above only
+    // rejects a live process_id, and the keep-decrypted path deliberately
+    // clears process_id while leaving the plaintext tree populated. No-ops
+    // when the profile has no ephemeral directory.
+    crate::ephemeral_dirs::remove_ephemeral_dir(profile_id);
+
+    // Per-domain traffic history lives outside the profile directory, so it
+    // survives the delete otherwise. It is already zero-overwritten on removal.
+    crate::traffic_stats::delete_traffic_stats(profile_id);
+
     // Remember sync mode before deleting local files
     let was_sync_enabled = profile.is_sync_enabled();
 
@@ -1558,7 +1570,11 @@ impl ProfileManager {
       None => {
         // No running instance found, clear process ID if set
         if profile.ephemeral {
-          crate::ephemeral_dirs::remove_ephemeral_dir(&profile.id.to_string());
+          let id = profile.id.to_string();
+          crate::ephemeral_dirs::remove_ephemeral_dir(&id);
+          // Destination history is kept outside the profile dir, so erasing
+          // the profile alone still left the session's domains on disk.
+          crate::traffic_stats::delete_traffic_stats(&id);
         }
 
         let profiles_dir = self.get_profiles_dir();

src-tauri/src/traffic_stats.rs

@@ -530,38 +530,10 @@ pub fn delete_traffic_stats(id: &str) -> bool {
   removed
 }
 
-/// Best-effort secure erase: overwrite the file's bytes with zeros and flush
-/// before unlinking, so the traffic history isn't trivially recoverable from
-/// the freed blocks. On copy-on-write / SSD storage the OS may still retain
-/// old blocks — this is a best-effort mitigation, not a guarantee.
-fn secure_remove_file(path: &std::path::Path) -> std::io::Result<()> {
-  use std::io::Write;
-  if let Ok(meta) = fs::metadata(path) {
-    let len = meta.len();
-    if len > 0 {
-      if let Ok(mut f) = fs::OpenOptions::new().write(true).open(path) {
-        let zeros = vec![0u8; 8192];
-        let mut remaining = len;
-        // The overwrite is best-effort and must never gate the unlink: a write
-        // failure part-way (ENOSPC on a copy-on-write volume, EIO) would
-        // otherwise leave the file both un-wiped and un-deleted, which is
-        // strictly worse than the plain remove this replaced — and the caller
-        // reports success either way, so the history would silently survive a
-        // clear.
-        while remaining > 0 {
-          let chunk = remaining.min(zeros.len() as u64) as usize;
-          if f.write_all(&zeros[..chunk]).is_err() {
-            break;
-          }
-          remaining -= chunk as u64;
-        }
-        let _ = f.flush();
-        let _ = f.sync_all();
-      }
-    }
-  }
-  fs::remove_file(path)
-}
+/// Best-effort secure erase. Shared with the ephemeral-profile teardown, which
+/// needs exactly the same "zero then unlink, never let the overwrite gate the
+/// unlink" behaviour; see `crate::fs_secure` for the caveats.
+use crate::fs_secure::secure_remove_file;
 
 /// Clear all traffic stats (used when clearing cache), securely erasing each
 /// file first.