Finish the wonderland: System told truthfully, in eight tabs instead of ten

Claude-Session: https://claude.ai/code/session_01Ms2FbjQy31TVf3CEvQhGM8

config/dot/quickshell/services/SystemLocale.qml

@@ -33,16 +33,100 @@ Singleton {
     // so the UI can stop claiming the new locale is already in use.
     property bool pendingRestart: false
 
+    // Guards read the Process objects directly; a derived binding is stale
+    // inside the handler that changes it. See DefaultApps.qml.
+    readonly property bool busy: apply.running || applyCategory.running || root.scanning
+
     readonly property string currentLabel: {
         const match = root.locales.find(locale => locale.value === root.current);
         return match ? match.label : root.current;
     }
 
+    // ── Per-category formats ────────────────────────────────────────────────
+    //
+    // Reading in one language while writing dates, numbers and currency the way
+    // your country does is the ordinary case. Each category is an OVERRIDE, and
+    // its absence -- "" here -- means "match language", which is not the same
+    // as an override that happens to equal LANG today: the two diverge the
+    // moment the language changes.
+    //
+    // Same restart discipline as the language itself. localectl only affects
+    // programs started afterwards, so an accepted change sets pendingRestart
+    // and the page says a sign-out is needed rather than claiming the new
+    // format is already in use.
+
+    readonly property var categories:
+        ["LC_TIME", "LC_NUMERIC", "LC_MONETARY", "LC_MEASUREMENT", "LC_PAPER"]
+
+    property var categoryValues: ({})
+
+    // Bumped whenever an override is read or accepted, and read at the top of
+    // categoryValue() so a binding built on that call has something to
+    // invalidate. A bare function call captures no dependency and every reader
+    // would go stale -- see DesktopPreferences.get() for the same reason.
+    property int categoryRevision: 0
+
+    // "" means match language. Anything else is an installed locale name.
+    function categoryValue(category: string): string {
+        root.categoryRevision;
+        return String(root.categoryValues[category] ?? "");
+    }
+
+    function categoryLabel(category: string): string {
+        const value = root.categoryValue(category);
+        if (value === "")
+            return "Match language";
+        const match = root.locales.find(locale => locale.value === value);
+        return match ? match.label : value;
+    }
+
+    // Pass "" to remove the override. Refused for anything that is not one of
+    // the five categories: this reaches a privileged command, and the caller
+    // does not get to name the variable being written.
+    function setCategory(category: string, locale: string): bool {
+        if (root.categories.indexOf(category) < 0)
+            return false;
+        if (locale !== "" && !root.locales.some(entry => entry.value === locale))
+            return false;
+        if (root.categoryValue(category) === locale)
+            return true;
+
+        // A click while a change is still applying is queued rather than
+        // fired: assigning running = true to a running Process is a no-op, so
+        // a second setCategory would be silently dropped and applyCategory's
+        // handler would then adopt it as though it had been applied. Same
+        // queue discipline as set() above.
+        root.requestedCategories = Object.assign({}, root.requestedCategories);
+        root.requestedCategories[category] = locale;
+        if (!applyCategory.running)
+            root._applyNextCategory();
+        return true;
+    }
+
+    property var requestedCategories: ({})
+
+    function _applyNextCategory(): void {
+        const keys = Object.keys(root.requestedCategories);
+        if (keys.length === 0)
+            return;
+        const category = keys[0];
+        const value = String(root.requestedCategories[category]);
+        const remaining = Object.assign({}, root.requestedCategories);
+        delete remaining[category];
+        root.requestedCategories = remaining;
+
+        applyCategory.pendingCategory = category;
+        applyCategory.pendingValue = value;
+        applyCategory.command = [root.helperPath, "set", category, value];
+        applyCategory.running = true;
+    }
+
     function refresh(): void {
         if (root.scanning)
             return;
         root.scanning = true;
         readCurrent.running = true;
+        readCategories.running = true;
         list.running = true;
     }
 
@@ -95,6 +179,49 @@ Singleton {
         }
     }
 
+    Process {
+        id: readCategories
+        command: [root.helperPath, "overrides"]
+        stdout: StdioCollector {
+            onStreamFinished: {
+                try {
+                    const parsed = JSON.parse(this.text);
+                    root.categoryValues = (parsed && typeof parsed === "object") ? parsed : ({});
+                } catch (error) {
+                    root.categoryValues = ({});
+                    console.warn("SystemLocale: could not parse the format overrides:", error);
+                }
+                root.categoryRevision += 1;
+            }
+        }
+    }
+
+    Process {
+        id: applyCategory
+
+        property string pendingCategory: ""
+        property string pendingValue: ""
+
+        // A refused change -- polkit dismissed, or a locale the system does not
+        // have -- must not move the UI. The value is only adopted on a zero
+        // exit, exactly as the language apply above does.
+        onExited: code => {
+            if (code === 0) {
+                const next = Object.assign({}, root.categoryValues);
+                next[applyCategory.pendingCategory] = applyCategory.pendingValue;
+                root.categoryValues = next;
+                root.categoryRevision += 1;
+                root.pendingRestart = true;
+                root.lastError = "";
+            } else {
+                root.lastError = "The system did not accept that format. It may have needed a password.";
+            }
+            applyCategory.pendingCategory = "";
+            applyCategory.pendingValue = "";
+            root._applyNextCategory();
+        }
+    }
+
     Process {
         id: apply