fix(ui): reconcile cleared date inputs

lib/ui/input_widgets.go

@@ -1,6 +1,7 @@
 package ui
 
 import (
+	"errors"
 	"html/template"
 	"io"
 	"strconv"
@@ -178,9 +179,10 @@ func (u *InputDate) JawsUpdate(elem *jaws.Element) {
 
 // JawsInput stores a browser-side date input value.
 //
-// The browser sends a calendar date (YYYY-MM-DD), which [time.Parse] resolves
-// to midnight UTC, so the stored [time.Time] drops any time-of-day and
-// [time.Location] the previously bound value carried. In a non-UTC deployment
+// An empty value maps to the zero [time.Time], which renders as "0001-01-01".
+// Non-empty values are calendar dates (YYYY-MM-DD). [time.Parse]
+// resolves them to midnight UTC, so the stored [time.Time] drops any time-of-day
+// and [time.Location] the previously bound value carried. In a non-UTC deployment
 // the stored instant therefore shifts by the zone offset, and because
 // [time.Time] inequality includes the location, re-selecting the same date
 // still reports a change and broadcasts it. Bind a date whose clock and zone are
@@ -193,15 +195,22 @@ func (u *InputDate) JawsUpdate(elem *jaws.Element) {
 // parse error and leaves the last accepted value in place instead of updating the
 // bound value. Keep bound years within 1..9999.
 func (u *InputDate) JawsInput(elem *jaws.Element, value string) (err error) {
+	input := value
 	if value == "" {
 		value = "0001-01-01"
 	}
 	var v time.Time
 	// Parse errors are malformed client frames: jaws.js reads elem.value from
 	// browser date controls. Leave Last as the last accepted value.
 	if v, err = time.Parse(assets.ISO8601, value); err == nil {
-		u.Last.Store(u.str(v))
-		err = u.maybeDirty(elem, u.Setter.JawsSet(elem, v))
+		u.Last.Store(input)
+		err = u.Setter.JawsSet(elem, v)
+		if input == "" && u.tag != nil && errors.Is(err, jaws.ErrValueUnchanged) {
+			elem.Dirty(elem)
+			err = nil
+			return
+		}
+		err = u.maybeDirty(elem, err)
 	}
 	return
 }

lib/ui/input_widgets_test.go

@@ -5,6 +5,7 @@ import (
 	"html/template"
 	"strings"
 	"testing"
+	"testing/synctest"
 	"time"
 
 	"github.com/linkdata/deadlock"
@@ -176,6 +177,74 @@ func TestInputDateWidget(t *testing.T) {
 	date.JawsUpdate(elem)
 }
 
+func TestInputDate_ClearReconcilesCanonicalZero(t *testing.T) {
+	synctest.Test(t, func(t *testing.T) {
+		jw, err := jaws.New()
+		if err != nil {
+			t.Fatal(err)
+		}
+		go jw.Serve()
+		tr := jawstest.NewTestRequest(jw, nil)
+		<-tr.ReadyCh
+		defer func() {
+			tr.Close()
+			jw.Close()
+			synctest.Wait()
+		}()
+
+		source := newTestSetter(time.Date(2026, time.August, 15, 0, 0, 0, 0, time.UTC))
+		originElem, _ := renderUI(t, tr.Request, NewDate(source))
+		peerElem, _ := renderUI(t, tr.Request, NewDate(source))
+
+		waitForUpdate := func() {
+			synctest.Wait()
+			time.Sleep(jaws.DefaultUpdateInterval + time.Millisecond)
+			synctest.Wait()
+		}
+		readCorrection := func() (msg wire.WsMsg) {
+			t.Helper()
+			select {
+			case msg = <-tr.OutCh:
+				if msg.What != what.Value || msg.Data != "0001-01-01" {
+					t.Fatalf("date correction = %#v, want Value %q", msg, "0001-01-01")
+				}
+			default:
+				t.Fatal("missing date correction")
+			}
+			return
+		}
+
+		tr.InCh <- wire.WsMsg{Jid: originElem.Jid(), What: what.Input, Data: ""}
+		waitForUpdate()
+		if got := source.Get(); !got.IsZero() {
+			t.Fatalf("cleared date = %v, want zero time", got)
+		}
+		corrections := map[jaws.Jid]bool{
+			readCorrection().Jid: true,
+			readCorrection().Jid: true,
+		}
+		if len(corrections) != 2 || !corrections[originElem.Jid()] || !corrections[peerElem.Jid()] {
+			t.Fatalf("corrected elements = %v, want origin and peer", corrections)
+		}
+		select {
+		case msg := <-tr.OutCh:
+			t.Fatalf("unexpected additional date output: %#v", msg)
+		default:
+		}
+
+		tr.InCh <- wire.WsMsg{Jid: originElem.Jid(), What: what.Input, Data: ""}
+		waitForUpdate()
+		if msg := readCorrection(); msg.Jid != originElem.Jid() {
+			t.Fatalf("unchanged correction Jid = %v, want %v", msg.Jid, originElem.Jid())
+		}
+		select {
+		case msg := <-tr.OutCh:
+			t.Fatalf("unexpected additional date output: %#v", msg)
+		default:
+		}
+	})
+}
+
 // TestInputDate_BrowserEditNormalizesToMidnightUTC locks in the documented
 // date-only behavior (issue #124): the control renders/reads a calendar date, so
 // a browser edit resolves through time.Parse to midnight UTC and drops the bound