M9 S3 (frontend): consolidate local-date helpers into notes/datetime.ts

The created-date range facets built local-day bounds by hand in two places
(FilterBar's onTo/toInput, TimelineView's buildQuery) — parse a
"YYYY-MM-DD", shift a day for the half-open upper bound, format back.

- datetime.ts: parseLocalDate() / addLocalDays() (non-mutating) / formatLocalDay().
- TimelineView: drops its inline localDate() + the +1-day Date math.
- FilterBar: drops its inline isoDay() + the setDate(±1) mutations.

Behavior-preserving and deliberately NOT unifying output: Timeline still
emits UTC (.toISOString()) bounds, FilterBar still emits naive-local
"…T00:00:00" strings — only the shared primitives are extracted. (The
naive-vs-UTC divergence is a separate backend-datetime-semantics question,
flagged for later, not silently changed.)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

frontend/src/components/FilterBar.vue

@@ -6,6 +6,7 @@ import { useSavedFiltersStore } from "../stores/savedFilters";
 import { useUiStore } from "../stores/ui";
 import type { NoteFacets } from "../stores/notes";
 import { facetCount, facetsFromQuery, facetsToQuery } from "../notes/facets";
+import { addLocalDays, formatLocalDay, parseLocalDate } from "../notes/datetime";
 import { NOTE_COLOR_KEYS, NOTE_COLOR_LABELS, NOTE_SWATCH_CLASSES, type NoteColor } from "../notes/colors";
 import Icon from "./Icon.vue";
 
@@ -56,30 +57,25 @@ function onQ(e: Event) {
   qTimer = setTimeout(() => patch({ q: v.trim() || undefined }), 300);
 }
 
-function isoDay(d: Date): string {
-  return `${d.getFullYear()}-${String(d.getMonth() + 1).padStart(2, "0")}-${String(d.getDate()).padStart(2, "0")}`;
-}
 function onFrom(e: Event) {
   const v = (e.target as HTMLInputElement).value;
   patch({ created_after: v ? `${v}T00:00:00` : undefined });
 }
 function onTo(e: Event) {
   const v = (e.target as HTMLInputElement).value;
-  if (!v) {
+  const d = v ? parseLocalDate(v) : null;
+  if (!d) {
     patch({ created_before: undefined });
     return;
   }
   // Half-open upper bound: the start of the day AFTER the chosen date (so it's inclusive).
-  const d = new Date(`${v}T00:00:00`);
+  patch({ created_before: `${formatLocalDay(addLocalDays(d, 1))}T00:00:00` });
-  d.setDate(d.getDate() + 1);
-  patch({ created_before: `${isoDay(d)}T00:00:00` });
 }
 const fromInput = computed(() => (facets.value.created_after ?? "").slice(0, 10));
 const toInput = computed(() => {
-  if (!facets.value.created_before) return "";
+  // Reverse the half-open bound (day-after) back to the chosen end day for the input.
-  const d = new Date(facets.value.created_before);
+  const d = facets.value.created_before ? parseLocalDate(facets.value.created_before.slice(0, 10)) : null;
-  d.setDate(d.getDate() - 1);
+  return d ? formatLocalDay(addLocalDays(d, -1)) : "";
-  return isoDay(d);
 });
 
 async function saveView() {

frontend/src/notes/datetime.ts

@@ -26,3 +26,26 @@ export function formatReminder(iso: string | null): string {
 export function isOverdue(iso: string | null): boolean {
   return !!iso && new Date(iso).getTime() < Date.now();
 }
+
+// --- Local calendar-date helpers (the created-date range facets work in the viewer's
+// LOCAL day; the board's FilterBar and the Timeline view both build day bounds). ---
+
+// Parse an <input type="date"> value ("YYYY-MM-DD") as a LOCAL calendar date (midnight
+// local), or null if it isn't a valid YYYY-MM-DD.
+export function parseLocalDate(value: string): Date | null {
+  const m = /^(\d{4})-(\d{2})-(\d{2})$/.exec(value);
+  if (!m) return null;
+  return new Date(Number(m[1]), Number(m[2]) - 1, Number(m[3]));
+}
+
+// A new local Date shifted by whole days — e.g. +1 for the half-open upper bound that
+// includes the whole end day, -1 to reverse it for display. Non-mutating.
+export function addLocalDays(d: Date, days: number): Date {
+  return new Date(d.getFullYear(), d.getMonth(), d.getDate() + days);
+}
+
+// Format a local Date as "YYYY-MM-DD" (the shape an <input type="date"> reads).
+export function formatLocalDay(d: Date): string {
+  const pad = (n: number) => String(n).padStart(2, "0");
+  return `${d.getFullYear()}-${pad(d.getMonth() + 1)}-${pad(d.getDate())}`;
+}

frontend/src/views/TimelineView.vue

@@ -2,6 +2,7 @@
 import { computed, onMounted, ref, watch } from "vue";
 import { api } from "../api/client";
 import { type Note } from "../stores/notes";
+import { addLocalDays, parseLocalDate } from "../notes/datetime";
 import { useNoteList } from "../composables/useNoteList";
 import { useNoteEditor } from "../composables/useNoteEditor";
 import AsyncState from "../components/AsyncState.vue";
@@ -18,23 +19,13 @@ const fromDate = ref("");
 const toDate = ref("");
 const hasRange = computed(() => !!fromDate.value || !!toDate.value);
 
-// Parse an <input type="date"> value ("YYYY-MM-DD") as a LOCAL calendar date.
-function localDate(value: string): Date | null {
-  const m = /^(\d{4})-(\d{2})-(\d{2})$/.exec(value);
-  if (!m) return null;
-  return new Date(Number(m[1]), Number(m[2]) - 1, Number(m[3]));
-}
-
 function buildQuery(): string {
   const params = new URLSearchParams({ filter: "active", sort: "created" });
-  const from = localDate(fromDate.value);
+  const from = parseLocalDate(fromDate.value);
   if (from) params.set("created_after", from.toISOString());
-  const to = localDate(toDate.value);
+  const to = parseLocalDate(toDate.value);
-  if (to) {
+  // Half-open upper bound: start of the day AFTER `to`, so the whole `to` day is included.
-    // Half-open upper bound: start of the day AFTER `to`, so the whole `to` day is included.
+  if (to) params.set("created_before", addLocalDays(to, 1).toISOString());
-    const end = new Date(to.getFullYear(), to.getMonth(), to.getDate() + 1);
-    params.set("created_before", end.toISOString());
-  }
   return params.toString();
 }