fix: a save merges this page's tracked token change into the stored list (closes #717)

A save wrote `trackedTokens` whole, so two pages on one network dropped each
other's adds and brought back each other's removals.

A save that keeps the network now merges this page's change into the stored
list by contract address. A save that switches networks is unchanged.

`mergeTrackedTokens()` does that merge, and the two other merges of tracked
tokens now call it. It keeps one record per contract address, this page's for
a token both lists hold, so a token held twice no longer multiplies.

Model: opus-5-5

src/shared/state.js

@@ -404,6 +404,36 @@ function mergeNetworkEndpoints(base, ours, theirs) {
     return mergeMapByKey(base, ours, theirs, mergeEndpointEntry);
 }
 
+// Merges one network's tracked tokens by contract address:
+//
+// - A token another page added or removed since this page's last save stays
+//   added or removed.
+// - A token that this page and `theirs` both hold keeps this page's record.
+// - The result holds one record per contract address.
+//
+// mergeListByIdentity() keeps records that share an identity, on purpose, for
+// wallets. A contract address names one token, so this keeps one record for it.
+// Without that, a token that `ours` and `theirs` each hold twice comes back four
+// times, and each later merge multiplies it again.
+//
+// `theirs` takes this page's records first. mergeListByIdentity() would
+// otherwise log an error for two different records of one token.
+function mergeTrackedTokens(base, ours, theirs) {
+    const contract = (token) => token.address.toLowerCase();
+    const oursByContract = new Map(
+        ours.map((token) => [contract(token), token]),
+    );
+    const merged = mergeListByIdentity(
+        base,
+        ours,
+        theirs.map((token) => oursByContract.get(contract(token)) || token),
+        contract,
+        (baseToken, ourToken) => ourToken,
+    );
+    const byContract = new Map(merged.map((token) => [contract(token), token]));
+    return [...byContract.values()];
+}
+
 // Returns a copy of `stored.networkTrackedTokens` for when this page has not yet
 // taken the switch in `stored`. `page` is this page's state. A token that this
 // page tracked or removed since its last save is tracked or removed in the list
@@ -411,12 +441,10 @@ function mergeNetworkEndpoints(base, ours, theirs) {
 function networkTrackedTokensWithChange(stored, page) {
     return {
         ...stored.networkTrackedTokens,
-        [page.networkId]: mergeListByIdentity(
+        [page.networkId]: mergeTrackedTokens(
             baseline.trackedTokens,
             page.trackedTokens,
-            stored.networkTrackedTokens[page.networkId],
-            (token) => token.address.toLowerCase(),
-            (base, ours) => ours,
+            stored.networkTrackedTokens[page.networkId] || [],
         ),
     };
 }
@@ -461,23 +489,27 @@ function networkTrackedTokensWithChange(stored, page) {
 // comment at mergeEndpointEntry() for why the collision this closes is
 // milder than the other two.
 //
+// `trackedTokens` is merged by contract address (mergeTrackedTokens()) when this
+// page has changed it, so a token another page added or removed since this
+// page's last save stays added or removed. A token both lists hold keeps this
+// page's record. Two saves differ:
+//
+// - When the stored record is on another network than this page's, a save keeps
+//   the stored `trackedTokens`. It merges this page's change into the list in
+//   `networkTrackedTokens` for this page's network, by contract address.
+// - A save that switches networks writes this page's list whole. A switch in
+//   Settings first merges that list by contract address
+//   (takeStoredTrackedTokens()).
+//
 // Every other persisted field stays a whole-field diff:
 // `fraudContracts`/`viewStack` are arrays of scalars with no per-element
-// identity to merge by; a save diffs `trackedTokens` whole, and a switch in
-// Settings first merges that list by contract address
-// (takeStoredTrackedTokens()); `networkTrackedTokens` is diffed whole like
-// `trackedTokens` and `networkId`, the two fields a network switch moves
-// together with it; `tokenHolderCache` is a map shaped like the ones above,
-// but nothing in src/ ever writes an entry into it — it is only ever reset
-// wholesale to `{}` (applyChainSwitchFields()) — so there is no in-place
-// mutation for a whole-field diff to collide with; `viewData` is this page's
-// own UI scratch space, not data another page has any reason to share
-// membership of.
-//
-// One exception: when the stored record is on another network than this
-// page's, a save keeps the stored `trackedTokens`. It merges this page's change
-// into the list in `networkTrackedTokens` for this page's network, by contract
-// address.
+// identity to merge by; `networkTrackedTokens` is diffed whole like `networkId`,
+// which a network switch moves together with it; `tokenHolderCache` is a map
+// shaped like the ones above, but nothing in src/ ever writes an entry into it —
+// it is only ever reset wholesale to `{}` (applyChainSwitchFields()) — so there
+// is no in-place mutation for a whole-field diff to collide with; `viewData` is
+// this page's own UI scratch space, not data another page has any reason to
+// share membership of.
 //
 // This does not make two pages that both change the SAME leaf concurrently
 // safe: last write wins on that one leaf, same as before. What it removes
@@ -564,6 +596,20 @@ async function saveStateOnce(beforeWrite) {
             fresh,
             current,
         );
+    } else if (
+        baseline !== null &&
+        baseline.networkId === current.networkId &&
+        !deepEqual(current.trackedTokens, baseline.trackedTokens)
+    ) {
+        // This page's network is the one it last saved on, and the stored
+        // record is on it too, so all three lists are of one network. This
+        // page's change goes into the stored list, and another page's add or
+        // removal stays (https://git.eeqj.de/sneak/AutistMask/issues/717).
+        merged.trackedTokens = mergeTrackedTokens(
+            baseline.trackedTokens,
+            current.trackedTokens,
+            fresh.trackedTokens,
+        );
     }
     merged.hasWallet = Boolean(merged.wallets && merged.wallets.length > 0);
     // Stamped on every write, never merged or diffed: the record that goes to
@@ -680,12 +726,10 @@ function takeStoredNetwork(stored) {
 // `baseline` takes the stored list, so the save stores the list in `state`
 // whenever the two differ.
 function takeStoredTrackedTokens(stored) {
-    rawState.trackedTokens = mergeListByIdentity(
+    rawState.trackedTokens = mergeTrackedTokens(
         baseline.trackedTokens,
         rawState.trackedTokens,
         stored.trackedTokens,
-        (token) => token.address.toLowerCase(),
-        (base, ours) => ours,
     );
     baseline.trackedTokens = structuredClone(stored.trackedTokens);
 }