fix: count the network fee in the confirm-screen balance check (closes #154)

The Send button was enabled whenever the amount alone fit the balance, so
a max-value ETH send passed the confirmation screen and failed at
broadcast, after the user had committed to it.

The arithmetic moves into src/shared/txValidation.js as a pure function
over 18-decimal fixed point: native ETH now requires amount + fee <=
balance, and an ERC-20 transfer requires the ETH balance to cover the fee
on top of the token check, reported as its own error. Validation re-runs
when the async estimate resolves; Send stays disabled while the estimate
is pending and when it fails, so an unknown fee is never treated as zero.
The fee messages are static elements that already reserve their space, so
nothing moves when the estimate lands.

The fee reserved is the one the node will actually require. The send pins
no fee fields, so ethers broadcasts a type-2 transaction and the node
validates it against value + gasLimit * maxFeePerGas; gating on gasPrice
would under-reserve by roughly gasLimit * baseFee and let through exactly
the broadcast failure this change exists to prevent. feeReserveWei()
derives that reserve, falling back to gasPrice only where no type-2
pricing exists. The reserve is read when the screen opens and the
broadcast derives its own, so a base fee that roughly doubles while the
user is at the password field can still outrun it: this turns a
deterministic failure on every max-value send into a rare one, not into
none.

The fee line shows both numbers rather than one - what the transfer is
expected to cost, and below it the larger amount reserved until it
confirms. Quoting only the reserve overstates the typical mainnet cost by
roughly double on every send; quoting only the estimate contradicts the
gate. The second line holds its space from the first paint.

validateTransfer() fails closed: a feeWei that is not a non-negative
bigint under FEE_KNOWN, any unrecognised feeStatus, and a negative amount
all block, rather than counting as a fee of zero or as an amount that
passes every comparison trivially.

README.md

@@ -123,8 +123,12 @@ unavailable). The suite lives in `tests/e2e/` and is driven by
 `playwright-core`, whose version must stay matched to the container's Playwright
 version — the browsers ship inside the image.
 
-It covers popup load, wallet creation through the UI, the Add Token screen and
-the transaction detail screen for an ERC-20 transfer. All outbound network is
+It covers popup load, wallet creation through the UI, the Add Token screen, the
+transaction detail screen for an ERC-20 transfer, and the recovery phrase screen
+— which wallet types are offered it, that it holds nothing before the password
+is accepted, that a wrong password reveals nothing, that leaving it by either
+route wipes it — including a leave taken while the decrypt is still running —
+and that reopening the popup does not land on it. All outbound network is
 intercepted at the browser level and served from fixtures in
 `tests/e2e/network.js`, so the run is deterministic and fully offline;
 unrecognised outbound requests are reported as failures rather than silently
@@ -406,8 +410,11 @@ runtime debug mode is on, or when the active network is a testnet. They are not
 repeated in the element lists below.
 
 Closing and reopening the popup returns to the screen the user was last on only
-for the views listed in `RESTORABLE_VIEWS` (`src/popup/index.js`). Every other
-screen, including ExportPrivKey, falls back to Home.
+for the views listed in `RESTORABLE_VIEWS` (`src/popup/restorableViews.js`).
+Every other screen falls back to Home. The screens that display a secret —
+ExportPrivKey and ShowRecoveryPhrase — are deliberately absent from that list,
+so the popup can never reopen onto one of them with no password prompt in front
+of it.
 
 #### Welcome (`welcome`)
 
@@ -575,16 +582,26 @@ screen, including ExportPrivKey, falls back to Home.
     - To: blockie + color dot + full address + etherscan link + ENS name
     - Amount: value + symbol (USD in parentheses)
     - Your balance: value + symbol (USD in parentheses)
-    - Estimated network fee: "Estimating..." then the ETH amount (USD in
-      parentheses) or "Unable to estimate", fetched async
+    - Network fee: "Estimating..." then two lines, or "Unable to estimate",
+      fetched async. The first line is what the transfer is expected to cost,
+      `gasLimit * gasPrice` (USD in parentheses); the second is the
+      `gasLimit * maxFeePerGas` reserve the node requires, which is what the
+      balance check gates on. The second line is omitted on a network with no
+      type-2 pricing, where the two are the same number, but its space is
+      reserved either way
     - Warnings: inline warnings from the local checks (scam address, self-send)
       plus four reserved warning boxes made visible by the async checks —
       recipient with no transaction history, recipient is a contract, burn
       address, and an Etherscan phishing/scam label
-    - Errors (insufficient balance)
+    - Errors (insufficient balance), plus three reserved error boxes — the
+      amount plus the fee exceeds the balance (ETH transfers), not enough ETH to
+      pay the fee for the transfer (ERC-20 transfers), and the fee could not be
+      estimated. The first two are mutually exclusive per transfer type, so only
+      the applicable one holds space
     - Password: an inline field on this screen, not a modal, with its own error
       line
-    - "Sign & Send" button (disabled if errors)
+    - "Sign & Send" button (disabled if errors, and while the network fee
+      estimate is pending or unavailable)
 - **Transitions**:
     - "Sign & Send" (correct password) → broadcast tx → **WaitTx**
     - "Sign & Send" (correct password) → broadcast fails → **ErrorTx**
@@ -707,12 +724,13 @@ screen, including ExportPrivKey, falls back to Home.
 - **When**: User tapped the Settings gear.
 - **Elements**:
     - "Back" button, "Settings" heading
-    - Wallets: one row per wallet with its name (tap to rename inline) and an
-      `[x]` delete button, plus a "+ Add wallet" button
+    - Wallets: one row per wallet with its name (tap to rename inline), a
+      `[recovery phrase]` button on HD wallets only, and an `[x]` delete button,
+      plus a "+ Add wallet" button
     - Tracked Tokens: one row per tracked token with an `[x]` remove button,
       plus a "+ Add token" button
-    - Display: "Show tracked tokens with zero balance" checkbox and a Theme
-      selector (System / Light / Dark)
+    - Display: "Show tracked tokens with zero balance" checkbox, "UTC
+      Timestamps" checkbox, and a Theme selector (System / Light / Dark)
     - Network: network selector (Ethereum Mainnet / Sepolia Testnet); switching
       resets the RPC and Blockscout endpoints to that network's defaults
     - Ethereum RPC: endpoint URL input + "Save" button (validated against
@@ -723,7 +741,6 @@ screen, including ExportPrivKey, falls back to Home.
         - "Hide tokens with fewer than 1,000 holders" checkbox
         - "Hide transactions from detected fraud contracts" checkbox
         - "Hide dust transactions below N gwei" checkbox + threshold input
-        - "UTC Timestamps" checkbox
     - Allowed Sites: list with remove buttons
     - Denied Sites: list with remove buttons
     - About: project link, license, author, version, release date, and the
@@ -733,6 +750,7 @@ screen, including ExportPrivKey, falls back to Home.
 - **Transitions**:
     - "+ Add wallet" → **AddWallet**
     - "+ Add token" → **SettingsAddToken**
+    - `[recovery phrase]` on an HD wallet → **ShowRecoveryPhrase**
     - `[x]` on a wallet → **DeleteWallet**
     - Tap wallet name → inline rename field (no screen change)
     - `[x]` on a tracked token or a site → removes it in place (no screen
@@ -740,6 +758,33 @@ screen, including ExportPrivKey, falls back to Home.
     - Ten clicks on the version → reveals the Debug well (no screen change)
     - "Back" (or Settings gear again) → previous screen (Home)
 
+#### ShowRecoveryPhrase (`show-phrase`)
+
+- **When**: User tapped `[recovery phrase]` on a wallet row in Settings. HD
+  wallets only: key and xprv wallets have no recovery phrase, so their rows do
+  not offer the action at all.
+- **Elements**:
+    - "Back" button, "Recovery Phrase" heading
+    - Wallet name
+    - Warning box stating that anyone holding these words can take everything in
+      the wallet, from any device, without the password
+    - Error line
+    - Password input + "Reveal" button, shown until the password is accepted
+    - The recovery phrase itself, in full and click-to-copy, shown only after a
+      correct password and in place of the password prompt
+- **Transitions**:
+    - "Reveal" (correct password) → the phrase replaces the password prompt (no
+      screen change)
+    - "Reveal" (wrong password) → full-sentence error, nothing revealed (no
+      screen change)
+    - "Back" → previous screen (Settings)
+- **Secret handling**: nothing is decrypted or written into the page until the
+  password is accepted; the phrase is never stored in state, and it is wiped
+  from the page whenever the screen is left by any route, including the Settings
+  gear. A decrypt still running when the screen is left is discarded rather than
+  written. The screen is not restorable, so reopening the popup lands on Home
+  rather than back on the phrase.
+
 #### DeleteWallet (`delete-wallet-confirm`)
 
 - **When**: User tapped the `[x]` next to a wallet in Settings.
@@ -1182,7 +1227,7 @@ Currently supported:
 
 - [x] Delete wallet (with confirmation)
 - [ ] Delete address from HD wallet (with confirmation)
-- [ ] Show wallet's recovery phrase (requires password)
+- [x] Show wallet's recovery phrase (requires password)
 
 ### Transactions
 

TODO.md

@@ -44,11 +44,31 @@ undefined identifiers, which is how
 
 # Completed Steps
 
+- 2026-08-11: `script/verify-build` now walks `dist/` NUL-delimited and asserts
+  `dist/` is a real directory, so a path with a trailing space or a newline can
+  no longer carry a debug marker past the unlisted-bundle check
+  ([#223](https://git.eeqj.de/sneak/AutistMask/issues/223)).
+- 2026-08-11: UTC Timestamps checkbox moved from the Token Spam Protection well
+  into Display, next to the theme selector
+  ([#212](https://git.eeqj.de/sneak/AutistMask/issues/212)).
+- 2026-08-11: Network fee counted in the confirmation-screen balance check for
+  both ETH and ERC-20 sends, reserving what the node actually charges a type-2
+  transaction, with the arithmetic in a pure, unit-tested
+  `src/shared/txValidation.js`
+  ([#154](https://git.eeqj.de/sneak/AutistMask/issues/154)).
 - 2026-08-11: A dust threshold of `0` now means "hide nothing" instead of
   falling back to the 100,000 gwei default, and every address comparison in
   `src/shared/transactions.js` goes through one case-normalising helper so a
   checksummed genuine contract is no longer read as a spoof
   ([#179](https://git.eeqj.de/sneak/AutistMask/issues/179)).
+- 2026-08-11: Password-gated recovery phrase display for HD wallets, reached
+  from the wallet row in Settings, wiped on leaving the screen and excluded from
+  the views the popup can reopen onto
+  ([#161](https://git.eeqj.de/sneak/AutistMask/issues/161)).
+- 2026-08-11: Extended-key import hardened — the base58 checksum is now enforced
+  on every xprv and xpub, and a non-master key is refused with an explanation
+  instead of being derived beneath
+  ([#210](https://git.eeqj.de/sneak/AutistMask/issues/210)).
 - 2026-08-11: Policy compliance sweep — conditional verbose test rerun, local
   Tailwind binary instead of `npx`, `--frozen-lockfile` on `make install`, and
   the Makefile-only targets documented in the README

docs/README.md

@@ -265,7 +265,10 @@ The confirmation screen shows:
 - **From and To addresses** with identicons and Etherscan links
 - **Amount** with USD estimate
 - **Your current balance** with USD estimate
-- **Estimated network fee** in ETH with USD estimate
+- **Network fee** — what the transfer is expected to cost, in ETH with a USD
+  estimate, and below it the larger amount reserved until it confirms. The
+  reserve is what the network requires up front and what the balance check gates
+  on; the refund of the difference is why the two differ
 - **Warnings** if the recipient is a contract, a burn address, one of your own
   addresses, on the bundled scam-address list, or labelled as a phisher on
   Etherscan
@@ -359,16 +362,16 @@ Click the gear icon on the home screen to access settings:
 - **Wallets**: Your wallets, and "+ Add wallet".
 - **Tracked Tokens**: The ERC-20 tokens tracked across all addresses, and "+ Add
   token".
-- **Display**: Toggle whether tracked tokens with zero balance are shown, and
-  choose the theme (System, Light, or Dark).
+- **Display**: Toggle whether tracked tokens with zero balance are shown, switch
+  timestamps to UTC, and choose the theme (System, Light, or Dark).
 - **Network**: Switch between Ethereum Mainnet and Sepolia Testnet. Switching
   resets the RPC and Blockscout endpoints to that network's defaults.
 - **Ethereum RPC**: Change the Ethereum node endpoint. Default is a public RPC.
   You can use your own node for maximum privacy.
 - **Blockscout API**: Change the Blockscout instance used for token balances and
   transaction history. You can use a self-hosted instance.
-- **Token Spam Protection**: Toggle individual scam filters, set the dust
-  transaction threshold, and switch timestamps to UTC.
+- **Token Spam Protection**: Toggle individual scam filters and set the dust
+  transaction threshold.
 - **Allowed Sites / Denied Sites**: View and manage web3 site permissions.
 - **About**: License, author, version, release date, and a link to the commit
   this build came from.

script/verify-build

@@ -22,6 +22,18 @@ set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
+# Absolute path to this script, resolved before anything cd's anywhere.
+# check_unlisted_bundles re-invokes it through xargs, and $0 on its own may be
+# relative to a directory we are about to leave.
+SELF="$(cd "$(dirname "$0")" && pwd -P)/$(basename "$0")"
+
+# Internal re-entry flag; see scan_dist_paths.
+SCAN_FLAG="--scan-dist-paths"
+
+# A literal newline, for the is_listed guard.
+NEWLINE='
+'
+
 MANIFEST="dist/constants-bundles.txt"
 MARKER_ON="autistmask-build-debug=on"
 MARKER_OFF="autistmask-build-debug=off"
@@ -29,11 +41,20 @@ MARKER_OFF="autistmask-build-debug=off"
 # Set by read_marker.
 MARKER=""
 
+# Temporary file holding the NUL-delimited dist/ listing, removed by the EXIT
+# trap because fail() exits from wherever it is called.
+LISTING=""
+
 fail() {
     echo "verify-build: FAIL: $*" >&2
     exit 1
 }
 
+cleanup() {
+    [ -z "$LISTING" ] || rm -f "$LISTING"
+}
+trap cleanup EXIT
+
 # Is the literal $1 present in the file $2? Match (grep exit 0) and no-match
 # (exit 1) are answers about the emitted output. Anything else (exit 2: the
 # file could not be read) is not an answer at all, and must not be reported as
@@ -58,7 +79,17 @@ has_marker() {
 # manifest could not be read and is not an answer at all. Without this, an
 # unreadable manifest reads as "this file is not listed" and every emitted
 # bundle gets reported as an unlisted one.
+#
+# A path containing a newline is answered without asking grep, because grep
+# would read the pattern as two patterns and report a match on either. That is
+# how such a path escaped this check even once the walk stopped splitting it:
+# the half before the newline matched a listed line and the file was skipped.
+# The manifest is line-delimited, so it cannot name such a path at all, and
+# "not listed" is the only true answer.
 is_listed() {
+    case "$1" in
+    *"$NEWLINE"*) return 1 ;;
+    esac
     _il_status=0
     grep -q -x -F -e "$1" -- "$MANIFEST" || _il_status=$?
     case "$_il_status" in
@@ -117,35 +148,66 @@ read_marker() {
 # an endsWith(".js") test; repeating that literal here would mean a bundle
 # emitted under some other extension escaped the manifest AND this check at
 # once, which is the correlated blind spot the two-source design exists to
-# avoid. Every file under dist/ is searched, so build.js's filter is the only
-# place the assumption lives and this check is what catches it being wrong.
+# avoid. Every regular file and every symlink under dist/ is searched — that
+# is the whole of what a build emits — so build.js's filter is the only place
+# the assumption lives and this check is what catches it being wrong.
 #
-# That claim only holds if the walk is exhaustive, so two things are enforced
-# here rather than assumed:
+# That claim only holds if the walk is exhaustive and every name survives it
+# intact, so four things are enforced here rather than assumed:
 #
+#   - the walk is NUL-delimited and the paths reach the check as arguments, so
+#     no name can be reshaped on the way in. Read line by line, a name with a
+#     trailing space lost it to read's field splitting and the remnant then
+#     matched a manifest line, and a name containing a newline arrived as a
+#     listed path plus an empty one. Both left a marker-carrying, unlisted file
+#     unchecked while the script still reported success. Delivering such a name
+#     intact is only half of it; is_listed also has to keep it out of grep's
+#     pattern, for the same reason.
 #   - find's exit status is checked. A subtree it cannot descend is reported on
 #     stderr and then simply missing from the listing, so an unchecked status
 #     turns "could not look" into "nothing was there" — the same conflation
-#     has_marker exists to prevent. The status cannot be read off a pipeline
-#     ending in sort, so the sort is a separate step.
+#     has_marker exists to prevent. The status cannot be read off a pipeline,
+#     so the listing lands in a file that xargs then reads back.
 #   - symlinks are walked too (-type l), not skipped. A marker-carrying bundle
 #     reachable under an unlisted path in dist/ is a stale manifest whether the
 #     path is a link or a file, and grep reads through the link. A link that
 #     cannot be read through — dangling, or pointing at a directory — fails
 #     hard via has_marker's exit-2 path, which is the fail-closed answer: the
 #     build emits neither, so their DEBUG state is unproven, not fine.
+#   - dist/ itself must be a directory and not a symlink, which main asserts
+#     before anything reads through it. find does not follow a symlink named on
+#     its own command line, so a linked dist/ collapses this walk to one entry
+#     and cross-checks nothing.
+#
+# Types other than regular files and symlinks are left out on purpose: a build
+# emits none of them, and grep on a fifo would hang rather than fail.
 check_unlisted_bundles() {
+    LISTING="$(mktemp "${TMPDIR:-/tmp}/verify-build-dist.XXXXXX")" ||
+        fail "could not create a temporary file for the dist/ listing, so the
+    tree was never walked. Refusing to report success."
+
     _find_status=0
-    _listing="$(find dist \( -type f -o -type l \) -print)" || _find_status=$?
+    find dist \( -type f -o -type l \) -print0 >"$LISTING" || _find_status=$?
     [ "$_find_status" -eq 0 ] ||
         fail "find exited $_find_status enumerating dist/, so part of the tree
     was never walked and nothing was established about the files in it. Any
     unlisted bundle there went unchecked. That is a permissions or I/O fault on
     the artifact, not a stale manifest. Refusing to report success."
-    _listing="$(printf '%s\n' "$_listing" | sort)"
 
-    while read -r _file; do
-        [ -n "$_file" ] || continue
+    _scan_status=0
+    xargs -0 "$SELF" "$SCAN_FLAG" <"$LISTING" || _scan_status=$?
+    [ "$_scan_status" -eq 0 ] ||
+        fail "the unlisted-bundle scan exited $_scan_status: either a path
+    under dist/ failed the check reported above, or the scan could not be run
+    at all. Refusing to report success."
+}
+
+# The per-path half of check_unlisted_bundles. It runs in a re-invocation of
+# this script, so it uses the same is_listed and has_marker as the rest of the
+# file rather than a second copy of them that could drift. Paths arrive as
+# arguments and are never split, joined or trimmed.
+scan_dist_paths() {
+    for _file in "$@"; do
         if is_listed "$_file"; then
             continue
         fi
@@ -154,9 +216,7 @@ check_unlisted_bundles() {
             fail "$_file carries a debug marker but is absent from $MANIFEST,
     so the manifest no longer describes the emitted bundles."
         fi
-    done <<EOF
-$_listing
-EOF
+    done
 }
 
 # The requested mode, read from our own environment using build.js's exact
@@ -173,9 +233,32 @@ expected_marker() {
 main() {
     cd "$ROOT"
 
+    # Internal re-entry from check_unlisted_bundles' xargs. Not part of the
+    # command-line interface: nothing else invokes it, and it is a distinct
+    # entry point rather than a mode flag threaded through the checks below.
+    if [ "${1-}" = "$SCAN_FLAG" ]; then
+        shift
+        scan_dist_paths "$@"
+        return 0
+    fi
+
     expected="$(expected_marker)"
     echo "Verifying emitted bundles (expecting $expected)..."
 
+    # Asserted here rather than left to grep. A symlinked dist/ used to fail
+    # only because GNU grep exits 2 on a directory, so check_unlisted_bundles'
+    # single entry hit has_marker's I/O path by luck; under a grep that exits 1
+    # instead, the whole cross-check would have collapsed into a pass.
+    if [ -h dist ]; then
+        fail "dist is a symlink, not a directory. find does not follow a
+    symlink named on its own command line, so the unlisted-bundle cross-check
+    would see one entry instead of the emitted tree and establish nothing about
+    it. Refusing to report success."
+    fi
+    [ -d dist ] ||
+        fail "dist is not a directory, so there is no emitted tree to verify.
+    build.js writes it; run make build first."
+
     [ -f "$MANIFEST" ] ||
         fail "$MANIFEST is missing. build.js writes it at the end of a
     successful build; run make build first."

src/popup/index.html

@@ -136,7 +136,9 @@
                 <div id="add-wallet-section-xprv" class="hidden">
                     <p class="mb-2">
                         Paste your extended private key (xprv) below. This will
-                        import the HD wallet and scan for used addresses.
+                        import the HD wallet and scan for used addresses. It
+                        must be the master key for the wallet; an account-level
+                        or child key is not supported.
                     </p>
                     <div class="mb-2">
                         <input
@@ -582,10 +584,18 @@
                     <div id="confirm-balance" class="text-xs"></div>
                 </div>
                 <div id="confirm-fee" class="mb-3" style="visibility: hidden">
-                    <div class="text-xs text-muted mb-1">
-                        Estimated network fee
-                    </div>
+                    <div class="text-xs text-muted mb-1">Network fee</div>
                     <div id="confirm-fee-amount" class="text-xs"></div>
+                    <!-- Holds its one line of space from the first paint, so
+                    the reserve appearing when the estimate lands moves
+                    nothing. The placeholder is never seen. -->
+                    <div
+                        id="confirm-fee-reserve"
+                        class="text-xs text-muted"
+                        style="visibility: hidden"
+                    >
+                        reserve pending
+                    </div>
                 </div>
                 <div
                     id="confirm-warnings"
@@ -647,6 +657,31 @@
                     class="mb-2 border border-border border-dashed p-2"
                     style="visibility: hidden; min-height: 1.25rem"
                 ></div>
+                <div
+                    id="confirm-amount-fee-error"
+                    class="mb-2 border border-border border-dashed p-2 text-xs"
+                    style="visibility: hidden"
+                >
+                    Your balance does not cover this amount plus the network
+                    fee. Please go back and send a smaller amount.
+                </div>
+                <div
+                    id="confirm-gas-error"
+                    class="mb-2 border border-border border-dashed p-2 text-xs"
+                    style="visibility: hidden"
+                >
+                    You do not have enough ETH to pay the network fee for this
+                    transfer. Please add ETH to this address and try again.
+                </div>
+                <div
+                    id="confirm-fee-unknown-error"
+                    class="mb-2 border border-border border-dashed p-2 text-xs"
+                    style="visibility: hidden"
+                >
+                    The network fee could not be estimated, so this transaction
+                    cannot be checked against your balance. Please go back and
+                    try again.
+                </div>
                 <div class="mb-2">
                     <label class="block mb-1 text-xs">Password</label>
                     <input
@@ -869,6 +904,12 @@
                         />
                         Show tracked tokens with zero balance
                     </label>
+                    <label
+                        class="text-xs flex items-center gap-1 cursor-pointer mb-2"
+                    >
+                        <input type="checkbox" id="settings-utc-timestamps" />
+                        UTC Timestamps
+                    </label>
                     <div class="text-xs flex items-center gap-1">
                         <label for="settings-theme">Theme:</label>
                         <select
@@ -979,12 +1020,6 @@
                         />
                         <span class="text-xs text-muted">gwei</span>
                     </div>
-                    <label
-                        class="text-xs flex items-center gap-1 cursor-pointer mb-1"
-                    >
-                        <input type="checkbox" id="settings-utc-timestamps" />
-                        UTC Timestamps
-                    </label>
                 </div>
 
                 <div class="bg-well p-3 mx-1 mb-3">
@@ -1098,6 +1133,52 @@
                 </button>
             </div>
 
+            <!-- ============ SHOW RECOVERY PHRASE ============ -->
+            <div id="view-show-phrase" class="view hidden">
+                <button
+                    id="btn-show-phrase-back"
+                    class="border border-border px-2 py-1 hover:bg-fg hover:text-bg cursor-pointer mb-2"
+                >
+                    &lt; Back
+                </button>
+                <h2 class="font-bold mb-1">Recovery Phrase</h2>
+                <p class="text-xs mb-3" id="show-phrase-wallet-name"></p>
+                <div
+                    class="text-xs mb-3 border border-border border-dashed p-2"
+                >
+                    Anyone who has these words can take every coin and token in
+                    this wallet, from any device, without your password. Never
+                    type them into a website and never show them to anyone.
+                </div>
+                <div
+                    id="show-phrase-flash"
+                    class="text-xs text-red-500 mb-2 min-h-[1.25rem]"
+                    style="visibility: hidden"
+                ></div>
+                <div id="show-phrase-password-section" class="mb-2">
+                    <label class="block mb-1">Password</label>
+                    <input
+                        type="password"
+                        id="show-phrase-password"
+                        class="border border-border p-1 w-full font-mono text-sm bg-bg text-fg"
+                        placeholder="Enter your password to continue"
+                    />
+                    <button
+                        id="btn-show-phrase-reveal"
+                        class="border border-border px-2 py-1 hover:bg-fg hover:text-bg cursor-pointer mt-2"
+                    >
+                        Reveal
+                    </button>
+                </div>
+                <div id="show-phrase-result" class="hidden">
+                    <div
+                        id="show-phrase-value"
+                        class="bg-danger-well rounded p-2 font-mono text-xs break-all cursor-pointer mb-1"
+                        title="Click to copy"
+                    ></div>
+                </div>
+            </div>
+
             <!-- ============ SETTINGS: ADD TOKEN ============ -->
             <div id="view-settings-addtoken" class="view hidden">
                 <button

src/popup/index.js

@@ -15,6 +15,10 @@ const {
     clearViewStack,
 } = require("./views/helpers");
 const { applyTheme } = require("./theme");
+// Views that can be fully re-rendered from persisted state. All others fall
+// back to the nearest restorable parent; see the module for why the
+// secret-bearing views are absent.
+const { RESTORABLE_VIEWS } = require("./restorableViews");
 
 const home = require("./views/home");
 const welcome = require("./views/welcome");
@@ -99,21 +103,6 @@ const ctx = {
     },
 };
 
-// Views that can be fully re-rendered from persisted state.
-// All others fall back to the nearest restorable parent.
-const RESTORABLE_VIEWS = new Set([
-    "main",
-    "address",
-    "address-token",
-    "receive",
-    "settings",
-    "settings-addtoken",
-    "confirm-tx",
-    "transaction",
-    "success-tx",
-    "error-tx",
-]);
-
 function needsAddress(view) {
     return (
         view === "address" ||

src/popup/restorableViews.js

@@ -0,0 +1,29 @@
+// Views the popup may reopen onto.
+//
+// The popup persists the current view so that reopening the toolbar popup
+// lands the user back where they were. Only views that can be fully
+// re-rendered from persisted state belong here; every other view falls back
+// to the nearest restorable parent (src/popup/index.js restoreView()).
+//
+// A view that displays a secret must NEVER be listed. Restoring onto one
+// would put a private key or a recovery phrase on screen with no password
+// prompt in front of it, on a popup the user may have reopened by accident.
+// That is why "export-privkey" and "show-phrase" are absent.
+//
+// Kept in its own module, with no dependencies, so tests can assert the
+// exclusion directly rather than trusting a reading of the popup entry
+// point, which cannot be required outside a browser.
+const RESTORABLE_VIEWS = new Set([
+    "main",
+    "address",
+    "address-token",
+    "receive",
+    "settings",
+    "settings-addtoken",
+    "confirm-tx",
+    "transaction",
+    "success-tx",
+    "error-tx",
+]);
+
+module.exports = { RESTORABLE_VIEWS };

src/popup/views/addWallet.js

@@ -6,6 +6,7 @@ const {
     addressFromPrivateKey,
     hdWalletFromXprv,
     isValidXprv,
+    isMasterExtendedKey,
 } = require("../../shared/wallet");
 const { encryptWithPassword } = require("../../shared/vault");
 const { state, saveState } = require("../../shared/state");
@@ -213,14 +214,25 @@ async function importXprvKey(ctx) {
         return;
     }
     if (!isValidXprv(xprv)) {
-        showFlash("Invalid extended private key.");
+        showFlash(
+            "That extended private key is not valid. Please check it and try again.",
+        );
+        return;
+    }
+    if (!isMasterExtendedKey(xprv)) {
+        showFlash(
+            "That is an account-level or child key, which cannot be imported. " +
+                "Please paste the master extended private key for the wallet.",
+        );
         return;
     }
     let result;
     try {
         result = hdWalletFromXprv(xprv);
     } catch (e) {
-        showFlash("Invalid extended private key.");
+        showFlash(
+            "That extended private key is not valid. Please check it and try again.",
+        );
         return;
     }
     const { xpub, firstAddress } = result;

src/popup/views/confirmTx.js

@@ -32,11 +32,24 @@ const {
     getFullWarnings,
 } = require("../../shared/addressWarnings");
 const { ERC20_ABI, isBurnAddress } = require("../../shared/constants");
+const {
+    CODES,
+    FEE_PENDING,
+    FEE_KNOWN,
+    FEE_UNAVAILABLE,
+    feeReserveWei,
+    feeEstimateWei,
+    validateTransfer,
+} = require("../../shared/txValidation");
 const { log } = require("../../shared/log");
 const makeBlockie = require("ethereum-blockies-base64");
 const txStatus = require("./txStatus");
 
 let pendingTx = null;
+// Network fee for the transaction currently on screen. Reset by show() and
+// filled in by estimateGas() when the estimate resolves or fails.
+let feeStatus = FEE_PENDING;
+let feeWei = null;
 
 function restore() {
     const d = state.viewData;
@@ -67,6 +80,8 @@ function valueWithUsd(text, usdAmount) {
 
 function show(txInfo) {
     pendingTx = txInfo;
+    feeStatus = FEE_PENDING;
+    feeWei = null;
 
     const isErc20 = txInfo.token !== "ETH";
     const symbol = isErc20 ? txInfo.tokenSymbol || "?" : "ETH";
@@ -153,50 +168,14 @@ function show(txInfo) {
         warningsEl.style.visibility = "hidden";
     }
 
-    // Check for errors
-    const errors = [];
-    if (isErc20) {
-        const tokenBal = parseFloat(txInfo.tokenBalance || "0");
-        if (parseFloat(txInfo.amount) > tokenBal) {
-            errors.push(
-                "Insufficient " +
-                    symbol +
-                    " balance. You have " +
-                    txInfo.tokenBalance +
-                    " " +
-                    symbol +
-                    " but are trying to send " +
-                    txInfo.amount +
-                    " " +
-                    symbol +
-                    ".",
-            );
-        }
-    } else if (parseFloat(txInfo.amount) > parseFloat(txInfo.balance)) {
-        errors.push(
-            "Insufficient balance. You have " +
-                txInfo.balance +
-                " ETH but are trying to send " +
-                txInfo.amount +
-                " ETH.",
-        );
-    }
+    // The two fee messages are mutually exclusive per transaction type, and
+    // the type is known here, before the first paint. Drop the one that can
+    // never apply and reserve the space of the one that can, so the async
+    // estimate landing later never moves anything.
+    $("confirm-amount-fee-error").classList.toggle("hidden", isErc20);
+    $("confirm-gas-error").classList.toggle("hidden", !isErc20);
 
-    const errorsEl = $("confirm-errors");
-    const sendBtn = $("btn-confirm-send");
-    if (errors.length > 0) {
-        errorsEl.innerHTML = errors
-            .map((e) => `<div class="text-xs">${e}</div>`)
-            .join("");
-        errorsEl.style.visibility = "visible";
-        sendBtn.disabled = true;
-        sendBtn.classList.add("text-muted");
-    } else {
-        errorsEl.innerHTML = "";
-        errorsEl.style.visibility = "hidden";
-        sendBtn.disabled = false;
-        sendBtn.classList.remove("text-muted");
-    }
+    renderValidation(txInfo);
 
     // Reset password field and error
     $("confirm-tx-password").value = "";
@@ -205,6 +184,7 @@ function show(txInfo) {
     // Gas estimate — show placeholder then fetch async
     $("confirm-fee").style.visibility = "visible";
     $("confirm-fee-amount").textContent = "Estimating...";
+    setVisible("confirm-fee-reserve", false);
     state.viewData = { pendingTx: txInfo };
     showView("confirm-tx");
     attachCopyHandlers("view-confirm-tx");
@@ -224,11 +204,101 @@ function show(txInfo) {
     checkRecipientHistory(txInfo);
 }
 
+// Render the balance check for the transaction on screen. Called once during
+// show() and again when the fee estimate resolves or fails. Every element it
+// touches already occupies its space, so re-running it never moves anything.
+function renderValidation(txInfo) {
+    const isErc20 = txInfo.token !== "ETH";
+    const symbol = isErc20 ? txInfo.tokenSymbol || "?" : "ETH";
+
+    const { canSend, codes } = validateTransfer({
+        isErc20,
+        amount: txInfo.amount,
+        ethBalance: txInfo.balance,
+        tokenBalance: txInfo.tokenBalance,
+        feeStatus,
+        feeWei,
+    });
+
+    // Messages carrying the user's own numbers are built here; the fixed
+    // sentences live in the reserved elements in index.html.
+    const messages = [];
+    if (codes.includes(CODES.AMOUNT_INVALID)) {
+        messages.push("Please enter a valid amount to send.");
+    }
+    if (codes.includes(CODES.INSUFFICIENT_TOKEN)) {
+        messages.push(
+            "Insufficient " +
+                symbol +
+                " balance. You have " +
+                txInfo.tokenBalance +
+                " " +
+                symbol +
+                " but are trying to send " +
+                txInfo.amount +
+                " " +
+                symbol +
+                ".",
+        );
+    }
+    if (codes.includes(CODES.INSUFFICIENT_ETH)) {
+        messages.push(
+            "Insufficient balance. You have " +
+                txInfo.balance +
+                " ETH but are trying to send " +
+                txInfo.amount +
+                " ETH.",
+        );
+    }
+
+    const errorsEl = $("confirm-errors");
+    if (messages.length > 0) {
+        errorsEl.innerHTML = messages
+            .map((m) => `<div class="text-xs">${escapeHtml(m)}</div>`)
+            .join("");
+        errorsEl.style.visibility = "visible";
+    } else {
+        errorsEl.innerHTML = "";
+        errorsEl.style.visibility = "hidden";
+    }
+
+    setVisible(
+        "confirm-amount-fee-error",
+        codes.includes(CODES.INSUFFICIENT_ETH_WITH_FEE),
+    );
+    setVisible(
+        "confirm-gas-error",
+        codes.includes(CODES.INSUFFICIENT_ETH_FOR_FEE),
+    );
+    setVisible(
+        "confirm-fee-unknown-error",
+        codes.includes(CODES.FEE_UNAVAILABLE),
+    );
+
+    // While the estimate is in flight there is no error to show — the fee
+    // line already reads "Estimating..." — but sending stays blocked so a
+    // transaction the fee would break cannot be signed in the meantime.
+    const sendBtn = $("btn-confirm-send");
+    sendBtn.disabled = !canSend;
+    sendBtn.classList.toggle("text-muted", !canSend);
+}
+
+function setVisible(id, visible) {
+    $(id).style.visibility = visible ? "visible" : "hidden";
+}
+
+// A fee in wei as an ETH string, truncated to 6 decimal places.
+function formatFeeEth(wei) {
+    const parts = formatEther(wei).split(".");
+    const dec =
+        parts.length > 1 ? parts[1].slice(0, 6).replace(/0+$/, "") || "0" : "0";
+    return parts[0] + "." + dec + " ETH";
+}
+
 async function estimateGas(txInfo) {
     try {
         const provider = getProvider(state.rpcUrl);
         const feeData = await provider.getFeeData();
-        const gasPrice = feeData.gasPrice;
         let gasLimit;
 
         if (txInfo.token === "ETH") {
@@ -246,21 +316,55 @@ async function estimateGas(txInfo) {
             });
         }
 
-        const gasCostWei = gasLimit * gasPrice;
-        const gasCostEth = formatEther(gasCostWei);
-        // Format to 6 significant decimal places
-        const parts = gasCostEth.split(".");
-        const dec =
-            parts.length > 1
-                ? parts[1].slice(0, 6).replace(/0+$/, "") || "0"
-                : "0";
-        const feeStr = parts[0] + "." + dec + " ETH";
+        // What the node will require to be reserved, which is what the gate
+        // must be: the send pins no fee fields, so it is broadcast as a
+        // type-2 transaction priced at maxFeePerGas.
+        const gasCostWei = feeReserveWei(gasLimit, feeData);
+        if (gasCostWei === null) {
+            throw new Error("no usable gas price from the provider");
+        }
+        // What the transaction is expected to cost, which is a different and
+        // usually much smaller number. Both are shown: quoting only the
+        // reserve overstates the typical cost by roughly double on mainnet,
+        // and quoting only the estimate contradicts the balance check.
+        const estimateWei = feeEstimateWei(gasLimit, feeData);
+        // The user may have left this transaction while the estimate was in
+        // flight; a stale fee must not reach the screen or the balance check.
+        if (pendingTx !== txInfo) return;
+
         const ethPrice = getPrice("ETH");
-        const feeUsd = ethPrice ? parseFloat(gasCostEth) * ethPrice : null;
-        $("confirm-fee-amount").textContent = valueWithUsd(feeStr, feeUsd);
+        const usd = (wei) =>
+            ethPrice ? parseFloat(formatEther(wei)) * ethPrice : null;
+
+        if (estimateWei !== null && estimateWei < gasCostWei) {
+            $("confirm-fee-amount").textContent = valueWithUsd(
+                "~" + formatFeeEth(estimateWei),
+                usd(estimateWei),
+            );
+            $("confirm-fee-reserve").textContent =
+                "up to " + formatFeeEth(gasCostWei) + " reserved";
+            setVisible("confirm-fee-reserve", true);
+        } else {
+            // No spread to report: either there is no estimate, or the node
+            // quotes a gas price at or above maxFeePerGas, so the expected
+            // cost is not below the reserve. Show the reserve alone.
+            $("confirm-fee-amount").textContent = valueWithUsd(
+                formatFeeEth(gasCostWei),
+                usd(gasCostWei),
+            );
+            setVisible("confirm-fee-reserve", false);
+        }
+        feeStatus = FEE_KNOWN;
+        feeWei = gasCostWei;
+        renderValidation(txInfo);
     } catch (e) {
         log.errorf("gas estimation failed:", e.message);
+        if (pendingTx !== txInfo) return;
         $("confirm-fee-amount").textContent = "Unable to estimate";
+        setVisible("confirm-fee-reserve", false);
+        feeStatus = FEE_UNAVAILABLE;
+        feeWei = null;
+        renderValidation(txInfo);
     }
 }
 

src/popup/views/helpers.js

@@ -31,8 +31,20 @@ const VIEWS = [
     "approve-tx",
     "approve-sign",
     "export-privkey",
+    "show-phrase",
 ];
 
+// Cleanup callbacks for views that hold a secret in the DOM. The view
+// registers one for itself and showView() runs it whenever that view is
+// navigated away from, so the secret is wiped no matter which control
+// caused the navigation — "Back", the settings gear, or a jump from
+// anywhere else. A per-button clear would only cover the one path.
+const viewLeaveHandlers = new Map();
+
+function onViewLeave(name, fn) {
+    viewLeaveHandlers.set(name, fn);
+}
+
 function $(id) {
     return document.getElementById(id);
 }
@@ -50,6 +62,11 @@ function hideError(id) {
 }
 
 function showView(name) {
+    const leaving = state.currentView;
+    if (leaving && leaving !== name) {
+        const onLeave = viewLeaveHandlers.get(leaving);
+        if (onLeave) onLeave();
+    }
     for (const v of VIEWS) {
         const el = document.getElementById(`view-${v}`);
         if (el) {
@@ -431,10 +448,12 @@ function flashCopyFeedback(el) {
 }
 
 module.exports = {
+    VIEWS,
     $,
     showError,
     hideError,
     showView,
+    onViewLeave,
     updateDebugBanner,
     setRenderMain,
     pushCurrentView,

src/popup/views/settings.js

@@ -14,6 +14,8 @@ const { NETWORKS, SUPPORTED_CHAIN_IDS } = require("../../shared/networks");
 const { onChainSwitch } = require("../../shared/chainSwitch");
 const { log, debugFetch, setRuntimeDebug } = require("../../shared/log");
 const deleteWallet = require("./deleteWallet");
+const showPhrase = require("./showPhrase");
+const { walletHasRecoveryPhrase } = require("../../shared/wallet");
 const {
     BUILD_VERSION,
     BUILD_LICENSE,
@@ -99,7 +101,14 @@ function renderWalletListSettings() {
         const name = escapeHtml(wallet.name || "Wallet " + (idx + 1));
         html += `<div class="flex justify-between items-center text-xs py-1 border-b border-border-light">`;
         html += `<span class="settings-wallet-name cursor-pointer underline decoration-dashed" data-idx="${idx}">${name}</span>`;
+        html += `<span class="flex items-center gap-1 flex-shrink-0">`;
+        // Key and xprv wallets have no recovery phrase, so they are never
+        // offered the action at all.
+        if (walletHasRecoveryPhrase(wallet)) {
+            html += `<button class="btn-show-phrase border border-border px-1 hover:bg-fg hover:text-bg cursor-pointer" data-idx="${idx}" title="Show recovery phrase">[recovery phrase]</button>`;
+        }
         html += `<button class="btn-delete-wallet border border-border px-1 hover:bg-fg hover:text-bg cursor-pointer" data-idx="${idx}">[x]</button>`;
+        html += `</span>`;
         html += `</div>`;
     });
     container.innerHTML = html;
@@ -111,6 +120,15 @@ function renderWalletListSettings() {
         });
     });
 
+    container.querySelectorAll(".btn-show-phrase").forEach((btn) => {
+        btn.addEventListener("click", () => {
+            const idx = parseInt(btn.dataset.idx, 10);
+            // No pushCurrentView() here: showPhrase.show() refuses
+            // non-HD wallets and pushes only when it navigates.
+            showPhrase.show(idx);
+        });
+    });
+
     // Inline rename on click
     container.querySelectorAll(".settings-wallet-name").forEach((span) => {
         span.addEventListener("click", () => {
@@ -191,6 +209,7 @@ function renderSiteLists() {
 
 function init(ctx) {
     deleteWallet.init(ctx);
+    showPhrase.init();
 
     $("btn-save-rpc").addEventListener("click", async () => {
         const url = $("settings-rpc").value.trim();

src/popup/views/showPhrase.js

@@ -0,0 +1,154 @@
+// Recovery phrase display for HD wallets.
+//
+// The phrase is the secret that owns every address in the wallet, so it is
+// handled under four rules:
+//
+//   1. Only an HD wallet reaches this screen (walletHasRecoveryPhrase).
+//   2. Nothing is decrypted, and nothing is written into the DOM, until
+//      decryptWithPassword has accepted the password.
+//   3. Leaving the screen by any path wipes it, via the onViewLeave hook,
+//      and a decrypt still in flight when that happens is discarded
+//      instead of written (revealGeneration).
+//   4. The phrase never reaches the logger. This module deliberately does
+//      not import src/shared/log.js, and the failed-decrypt path reports a
+//      fixed sentence rather than the caught error.
+//
+// The phrase is also never assigned to `state`, so it cannot be persisted
+// to extension storage, and "show-phrase" is excluded from RESTORABLE_VIEWS
+// so the popup can never reopen onto it.
+
+const {
+    $,
+    showView,
+    showFlash,
+    flashCopyFeedback,
+    goBack,
+    onViewLeave,
+    pushCurrentView,
+} = require("./helpers");
+const { state } = require("../../shared/state");
+const { decryptWithPassword } = require("../../shared/vault");
+const { walletHasRecoveryPhrase } = require("../../shared/wallet");
+
+const VIEW = "show-phrase";
+
+let walletIndex = null;
+
+// Bumped by every clear(), which is what leaving the screen runs. reveal()
+// captures it before awaiting the decrypt and refuses to touch the DOM if
+// it has moved: a decrypt still in flight when the screen is left would
+// otherwise write the phrase *after* the wipe, with nothing scheduled to
+// wipe it again, leaving it in the hidden view for the life of the popup.
+let revealGeneration = 0;
+
+// True only if the reveal that captured `generation` is still the live one:
+// the screen has not been left, cleared, or re-entered for another wallet
+// since it started.
+function isCurrentReveal(generation) {
+    return (
+        generation === revealGeneration &&
+        walletIndex !== null &&
+        state.currentView === VIEW
+    );
+}
+
+function fail(message) {
+    $("show-phrase-flash").textContent = message;
+    $("show-phrase-flash").style.visibility = "visible";
+}
+
+// Wipe every trace of the phrase and drop the wallet selection. Safe to
+// call when nothing was ever revealed, and safe to call twice.
+function clear() {
+    walletIndex = null;
+    revealGeneration += 1;
+    $("show-phrase-value").textContent = "";
+    $("show-phrase-password").value = "";
+    $("show-phrase-result").classList.add("hidden");
+    $("show-phrase-password-section").classList.remove("hidden");
+    $("show-phrase-flash").textContent = "";
+    $("show-phrase-flash").style.visibility = "hidden";
+}
+
+function show(walletIdx) {
+    const wallet = state.wallets[walletIdx];
+    if (!walletHasRecoveryPhrase(wallet)) {
+        showFlash("This wallet does not have a recovery phrase.");
+        return;
+    }
+    clear();
+    walletIndex = walletIdx;
+    $("show-phrase-wallet-name").textContent =
+        wallet.name || "Wallet " + (walletIdx + 1);
+    // Pushed here rather than by the caller: this function can return
+    // without navigating, and a push that happened anyway would leave an
+    // entry on the stack that no screen transition matches.
+    pushCurrentView();
+    showView(VIEW);
+}
+
+async function reveal() {
+    const password = $("show-phrase-password").value;
+    if (!password) {
+        fail("Please enter your password.");
+        return;
+    }
+    if (walletIndex === null) {
+        fail("No wallet is selected.");
+        return;
+    }
+    const wallet = state.wallets[walletIndex];
+    if (!walletHasRecoveryPhrase(wallet)) {
+        fail("This wallet does not have a recovery phrase.");
+        return;
+    }
+
+    const btn = $("btn-show-phrase-reveal");
+    btn.disabled = true;
+    btn.classList.add("text-muted");
+    const generation = revealGeneration;
+    try {
+        const phrase = await decryptWithPassword(
+            wallet.encryptedSecret,
+            password,
+        );
+        // The only suspension point in this view, and the only place a
+        // secret is written: if the screen was left while the decrypt ran,
+        // the wipe has already happened and this write must not land.
+        if (!isCurrentReveal(generation)) return;
+        $("show-phrase-password").value = "";
+        $("show-phrase-password-section").classList.add("hidden");
+        $("show-phrase-value").textContent = phrase;
+        $("show-phrase-result").classList.remove("hidden");
+        $("show-phrase-flash").textContent = "";
+        $("show-phrase-flash").style.visibility = "hidden";
+    } catch {
+        if (!isCurrentReveal(generation)) return;
+        // Deliberately not the caught error: the message is fixed so that
+        // nothing derived from the ciphertext or the attempt can surface.
+        fail("That password is not correct. Please try again.");
+    } finally {
+        btn.disabled = false;
+        btn.classList.remove("text-muted");
+    }
+}
+
+function init() {
+    onViewLeave(VIEW, clear);
+
+    $("btn-show-phrase-back").addEventListener("click", () => {
+        goBack();
+    });
+
+    $("btn-show-phrase-reveal").addEventListener("click", reveal);
+
+    $("show-phrase-value").addEventListener("click", () => {
+        const phrase = $("show-phrase-value").textContent;
+        if (!phrase) return;
+        navigator.clipboard.writeText(phrase);
+        showFlash("Copied!");
+        flashCopyFeedback($("show-phrase-value"));
+    });
+}
+
+module.exports = { init, show };

src/shared/txValidation.js

@@ -0,0 +1,171 @@
+// Balance arithmetic for the transaction confirmation screen.
+//
+// Pure: no DOM, no network, no state. Everything is exact integer math on
+// 18-decimal fixed point (wei for ETH), so it can be unit tested directly
+// instead of through the confirmation view. The caller maps the returned
+// codes to the reserved message elements on the screen.
+//
+// Human decimal strings ("1.25") are scaled to 18 decimals for comparison.
+// That scale is independent of a token's own decimals: both the amount and
+// the token balance arrive as human decimal strings, so comparing them at a
+// common scale is exact.
+
+const { parseUnits } = require("ethers");
+
+const SCALE_DECIMALS = 18;
+
+// Whether the asynchronous fee estimate has arrived yet.
+const FEE_PENDING = "pending";
+const FEE_KNOWN = "known";
+const FEE_UNAVAILABLE = "unavailable";
+
+const CODES = {
+    // The amount is not a non-negative number we can do exact arithmetic on.
+    AMOUNT_INVALID: "amount-invalid",
+    // ERC-20: the token amount exceeds the token balance.
+    INSUFFICIENT_TOKEN: "insufficient-token",
+    // ETH: the amount alone already exceeds the ETH balance.
+    INSUFFICIENT_ETH: "insufficient-eth",
+    // ETH: the amount fits, the amount plus the network fee does not.
+    INSUFFICIENT_ETH_WITH_FEE: "insufficient-eth-with-fee",
+    // ERC-20: the token balance covers the transfer, the ETH balance does
+    // not cover the network fee it costs.
+    INSUFFICIENT_ETH_FOR_FEE: "insufficient-eth-for-fee",
+    // The fee estimate has not arrived yet.
+    FEE_PENDING: "fee-pending",
+    // The fee estimate failed. Unknown is never treated as zero.
+    FEE_UNAVAILABLE: "fee-unavailable",
+};
+
+// The fee that must be reserved for a transaction, in wei: the amount the
+// node will require, not the amount the transaction is expected to cost.
+//
+// A send that pins no fee fields is populated by ethers as a type-2
+// (EIP-1559) transaction, and a node validates that against
+// `value + gasLimit * maxFeePerGas`. ethers derives maxFeePerGas as
+// `baseFeePerGas * 2 + maxPriorityFeePerGas`, so reserving `gasPrice`
+// (roughly `baseFee + tip`) under-reserves by about `gasLimit * baseFee` and
+// lets through a transaction the node then rejects with "insufficient funds
+// for gas * price + value". gasPrice is the fallback only for a network that
+// offers no type-2 pricing at all.
+//
+// Returns null when no usable price is available, which the caller must treat
+// as a failed estimate rather than as a free transaction.
+function feeReserveWei(gasLimit, feeData) {
+    if (typeof gasLimit !== "bigint" || gasLimit < 0n) return null;
+    const price = feeData?.maxFeePerGas ?? feeData?.gasPrice;
+    if (typeof price !== "bigint" || price < 0n) return null;
+    return gasLimit * price;
+}
+
+// What the transaction is expected to actually cost, in wei — not what must
+// be reserved for it. A type-2 transaction is charged `baseFee + tip` per gas
+// and refunded the rest of the cap, and `eth_gasPrice` reports roughly that,
+// so gasPrice is the estimate and maxFeePerGas is the reserve. On a network
+// with no type-2 pricing the two are the same number.
+//
+// Display only: nothing gates on this. Returns null on the same unusable
+// inputs as feeReserveWei().
+function feeEstimateWei(gasLimit, feeData) {
+    if (typeof gasLimit !== "bigint" || gasLimit < 0n) return null;
+    const price = feeData?.gasPrice ?? feeData?.maxFeePerGas;
+    if (typeof price !== "bigint" || price < 0n) return null;
+    return gasLimit * price;
+}
+
+// Scale a human decimal string to 18-decimal fixed point. Returns null when
+// the value is not a decimal number or carries more precision than the scale
+// can hold, which the caller must treat as unusable rather than as zero.
+function toFixedPoint(value) {
+    if (typeof value !== "string" && typeof value !== "number") return null;
+    const text = String(value).trim();
+    if (text === "") return null;
+    try {
+        return parseUnits(text, SCALE_DECIMALS);
+    } catch (e) {
+        return null;
+    }
+}
+
+// Validate a pending transfer against the balances that must cover it.
+//
+//   isErc20      — token transfer rather than a native ETH transfer
+//   amount       — human decimal string being sent, non-negative. Anything
+//                  else, a negative value included, is an unusable amount
+//                  rather than an amount that passes every comparison.
+//   ethBalance   — human decimal string, the sender's ETH balance
+//   tokenBalance — human decimal string, the sender's token balance
+//   feeStatus    — FEE_PENDING, FEE_KNOWN or FEE_UNAVAILABLE. Anything else
+//                  is treated as FEE_UNAVAILABLE.
+//   feeWei       — the fee reserve in wei from feeReserveWei(), as a
+//                  non-negative bigint, when FEE_KNOWN. Any other value makes
+//                  the fee unavailable rather than zero.
+//
+// Returns { canSend, codes }. Every code blocks sending: canSend is true
+// only when nothing was found.
+function validateTransfer({
+    isErc20 = false,
+    amount,
+    ethBalance,
+    tokenBalance,
+    feeStatus = FEE_PENDING,
+    feeWei = null,
+} = {}) {
+    const codes = [];
+
+    const amountFp = toFixedPoint(amount);
+    const ethFp = toFixedPoint(ethBalance) ?? 0n;
+
+    // A negative amount parses to a valid bigint, so every comparison below
+    // is trivially false and the send clears the screen — then dies at encode
+    // time in parseEther(). Unusable, on the same footing as a malformed fee.
+    if (amountFp === null || amountFp < 0n) {
+        codes.push(CODES.AMOUNT_INVALID);
+        return { canSend: false, codes };
+    }
+
+    // Fail closed. Anything that is not a usable fee under a recognised
+    // status — a malformed feeWei, or a status this module does not know —
+    // is an unavailable estimate, never a fee of zero. Every such input errs
+    // in the direction that lets money out, so none of them is trusted.
+    const known =
+        feeStatus === FEE_KNOWN && typeof feeWei === "bigint" && feeWei >= 0n;
+    let status = feeStatus;
+    if (feeStatus === FEE_KNOWN && !known) status = FEE_UNAVAILABLE;
+    if (status !== FEE_KNOWN && status !== FEE_PENDING) {
+        status = FEE_UNAVAILABLE;
+    }
+
+    const feeFp = known ? feeWei : null;
+
+    if (isErc20) {
+        const tokenFp = toFixedPoint(tokenBalance) ?? 0n;
+        if (amountFp > tokenFp) codes.push(CODES.INSUFFICIENT_TOKEN);
+        if (feeFp !== null && feeFp > ethFp) {
+            codes.push(CODES.INSUFFICIENT_ETH_FOR_FEE);
+        }
+    } else if (amountFp > ethFp) {
+        codes.push(CODES.INSUFFICIENT_ETH);
+    } else if (feeFp !== null && amountFp + feeFp > ethFp) {
+        codes.push(CODES.INSUFFICIENT_ETH_WITH_FEE);
+    }
+
+    // An unknown fee is never assumed to be zero: sending stays blocked
+    // until the estimate arrives, and stays blocked if it never does.
+    if (status === FEE_PENDING) codes.push(CODES.FEE_PENDING);
+    if (status === FEE_UNAVAILABLE) codes.push(CODES.FEE_UNAVAILABLE);
+
+    return { canSend: codes.length === 0, codes };
+}
+
+module.exports = {
+    CODES,
+    FEE_PENDING,
+    FEE_KNOWN,
+    FEE_UNAVAILABLE,
+    SCALE_DECIMALS,
+    feeReserveWei,
+    feeEstimateWei,
+    toFixedPoint,
+    validateTransfer,
+};

src/shared/wallet.js

@@ -16,8 +16,60 @@ function generateMnemonic() {
     return m.phrase;
 }
 
+// Every extended key (xprv or xpub) entering the app goes through this.
+//
+// ethers' HDNodeWallet.fromExtendedKey does NOT verify the base58 checksum
+// when the decoded payload is the usual 82 bytes, which is exactly the case
+// the checksum exists to catch: a key with a one-character typo parses into a
+// *different* wallet instead of being rejected. Re-encoding the parsed node
+// reproduces a well-formed key byte for byte, checksum included, so comparing
+// the round trip against the input rejects any altered character. Measured by
+// the sweep in tests/wallet.test.js over every single-character substitution
+// of the BIP-32 vector 1 master key: 199 parse without the round-trip
+// comparison, 0 with it.
+//
+// Returns the parsed node, or null if the key is not a well-formed extended
+// key. Callers turn null into a user-facing error; none of them may fall back
+// to fromExtendedKey directly.
+function parseExtendedKey(key) {
+    if (typeof key !== "string") return null;
+    try {
+        const node = HDNodeWallet.fromExtendedKey(key);
+        return node.extendedKey === key ? node : null;
+    } catch {
+        return null;
+    }
+}
+
+// A master key is at depth 0. Only from there is BIP44_ETH_PATH the absolute
+// path it names; deriving it under an account-level or child key yields
+// addresses that correspond to nothing the user holds.
+const MASTER_DEPTH = 0;
+
+// Parse an extended private key that the BIP-44 Ethereum account path can be
+// derived from, or throw. Both callers derive BIP44_ETH_PATH from the result.
+function masterXprvOrThrow(key) {
+    const node = parseExtendedKey(key);
+    if (!node) {
+        throw new Error("Not a valid extended private key (xprv).");
+    }
+    if (!node.privateKey) {
+        throw new Error("Not an extended private key (xprv).");
+    }
+    if (node.depth !== MASTER_DEPTH) {
+        throw new Error(
+            "Not a master extended private key (xprv): an account-level or " +
+                "child key cannot be imported.",
+        );
+    }
+    return node;
+}
+
 function deriveAddressFromXpub(xpub, index) {
-    const node = HDNodeWallet.fromExtendedKey(xpub);
+    const node = parseExtendedKey(xpub);
+    if (!node) {
+        throw new Error("Not a valid extended key.");
+    }
     return node.deriveChild(index).address;
 }
 
@@ -29,23 +81,28 @@ function hdWalletFromMnemonic(mnemonic) {
 }
 
 function hdWalletFromXprv(xprv) {
-    const root = HDNodeWallet.fromExtendedKey(xprv);
-    if (!root.privateKey) {
-        throw new Error("Not an extended private key (xprv).");
-    }
-    const node = root.derivePath("44'/60'/0'/0");
+    // BIP44_ETH_PATH is absolute ("m/..."), which ethers will only derive from
+    // a depth-0 node. The relative form this used to derive would have been
+    // applied *beneath* an account-level key instead of being refused.
+    const node = masterXprvOrThrow(xprv).derivePath(BIP44_ETH_PATH);
     const xpub = node.neuter().extendedKey;
     const firstAddress = node.deriveChild(0).address;
     return { xpub, firstAddress };
 }
 
+// Well-formed extended private key. Says nothing about depth: the import view
+// reports a non-master key separately, since "check it for a typo" is the
+// wrong advice for a key the user copied correctly.
 function isValidXprv(key) {
-    try {
-        const node = HDNodeWallet.fromExtendedKey(key);
-        return !!node.privateKey;
-    } catch {
-        return false;
-    }
+    const node = parseExtendedKey(key);
+    return !!(node && node.privateKey);
+}
+
+// Whether an extended key is a master key, i.e. the one BIP44_ETH_PATH can be
+// derived from. False for anything parseExtendedKey rejects.
+function isMasterExtendedKey(key) {
+    const node = parseExtendedKey(key);
+    return !!node && node.depth === MASTER_DEPTH;
 }
 
 function addressFromPrivateKey(key) {
@@ -63,8 +120,8 @@ function getSignerForAddress(walletData, addrIndex, decryptedSecret) {
         return node.deriveChild(addrIndex);
     }
     if (walletData.type === "xprv") {
-        const root = HDNodeWallet.fromExtendedKey(decryptedSecret);
-        const node = root.derivePath("44'/60'/0'/0");
+        const node =
+            masterXprvOrThrow(decryptedSecret).derivePath(BIP44_ETH_PATH);
         return node.deriveChild(addrIndex);
     }
     return new Wallet(decryptedSecret);
@@ -74,13 +131,24 @@ function isValidMnemonic(mnemonic) {
     return Mnemonic.isValidMnemonic(mnemonic);
 }
 
+// Only an HD wallet has a recovery phrase. A "key" wallet holds a bare
+// private key and an "xprv" wallet an extended private key; neither can be
+// turned back into words, so neither may ever be offered the phrase display.
+// Written as an allowlist on purpose: a wallet type added later is excluded
+// until someone decides otherwise.
+function walletHasRecoveryPhrase(walletData) {
+    return !!walletData && walletData.type === "hd";
+}
+
 module.exports = {
     generateMnemonic,
     deriveAddressFromXpub,
     hdWalletFromMnemonic,
     hdWalletFromXprv,
     isValidXprv,
+    isMasterExtendedKey,
     addressFromPrivateKey,
     getSignerForAddress,
     isValidMnemonic,
+    walletHasRecoveryPhrase,
 };

tests/e2e/harness.js

@@ -255,6 +255,11 @@ async function openPopup(ctx, popupUrl) {
 
 // Full wallet creation through the real UI: BIP-39 generation, libsodium
 // vault encryption and extension storage persistence, for real.
+//
+// Returns the recovery phrase it generated. Tests that assert on a secret
+// need the real value — checking for "some 12 words" would pass against the
+// wrong wallet's phrase, and checking for nothing at all would pass against
+// a screen that shows the phrase it was supposed to hide.
 async function createWallet(page) {
     await page.click("#btn-welcome-add");
     await visible(page, "#view-add-wallet");
@@ -263,10 +268,12 @@ async function createWallet(page) {
         const el = document.getElementById("wallet-mnemonic");
         return el && el.value.trim().split(/\s+/).length >= 12;
     });
+    const phrase = (await page.inputValue("#wallet-mnemonic")).trim();
     await page.fill("#add-wallet-password", PASSWORD);
     await page.fill("#add-wallet-password-confirm", PASSWORD);
     await page.click("#btn-add-wallet-confirm");
     await visible(page, "#view-main", 60000);
+    return phrase;
 }
 
 // Reach the address detail screen from wherever the popup restored to.
@@ -281,6 +288,7 @@ async function openAddressDetail(page) {
 }
 
 module.exports = {
+    PASSWORD,
     createWallet,
     launch,
     openAddressDetail,

tests/e2e/run.js

@@ -10,6 +10,7 @@
 "use strict";
 
 const {
+    PASSWORD,
     createWallet,
     launch,
     openAddressDetail,
@@ -34,6 +35,10 @@ function assert(cond, message) {
     if (!cond) throw new Error(message);
 }
 
+function sleep(ms) {
+    return new Promise((resolve) => setTimeout(resolve, ms));
+}
+
 function withTimeout(promise, name) {
     let timer;
     const timeout = new Promise((_, reject) => {
@@ -56,7 +61,11 @@ test("popup loads and reaches the welcome view", async (env) => {
 });
 
 test("wallet creation through the UI reaches the main view", async (env) => {
-    await createWallet(env.page);
+    env.phrase = await createWallet(env.page);
+    assert(
+        env.phrase.split(/\s+/).length >= 12,
+        "wallet creation did not yield a recovery phrase",
+    );
     const addrCount = await env.page
         .locator("#wallet-list .btn-addr-info")
         .count();
@@ -117,6 +126,256 @@ test("transaction detail renders an ERC-20 transfer (#151)", async (env) => {
     assert(dots > 0, "token contract row rendered without its colour dot");
 });
 
+// -------------------------------------------- recovery phrase (#161)
+
+// The gear toggles, so pressing it while Settings is already up leaves it.
+async function openSettings(page) {
+    if (!(await page.isVisible("#view-settings"))) {
+        await page.click("#btn-settings");
+    }
+    await visible(page, "#view-settings");
+}
+
+// Everything the recovery phrase screen is holding, read straight out of
+// the DOM whether or not that screen is the one on top. Reading it while it
+// is hidden is the point: "cleared on leave" means the node is empty, not
+// merely off-screen.
+async function phraseScreenState(page) {
+    return page.evaluate(() => ({
+        value: document.getElementById("show-phrase-value").textContent,
+        error: document.getElementById("show-phrase-flash").textContent,
+        html: document.getElementById("view-show-phrase").innerHTML,
+        resultHidden: document
+            .getElementById("show-phrase-result")
+            .classList.contains("hidden"),
+        viewHidden: document
+            .getElementById("view-show-phrase")
+            .classList.contains("hidden"),
+    }));
+}
+
+async function openPhraseScreen(page) {
+    await openSettings(page);
+    await page.click("#settings-wallet-list .btn-show-phrase");
+    await visible(page, "#view-show-phrase");
+}
+
+async function revealPhrase(page) {
+    await page.fill("#show-phrase-password", PASSWORD);
+    await page.click("#btn-show-phrase-reveal");
+    await visible(page, "#show-phrase-result", 60000);
+}
+
+function assertWiped(st, phrase, where) {
+    assert(st.value === "", "phrase still in the DOM " + where);
+    assert(st.resultHidden, "result section still shown " + where);
+    assert(
+        !st.html.includes(phrase),
+        "the recovery phrase is still somewhere in the screen markup " + where,
+    );
+}
+
+test("only an HD wallet is offered the recovery phrase action (#161)", async (env) => {
+    await openSettings(env.page);
+    const offered = await env.page
+        .locator("#settings-wallet-list .btn-show-phrase")
+        .count();
+    const wallets = await env.page
+        .locator("#settings-wallet-list .btn-delete-wallet")
+        .count();
+    assert(wallets === 1, "expected exactly one wallet row, got " + wallets);
+    assert(
+        offered === 1,
+        "the HD wallet was not offered the recovery phrase action",
+    );
+});
+
+// The other half of the gate, against the real UI: a wallet holding a bare
+// private key has no phrase to show, so no row of it may offer the action.
+// The key is generated here rather than committed — the repo holds no
+// private keys, test ones included.
+test("a key wallet is not offered the recovery phrase action (#161)", async (env) => {
+    const { Wallet } = require("ethers");
+
+    await openSettings(env.page);
+    await env.page.click("#btn-main-add-wallet");
+    await visible(env.page, "#view-add-wallet");
+    await env.page.click("#tab-privkey");
+    await env.page.fill(
+        "#import-private-key",
+        Wallet.createRandom().privateKey,
+    );
+    await env.page.fill("#add-wallet-password", PASSWORD);
+    await env.page.fill("#add-wallet-password-confirm", PASSWORD);
+    await env.page.click("#btn-add-wallet-confirm");
+    await visible(env.page, "#view-main", 60000);
+
+    await openSettings(env.page);
+    const wallets = await env.page
+        .locator("#settings-wallet-list .btn-delete-wallet")
+        .count();
+    const offered = await env.page
+        .locator("#settings-wallet-list .btn-show-phrase")
+        .count();
+    assert(wallets === 2, "expected two wallet rows, got " + wallets);
+    assert(
+        offered === 1,
+        "the key wallet was offered the recovery phrase action",
+    );
+});
+
+test("the recovery phrase screen holds nothing before the password (#161)", async (env) => {
+    await openPhraseScreen(env.page);
+    const st = await phraseScreenState(env.page);
+    assertWiped(st, env.phrase, "before any password was entered");
+    const passwordShown = await env.page.isVisible(
+        "#show-phrase-password-section",
+    );
+    assert(passwordShown, "the password prompt is not shown");
+});
+
+test("a wrong password reveals nothing (#161)", async (env) => {
+    await env.page.fill("#show-phrase-password", "not-the-password");
+    await env.page.click("#btn-show-phrase-reveal");
+    await env.page.waitForFunction(
+        () =>
+            document.getElementById("show-phrase-flash").textContent.length > 0,
+        null,
+        { timeout: 60000 },
+    );
+
+    const st = await phraseScreenState(env.page);
+    assertWiped(st, env.phrase, "after a wrong password");
+    assert(
+        /^[A-Z].*\.$/.test(st.error.trim()),
+        "the wrong-password error is not a full sentence: " +
+            JSON.stringify(st.error),
+    );
+});
+
+test("the correct password reveals the full phrase, and nothing logs it (#161)", async (env) => {
+    const console_ = [];
+    const listener = (msg) => console_.push(msg.text());
+    env.page.on("console", listener);
+    try {
+        await revealPhrase(env.page);
+
+        const st = await phraseScreenState(env.page);
+        assert(
+            st.value === env.phrase,
+            "the displayed phrase is not the wallet's phrase, verbatim",
+        );
+        const promptShown = await env.page.isVisible(
+            "#show-phrase-password-section",
+        );
+        assert(!promptShown, "the password prompt is still shown after unlock");
+
+        // Full Identifiers Policy: shown whole, and copyable.
+        const title = await env.page.getAttribute(
+            "#show-phrase-value",
+            "title",
+        );
+        assert(title === "Click to copy", "the phrase is not click-to-copy");
+
+        const leaked = console_.filter((line) => line.includes(env.phrase));
+        assert(
+            leaked.length === 0,
+            "the recovery phrase reached the console: " +
+                JSON.stringify(leaked),
+        );
+    } finally {
+        env.page.off("console", listener);
+    }
+});
+
+test('"Back" wipes the revealed phrase (#161)', async (env) => {
+    await env.page.click("#btn-show-phrase-back");
+    await visible(env.page, "#view-settings");
+    const st = await phraseScreenState(env.page);
+    assert(st.viewHidden, "the recovery phrase screen is still on top");
+    assertWiped(st, env.phrase, "after Back");
+});
+
+// The settings gear leaves the screen without touching its Back button. A
+// clear wired only to Back would pass the test above and leak here.
+test("leaving by the settings gear wipes it too (#161)", async (env) => {
+    await openPhraseScreen(env.page);
+    await revealPhrase(env.page);
+    await env.page.click("#btn-settings");
+    await visible(env.page, "#view-settings");
+    const st = await phraseScreenState(env.page);
+    assertWiped(st, env.phrase, "after leaving via the settings gear");
+});
+
+// The same leave, but taken while the decrypt is still running. Both
+// clicks are dispatched inside one page task on purpose: "Reveal" runs its
+// handler up to the await, the gear then runs the leave — and the wipe with
+// it — to completion, and the decrypt's continuation resumes afterwards.
+// Without a liveness check that continuation writes the phrase into the
+// hidden screen after the wipe, and nothing is left to wipe it again.
+//
+// A human cannot produce this interleaving by hand once libsodium's wasm is
+// warm, because crypto_pwhash is synchronous and the only suspension point
+// is a microtask; the window a user can actually hit is a still-pending
+// sodium.ready on the first vault use of a page load. Forcing it here is
+// the only way to test the guard deterministically.
+test("leaving while the decrypt is in flight reveals nothing (#161)", async (env) => {
+    await openPhraseScreen(env.page);
+    await env.page.fill("#show-phrase-password", PASSWORD);
+    await env.page.evaluate(() => {
+        document.getElementById("btn-show-phrase-reveal").click();
+        document.getElementById("btn-settings").click();
+    });
+    await visible(env.page, "#view-settings");
+
+    // The Reveal button is disabled for exactly the duration of the
+    // decrypt and re-enabled in the same continuation that would have
+    // written the phrase, so waiting for it to come back is a precise
+    // "the decrypt has settled and its handler has finished" signal
+    // rather than a guess at a duration.
+    await env.page.waitForFunction(
+        () => !document.getElementById("btn-show-phrase-reveal").disabled,
+        null,
+        { timeout: 60000 },
+    );
+    await sleep(2000);
+
+    const st = await phraseScreenState(env.page);
+    // Printed on every run, pass or fail: "the phrase is not there" is
+    // worth more as a measurement than as a silent assertion, and the
+    // same line read from a build without the guard is what this test
+    // exists to prevent.
+    console.log(
+        "# probe: len=" +
+            st.value.length +
+            " equalsPhrase=" +
+            (st.value === env.phrase) +
+            " resultHidden=" +
+            st.resultHidden +
+            " viewHidden=" +
+            st.viewHidden,
+    );
+    assert(st.viewHidden, "the recovery phrase screen is still on top");
+    assertWiped(st, env.phrase, "after leaving mid-decrypt");
+});
+
+// Closing and reopening the page rather than reloading it: that is what
+// the toolbar popup actually does, and the persisted currentView is
+// "show-phrase" at the moment it happens, which is precisely the state
+// RESTORABLE_VIEWS has to refuse.
+test("reopening the popup never lands on the phrase screen (#161)", async (env) => {
+    await openPhraseScreen(env.page);
+    await revealPhrase(env.page);
+
+    await env.page.close();
+    env.page = await openPopup(env.ctx, env.popupUrl);
+    await visible(env.page, "#view-main");
+
+    const st = await phraseScreenState(env.page);
+    assert(st.viewHidden, "the popup reopened onto the recovery phrase screen");
+    assertWiped(st, env.phrase, "after reopening the popup");
+});
+
 // ---------------------------------------------------------------- runner
 
 async function main() {
@@ -154,6 +413,9 @@ async function main() {
         popupUrl: session.popupUrl,
         routeOpts,
         page: null,
+        // The recovery phrase of the wallet created in test 2, so later
+        // tests can assert on the real secret rather than its shape.
+        phrase: null,
     };
 
     // Attribution of collected errors is total. session.errors has no

tests/settingsUtcTimestamps.test.js

@@ -0,0 +1,111 @@
+// Tests for the UTC Timestamps setting.
+//
+// The checkbox was moved out of the Token Spam Protection well and into the
+// Display well next to the theme selector.  It is wired by id through the $()
+// helper, so the move cannot break the handler — but nothing in the suite said
+// so.  These tests pin both halves down: the markup lives in Display and
+// nowhere else, and the value still round-trips through storage.
+
+const fs = require("fs");
+const path = require("path");
+
+const POPUP_HTML = fs.readFileSync(
+    path.join(__dirname, "..", "src", "popup", "index.html"),
+    "utf8",
+);
+
+// The body of one `<div class="bg-well ...">` well, selected by its heading.
+function wellWithHeading(html, heading) {
+    const headingIndex = html.indexOf(
+        '<h3 class="font-bold mb-1">' + heading + "</h3>",
+    );
+    expect(headingIndex).toBeGreaterThan(-1);
+    const start = html.lastIndexOf('<div class="bg-well', headingIndex);
+    const end = html.indexOf('<div class="bg-well', headingIndex);
+    return html.slice(start, end === -1 ? html.length : end);
+}
+
+describe("the UTC Timestamps checkbox placement", () => {
+    test("the checkbox appears exactly once in the popup markup", () => {
+        const matches = POPUP_HTML.match(/id="settings-utc-timestamps"/g);
+        expect(matches).toHaveLength(1);
+    });
+
+    test("it renders in the Display well, alongside the theme selector", () => {
+        const display = wellWithHeading(POPUP_HTML, "Display");
+
+        expect(display).toContain('id="settings-utc-timestamps"');
+        expect(display).toContain('id="settings-theme"');
+    });
+
+    test("it does not render in the Token Spam Protection well", () => {
+        const spam = wellWithHeading(POPUP_HTML, "Token Spam Protection");
+
+        expect(spam).not.toContain('id="settings-utc-timestamps"');
+        // The filters that do belong there are untouched.
+        expect(spam).toContain('id="settings-hide-low-holders"');
+        expect(spam).toContain('id="settings-hide-fraud-contracts"');
+        expect(spam).toContain('id="settings-hide-dust"');
+        expect(spam).toContain('id="settings-dust-threshold"');
+    });
+});
+
+describe("the UTC Timestamps setting round-trips through storage", () => {
+    let store;
+
+    function loadStateModule() {
+        store = {};
+        global.chrome = {
+            storage: {
+                local: {
+                    get: async (key) =>
+                        key in store ? { [key]: store[key] } : {},
+                    set: async (obj) => Object.assign(store, obj),
+                },
+            },
+        };
+        jest.resetModules();
+        return require("../src/shared/state");
+    }
+
+    afterEach(() => {
+        delete global.chrome;
+    });
+
+    test("defaults to off with nothing persisted", async () => {
+        const { state, loadState } = loadStateModule();
+
+        await loadState();
+
+        expect(state.utcTimestamps).toBe(false);
+    });
+
+    test("an enabled checkbox is persisted and read back", async () => {
+        const first = loadStateModule();
+
+        // What the change handler in views/settings.js does.
+        first.state.utcTimestamps = true;
+        await first.saveState();
+        expect(store.autistmask.utcTimestamps).toBe(true);
+
+        // A fresh popup load sees it.
+        jest.resetModules();
+        const second = require("../src/shared/state");
+        expect(second.state.utcTimestamps).toBe(false);
+        await second.loadState();
+        expect(second.state.utcTimestamps).toBe(true);
+    });
+
+    test("turning it back off is persisted too", async () => {
+        const { state, saveState, loadState } = loadStateModule();
+
+        state.utcTimestamps = true;
+        await saveState();
+        state.utcTimestamps = false;
+        await saveState();
+
+        state.utcTimestamps = true;
+        await loadState();
+        expect(state.utcTimestamps).toBe(false);
+    });
+});

tests/showPhrase.test.js

@@ -0,0 +1,94 @@
+// Tests for the recovery phrase display (issue #161).
+//
+// These cover the parts that do not need a DOM: which wallet types may be
+// offered the action at all, the exclusion of the screen from the set of
+// views the popup may reopen onto, and the absence of any path from this
+// module to the logger. The DOM behaviour it guards — nothing rendered
+// before the password is accepted, a wrong password revealing nothing, and
+// the wipe on leaving — is driven against the real popup in a real browser
+// by tests/e2e/run.js, which is where every other view behaviour is tested.
+
+const fs = require("fs");
+const path = require("path");
+
+const { walletHasRecoveryPhrase } = require("../src/shared/wallet");
+const { RESTORABLE_VIEWS } = require("../src/popup/restorableViews");
+
+const SHOW_PHRASE_VIEW = "show-phrase";
+
+// helpers.js pulls in state.js, which reads chrome.storage.local at load.
+function loadHelpers() {
+    globalThis.chrome = {
+        storage: { local: { get: async () => ({}), set: async () => {} } },
+    };
+    return require("../src/popup/views/helpers");
+}
+
+describe("which wallets have a recovery phrase", () => {
+    test("an HD wallet does", () => {
+        expect(walletHasRecoveryPhrase({ type: "hd" })).toBe(true);
+    });
+
+    // A key wallet holds a bare private key and an xprv wallet an extended
+    // private key. Neither can be turned back into words, so neither may be
+    // offered the action.
+    test("a key wallet does not", () => {
+        expect(walletHasRecoveryPhrase({ type: "key" })).toBe(false);
+    });
+
+    test("an xprv wallet does not", () => {
+        expect(walletHasRecoveryPhrase({ type: "xprv" })).toBe(false);
+    });
+
+    test("an unknown or missing wallet type does not", () => {
+        expect(walletHasRecoveryPhrase({ type: "something-new" })).toBe(false);
+        expect(walletHasRecoveryPhrase({})).toBe(false);
+        expect(walletHasRecoveryPhrase(undefined)).toBe(false);
+    });
+});
+
+describe("views the popup may reopen onto", () => {
+    // Restoring onto a secret screen would put the phrase on screen with no
+    // password prompt in front of it, on a popup the user may have reopened
+    // by accident.
+    test("the recovery phrase screen is not restorable", () => {
+        expect(RESTORABLE_VIEWS.has(SHOW_PHRASE_VIEW)).toBe(false);
+    });
+
+    test("the private key export screen is not restorable either", () => {
+        expect(RESTORABLE_VIEWS.has("export-privkey")).toBe(false);
+    });
+
+    test("the recovery phrase screen is still a registered view", () => {
+        const { VIEWS } = loadHelpers();
+        expect(VIEWS).toContain(SHOW_PHRASE_VIEW);
+    });
+
+    // Guards the other direction: a restorable name that is not a real view
+    // would leave restoreView() showing nothing at all.
+    test("every restorable view is a registered view", () => {
+        const { VIEWS } = loadHelpers();
+        for (const view of RESTORABLE_VIEWS) {
+            expect(VIEWS).toContain(view);
+        }
+    });
+});
+
+describe("the phrase cannot reach the logger", () => {
+    const source = fs.readFileSync(
+        path.join(__dirname, "..", "src", "popup", "views", "showPhrase.js"),
+        "utf8",
+    );
+
+    // The decrypted phrase only ever lives in a local and in the DOM node
+    // that displays it. The module has no logger to hand it to, and this
+    // pins that: src/shared/log.js writes to the console, and a console
+    // record of a recovery phrase outlives the popup.
+    test("the view does not import src/shared/log.js", () => {
+        expect(source).not.toMatch(/require\(["'][^"']*shared\/log["']\)/);
+    });
+
+    test("the view calls no logger method", () => {
+        expect(source).not.toMatch(/\blog\.(debugf|infof|warnf|errorf)\b/);
+    });
+});

tests/txValidation.test.js

@@ -0,0 +1,357 @@
+const { parseEther } = require("ethers");
+const {
+    CODES,
+    FEE_PENDING,
+    FEE_KNOWN,
+    FEE_UNAVAILABLE,
+    feeReserveWei,
+    feeEstimateWei,
+    toFixedPoint,
+    validateTransfer,
+} = require("../src/shared/txValidation");
+
+// A plausible mainnet fee: 21000 gas at 20 gwei.
+const FEE = 21000n * 20000000000n; // 0.00042 ETH
+
+const GWEI = 1000000000n;
+const GAS_LIMIT = 21000n;
+
+describe("toFixedPoint", () => {
+    test("scales human decimals to 18 places", () => {
+        expect(toFixedPoint("1.5")).toBe(parseEther("1.5"));
+        expect(toFixedPoint("0")).toBe(0n);
+    });
+
+    test("rejects values it cannot represent exactly", () => {
+        expect(toFixedPoint("not a number")).toBe(null);
+        expect(toFixedPoint("")).toBe(null);
+        expect(toFixedPoint(null)).toBe(null);
+        // More precision than 18 decimals can hold.
+        expect(toFixedPoint("0.0000000000000000001")).toBe(null);
+    });
+});
+
+describe("validateTransfer, native ETH", () => {
+    const eth = (over) => ({
+        isErc20: false,
+        amount: "0.5",
+        ethBalance: "1.0",
+        feeStatus: FEE_KNOWN,
+        feeWei: FEE,
+        ...over,
+    });
+
+    test("allows a send comfortably within balance", () => {
+        const r = validateTransfer(eth());
+        expect(r).toEqual({ canSend: true, codes: [] });
+    });
+
+    test("blocks a send whose amount plus fee exceeds the balance", () => {
+        // The whole balance: passes an amount-only check, fails once the fee
+        // is counted. This is the bug this module exists to prevent.
+        const r = validateTransfer(eth({ amount: "1.0", ethBalance: "1.0" }));
+        expect(r.canSend).toBe(false);
+        expect(r.codes).toEqual([CODES.INSUFFICIENT_ETH_WITH_FEE]);
+    });
+
+    test("blocks a send left short by less than one fee", () => {
+        const balance = "1.0";
+        // One wei less headroom than the fee needs.
+        const amount = "0.99958000000000001"; // 1.0 - 0.00042 + 1e-17
+        const r = validateTransfer(eth({ amount, ethBalance: balance }));
+        expect(r.codes).toEqual([CODES.INSUFFICIENT_ETH_WITH_FEE]);
+    });
+
+    test("allows a send that leaves exactly the fee behind", () => {
+        const r = validateTransfer(
+            eth({ amount: "0.99958", ethBalance: "1.0" }),
+        );
+        expect(r).toEqual({ canSend: true, codes: [] });
+    });
+
+    test("reports plain insufficient balance when the amount alone is too big", () => {
+        const r = validateTransfer(eth({ amount: "2.0", ethBalance: "1.0" }));
+        expect(r.codes).toEqual([CODES.INSUFFICIENT_ETH]);
+    });
+
+    test("blocks while the fee estimate is still pending", () => {
+        const r = validateTransfer(
+            eth({ feeStatus: FEE_PENDING, feeWei: null }),
+        );
+        expect(r.canSend).toBe(false);
+        expect(r.codes).toEqual([CODES.FEE_PENDING]);
+    });
+
+    test("blocks when the fee estimate failed, without assuming zero", () => {
+        const r = validateTransfer(
+            eth({
+                amount: "1.0",
+                ethBalance: "1.0",
+                feeStatus: FEE_UNAVAILABLE,
+                feeWei: null,
+            }),
+        );
+        expect(r.canSend).toBe(false);
+        expect(r.codes).toEqual([CODES.FEE_UNAVAILABLE]);
+        // A zero fee would have let this exact transfer through.
+        expect(
+            validateTransfer(
+                eth({ amount: "1.0", ethBalance: "1.0", feeWei: 0n }),
+            ).canSend,
+        ).toBe(true);
+    });
+
+    test("still reports an over-balance amount before the estimate lands", () => {
+        const r = validateTransfer(
+            eth({
+                amount: "2.0",
+                ethBalance: "1.0",
+                feeStatus: FEE_PENDING,
+                feeWei: null,
+            }),
+        );
+        expect(r.codes).toEqual([CODES.INSUFFICIENT_ETH, CODES.FEE_PENDING]);
+    });
+
+    test("rejects an amount it cannot do exact arithmetic on", () => {
+        const r = validateTransfer(eth({ amount: "abc" }));
+        expect(r.canSend).toBe(false);
+        expect(r.codes).toEqual([CODES.AMOUNT_INVALID]);
+    });
+
+    test("rejects a negative amount", () => {
+        // A negative amount parses to a perfectly good bigint, so neither
+        // balance comparison can fire: both are trivially false against it.
+        // Left unblocked it clears the screen and then dies at encode time.
+        const r = validateTransfer(
+            eth({ amount: "-1", ethBalance: "1.0", feeWei: 861000000000000n }),
+        );
+        expect(r).toEqual({ canSend: false, codes: [CODES.AMOUNT_INVALID] });
+        expect(
+            validateTransfer(eth({ amount: "-0.000000000000000001" })),
+        ).toEqual({ canSend: false, codes: [CODES.AMOUNT_INVALID] });
+    });
+
+    test("treats a missing balance as zero, not as unlimited", () => {
+        const r = validateTransfer(eth({ ethBalance: undefined }));
+        expect(r.codes).toEqual([CODES.INSUFFICIENT_ETH]);
+    });
+});
+
+describe("validateTransfer, ERC-20", () => {
+    const erc20 = (over) => ({
+        isErc20: true,
+        amount: "100.0",
+        tokenBalance: "250.0",
+        ethBalance: "1.0",
+        feeStatus: FEE_KNOWN,
+        feeWei: FEE,
+        ...over,
+    });
+
+    test("allows a transfer with tokens to spend and ETH for the fee", () => {
+        expect(validateTransfer(erc20())).toEqual({ canSend: true, codes: [] });
+    });
+
+    test("checks the token amount against the token balance", () => {
+        const r = validateTransfer(erc20({ amount: "250.000001" }));
+        expect(r.codes).toEqual([CODES.INSUFFICIENT_TOKEN]);
+    });
+
+    test("does not charge the fee against the token balance", () => {
+        // The full token balance is sendable: the fee is paid in ETH.
+        expect(validateTransfer(erc20({ amount: "250.0" })).canSend).toBe(true);
+    });
+
+    test("blocks when the ETH balance does not cover the fee", () => {
+        const r = validateTransfer(erc20({ ethBalance: "0.0001" }));
+        expect(r.canSend).toBe(false);
+        expect(r.codes).toEqual([CODES.INSUFFICIENT_ETH_FOR_FEE]);
+    });
+
+    test("allows a fee exactly equal to the ETH balance", () => {
+        const r = validateTransfer(erc20({ ethBalance: "0.00042" }));
+        expect(r).toEqual({ canSend: true, codes: [] });
+    });
+
+    test("reports both shortfalls when tokens and ETH are both short", () => {
+        const r = validateTransfer(
+            erc20({ amount: "300.0", ethBalance: "0.0" }),
+        );
+        expect(r.codes).toEqual([
+            CODES.INSUFFICIENT_TOKEN,
+            CODES.INSUFFICIENT_ETH_FOR_FEE,
+        ]);
+    });
+
+    test("blocks while the fee estimate is pending or failed", () => {
+        expect(
+            validateTransfer(erc20({ feeStatus: FEE_PENDING, feeWei: null }))
+                .codes,
+        ).toEqual([CODES.FEE_PENDING]);
+        expect(
+            validateTransfer(
+                erc20({ feeStatus: FEE_UNAVAILABLE, feeWei: null }),
+            ).codes,
+        ).toEqual([CODES.FEE_UNAVAILABLE]);
+    });
+
+    test("rejects a negative token amount", () => {
+        const r = validateTransfer(
+            erc20({ amount: "-0.5", feeWei: 861000000000000n }),
+        );
+        expect(r).toEqual({ canSend: false, codes: [CODES.AMOUNT_INVALID] });
+    });
+
+    test("treats a missing token balance as zero", () => {
+        const r = validateTransfer(erc20({ tokenBalance: undefined }));
+        expect(r.codes).toEqual([CODES.INSUFFICIENT_TOKEN]);
+    });
+});
+
+// The reserve a node requires, not the fee the transaction is expected to
+// actually cost. An unpinned send goes out as type-2, and the node checks it
+// against maxFeePerGas; reserving gasPrice lets a transaction the node will
+// reject pass the gate.
+describe("feeReserveWei", () => {
+    // baseFee 20 gwei, tip 1 gwei: eth_gasPrice reports ~21 gwei, while
+    // ethers populates maxFeePerGas as baseFee * 2 + tip = 41 gwei.
+    const type2 = {
+        gasPrice: 21n * GWEI,
+        maxFeePerGas: 41n * GWEI,
+        maxPriorityFeePerGas: 1n * GWEI,
+    };
+
+    test("reserves gasLimit * maxFeePerGas, not gasLimit * gasPrice", () => {
+        expect(feeReserveWei(GAS_LIMIT, type2)).toBe(GAS_LIMIT * 41n * GWEI);
+        expect(feeReserveWei(GAS_LIMIT, type2)).toBe(861000000000000n);
+        // The number the node would not have accepted.
+        expect(feeReserveWei(GAS_LIMIT, type2)).not.toBe(441000000000000n);
+    });
+
+    test("gates out a send the type-2 reserve cannot fund", () => {
+        // Exactly fundable against a gasPrice reserve (0.999559 + 0.000441 is
+        // the whole balance to the wei), and short against the reserve the
+        // node will actually require.
+        const send = {
+            isErc20: false,
+            amount: "0.999559",
+            ethBalance: "1.0",
+            feeStatus: FEE_KNOWN,
+        };
+        expect(
+            validateTransfer({
+                ...send,
+                feeWei: GAS_LIMIT * type2.gasPrice,
+            }).canSend,
+        ).toBe(true);
+        const r = validateTransfer({
+            ...send,
+            feeWei: feeReserveWei(GAS_LIMIT, type2),
+        });
+        expect(r.canSend).toBe(false);
+        expect(r.codes).toEqual([CODES.INSUFFICIENT_ETH_WITH_FEE]);
+    });
+
+    test("falls back to gasPrice on a network with no type-2 pricing", () => {
+        const legacy = { gasPrice: 21n * GWEI, maxFeePerGas: null };
+        expect(feeReserveWei(GAS_LIMIT, legacy)).toBe(GAS_LIMIT * 21n * GWEI);
+    });
+
+    test("returns null when no usable price or gas limit is available", () => {
+        expect(feeReserveWei(GAS_LIMIT, { gasPrice: null })).toBe(null);
+        expect(feeReserveWei(GAS_LIMIT, {})).toBe(null);
+        expect(feeReserveWei(GAS_LIMIT, null)).toBe(null);
+        expect(feeReserveWei(21000, type2)).toBe(null);
+    });
+});
+
+// The display counterpart of the reserve: what the transaction is expected to
+// cost. Shown alongside the reserve so the screen neither contradicts the gate
+// nor quotes the user roughly double what they will pay.
+describe("feeEstimateWei", () => {
+    const type2 = {
+        gasPrice: 21n * GWEI,
+        maxFeePerGas: 41n * GWEI,
+        maxPriorityFeePerGas: 1n * GWEI,
+    };
+
+    test("estimates gasLimit * gasPrice, below the reserve", () => {
+        expect(feeEstimateWei(GAS_LIMIT, type2)).toBe(441000000000000n);
+        expect(feeReserveWei(GAS_LIMIT, type2)).toBe(861000000000000n);
+        expect(feeEstimateWei(GAS_LIMIT, type2)).toBeLessThan(
+            feeReserveWei(GAS_LIMIT, type2),
+        );
+    });
+
+    test("equals the reserve when the network has no type-2 pricing", () => {
+        const legacy = { gasPrice: 21n * GWEI, maxFeePerGas: null };
+        expect(feeEstimateWei(GAS_LIMIT, legacy)).toBe(
+            feeReserveWei(GAS_LIMIT, legacy),
+        );
+    });
+
+    test("falls back to maxFeePerGas when there is no gasPrice", () => {
+        const noLegacy = { gasPrice: null, maxFeePerGas: 41n * GWEI };
+        expect(feeEstimateWei(GAS_LIMIT, noLegacy)).toBe(
+            feeReserveWei(GAS_LIMIT, noLegacy),
+        );
+    });
+
+    test("returns null on the same unusable inputs as the reserve", () => {
+        expect(feeEstimateWei(GAS_LIMIT, {})).toBe(null);
+        expect(feeEstimateWei(GAS_LIMIT, null)).toBe(null);
+        expect(feeEstimateWei(GAS_LIMIT, { gasPrice: -1n })).toBe(null);
+        expect(feeEstimateWei(21000, type2)).toBe(null);
+    });
+});
+
+// Everything that is not a usable fee blocks exactly as FEE_UNAVAILABLE does.
+// Each of these previously returned { canSend: true, codes: [] } — counting no
+// fee at all, on a full-balance send, in the direction that lets money out.
+describe("validateTransfer, unusable fee input fails closed", () => {
+    const fullBalanceSend = (over) => ({
+        isErc20: false,
+        amount: "1.0",
+        ethBalance: "1.0",
+        ...over,
+    });
+
+    test("blocks a null fee claiming to be known", () => {
+        const r = validateTransfer(
+            fullBalanceSend({ feeStatus: FEE_KNOWN, feeWei: null }),
+        );
+        expect(r).toEqual({ canSend: false, codes: [CODES.FEE_UNAVAILABLE] });
+    });
+
+    test("blocks a known fee that is a number rather than a bigint", () => {
+        const r = validateTransfer(
+            fullBalanceSend({ feeStatus: FEE_KNOWN, feeWei: 420000000000000 }),
+        );
+        expect(r).toEqual({ canSend: false, codes: [CODES.FEE_UNAVAILABLE] });
+    });
+
+    test("blocks an unrecognised fee status", () => {
+        const r = validateTransfer(fullBalanceSend({ feeStatus: "bogus" }));
+        expect(r).toEqual({ canSend: false, codes: [CODES.FEE_UNAVAILABLE] });
+    });
+
+    test("blocks a negative fee", () => {
+        const r = validateTransfer(
+            fullBalanceSend({ feeStatus: FEE_KNOWN, feeWei: -1n }),
+        );
+        expect(r).toEqual({ canSend: false, codes: [CODES.FEE_UNAVAILABLE] });
+    });
+
+    test("blocks an ERC-20 transfer on an unusable fee too", () => {
+        const r = validateTransfer({
+            isErc20: true,
+            amount: "100.0",
+            tokenBalance: "250.0",
+            ethBalance: "1.0",
+            feeStatus: FEE_KNOWN,
+            feeWei: null,
+        });
+        expect(r).toEqual({ canSend: false, codes: [CODES.FEE_UNAVAILABLE] });
+    });
+});

tests/wallet.test.js

@@ -160,6 +160,31 @@ function masterXprv(phrase, passphrase = "") {
     ).extendedKey;
 }
 
+// The account-level (depth-3) extended private key m/44'/60'/0' for a phrase.
+// A normal thing for a user to hold, and not something the import flow can
+// derive the BIP-44 account path from.
+function accountXprv(phrase) {
+    return HDNodeWallet.fromSeed(
+        Mnemonic.fromPhrase(phrase, "").computeSeed(),
+    ).derivePath("m/44'/60'/0'").extendedKey;
+}
+
+// Every single-character substitution of `key`, using base58 characters that
+// are not the original. Base58 has no visually ambiguous characters, so each
+// of these is a plausible typo rather than a contrived string.
+const TYPO_CHARS = ["a", "b", "2", "Z"];
+
+function singleCharacterTypos(key) {
+    const out = [];
+    for (let i = 0; i < key.length; i++) {
+        for (const c of TYPO_CHARS) {
+            if (c === key[i]) continue;
+            out.push(key.slice(0, i) + c + key.slice(i + 1));
+        }
+    }
+    return out;
+}
+
 describe("hdWalletFromMnemonic", () => {
     test("first address matches the published vector for m/44'/60'/0'/0/0", () => {
         expect(wallet.hdWalletFromMnemonic(VECTOR_PHRASE).firstAddress).toBe(
@@ -299,19 +324,7 @@ describe("isValidXprv", () => {
         expect(wallet.isValidXprv(xpub)).toBe(false);
     });
 
-    // Skipped: this asserts the correct behaviour, which the code does not
-    // currently have. isValidXprv gates the paste-your-extended-private-key
-    // import in src/popup/views/addWallet.js:215, and it accepts a key with a
-    // one-character typo: ethers' HDNodeWallet.fromExtendedKey skips base58
-    // checksum verification whenever the decoded payload is the usual 82
-    // bytes, which is the whole point of that checksum. Measured on this
-    // vector: changing any one of the last 14 characters passes validation,
-    // and for 9 of those 14 positions the import silently yields a *different*
-    // wallet (e.g. 0x3F334f0a356d6B46B1d70B590E7437D77100d28D instead of
-    // 0x022b971dFF0C43305e691DEd7a14367AF19D6407) with no error shown.
-    // Tracked as https://git.eeqj.de/sneak/AutistMask/issues/210; out of scope
-    // here, which is tests only. Unskip when it is fixed.
-    test.skip("rejects an extended key with a one-character typo", () => {
+    test("rejects an extended key with a one-character typo", () => {
         const index = BIP32_VECTOR_1_XPRV.length - 8;
         const typo =
             BIP32_VECTOR_1_XPRV.slice(0, index) +
@@ -320,6 +333,125 @@ describe("isValidXprv", () => {
 
         expect(wallet.isValidXprv(typo)).toBe(false);
     });
+
+    // The base58 checksum exists to make a mistyped key impossible to use, and
+    // ethers does not enforce it: HDNodeWallet.fromExtendedKey skips checksum
+    // verification whenever the decoded payload is the usual 82 bytes, which
+    // is precisely the case it is there to catch. A typo anywhere in the key
+    // must be refused, not silently turned into someone else's wallet.
+    test("no single-character typo anywhere in the key is accepted", () => {
+        const accepted = singleCharacterTypos(BIP32_VECTOR_1_XPRV).filter(
+            (typo) => wallet.isValidXprv(typo),
+        );
+
+        expect(accepted).toEqual([]);
+    });
+
+    test("a typo never yields a wallet, let alone a different one", () => {
+        const correct = wallet.hdWalletFromXprv(BIP32_VECTOR_1_XPRV);
+        const derived = [];
+        for (const typo of singleCharacterTypos(BIP32_VECTOR_1_XPRV)) {
+            try {
+                derived.push(wallet.hdWalletFromXprv(typo).firstAddress);
+            } catch {
+                // Rejected, which is the required behaviour.
+            }
+        }
+
+        expect(derived).toEqual([]);
+        expect(correct.firstAddress).toBe(
+            "0x022b971dFF0C43305e691DEd7a14367AF19D6407",
+        );
+    });
+});
+
+describe("extended key depth", () => {
+    // hdWalletFromXprv derives the BIP-44 Ethereum account path from the key
+    // it is given. That is only the path it names when the key is the master
+    // key. Under an account-level key the same derivation lands at
+    // m/44'/60'/0'/44'/60'/0'/0, whose addresses correspond to nothing the
+    // user holds, so a non-master key is refused rather than derived from.
+    test("a master key is a master key", () => {
+        expect(wallet.isMasterExtendedKey(masterXprv(VECTOR_PHRASE))).toBe(
+            true,
+        );
+        expect(wallet.isMasterExtendedKey(BIP32_VECTOR_1_XPRV)).toBe(true);
+    });
+
+    test("an account-level key is not a master key", () => {
+        expect(wallet.isMasterExtendedKey(accountXprv(VECTOR_PHRASE))).toBe(
+            false,
+        );
+    });
+
+    test("a derived xpub is not a master key", () => {
+        expect(
+            wallet.isMasterExtendedKey(
+                wallet.hdWalletFromMnemonic(VECTOR_PHRASE).xpub,
+            ),
+        ).toBe(false);
+    });
+
+    test("a mistyped key is not a master key either", () => {
+        expect(wallet.isMasterExtendedKey(BIP32_VECTOR_1_XPRV + "a")).toBe(
+            false,
+        );
+    });
+
+    test("hdWalletFromXprv rejects an account-level key", () => {
+        expect(() =>
+            wallet.hdWalletFromXprv(accountXprv(VECTOR_PHRASE)),
+        ).toThrow(/master/i);
+    });
+
+    test("getSignerForAddress rejects an account-level key", () => {
+        expect(() =>
+            wallet.getSignerForAddress(
+                { type: "xprv" },
+                0,
+                accountXprv(VECTOR_PHRASE),
+            ),
+        ).toThrow(/master/i);
+    });
+
+    test("the account-level key is well-formed, so only depth rejects it", () => {
+        expect(wallet.isValidXprv(accountXprv(VECTOR_PHRASE))).toBe(true);
+    });
+
+    test("a master key still imports and derives the published addresses", () => {
+        const { xpub, firstAddress } = wallet.hdWalletFromXprv(
+            masterXprv(VECTOR_PHRASE),
+        );
+
+        expect(firstAddress).toBe(VECTOR_ADDRESSES[0]);
+        expect(
+            [0, 1, 2].map((i) => wallet.deriveAddressFromXpub(xpub, i)),
+        ).toEqual(VECTOR_ADDRESSES);
+    });
+});
+
+describe("deriveAddressFromXpub checksum enforcement", () => {
+    // The xpub path shares the hole: fromExtendedKey accepts a mistyped xpub
+    // just as readily, and deriveAddressFromXpub would hand back addresses
+    // from a different tree.
+    const { xpub } = wallet.hdWalletFromMnemonic(VECTOR_PHRASE);
+
+    test("the correct xpub still derives the published addresses", () => {
+        expect(wallet.deriveAddressFromXpub(xpub, 0)).toBe(VECTOR_ADDRESSES[0]);
+    });
+
+    test("no single-character typo anywhere in an xpub is accepted", () => {
+        const derived = [];
+        for (const typo of singleCharacterTypos(xpub)) {
+            try {
+                derived.push(wallet.deriveAddressFromXpub(typo, 0));
+            } catch {
+                // Rejected, which is the required behaviour.
+            }
+        }
+
+        expect(derived).toEqual([]);
+    });
 });
 
 describe("isValidMnemonic", () => {