fix: store an absent explorer decimals as unknown instead of fabricating 18 (closes #349)

parseInt(decimals || "18") ran before writing stored tokenBalances[].decimals, so an explorer reporting no decimals produced a fabricated 18 indistinguishable from a real one at read time. That defeated the resolve-or-refuse guarantees of #306 and #340: their refusal paths were intact but never fired, because the guess was laundered upstream of them.

An absent scale is now stored as unknown, and a holding whose scale nothing knows carries a null balance -- unknown, never zero -- with six reader sites saying so rather than printing 0.0000. The Send screen resolves the display scale rather than reading the stored one, so a bundled token whose explorer row omits decimals still sends; when the scale cannot be resolved the stored quantity is withdrawn too, so the user is told the balance is unknown rather than only that the fee failed.

Existing fabricated 18s cannot be told apart retroactively and are replaced wholesale on the next balance refresh. An explorer-sourced scale stays trusted -- only fabrication is removed; the reasoning is recorded on the issue.

src/shared/transactions.js

@@ -11,6 +11,10 @@ const { log, debugFetch } = require("./log");
 const { TOKEN_BY_ADDRESS } = require("./tokenList");
 const { parseHoldersCount, isLowHolderCount } = require("./holders");
 const { isSpoofedSymbol } = require("./symbolSpoof");
+// The uint8 test every scale in this wallet goes through. Shared, not copied:
+// a scale is either reported or it is unknown, and "unknown" must mean the
+// same thing here as it does on the screens that refuse to format one.
+const { toDecimals } = require("./transferAmount");
 // The plain 4-decimal rule. The history and balance lists deliberately keep
 // truncation without the approval screens' nonzero floor: the transaction
 // detail view is the authoritative record and already shows exact precision.
@@ -92,21 +96,37 @@ function parseTx(tx, addrLower) {
 function parseTokenTransfer(tt, addrLower) {
     const from = tt.from?.hash || "";
     const to = tt.to?.hash || "";
-    const decimals = parseInt(tt.total?.decimals || "18", 10);
+    // The explorer's own answer, or null. Never a default: a transfer of
+    // 5000000000 units formatted at a guessed 18 reads as 0.000000005, and
+    // nothing downstream can tell that from a real 18-decimal transfer of
+    // that size. `parseInt(x || "18", 10)` also collapsed a genuine scale of
+    // ZERO into 18 (https://git.eeqj.de/sneak/AutistMask/issues/246).
+    const decimals = toDecimals(tt.total?.decimals);
     const rawVal = tt.total?.value || "0";
     const direction =
         normalizeAddress(from) === addrLower ? "sent" : "received";
     const sym = tt.token?.symbol || "?";
+    // Without a scale there is no token quantity, so none is stated: the list
+    // row falls back to the symbol alone and the detail screen to its
+    // direction label, exactly as the contract-call rows above already do.
+    // The exact figure is not lost — it is the base-unit line below, which is
+    // the one number that needs no scale to be true.
+    const formatted =
+        decimals === null ? "" : formatTxValue(formatUnits(rawVal, decimals));
+    const exact = decimals === null ? "" : formatUnits(rawVal, decimals);
     return {
         hash: tt.transaction_hash,
         blockNumber: tt.block_number,
         timestamp: Math.floor(new Date(tt.timestamp).getTime() / 1000),
         from: from,
         to: to,
-        value: formatTxValue(formatUnits(rawVal, decimals)),
-        exactValue: formatUnits(rawVal, decimals),
+        value: formatted,
+        exactValue: exact,
         rawAmount: rawVal,
-        rawUnit: sym + " base units (10^-" + decimals + ")",
+        rawUnit:
+            decimals === null
+                ? sym + " base units (decimals unknown)"
+                : sym + " base units (10^-" + decimals + ")",
         valueGwei: null,
         symbol: sym,
         direction: direction,