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

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

config/dot/quickshell/services/DateTime.qml

@@ -24,15 +24,44 @@ Singleton {
     property string timezone: ""
     property bool ntpEnabled: false
     property bool ntpSynchronized: false
+
+    // Whether timedatectl has answered even once. The status query is async, so
+    // for the first moment of the shell's life `ntpEnabled` is false because
+    // nothing has looked, not because network time is off -- and setTime's
+    // whole job is to refuse while it is on. Treating "not looked yet" as "off"
+    // is the same wrong answer that looks fine as everywhere else in Panama.
+    property bool statusRead: false
+
+    // What timedatectl last said the three clocks read. localTime is what the
+    // Clock card shows and what seeds the manual-set field, so it is kept
+    // ticking (see clockTick below) rather than frozen at the last scan;
+    // universalTime and rtcTime are facts, shown as read.
     property string localTime: ""
     property string universalTime: ""
     property string rtcTime: ""
     property string lastError: ""
 
+    // Milliseconds between this shell's own clock and the one timedatectl
+    // reported. Normally zero -- both read the same system clock -- but
+    // deriving the displayed time from the system's own answer rather than
+    // from QML's assumption means a clock that moves under us shows the move.
+    property real systemOffsetMs: 0
+
+    // Set by the page while the Clock card is on screen. The tick is a local
+    // recomputation, never another timedatectl call: a process per second to
+    // learn a value the local clock already tracks exactly would be a
+    // remarkable amount of work for a second hand.
+    property bool tracking: false
+
     property var zones: []
 
     readonly property bool busy: statusQuery.running || zonesQuery.running || writeRun.running
 
+    // The shape `setTime` accepts, and the shape the field should be seeded
+    // with. Seconds are optional because "set it to 9:30" is a whole request.
+    readonly property var timePattern:
+        new RegExp("^\\d{4}-\\d{2}-\\d{2} \\d{2}:\\d{2}(?::\\d{2})?$")
+
     // "America/New_York" -> "New York" for display, keeping the region as a
     // separate field so the list can be grouped and searched sensibly.
     function regionOf(zone: string): string {
@@ -102,10 +131,83 @@ Singleton {
                 root.ntpEnabled = value === "yes";
             else if (key === "NTPSynchronized")
                 root.ntpSynchronized = value === "yes";
+            else if (key === "TimeUSec")
+                root.anchorClock(value);
+            else if (key === "RTCTimeUSec")
+                root.rtcTime = root.tidyStamp(value);
         }
+        root.statusRead = true;
         root.lastError = "";
     }
 
+    // timedatectl prints "Mon 2026-08-24 21:22:55 EDT". The weekday is a
+    // duplicate of the date and the zone is already its own row, so what is
+    // left is the part a clock actually shows.
+    function tidyStamp(value: string): string {
+        const match = String(value).match(/(\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2})/);
+        return match ? match[1] : String(value).trim();
+    }
+
+    function anchorClock(value: string): void {
+        const stamp = root.tidyStamp(value);
+        // Parsed as local wall time, which is what timedatectl printed. A
+        // stamp this cannot read leaves the offset alone rather than jumping
+        // the displayed clock by whatever the misparse happened to produce.
+        const parsed = Date.parse(stamp.replace(" ", "T"));
+        root.systemOffsetMs = Number.isFinite(parsed) ? parsed - Date.now() : 0;
+        root.tickClock();
+    }
+
+    function tickClock(): void {
+        const now = new Date(Date.now() + root.systemOffsetMs);
+        root.localTime = Qt.formatDateTime(now, "yyyy-MM-dd HH:mm:ss");
+        // toISOString is already UTC, which is the whole question here; doing
+        // the offset arithmetic by hand is a way to get it wrong twice a year.
+        root.universalTime = now.toISOString().slice(0, 19).replace("T", " ") + " UTC";
+    }
+
+    Timer {
+        id: clockTick
+        interval: 1000
+        repeat: true
+        running: root.tracking
+        onTriggered: root.tickClock()
+    }
+
+    // Setting the clock by hand, which is only a coherent request while
+    // network time is off. With NTP on, timedatectl refuses outright and a
+    // toggle-then-set from the page would race the daemon putting the time
+    // back -- so the refusal happens here, where it can be explained, rather
+    // than as an opaque failure from a command the user did not type.
+    function setTime(iso: string): bool {
+        if (!root.statusRead) {
+            root.lastError = "The clock settings have not been read yet.";
+            root.refresh();
+            return false;
+        }
+        if (root.ntpEnabled) {
+            root.lastError = "Turn off network time before setting the clock by hand.";
+            return false;
+        }
+        const stamp = String(iso).trim();
+        if (!root.timePattern.test(stamp)) {
+            root.lastError = "Enter the time as YYYY-MM-DD HH:MM, with optional seconds.";
+            return false;
+        }
+        // Shape is not enough: "2026-13-45 99:99" matches the pattern and is
+        // not a moment. Round-tripping through Date is what rejects it.
+        const parsed = new Date(stamp.replace(" ", "T"));
+        if (!Number.isFinite(parsed.getTime())
+                || Qt.formatDateTime(parsed, "yyyy-MM-dd HH:mm") !== stamp.slice(0, 16)) {
+            root.lastError = "That is not a real date and time.";
+            return false;
+        }
+        if (writeRun.running)
+            return false;
+        writeRun.exec(["timedatectl", "set-time", stamp]);
+        return true;
+    }
+
     function refresh(): void {
         if (!statusQuery.running)
             statusQuery.running = true;