Add transport sync button and allow dropping stays onto band-covered days

- Auto-created transports carry auto_ref {from,to} stay ids; new
  POST /api/trips/:id/transports/regenerate reconciles them against the
  current stay order (re-date/re-title kept bridges preserving mode and
  price, delete orphans, create missing) without touching manual
  transports or flight-covered gaps
- Sync transports button in the calendar header with result toast
- The week band strip is now a drop target resolving the day from the
  pointer position, so stays can be dropped onto spots covered by other
  stays; overlapping stays stack in band lanes

docs/API.md

@@ -48,6 +48,7 @@ entries      (id INTEGER PK, trip_id INTEGER NOT NULL REFERENCES trips(id),
               segments TEXT,                          -- JSON array, flight entries only (see below)
               rental TEXT,                            -- JSON object, rental entries only (see below)
               transport_mode TEXT,                    -- transport entries only (see below)
+              auto_ref TEXT,                          -- JSON {from,to} stay ids; non-null = auto-created transport (see below)
               created_at TEXT DEFAULT current_timestamp)
 entry_participants (entry_id INTEGER REFERENCES entries(id), user_id INTEGER REFERENCES users(id),
               PRIMARY KEY (entry_id, user_id))
@@ -62,7 +63,15 @@ Entry `type` ∈ `flight | transport | activity | rental | stay | note`.
 
 `transport` covers ground/sea travel (the old `travel` type). Optional `transport_mode` ∈ `train | bus | ferry | taxi | drive | other` (nullable; drives the icon in the UI). Validation: only allowed when the effective `type === 'transport'` (else 400 `transport_mode is only allowed on transport entries`); PATCH `transport_mode: null` clears it. Entry JSON always includes `transport_mode` (string or null).
 
-**Auto-transport between stays**: when a `stay` entry is POSTed and it has a chronological neighbour stay (the nearest stay before and/or after it, ordered by `date`), the server auto-creates one `transport` entry per neighbour pair — titled `"<from short name> → <to short name>"` (short name = first comma-segment of the stay's `location_name`, fallback `title`), dated on the **later** stay's `date`, `transport_mode` null, no price/location, `sort_order` 0. Skipped when any `transport` or `flight` entry already exists with `date` between the earlier stay's end (`end_date` or `date`) and the later stay's `date` (inclusive). One-shot: fires only on stay **creation** (never PATCH), so deleting an auto-created transport does not resurrect it. The POST response is unchanged (`201 {entry}` = the stay); clients should refetch the entry list.
+**Auto-transport between stays**: when a `stay` entry is POSTed and it has a chronological neighbour stay (the nearest stay before and/or after it, ordered by `date`), the server auto-creates one `transport` entry per neighbour pair — titled `"<from short name> → <to short name>"` (short name = first comma-segment of the stay's `location_name`, fallback `title`), dated on the **later** stay's `date`, `transport_mode` null, no price/location, `sort_order` 0, and `auto_ref` set to `{"from": <earlier stay id>, "to": <later stay id>}` (stored JSON, returned parsed; null on every other entry — the marker for "auto-created"). Skipped when any `transport` or `flight` entry already exists with `date` between the earlier stay's end (`end_date` or `date`) and the later stay's `date` (inclusive). One-shot: fires only on stay **creation** (never PATCH), so deleting an auto-created transport does not resurrect it. The POST response is unchanged (`201 {entry}` = the stay); clients should refetch the entry list.
+
+**Regenerating auto-transports** — `POST /api/trips/:id/transports/regenerate` (any member, no body) reconciles auto transports after stays have been moved/reshuffled:
+
+1. Compute the **desired pairs**: stays in chronological `(date, id)` order → each adjacent pair `(earlier, later)`, skipping pairs whose window (`earlier.end_date||date` .. `later.date`, inclusive; skip if inverted/overlapping) contains a **manual** transport (`auto_ref` null) or any flight.
+2. Existing auto transports (`type='transport'`, `auto_ref` non-null) whose `{from,to}` matches a desired pair are **kept but re-synced**: `date` set to the pair's current transition date (`later.date`), title regenerated to the current `"A → B"`; `transport_mode`, price/split, times, details are preserved. Auto transports matching no desired pair are **deleted**.
+3. Missing desired pairs get a fresh auto transport (same shape as creation-time).
+
+Response: `200 {created, updated, deleted}` (counts). Auto transports from databases predating `auto_ref` have it null and are treated as manual (never touched). Stays MAY overlap in dates (two locations on the same day, e.g. temporarily while reshuffling) — overlapping adjacent pairs simply produce no auto transport, and the calendar renders overlapping stays in stacked band lanes.
 
 ### Multi-day entries & stays
 
@@ -171,7 +180,7 @@ User JSON shape everywhere: `{id, display_name}`.
 | `PATCH /api/entries/:id` | any subset of the above | `200 {entry}` (member of the entry's trip required; `participants` replaces the whole set) |
 | `DELETE /api/entries/:id` | — | `204` (also deletes its entry_participants rows) |
 
-Entry JSON shape (always full row): `{id, trip_id, date, end_date, type, title, details, start_time, end_time, location_name, lat, lng, sort_order, price, paid_by, split_mode, participants, segments, rental, transport_mode}` where `participants` is an array of user ids (`[]` = all members) and `segments` is the parsed array or `null`.
+Entry JSON shape (always full row): `{id, trip_id, date, end_date, type, title, details, start_time, end_time, location_name, lat, lng, sort_order, price, paid_by, split_mode, participants, segments, rental, transport_mode, auto_ref}` where `participants` is an array of user ids (`[]` = all members), `segments` is the parsed array or `null`, and `auto_ref` is the parsed `{from,to}` object or `null`. `auto_ref` is server-managed (not accepted in POST/PATCH bodies; editing an auto transport keeps its `auto_ref`).
 
 ### Route & summary (computed)
 

public/css/styles.css

@@ -143,6 +143,7 @@ textarea.input { resize: vertical; }
 .page { max-width: 1180px; margin: 0 auto; padding: 1.4rem; display: flex; flex-direction: column; gap: 1.2rem; }
 .page-head { display: flex; align-items: flex-end; justify-content: space-between; gap: 1rem; flex-wrap: wrap; }
 .section-head { margin-bottom: 0.8rem; }
+.cal-section-head { display: flex; align-items: flex-start; justify-content: space-between; gap: 1rem; flex-wrap: wrap; }
 .form-slot:empty { display: none; }
 
 /* ---------- Auth ---------- */
@@ -272,6 +273,7 @@ textarea.input { resize: vertical; }
 .cal-band-draggable:active { cursor: grabbing; }
 .cal-band.dragging { opacity: 0.4; }
 .cal-day-drop { border-color: var(--brand); box-shadow: 0 0 0 2px var(--brand); background: var(--brand-soft); }
+.cal-week-bands.cal-bands-drop { outline: 2px dashed var(--brand); outline-offset: 2px; border-radius: 6px; }
 
 /* ---------- Detail grid (map + summary) ---------- */
 .detail-grid { display: grid; grid-template-columns: 1.7fr 1fr; gap: 1.2rem; align-items: start; }

public/js/api.js

@@ -71,6 +71,7 @@ export const api = {
     removeMember: (id, userId) => del(`/api/trips/${id}/members/${userId}`),
     route: (id) => get(`/api/trips/${id}/route`),
     costs: (id) => get(`/api/trips/${id}/costs`),
+    regenerateTransports: (id) => post(`/api/trips/${id}/transports/regenerate`, {}),
   },
   entries: {
     create: (tripId, payload) => post(`/api/trips/${tripId}/entries`, payload),

public/js/views/calendar.js

@@ -1,7 +1,8 @@
 // Calendar grid for the trip's date range. Real weeks as rows (Mon–Sun
 // columns); days outside the range are greyed. Each in-range day shows its
 // entries as compact, type-coloured chips. Clicking a day opens the editor.
-import { el } from '../dom.js';
+import { el, toast } from '../dom.js';
+import { api } from '../api.js';
 import {
   ENTRY_TYPES,
   typeInfo,
@@ -68,9 +69,14 @@ export function renderCalendar(tctx) {
     { class: 'card calendar-section' },
     el(
       'div',
-      { class: 'section-head' },
-      el('h2', {}, 'Calendar'),
-      el('p', { class: 'muted' }, 'Click a day to add or edit entries.'),
+      { class: 'section-head cal-section-head' },
+      el(
+        'div',
+        {},
+        el('h2', {}, 'Calendar'),
+        el('p', { class: 'muted' }, 'Click a day to add or edit entries.'),
+      ),
+      syncTransportsButton(tctx),
     ),
     legend(),
   );
@@ -97,7 +103,7 @@ export function renderCalendar(tctx) {
   for (const week of weeks) {
     // Each week is a stay-bands strip (all-day bars) above a row of day cells.
     const weekEl = el('div', { class: 'cal-week' });
-    const bands = renderWeekBands(week.map(ymd), stayLayout, tctx);
+    const bands = renderWeekBands(week.map(ymd), stayLayout, entriesById, tctx);
     if (bands) weekEl.appendChild(bands);
     const daysRow = el('div', { class: 'cal-week-days' });
     for (const date of week) {
@@ -111,12 +117,39 @@ export function renderCalendar(tctx) {
   // which bubbles up here — sweep any lingering drop highlight.
   cal.addEventListener('dragend', () => {
     for (const n of cal.querySelectorAll('.cal-day-drop')) n.classList.remove('cal-day-drop');
+    for (const n of cal.querySelectorAll('.cal-bands-drop')) n.classList.remove('cal-bands-drop');
   });
 
   section.appendChild(cal);
   return section;
 }
 
+// "↻ Sync transports" — reconciles auto-created transport entries after stays
+// have been dragged/reshuffled (see docs/API.md, "Regenerating auto-transports").
+function syncTransportsButton(tctx) {
+  const btn = el('button', { class: 'btn btn-sm btn-ghost', type: 'button' }, '↻ Sync transports');
+  btn.addEventListener('click', async () => {
+    btn.disabled = true;
+    const original = btn.textContent;
+    btn.textContent = 'Syncing…';
+    try {
+      const res = await api.trips.regenerateTransports(tctx.tripId);
+      const parts = [];
+      if (res.created) parts.push(`${res.created} added`);
+      if (res.updated) parts.push(`${res.updated} updated`);
+      if (res.deleted) parts.push(`${res.deleted} removed`);
+      toast(parts.length ? `Transports synced: ${parts.join(', ')}` : 'Transports already in sync', 'success');
+      await tctx.refreshTrip();
+    } catch (err) {
+      toast(err.message);
+    } finally {
+      btn.disabled = false;
+      btn.textContent = original;
+    }
+  });
+  return btn;
+}
+
 function dayCell(date, rangeStart, rangeEnd, byDate, contByDate, dropoffByDate, entriesById, tctx, currency) {
   const key = ymd(date);
   const inRange = date >= rangeStart && date <= rangeEnd;

public/js/views/dayEditor.js

@@ -137,6 +137,7 @@ export function openDayEditor(tctx, date) {
           time ? ` · ${time}` : '',
           flight ? ` · ✈️ ${flightChain(entry.segments)}` : '',
           !flight && entry.location_name ? ` · 📍 ${entry.location_name}` : '',
+          entry.auto_ref ? ' · ↻ auto' : '',
         ),
         isMultiDay(entry) ? el('div', { class: 'entry-span muted' }, spanText(entry)) : null,
         flight ? renderSegmentLines(entry.segments) : null,

public/js/views/dragdrop.js

@@ -46,10 +46,29 @@ export function makeBandDraggable(node, entry) {
   node.addEventListener('dragend', () => node.classList.remove('dragging'));
 }
 
-// Wire an in-range day cell as a drop target. On drop the dragged entry moves to
-// `targetDate` with sort_order = `targetCount` (appended after that day's
-// entries); an entry with an end_date has it shifted by the same day-delta in
-// the SAME patch (the backend rejects date > stored end_date otherwise).
+// Shared move-commit: PATCHes the dragged entry to `targetDate` with the given
+// `sortOrder`, shifting `end_date` by the same day-delta in the SAME patch (the
+// backend rejects date > stored end_date otherwise). No-ops when dropped back
+// on its own day. Used by both the day-cell and week-bands drop targets below.
+async function commitEntryMove(id, targetDate, sortOrder, entriesById, tctx) {
+  const entry = entriesById.get(id);
+  if (!entry || entry.date === targetDate) return; // dropped on its own day
+  const patch = { date: targetDate, sort_order: sortOrder };
+  if (entry.end_date) {
+    const delta = dayDelta(entry.date, targetDate);
+    patch.end_date = ymd(addDays(parseYMD(entry.end_date), delta));
+  }
+  try {
+    await api.entries.update(id, patch);
+    await tctx.refreshTrip();
+  } catch (err) {
+    toast(err.message);
+  }
+}
+
+// Wire an in-range day cell as a drop target. On drop the dragged entry moves
+// to `targetDate` with sort_order = `targetCount` (appended after that day's
+// entries).
 export function makeDayDropTarget(cell, targetDate, targetCount, entriesById, tctx) {
   cell.addEventListener('dragover', (e) => {
     e.preventDefault();
@@ -64,19 +83,33 @@ export function makeDayDropTarget(cell, targetDate, targetCount, entriesById, tc
     cell.classList.remove('cal-day-drop');
     const id = Number(e.dataTransfer.getData(DND_MIME));
     if (!id) return;
-    const entry = entriesById.get(id);
-    if (!entry || entry.date === targetDate) return; // dropped on its own day
-    const patch = { date: targetDate, sort_order: targetCount };
-    if (entry.end_date) {
-      const delta = dayDelta(entry.date, targetDate);
-      patch.end_date = ymd(addDays(parseYMD(entry.end_date), delta));
-    }
-    try {
-      await api.entries.update(id, patch);
-      await tctx.refreshTrip();
-    } catch (err) {
-      toast(err.message);
-    }
+    await commitEntryMove(id, targetDate, targetCount, entriesById, tctx);
+  });
+}
+
+// Wire a week's stay-bands strip as a drop target, so dragging a chip/band
+// onto a spot already covered by another stay's band still moves the entry
+// (day cells sit below the bands strip and are otherwise unreachable there).
+// The target day is derived from the pointer's x-position across the 7-column
+// strip; the moved entry is appended (sort_order 0 — bands don't track a
+// day's chip order).
+export function makeWeekBandsDropTarget(strip, weekYmd, entriesById, tctx) {
+  strip.addEventListener('dragover', (e) => {
+    e.preventDefault();
+    e.dataTransfer.dropEffect = 'move';
+    strip.classList.add('cal-bands-drop');
+  });
+  strip.addEventListener('dragleave', (e) => {
+    if (!strip.contains(e.relatedTarget)) strip.classList.remove('cal-bands-drop');
+  });
+  strip.addEventListener('drop', async (e) => {
+    e.preventDefault();
+    strip.classList.remove('cal-bands-drop');
+    const id = Number(e.dataTransfer.getData(DND_MIME));
+    if (!id) return;
+    const rect = strip.getBoundingClientRect();
+    const idx = Math.min(6, Math.max(0, Math.floor((e.clientX - rect.left) / (rect.width / 7))));
+    await commitEntryMove(id, weekYmd[idx], 0, entriesById, tctx);
   });
 }
 

public/js/views/stayBands.js

@@ -4,7 +4,7 @@
 // partitioning) so a stay keeps the same vertical position across weeks.
 import { el } from '../dom.js';
 import { parseYMD, daysBetweenInclusive, typeInfo, stayShortName, entrySpanDays } from '../format.js';
-import { makeBandDraggable } from './dragdrop.js';
+import { makeBandDraggable, makeWeekBandsDropTarget } from './dragdrop.js';
 
 // Per-instance band palette: each stay gets its own hue (not the generic stay
 // type colour) so overlapping/adjacent areas read apart. Muted-but-distinct
@@ -63,7 +63,10 @@ export function computeStayLayout(entries) {
 }
 
 // Bands strip for one week (7 ymd strings). Returns null if no stay intersects.
-export function renderWeekBands(weekYmd, layout, tctx) {
+// `entriesById`/`tctx` are threaded through to wire the strip itself as a drop
+// target (see makeWeekBandsDropTarget) so dragging onto a spot already covered
+// by a band still moves the dragged entry.
+export function renderWeekBands(weekYmd, layout, entriesById, tctx) {
   const weekStart = weekYmd[0];
   const weekEnd = weekYmd[6];
   const inWeek = layout.stays.filter((s) => s.start <= weekEnd && s.end >= weekStart);
@@ -103,6 +106,7 @@ export function renderWeekBands(weekYmd, layout, tctx) {
     makeBandDraggable(band, s.entry);
     strip.appendChild(band);
   }
+  makeWeekBandsDropTarget(strip, weekYmd, entriesById, tctx);
   return strip;
 }
 

src/server/db.js

@@ -47,6 +47,7 @@ CREATE TABLE IF NOT EXISTS entries (
   segments TEXT,
   rental TEXT,
   transport_mode TEXT,
+  auto_ref TEXT,
   created_at TEXT DEFAULT current_timestamp
 );
 
@@ -73,6 +74,7 @@ const MIGRATIONS = [
   { table: 'entries', column: 'rental', ddl: 'ALTER TABLE entries ADD COLUMN rental TEXT' },
   { table: 'entries', column: 'end_date', ddl: 'ALTER TABLE entries ADD COLUMN end_date TEXT' },
   { table: 'entries', column: 'transport_mode', ddl: 'ALTER TABLE entries ADD COLUMN transport_mode TEXT' },
+  { table: 'entries', column: 'auto_ref', ddl: 'ALTER TABLE entries ADD COLUMN auto_ref TEXT' },
   { table: 'trip_members', column: 'sort_order', ddl: 'ALTER TABLE trip_members ADD COLUMN sort_order INTEGER NOT NULL DEFAULT 0' },
 ];
 

src/server/routes/entries.js

@@ -4,6 +4,7 @@ import { membership } from '../util/access.js';
 import { ENTRY_COLUMNS, attachParticipants } from '../util/entrySerialize.js';
 import { validateSegments } from '../util/segments.js';
 import { validateRental } from '../util/rental.js';
+import { autoTransportTitle } from '../util/autoTransport.js';
 
 const ENTRY_TYPES = new Set(['flight', 'transport', 'activity', 'rental', 'stay', 'note']);
 const TRANSPORT_MODES = new Set(['train', 'bus', 'ferry', 'taxi', 'drive', 'other']);
@@ -234,8 +235,8 @@ export default function entriesRoutes(db) {
      AND date >= ? AND date <= ? LIMIT 1`
   );
   const insertAutoTransport = db.prepare(
-    `INSERT INTO entries (trip_id, date, type, title, details, sort_order, split_mode)
-     VALUES (?, ?, 'transport', ?, '', 0, 'equal')`
+    `INSERT INTO entries (trip_id, date, type, title, details, sort_order, split_mode, auto_ref)
+     VALUES (?, ?, 'transport', ?, '', 0, 'equal', ?)`
   );
 
   const memberIdSet = (tripId) => new Set(getMemberIds.all(tripId).map((r) => r.user_id));
@@ -247,12 +248,6 @@ export default function entriesRoutes(db) {
     }
   }
 
-  // Short name for an auto-transport title: first comma-segment of the stay's
-  // location_name, falling back to its title.
-  function shortName(stay) {
-    return (stay.location_name || stay.title).split(',')[0].trim();
-  }
-
   // Auto-create a transport entry bridging `earlier` -> `later` (both stay
   // rows) unless a transport/flight already covers the gap, or the window is
   // inverted (overlapping stays).
@@ -261,8 +256,12 @@ export default function entriesRoutes(db) {
     const windowEnd = later.date;
     if (windowStart > windowEnd) return;
     if (existsTransportOrFlightInWindow.get(tripId, windowStart, windowEnd)) return;
-    const title = `${shortName(earlier)} → ${shortName(later)}`;
-    insertAutoTransport.run(tripId, later.date, title);
+    insertAutoTransport.run(
+      tripId,
+      later.date,
+      autoTransportTitle(earlier, later),
+      JSON.stringify({ from: earlier.id, to: later.id })
+    );
   }
 
   // Fires once, on stay creation: bridges the new stay to its nearest

src/server/routes/trips.js

@@ -10,6 +10,7 @@ import {
   parseRental,
 } from '../util/entrySerialize.js';
 import { generateJoinCode, formatJoinCode, normalizeCode } from '../util/token.js';
+import { regenerateAutoTransports } from '../util/autoTransport.js';
 
 const MAX_RANGE_DAYS = 365;
 const MIN_LEG_KM = 0.05;
@@ -295,6 +296,15 @@ export default function tripsRoutes(db) {
     res.status(204).end();
   });
 
+  // POST /api/trips/:id/transports/regenerate  (any member) — reconcile
+  // auto-created transports against the trip's current stays.
+  router.post('/:id/transports/regenerate', (req, res) => {
+    const ctx = requireMember(req, res);
+    if (!ctx) return;
+    const result = db.transaction(() => regenerateAutoTransports(db, ctx.tripId))();
+    res.status(200).json(result);
+  });
+
   // GET /api/trips/:id/route  (computed legs + summary)
   router.get('/:id/route', (req, res) => {
     const ctx = requireMember(req, res);

src/server/util/autoTransport.js

@@ -0,0 +1,122 @@
+// Auto-created transport entries bridging chronologically adjacent stays.
+// Shared between entries.js (creation-time auto-transport, fires once when a
+// stay is POSTed) and trips.js (the regenerate endpoint, which reconciles
+// auto transports after stays have been moved/added/removed). See
+// "Auto-transport between stays" / "Regenerating auto-transports" in
+// docs/API.md.
+
+// Short name for an auto-transport title: first comma-segment of the stay's
+// location_name, falling back to its title.
+export function shortName(stay) {
+  return (stay.location_name || stay.title).split(',')[0].trim();
+}
+
+export function autoTransportTitle(earlier, later) {
+  return `${shortName(earlier)} → ${shortName(later)}`;
+}
+
+// Reconcile auto-created transport entries against the trip's current stays.
+// Returns { created, updated, deleted }. Caller is responsible for wrapping
+// this in a db.transaction.
+export function regenerateAutoTransports(db, tripId) {
+  const stays = db
+    .prepare(
+      `SELECT id, date, end_date, location_name, title FROM entries
+       WHERE trip_id = ? AND type = 'stay' ORDER BY date, id`
+    )
+    .all(tripId);
+
+  // Manual coverage: any flight, or any transport entry with no auto_ref
+  // (a human-created transport), blocks auto-transport for a window.
+  const blockers = db
+    .prepare(
+      `SELECT date FROM entries WHERE trip_id = ?
+       AND (type = 'flight' OR (type = 'transport' AND auto_ref IS NULL))`
+    )
+    .all(tripId);
+
+  const desired = [];
+  for (let i = 0; i < stays.length - 1; i++) {
+    const earlier = stays[i];
+    const later = stays[i + 1];
+    const windowStart = earlier.end_date || earlier.date;
+    const windowEnd = later.date;
+    if (windowStart > windowEnd) continue; // inverted/overlapping window
+    const blocked = blockers.some((b) => b.date >= windowStart && b.date <= windowEnd);
+    if (blocked) continue;
+    desired.push({ from: earlier.id, to: later.id, earlier, later });
+  }
+
+  // Existing auto transports (auto_ref non-null and parseable); unparseable
+  // auto_ref is treated as manual (never touched, per predating-databases rule).
+  const existingRows = db
+    .prepare(
+      `SELECT id, auto_ref FROM entries WHERE trip_id = ? AND type = 'transport' AND auto_ref IS NOT NULL`
+    )
+    .all(tripId);
+  const existingAuto = [];
+  for (const row of existingRows) {
+    let ref;
+    try {
+      ref = JSON.parse(row.auto_ref);
+    } catch {
+      continue;
+    }
+    if (!ref || typeof ref !== 'object' || !Number.isInteger(ref.from) || !Number.isInteger(ref.to)) {
+      continue;
+    }
+    existingAuto.push({ id: row.id, from: ref.from, to: ref.to });
+  }
+
+  const updateStmt = db.prepare('UPDATE entries SET date = ?, title = ? WHERE id = ?');
+  const deleteStmt = db.prepare('DELETE FROM entries WHERE id = ?');
+  const deleteParticipantsStmt = db.prepare('DELETE FROM entry_participants WHERE entry_id = ?');
+  const insertStmt = db.prepare(
+    `INSERT INTO entries (trip_id, date, type, title, details, sort_order, split_mode, auto_ref)
+     VALUES (?, ?, 'transport', ?, '', 0, 'equal', ?)`
+  );
+
+  function removeEntry(id) {
+    deleteParticipantsStmt.run(id);
+    deleteStmt.run(id);
+  }
+
+  let created = 0;
+  let updated = 0;
+  let deleted = 0;
+  const matchedIds = new Set();
+
+  for (const pair of desired) {
+    const matches = existingAuto
+      .filter((e) => e.from === pair.from && e.to === pair.to)
+      .sort((a, b) => a.id - b.id);
+    if (matches.length > 0) {
+      const [keep, ...dupes] = matches;
+      matchedIds.add(keep.id);
+      updateStmt.run(pair.later.date, autoTransportTitle(pair.earlier, pair.later), keep.id);
+      updated++;
+      for (const dupe of dupes) {
+        matchedIds.add(dupe.id);
+        removeEntry(dupe.id);
+        deleted++;
+      }
+    } else {
+      insertStmt.run(
+        tripId,
+        pair.later.date,
+        autoTransportTitle(pair.earlier, pair.later),
+        JSON.stringify({ from: pair.from, to: pair.to })
+      );
+      created++;
+    }
+  }
+
+  for (const e of existingAuto) {
+    if (!matchedIds.has(e.id)) {
+      removeEntry(e.id);
+      deleted++;
+    }
+  }
+
+  return { created, updated, deleted };
+}

src/server/util/entrySerialize.js

@@ -4,7 +4,7 @@
 
 export const ENTRY_COLUMNS =
   'id, trip_id, date, end_date, type, title, details, start_time, end_time, ' +
-  'location_name, lat, lng, sort_order, price, paid_by, split_mode, segments, rental, transport_mode';
+  'location_name, lat, lng, sort_order, price, paid_by, split_mode, segments, rental, transport_mode, auto_ref';
 
 // Parse the stored segments JSON text into an array, or null if absent/invalid.
 export function parseSegments(value) {
@@ -28,6 +28,19 @@ export function parseRental(value) {
   }
 }
 
+// Parse the stored auto_ref JSON text into a {from,to} object, or null if
+// absent/invalid. Non-null marks an entry as auto-created (see "Auto-transport
+// between stays" in docs/API.md).
+export function parseAutoRef(value) {
+  if (!value) return null;
+  try {
+    const parsed = JSON.parse(value);
+    return parsed && typeof parsed === 'object' && !Array.isArray(parsed) ? parsed : null;
+  } catch {
+    return null;
+  }
+}
+
 export function attachParticipants(db, row) {
   if (!row) return row;
   const rows = db
@@ -36,6 +49,7 @@ export function attachParticipants(db, row) {
   row.participants = rows.map((r) => r.user_id);
   row.segments = parseSegments(row.segments);
   row.rental = parseRental(row.rental);
+  row.auto_ref = parseAutoRef(row.auto_ref);
   return row;
 }
 

tests/api.test.js

@@ -325,7 +325,7 @@ test('entry CRUD and full-row shape', async () => {
   const entry = create.body.entry;
   assert.deepEqual(
     Object.keys(entry).sort(),
-    ['date', 'end_date', 'details', 'end_time', 'id', 'lat', 'lng', 'location_name', 'paid_by', 'participants', 'price', 'rental', 'segments', 'sort_order', 'split_mode', 'start_time', 'title', 'transport_mode', 'trip_id', 'type'].sort()
+    ['auto_ref', 'date', 'end_date', 'details', 'end_time', 'id', 'lat', 'lng', 'location_name', 'paid_by', 'participants', 'price', 'rental', 'segments', 'sort_order', 'split_mode', 'start_time', 'title', 'transport_mode', 'trip_id', 'type'].sort()
   );
   assert.equal(entry.end_date, null);
   assert.equal(entry.details, '');

tests/transport.test.js

@@ -178,6 +178,8 @@ test('auto-transport: creates a bridging entry between two consecutive stays', a
   assert.equal(transports[0].title, 'Venice → Berlin');
   assert.equal(transports[0].date, berlin.date);
   assert.equal(transports[0].sort_order, 0);
+  assert.ok(transports[0].auto_ref);
+  assert.equal(transports[0].auto_ref.to, berlin.id);
 
   const route = await agent.get(`/api/trips/${trip.id}/route`);
   assert.equal(route.body.summary.transports, 1);
@@ -275,3 +277,158 @@ test('auto-transport: deleting it is not resurrected by an unrelated later stay'
   list = (await agent.get(base)).body.entries;
   assert.ok(!list.some((e) => e.type === 'transport' && e.title === 'Venice → Berlin'));
 });
+
+// ---------------------------------------------------------------------------
+// Regenerating auto-transports
+// ---------------------------------------------------------------------------
+
+test('auto_ref cannot be set via POST/PATCH bodies', async () => {
+  const { agent } = await createAccount();
+  const trip = await makeTrip(agent);
+  const base = `/api/trips/${trip.id}/entries`;
+
+  const posted = await agent.post(base).send({
+    date: '2026-08-01', type: 'transport', title: 'x', auto_ref: { from: 1, to: 2 },
+  });
+  assert.equal(posted.status, 201);
+  assert.equal(posted.body.entry.auto_ref, null);
+
+  const patched = await agent.patch(`/api/entries/${posted.body.entry.id}`).send({
+    auto_ref: { from: 1, to: 2 },
+  });
+  assert.equal(patched.status, 200);
+  assert.equal(patched.body.entry.auto_ref, null);
+});
+
+test('regenerate: non-member gets 404', async () => {
+  const { agent } = await createAccount();
+  const trip = await makeTrip(agent);
+  const { agent: other } = await createAccount();
+
+  const res = await other.post(`/api/trips/${trip.id}/transports/regenerate`);
+  assert.equal(res.status, 404);
+});
+
+test('regenerate: re-dates and re-titles the auto transport after a stay moves, preserving transport_mode', async () => {
+  const { agent } = await createAccount();
+  const trip = await makeTrip(agent);
+  const base = `/api/trips/${trip.id}/entries`;
+
+  await agent.post(base).send({
+    date: '2026-08-01', end_date: '2026-08-03', type: 'stay', title: 'V', location_name: 'Venice',
+  });
+  const berlin = (await agent.post(base).send({
+    date: '2026-08-04', type: 'stay', title: 'B', location_name: 'Berlin',
+  })).body.entry;
+
+  let list = (await agent.get(base)).body.entries;
+  const auto = list.find((e) => e.type === 'transport');
+  assert.ok(auto);
+  await agent.patch(`/api/entries/${auto.id}`).send({ transport_mode: 'train' });
+
+  // Move Berlin later; still the second stay -> same (from,to) pair.
+  await agent.patch(`/api/entries/${berlin.id}`).send({ date: '2026-08-20' });
+
+  const res = await agent.post(`/api/trips/${trip.id}/transports/regenerate`);
+  assert.equal(res.status, 200);
+  assert.deepEqual(res.body, { created: 0, updated: 1, deleted: 0 });
+
+  list = (await agent.get(base)).body.entries;
+  const updated = list.find((e) => e.type === 'transport');
+  assert.equal(updated.id, auto.id);
+  assert.equal(updated.date, '2026-08-20');
+  assert.equal(updated.title, 'Venice → Berlin');
+  assert.equal(updated.transport_mode, 'train');
+});
+
+test('regenerate: deletes an auto transport orphaned by a deleted stay', async () => {
+  const { agent } = await createAccount();
+  const trip = await makeTrip(agent);
+  const base = `/api/trips/${trip.id}/entries`;
+
+  await agent.post(base).send({
+    date: '2026-08-01', end_date: '2026-08-03', type: 'stay', title: 'V', location_name: 'Venice',
+  });
+  const berlin = (await agent.post(base).send({
+    date: '2026-08-04', type: 'stay', title: 'B', location_name: 'Berlin',
+  })).body.entry;
+
+  await agent.delete(`/api/entries/${berlin.id}`);
+
+  const res = await agent.post(`/api/trips/${trip.id}/transports/regenerate`);
+  assert.equal(res.status, 200);
+  assert.deepEqual(res.body, { created: 0, updated: 0, deleted: 1 });
+
+  const list = (await agent.get(base)).body.entries;
+  assert.equal(list.filter((e) => e.type === 'transport').length, 0);
+});
+
+test('regenerate: recreates a missing auto transport', async () => {
+  const { agent } = await createAccount();
+  const trip = await makeTrip(agent);
+  const base = `/api/trips/${trip.id}/entries`;
+
+  await agent.post(base).send({
+    date: '2026-08-01', end_date: '2026-08-03', type: 'stay', title: 'V', location_name: 'Venice',
+  });
+  await agent.post(base).send({
+    date: '2026-08-04', type: 'stay', title: 'B', location_name: 'Berlin',
+  });
+
+  let list = (await agent.get(base)).body.entries;
+  const auto = list.find((e) => e.type === 'transport');
+  await agent.delete(`/api/entries/${auto.id}`);
+
+  const res = await agent.post(`/api/trips/${trip.id}/transports/regenerate`);
+  assert.equal(res.status, 200);
+  assert.deepEqual(res.body, { created: 1, updated: 0, deleted: 0 });
+
+  list = (await agent.get(base)).body.entries;
+  const recreated = list.find((e) => e.type === 'transport');
+  assert.ok(recreated);
+  assert.equal(recreated.title, 'Venice → Berlin');
+  assert.ok(recreated.auto_ref);
+});
+
+test('regenerate: respects manual transport coverage — creates nothing and does not delete it', async () => {
+  const { agent } = await createAccount();
+  const trip = await makeTrip(agent);
+  const base = `/api/trips/${trip.id}/entries`;
+
+  await agent.post(base).send({
+    date: '2026-08-01', end_date: '2026-08-03', type: 'stay', title: 'V', location_name: 'Venice',
+  });
+  const manual = (await agent.post(base).send({
+    date: '2026-08-03', type: 'transport', title: 'Manual train',
+  })).body.entry;
+  await agent.post(base).send({
+    date: '2026-08-04', type: 'stay', title: 'B', location_name: 'Berlin',
+  });
+
+  // No auto transport was created at stay-creation time (manual already covers the window).
+  let list = (await agent.get(base)).body.entries;
+  assert.equal(list.filter((e) => e.type === 'transport').length, 1);
+
+  const res = await agent.post(`/api/trips/${trip.id}/transports/regenerate`);
+  assert.equal(res.status, 200);
+  assert.deepEqual(res.body, { created: 0, updated: 0, deleted: 0 });
+
+  list = (await agent.get(base)).body.entries;
+  const transports = list.filter((e) => e.type === 'transport');
+  assert.equal(transports.length, 1);
+  assert.equal(transports[0].id, manual.id);
+  assert.equal(transports[0].auto_ref, null);
+});
+
+test('regenerate: overlapping stays (inverted window) produce no pair and do not crash', async () => {
+  const { agent } = await createAccount();
+  const trip = await makeTrip(agent);
+  const base = `/api/trips/${trip.id}/entries`;
+
+  await agent.post(base).send({ date: '2026-08-01', end_date: '2026-08-10', type: 'stay', title: 'Region' });
+  await agent.post(base).send({ date: '2026-08-05', type: 'stay', title: 'City inside' });
+
+  const res = await agent.post(`/api/trips/${trip.id}/transports/regenerate`);
+  assert.equal(res.status, 200);
+  assert.deepEqual(res.body, { created: 0, updated: 0, deleted: 0 });
+});