Don't quietly write over a save that couldn't be read

Last change made a failing save say so. This is the other direction, and it turned out
to be worse.

load() is well defended -- try/catch, a shape check, sensible fallbacks -- and every
one of those paths ends in `return this.createDefault()`. So an unreadable save becomes
an empty table. Driven with a save truncated to 70% of its length, the way an
interrupted write leaves one:

  1762 bytes stored, 1233 after truncating
  loaded: 0 named seats, hand #1 instead of #34
  toast: none.  warning: none.  anything on the page: no.

A dealer mid-session sees an empty felt and cannot tell whether they mis-tapped Reset,
whether the browser lost the night, or what.

And then the first edit destroys the evidence. I typed a name into a seat and storage
went from the 1233 unreadable bytes to 2549 bytes of fresh default state. Whatever a
person could have picked out of that JSON -- the names, the buy-ins, the standings --
was gone one tap after the tool decided it could not read it.

Now the unreadable value is moved aside to its own key before the fallback, and the
table says what happened:

  toast:  "The saved table couldn't be read, so this one started empty."
  panel:  "The saved table couldn't be read, so this one started empty. The
           unreadable copy has been kept rather than written over."

It is deliberately not offered as a restore. Half a JSON document is not a table, and
pretending otherwise would be worse than an empty one. It just stops being destroyed.

The two warnings share the Session panel line and both can show at once -- a browser
having trouble with storage tends to have it in both directions -- with the load
message first, because "why is my table empty" is the question the dealer is standing
there asking.

8 tests (263 total): nothing stored is a new table rather than a failure, a good save
loads clean, a truncated one is reported, valid JSON of the wrong shape counts too, the
copy is kept, a later save does not touch it, the listener fires once across three
reads, and storage with no room to keep the copy is not a crash -- which is exactly the
storage most likely to hand back half a value in the first place.

Driven through the UI: warning and toast on a corrupted save, the set-aside copy still
1233 bytes intact after editing a seat, and nothing shown at all on a healthy table.

One audit correction rides along. The collapsed-column check measured inside hidden
elements, so the standings header -- hidden with its table until somebody buys in --
was reported as three collapsed columns on every empty table. It skips hidden subtrees
now, and still catches a real one: squeezing a visible column reports the header and
all three rows.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_015bnp7xKUPFFSpwkYNFaPgb

JoshHeaps.Net/wwwroot/js/casino/holdem/main.js

@@ -571,4 +571,14 @@ document.addEventListener("DOMContentLoaded", () => {
         if ((state.handHistory || []).length === 0) return;
         HandHistoryExport.download(state.handHistory, HoldemState.sessionStandings(state));
     });
+
+    // The load happens on the first line of this file, long before there's a Toast to
+    // show it in, so this is checked here rather than wired as a callback. The standing
+    // warning in the Session panel doesn't need it — that reads the flag every render —
+    // but an empty table is a thing a dealer needs told, not left to notice.
+    if (HoldemState.loadFailed) {
+        Toast.show(
+            "The saved table couldn't be read, so this one started empty.",
+            { duration: 12000 });
+    }
 });

JoshHeaps.Net/wwwroot/js/casino/holdem/render.js

@@ -761,11 +761,24 @@ const Render = {
     renderStorageWarning() {
         const host = document.getElementById("storageWarning");
         if (!host) return;
-        host.hidden = !HoldemState.saveFailed;
+        host.hidden = !HoldemState.saveFailed && !HoldemState.loadFailed;
         if (host.hidden) return;
-        host.textContent =
-            "This table isn't being saved — the browser refused. It'll keep working, " +
-            "but closing or refreshing this tab loses the session. Export CSV below keeps a copy.";
+
+        // Both can be true at once — a browser having trouble with storage tends to
+        // have it in both directions — and the one that explains an empty table goes
+        // first, because that's the question the dealer is standing there asking.
+        const lines = [];
+        if (HoldemState.loadFailed) {
+            lines.push(
+                "The saved table couldn't be read, so this one started empty. " +
+                "The unreadable copy has been kept rather than written over.");
+        }
+        if (HoldemState.saveFailed) {
+            lines.push(
+                "This table isn't being saved — the browser refused. It'll keep working, " +
+                "but closing or refreshing this tab loses the session. Export CSV below keeps a copy.");
+        }
+        host.textContent = lines.join(" ");
     },
 
     // The last step the standings stopped short of. Six signed numbers at 2am is not

JoshHeaps.Net/wwwroot/js/casino/holdem/state.js

@@ -81,12 +81,45 @@ const HoldemState = {
         };
     },
 
+    // Where an unreadable save is kept instead of being written over.
+    RECOVERY_KEY: "casino.holdem.state.v1.unreadable",
+
+    // True when there was a saved table and it couldn't be read. Same pair as
+    // saveFailed above, for the same reason: the UI has to be able to say so.
+    loadFailed: false,
+    onLoadFailed: null,
+
+    // A saved table that won't parse becomes an empty table, which is the only thing
+    // it can become — but it used to become one silently, and then the first edit
+    // saved over the top of it. A dealer mid-session saw an empty felt with no idea
+    // whether they'd mis-tapped Reset or the browser had lost the night, and whatever
+    // a person might have picked out of the raw JSON was gone a tap later.
+    //
+    // So the unreadable value is moved aside first. It is not offered as a restore —
+    // half a JSON document isn't a table, and pretending otherwise would be worse than
+    // an empty one — but it stops being destroyed, and somebody who wants the
+    // standings out of it still can.
+    failedLoad(raw) {
+        if (!this.loadFailed) {
+            this.loadFailed = true;
+            try {
+                if (raw) localStorage.setItem(this.RECOVERY_KEY, raw);
+            } catch {
+                // No room to keep it. Nothing more to try, and the warning below is
+                // the part that actually matters.
+            }
+            if (typeof this.onLoadFailed === "function") this.onLoadFailed();
+        }
+        return this.createDefault();
+    },
+
     load() {
+        let raw = null;
         try {
-            const raw = localStorage.getItem(this.STORAGE_KEY);
+            raw = localStorage.getItem(this.STORAGE_KEY);
             if (!raw) return this.createDefault();
             const parsed = JSON.parse(raw);
-            if (!parsed || !Array.isArray(parsed.seats)) return this.createDefault();
+            if (!parsed || !Array.isArray(parsed.seats)) return this.failedLoad(raw);
             if (typeof parsed.handNumber !== "number" || parsed.handNumber < 1) parsed.handNumber = 1;
             if (!Array.isArray(parsed.handHistory)) parsed.handHistory = [];
 
@@ -118,7 +151,8 @@ const HoldemState = {
 
             return parsed;
         } catch {
-            return this.createDefault();
+            // Malformed JSON — a truncated write, another tab, a browser hiccup.
+            return this.failedLoad(raw);
         }
     },
 

tests/holdem/loadFailure.test.js

@@ -0,0 +1,114 @@
+// What happens when the saved table can't be read.
+//
+// An unreadable save can only become an empty table. What it must not do is become
+// one silently and then get written over by the first edit.
+const test = require("node:test");
+const assert = require("node:assert");
+const { HoldemState } = require("./load");
+
+function withStored(value, { readOnly = false } = {}) {
+    const store = new Map();
+    if (value !== undefined) store.set(HoldemState.STORAGE_KEY, value);
+    globalThis.localStorage = {
+        getItem: key => (store.has(key) ? store.get(key) : null),
+        setItem(key, val) {
+            if (readOnly) throw new Error("QuotaExceededError");
+            store.set(key, val);
+        },
+        removeItem: key => store.delete(key),
+    };
+    return store;
+}
+
+test.beforeEach(() => {
+    HoldemState.loadFailed = false;
+    HoldemState.onLoadFailed = null;
+});
+
+test.after(() => {
+    delete globalThis.localStorage;
+    HoldemState.loadFailed = false;
+    HoldemState.onLoadFailed = null;
+});
+
+test("nothing stored is a new table, not a failure", () => {
+    withStored(undefined);
+    const state = HoldemState.load();
+
+    assert.equal(HoldemState.loadFailed, false);
+    assert.ok(Array.isArray(state.seats));
+});
+
+test("a good save loads and reports nothing", () => {
+    const store = withStored(undefined);
+    const original = HoldemState.createDefault();
+    original.handNumber = 34;
+    HoldemState.save(original);
+
+    const state = HoldemState.load();
+    assert.equal(HoldemState.loadFailed, false);
+    assert.equal(state.handNumber, 34);
+    assert.equal(store.has(HoldemState.RECOVERY_KEY), false);
+});
+
+test("a truncated save is reported rather than silently becoming an empty table", () => {
+    const good = JSON.stringify(HoldemState.createDefault());
+    withStored(good.slice(0, Math.floor(good.length * 0.7)));
+
+    const state = HoldemState.load();
+    assert.equal(HoldemState.loadFailed, true);
+    assert.ok(Array.isArray(state.seats), "it still hands back a usable table");
+});
+
+test("valid JSON of the wrong shape counts as unreadable too", () => {
+    withStored(JSON.stringify({ hello: "world" }));
+
+    HoldemState.load();
+    assert.equal(HoldemState.loadFailed, true);
+});
+
+test("the unreadable copy is kept instead of being written over", () => {
+    // This is the half that matters: whatever a person could have picked out of the
+    // raw JSON used to be gone the moment the dealer touched a seat.
+    const broken = '{"seats":[{"name":"Ann","stack":250},{"name":"Ben"';
+    const store = withStored(broken);
+
+    HoldemState.load();
+
+    assert.equal(store.get(HoldemState.RECOVERY_KEY), broken);
+});
+
+test("a later save doesn't touch the copy that was set aside", () => {
+    const broken = '{"seats":[{"name":"Ann"';
+    const store = withStored(broken);
+
+    const state = HoldemState.load();
+    state.handNumber = 2;
+    HoldemState.save(state);
+
+    assert.equal(store.get(HoldemState.RECOVERY_KEY), broken);
+    assert.notEqual(store.get(HoldemState.STORAGE_KEY), broken);
+});
+
+test("the listener fires once, not on every read", () => {
+    withStored("{not json");
+    let told = 0;
+    HoldemState.onLoadFailed = () => { told++; };
+
+    HoldemState.load();
+    HoldemState.load();
+    HoldemState.load();
+
+    assert.equal(told, 1);
+});
+
+test("no room to keep the copy is not a crash", () => {
+    // Storage that refuses writes is exactly the storage most likely to hand back a
+    // half-written value in the first place.
+    withStored("{not json", { readOnly: true });
+
+    let state;
+    assert.doesNotThrow(() => { state = HoldemState.load(); });
+    assert.ok(Array.isArray(state.seats));
+    assert.equal(HoldemState.loadFailed, true);
+});

tests/holdem/uiAudit.js

@@ -180,6 +180,12 @@ const LayoutAudit = {
     collapsedColumns() {
         const offenders = [];
         [...document.querySelectorAll("[class*='Row'], [class*='row']")].forEach(row => {
+            // Nothing inside something the page has hidden. A hidden element's children
+            // all measure zero wide, so the standings header — which is hidden along
+            // with its table until somebody has bought in — was reported as three
+            // collapsed columns on every empty table. A column nobody can see hasn't
+            // collapsed; it isn't there.
+            if (row.closest("[hidden]")) return;
             if (getComputedStyle(row).display !== "grid") return;
             [...row.children].forEach(cell => {
                 if (getComputedStyle(cell).display === "none") return;