Fix a real credential-leak vector a review found, plus four smaller issues

The headline finding: WebTerminalSettings::access_token is a live bearer
credential for a server that binds every interface, stored as a plain
field on AppSettings — which this feature was exporting and importing
wholesale as if it were as inert as a port number. A crafted export file
could set web_terminal.enabled and access_token together, and importing
it (with no more warning than any other setting change) would silently
stand up a LAN-listening terminal server with an attacker-known token on
the victim's next launch.

Fixed by carving the token out into ExportedSecrets, same as the other
three global secrets, with the same "only overwrite what the import
actually has" treatment — except that has to be done by hand here, since
this one lives inside the AppSettings blob that gets replaced wholesale
rather than in the keychain. Added SettingsImportPreview::
enables_web_terminal so "this turns on a listening service" gets its own
visible warning in the confirmation modal rather than hiding inside a
generic "settings replaced" bullet list.

Also fixed:

- read_and_decrypt checked format_version only after attempting to parse
  the full payload, so a future version bump that isn't
  deserialize-compatible would fail on the shape mismatch before the
  version check ever ran — and serde's type-mismatch errors quote the
  offending value inline, which is a real leak path since the plaintext
  here can hold a live credential. Now probes just the version field
  first, and neither error path interpolates the underlying serde message
  into what the user sees.
- apply_settings_import cleared the pending-import path before it could
  fail, so a rejected import (an invalid host path, anything
  update_settings validates) dead-ended the modal with no way back except
  cancelling and reopening the file picker. The path is now only cleared
  on success.
- Secrets are restored before the settings replace runs, not after —
  replacing settings is what triggers reconcile_gateway, and restoring
  secrets afterward left a real window where a gateway recreation
  happened against the destination's stale keys.
- The 8-character password minimum was frontend-only; export_settings now
  enforces it too, since that's the actual boundary a weak password has
  to cross. The derived key and decrypted plaintext are wrapped in
  zeroize::Zeroizing (already in the tree via aes-gcm).

Added test coverage the review named as missing: format-version
ordering, the generic-error-message guarantee, non_blank's blank-vs-
absent handling, and the new web-terminal preview/warning behavior on
both sides of the IPC boundary.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FGjXq6fqtAFHdbhk4f3PfZ

app/src-tauri/src/commands/settings_export_commands.rs

@@ -20,20 +20,35 @@
 //! The password is re-entered (not cached) between preview and apply, so
 //! that nothing here holds decrypted plaintext — export/import secrets
 //! included — in memory for longer than one command's execution.
+//!
+//! **This is new attack surface**: a settings export is a file one person
+//! can hand another and ask them to import, together with a password, and
+//! `apply_settings_import` applies whatever `AppSettings` it decrypts to
+//! wholesale — see the module doc on `models::settings_export` for the
+//! `web_terminal.access_token` carve-out a review of this feature found,
+//! and treat that as the standing example of the class of thing to keep
+//! checking for here, not a one-off fixed bug.
 
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 
 use tauri::State;
 use tauri_plugin_dialog::DialogExt;
 
 use crate::models::{
-    ExportedSecrets, SettingsExportPayload, SettingsImportPreview, SETTINGS_EXPORT_FORMAT_VERSION,
+    AppSettings, ExportedSecrets, SettingsExportPayload, SettingsImportPreview,
+    SETTINGS_EXPORT_FORMAT_VERSION,
 };
 use crate::storage::{secure, settings_crypto};
 use crate::AppState;
 
 const FILE_EXTENSION: &str = "triplec";
 
+/// Enforced here, not only in the export modal: the frontend's minimum is a
+/// UX nudge, but `export_settings` is the actual boundary a weak password
+/// has to cross, and Argon2id's memory-hardness buys little against an
+/// attacker who can just try a three-character password directly.
+const MIN_PASSWORD_LEN: usize = 8;
+
 fn suggested_export_name() -> String {
     // Timestamped so exporting more than once doesn't silently overwrite an
     // earlier file just because the save dialog defaults to the same name.
@@ -73,17 +88,28 @@ async fn pick_import_open_path(window: &tauri::Window) -> Option<PathBuf> {
     rx.await.ok().flatten().and_then(|p| p.into_path().ok())
 }
 
-/// Gather the current global secrets. A missing secret reads as `None` — a
-/// keychain read failure is treated as "nothing to export" for that one
-/// entry rather than aborting the whole export, matching how the rest of
-/// this app degrades a keychain error to "absent" (`has_claude_oauth_token`,
-/// `has_gateway_api_key`) rather than surfacing it as a hard failure.
-fn gather_secrets() -> ExportedSecrets {
-    ExportedSecrets {
+/// Gather the current global secrets, and hand back the `AppSettings` to
+/// export with the web-terminal token blanked out of it — see the module
+/// doc comment on `models::settings_export` for why that field cannot
+/// travel through `settings` like the rest of this struct.
+///
+/// A missing keychain secret reads as `None` — a keychain read failure is
+/// treated as "nothing to export" for that one entry rather than aborting
+/// the whole export, matching how the rest of this app degrades a keychain
+/// error to "absent" (`has_claude_oauth_token`, `has_gateway_api_key`)
+/// rather than surfacing it as a hard failure.
+fn split_settings_and_secrets(current: AppSettings) -> (AppSettings, ExportedSecrets) {
+    let mut settings = current;
+    let web_terminal_access_token = settings.web_terminal.access_token.take();
+
+    let secrets = ExportedSecrets {
         claude_oauth_token: secure::get_claude_oauth_token().unwrap_or_default(),
         gateway_api_key: secure::get_gateway_api_key().unwrap_or_default(),
         gateway_master_key: secure::get_gateway_master_key().unwrap_or_default(),
-    }
+        web_terminal_access_token,
+    };
+
+    (settings, secrets)
 }
 
 /// Export the current global settings and secrets to a password-encrypted
@@ -96,15 +122,18 @@ pub async fn export_settings(
     window: tauri::Window,
     state: State<'_, AppState>,
 ) -> Result<bool, String> {
-    if password.is_empty() {
-        return Err("A password is required to export settings.".to_string());
+    if password.len() < MIN_PASSWORD_LEN {
+        return Err(format!(
+            "Use a password of at least {} characters.",
+            MIN_PASSWORD_LEN
+        ));
     }
 
     let Some(dest) = pick_export_save_path(&window, &suggested_export_name()).await else {
         return Ok(false);
     };
 
-    let secrets = gather_secrets();
+    let (settings, secrets) = split_settings_and_secrets(state.settings_store.get());
     if secrets.is_empty() {
         log::info!("Exporting settings with no global secrets configured on this machine");
     }
@@ -113,7 +142,7 @@ pub async fn export_settings(
         format_version: SETTINGS_EXPORT_FORMAT_VERSION,
         exported_at: chrono::Utc::now().to_rfc3339(),
         app_version: env!("CARGO_PKG_VERSION").to_string(),
-        settings: state.settings_store.get(),
+        settings,
         secrets,
     };
 
@@ -121,7 +150,7 @@ pub async fn export_settings(
         .map_err(|e| format!("Failed to prepare settings for export: {}", e))?;
     let encrypted = settings_crypto::encrypt(&plaintext, &password)?;
 
-    std::fs::write(&dest, encrypted).map_err(|e| format!("Failed to write export file: {}", e))?;
+    std::fs::write(&dest, &encrypted).map_err(|e| format!("Failed to write export file: {}", e))?;
 
     Ok(true)
 }
@@ -170,11 +199,24 @@ pub async fn preview_settings_import(
 /// means "the source machine never had this configured," not "delete this
 /// on import." A user who wants to clear a secret already has dedicated UI
 /// for that (signing out of shared auth, clearing the gateway key).
+///
+/// Order matters here: secrets are restored **before** the settings replace
+/// runs (which is what triggers `reconcile_gateway`), so a gateway
+/// recreation that replace provokes sees the final key material rather than
+/// racing it — restoring the other way round left a real window where the
+/// running gateway and the keychain briefly disagreed.
+///
+/// The pending path is only cleared on success. A failure here (a rejected
+/// host path, a keychain write failure surfaced some other way) leaves the
+/// import pending so the frontend can let the user retry `apply` without
+/// making them pick the file and re-enter the password again — the
+/// preview's job was confirming *what* to import, not spending the one
+/// attempt at applying it.
 #[tauri::command]
 pub async fn apply_settings_import(
     password: String,
     state: State<'_, AppState>,
-) -> Result<crate::models::AppSettings, String> {
+) -> Result<AppSettings, String> {
     if password.is_empty() {
         return Err("A password is required to import settings.".to_string());
     }
@@ -183,13 +225,11 @@ pub async fn apply_settings_import(
         .pending_settings_import
         .lock()
         .await
-        .take()
+        .clone()
         .ok_or_else(|| "No import is pending — choose a file first.".to_string())?;
 
     let payload = read_and_decrypt(&path, &password)?;
 
-    let saved = crate::commands::settings_commands::update_settings(payload.settings, state).await?;
-
     if let Some(token) = non_blank(payload.secrets.claude_oauth_token) {
         if let Err(e) = secure::store_claude_oauth_token(&token) {
             log::warn!("Settings import: could not restore the shared Claude login: {}", e);
@@ -206,6 +246,20 @@ pub async fn apply_settings_import(
         }
     }
 
+    // The web-terminal token lives inside `AppSettings` itself rather than
+    // the keychain, so "leave an absent secret alone" has to be done by
+    // hand here: carry the destination's current token forward when the
+    // import doesn't have one, instead of letting the wholesale replace
+    // below blank it (every export writes `None` there — see
+    // `split_settings_and_secrets`).
+    let mut settings = payload.settings;
+    settings.web_terminal.access_token = non_blank(payload.secrets.web_terminal_access_token)
+        .or_else(|| state.settings_store.get().web_terminal.access_token);
+
+    let saved = crate::commands::settings_commands::update_settings(settings, state.clone()).await?;
+
+    state.pending_settings_import.lock().await.take();
+
     Ok(saved)
 }
 
@@ -213,20 +267,150 @@ fn non_blank(value: Option<String>) -> Option<String> {
     value.filter(|v| !v.trim().is_empty())
 }
 
-fn read_and_decrypt(path: &std::path::Path, password: &str) -> Result<SettingsExportPayload, String> {
+/// Only the field `read_and_decrypt` needs before deciding whether the rest
+/// of the payload is even worth attempting to parse.
+#[derive(serde::Deserialize)]
+struct FormatVersionProbe {
+    format_version: u32,
+}
+
+/// Decrypt and parse an export file, checking the format version **before**
+/// attempting to deserialize the full payload.
+///
+/// That ordering is not just tidiness: a version bump that isn't
+/// deserialize-compatible (a field's type changes, not just a new
+/// `#[serde(default)]`-covered one) is exactly the case this check exists
+/// for, and parsing the full struct first would fail on the shape mismatch
+/// before the version check ever ran, surfacing a raw parse error instead
+/// of "update Triple-C" — and, more seriously, `serde_json`'s type-mismatch
+/// errors quote the offending value inline. This file is not attacker
+/// content in the usual sense (it must still decrypt under the right
+/// password), but the plaintext it decrypts to can hold a live credential,
+/// so neither error path below ever interpolates what `serde_json`
+/// actually says — only a fixed, generic message.
+fn read_and_decrypt(path: &Path, password: &str) -> Result<SettingsExportPayload, String> {
     let encrypted = std::fs::read(path).map_err(|e| format!("Failed to read export file: {}", e))?;
     let plaintext = settings_crypto::decrypt(&encrypted, password)?;
 
-    let payload: SettingsExportPayload = serde_json::from_slice(&plaintext)
-        .map_err(|e| format!("This file doesn't look like a valid settings export: {}", e))?;
-
-    if payload.format_version > SETTINGS_EXPORT_FORMAT_VERSION {
+    let probe: FormatVersionProbe = serde_json::from_slice(&plaintext)
+        .map_err(|_| "This file doesn't look like a valid settings export.".to_string())?;
+    if probe.format_version > SETTINGS_EXPORT_FORMAT_VERSION {
         return Err(format!(
             "This export was made by a newer version of Triple-C (format {}, this app supports up to {}). \
              Update Triple-C before importing it.",
-            payload.format_version, SETTINGS_EXPORT_FORMAT_VERSION
+            probe.format_version, SETTINGS_EXPORT_FORMAT_VERSION
         ));
     }
 
-    Ok(payload)
+    serde_json::from_slice(&plaintext)
+        .map_err(|_| "This file doesn't look like a valid settings export (unexpected shape).".to_string())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn non_blank_treats_whitespace_only_as_absent() {
+        assert_eq!(non_blank(Some("   ".to_string())), None);
+        assert_eq!(non_blank(Some("".to_string())), None);
+        assert_eq!(non_blank(None), None);
+        assert_eq!(non_blank(Some(" a ".to_string())), Some(" a ".to_string()));
+    }
+
+    fn write_export(dir: &std::path::Path, name: &str, payload: &SettingsExportPayload, password: &str) -> PathBuf {
+        let plaintext = serde_json::to_vec(payload).unwrap();
+        let encrypted = settings_crypto::encrypt(&plaintext, password).unwrap();
+        let path = dir.join(name);
+        std::fs::write(&path, &encrypted).unwrap();
+        path
+    }
+
+    fn sample_payload(format_version: u32) -> SettingsExportPayload {
+        SettingsExportPayload {
+            format_version,
+            exported_at: "2026-08-27T00:00:00Z".to_string(),
+            app_version: "0.4.14".to_string(),
+            settings: AppSettings::default(),
+            secrets: ExportedSecrets::default(),
+        }
+    }
+
+    fn temp_dir(name: &str) -> PathBuf {
+        let dir = std::env::temp_dir().join(format!(
+            "triple-c-settings-export-test-{}-{}",
+            name,
+            uuid::Uuid::new_v4().simple()
+        ));
+        std::fs::create_dir_all(&dir).unwrap();
+        dir
+    }
+
+    #[test]
+    fn a_file_from_a_newer_format_is_refused_before_the_full_shape_is_parsed() {
+        let dir = temp_dir("newer-format");
+        let path = write_export(
+            &dir,
+            "export.triplec",
+            &sample_payload(SETTINGS_EXPORT_FORMAT_VERSION + 1),
+            "correct password",
+        );
+
+        let err = read_and_decrypt(&path, "correct password").unwrap_err();
+        assert!(err.contains("newer version"), "unexpected message: {}", err);
+        assert!(err.contains("Update Triple-C"));
+
+        std::fs::remove_dir_all(&dir).ok();
+    }
+
+    #[test]
+    fn a_file_at_the_current_format_is_accepted() {
+        let dir = temp_dir("current-format");
+        let path = write_export(
+            &dir,
+            "export.triplec",
+            &sample_payload(SETTINGS_EXPORT_FORMAT_VERSION),
+            "correct password",
+        );
+
+        let payload = read_and_decrypt(&path, "correct password").unwrap();
+        assert_eq!(payload.format_version, SETTINGS_EXPORT_FORMAT_VERSION);
+
+        std::fs::remove_dir_all(&dir).ok();
+    }
+
+    #[test]
+    fn a_malformed_payload_produces_a_generic_error_not_a_raw_serde_message() {
+        // Encrypt something that decrypts fine but isn't a valid payload
+        // shape at all — this must not happen in practice (only this app
+        // ever writes these files), but the error path must still never
+        // echo back plaintext content, generic malformed-shape or not.
+        let dir = temp_dir("malformed");
+        let plaintext = b"{\"not\": \"a real export\"}".to_vec();
+        let encrypted = settings_crypto::encrypt(&plaintext, "correct password").unwrap();
+        let path = dir.join("export.triplec");
+        std::fs::write(&path, &encrypted).unwrap();
+
+        let err = read_and_decrypt(&path, "correct password").unwrap_err();
+        assert!(!err.contains("not a real export"), "leaked plaintext into the error: {}", err);
+        assert!(err.contains("doesn't look like a valid settings export"));
+
+        std::fs::remove_dir_all(&dir).ok();
+    }
+
+    #[test]
+    fn the_wrong_password_is_reported_without_a_version_check_ever_running() {
+        let dir = temp_dir("wrong-password");
+        let path = write_export(
+            &dir,
+            "export.triplec",
+            &sample_payload(SETTINGS_EXPORT_FORMAT_VERSION),
+            "correct password",
+        );
+
+        let err = read_and_decrypt(&path, "wrong password").unwrap_err();
+        assert!(err.contains("Wrong password"), "unexpected message: {}", err);
+
+        std::fs::remove_dir_all(&dir).ok();
+    }
 }