trip-plan/docs/API.md

# Trip Plan — API Contract

All endpoints are JSON over REST, prefixed with `/api`. This document is the **binding contract** between backend and frontend. Do not deviate; extend only by agreement.

## Conventions

- Dates: `YYYY-MM-DD` strings. Times: `HH:MM` 24h strings (optional fields).
- Auth: cookie session (`cookie-session`). All endpoints except `account` (create) / `login` require auth → otherwise `401 {"error":"unauthorized"}`.
- Identity is Mullvad-style: an account is a random **account token** (the only credential — no username/password). Users additionally have a non-unique, editable `display_name` for humans.
- Trip access: user must be a member of the trip → otherwise `404 {"error":"not found"}` (don't leak existence).
- Errors: `4xx/5xx` with body `{"error": "<human readable message>"}`.
- IDs are integers.

## Server layout

- `src/server/app.js` — builds and **exports** the Express app (`export function createApp(dbPath)` and `export default` a ready app is fine, but `createApp` must exist for tests).
- `src/server/index.js` — reads env (`PORT` default 3000, `DATA_DIR` default `./data`, `SESSION_SECRET` default dev value with console warning), ensures DATA_DIR exists, starts listener, serves `public/` statically.
- `src/server/db.js` — `better-sqlite3` connection + schema creation (idempotent `CREATE TABLE IF NOT EXISTS`).
- `src/server/routes/` — `auth.js`, `trips.js`, `entries.js`, `geocode.js`, `checklist.js`.
- `src/server/util/distance.js` — `haversineKm(lat1, lng1, lat2, lng2)` returns km (number).

## Data model (SQLite)

```sql
users        (id INTEGER PK, token_hash TEXT UNIQUE NOT NULL,   -- sha256 hex of the account token
              display_name TEXT NOT NULL,                        -- auto-generated, editable, NOT unique
              created_at TEXT DEFAULT current_timestamp)
trips        (id INTEGER PK, name TEXT NOT NULL, start_date TEXT NOT NULL, end_date TEXT NOT NULL,
              owner_id INTEGER NOT NULL REFERENCES users(id),
              currency TEXT NOT NULL DEFAULT 'USD',   -- 3-letter code, display only (no FX)
              join_code TEXT UNIQUE NOT NULL,         -- share code for joining the trip
              created_at TEXT DEFAULT current_timestamp)
trip_members (trip_id INTEGER REFERENCES trips(id), user_id INTEGER REFERENCES users(id),
              role TEXT NOT NULL DEFAULT 'editor',  -- 'owner' | 'editor'
              sort_order INTEGER NOT NULL DEFAULT 0, -- per-user dashboard order (drag & drop)
              PRIMARY KEY (trip_id, user_id))
entries      (id INTEGER PK, trip_id INTEGER NOT NULL REFERENCES trips(id),
              date TEXT NOT NULL,          -- start date
              end_date TEXT,               -- optional inclusive end date (multi-day entries; null = single day)
              type TEXT NOT NULL,
              title TEXT NOT NULL, details TEXT DEFAULT '',
              start_time TEXT, end_time TEXT,
              location_name TEXT, lat REAL, lng REAL,
              sort_order INTEGER NOT NULL DEFAULT 0,
              price REAL,                             -- null = no cost tracked
              paid_by INTEGER REFERENCES users(id),   -- who paid (null = unassigned)
              split_mode TEXT NOT NULL DEFAULT 'equal', -- 'equal' | 'own' | 'payer'
              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)
              waypoints TEXT,                         -- JSON [{lat,lng,name?}] scenic via-points, transport entries only (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))
              -- no rows for an entry = "all trip members participate" (dynamic default)
checklist_items (id INTEGER PK, trip_id INTEGER NOT NULL REFERENCES trips(id),
              user_id INTEGER REFERENCES users(id),   -- null = shared trip item; else personal to that user
              text TEXT NOT NULL,                     -- what to pack/do, ≤120 chars
              category TEXT NOT NULL DEFAULT 'General',
              qty INTEGER,                            -- optional count (null = unspecified)
              checked INTEGER NOT NULL DEFAULT 0,     -- 0/1
              checked_by INTEGER REFERENCES users(id),-- who ticked it (null when unchecked)
              sort_order INTEGER NOT NULL DEFAULT 0,
              suggestion_key TEXT,                    -- non-null = added from packing advice (dedupe key)
              created_at TEXT DEFAULT current_timestamp)
```

Entry `type` ∈ `flight | transport | activity | rental | stay | note`.

**Legacy types** (removed 2026-07): `hotel`, `travel`, `immigration`. Idempotent data migrations run at startup: `hotel` rows become `stay`, `travel` rows become `transport`, `immigration` rows become `activity` with the title prefixed `🛂 `. POST/PATCH with a legacy type is a 400 (`invalid entry type`).

### Transport entries

`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).

**Scenic waypoints** — a transport entry may carry `waypoints`: an ordered JSON array of via-points the road route should pass through (e.g. a mountain pass instead of the highway). Shape `[{"lat": 46.5, "lng": 10.45, "name": "Stelvio Pass"}]`. Validation: only allowed when the effective `type === 'transport'` (else 400 `waypoints are only allowed on transport entries`); array of 0–8 objects; each needs `lat`/`lng` (finite, lat [-90,90], lng [-180,180]); `name` optional string ≤120 chars; `waypoints: null` or `[]` clears them. Entry JSON always includes `waypoints` (parsed array or null; `[]` is normalized to null on store). Not accepted on non-transport types.

Waypoints attach to a **route leg** (see Route below): a ground leg between two located stops is drawn through the via-points of the transport entry that bridges it.

**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

Any entry may carry an optional `end_date` (inclusive, `YYYY-MM-DD`, must be ≥ `date`; PATCH `end_date: null` clears it). Use cases:

- **Flights/travel longer than 24 h** — dep on `date` at `start_time`, arr on `end_date` at `end_time`.
- **`stay` entries ("area blocks")** — "3 days Venice", "7 days Berlin": a location plus a date range. The frontend renders stays as continuous bands across the calendar days (all-day-event style), not as chips; other multi-day entries show a chip on the start day and lightweight "…continues" markers on the days up to `end_date`.

Stays behave like normal entries otherwise: optional geocoded location (feeds the route as one stop, positioned at the start date), optional price/split (e.g. an apartment for the whole block).

Summary additions: `stays` (count) and `areas` — stay entries in chronological order as `[{ "name": "Venice", "days": 3 }]` where `name` is the stay's `location_name` (fallback: title) and `days` is the inclusive span (`end_date` null → 1). Example: `"areas": [{"name":"Venice","days":3},{"name":"Berlin","days":7}]`.

### Rental car details

`rental`-type entries can carry structured rental data in `entries.rental` (TEXT, JSON — same storage pattern as flight segments). `null`/absent = plain entry.

```json
"rental": {
  "brand": "Toyota", "model": "Yaris Cross", "car_type": "SUV",
  "booking_ref": "RC-889231", "included_km": 1500,
  "pickup":  { "date": "2026-08-01", "time": "09:00", "location_name": "CNX Airport",
               "lat": 18.77, "lng": 98.96 },
  "dropoff": { "date": "2026-08-07", "time": "18:00", "location_name": "Chiang Mai Old Town",
               "lat": 18.79, "lng": 98.98 }
}
```

Validation (POST/PATCH entries): only allowed when `type === 'rental'` (else 400); all fields optional; `brand`/`model` ≤60, `car_type` ≤40, `booking_ref` ≤60 chars; `included_km` null (= unlimited/unknown) or number ≥ 0; `pickup`/`dropoff` objects with `date` (YYYY-MM-DD, required within the object), optional `time` HH:MM, `location_name` ≤120, lat/lng both-or-neither in range. PATCH `rental: null` clears. Entry JSON always includes `rental` (parsed or null). The entry's own `date` should be the pickup date (frontend sets this); the entry's price/split fields carry the rental cost as usual.

Summary impact: `summary.rentals` counts rental entries; `summary.includedKm` = sum of non-null `included_km` across rentals, or null when no rental specifies one — the frontend pairs it with `kmDriven` ("≈ 520 km driven / 1,500 km included"). Rental pickup/dropoff locations do NOT feed the route (use the entry's normal location field for a map point if wanted).

### Flight segments

Flight entries can carry structured **segments** for multi-leg itineraries (e.g. CNX→BKK→DXB→FRA = 3 segments). Stored as JSON in `entries.segments`, returned parsed. `null`/absent = no segments (plain entry).

```json
"segments": [
  { "flight_no": "TG103", "dep_time": "10:30", "arr_time": "11:45",
    "from": {"code": "CNX", "name": "Chiang Mai Intl", "lat": 18.77, "lng": 98.96},
    "to":   {"code": "BKK", "name": "Suvarnabhumi",    "lat": 13.68, "lng": 100.75} },
  { "flight_no": "EK385", "dep_time": "13:05", "arr_time": "17:10",
    "from": {"code": "BKK", "name": "Suvarnabhumi",    "lat": 13.68, "lng": 100.75},
    "to":   {"code": "DXB", "name": "Dubai Intl",      "lat": 25.25, "lng": 55.36} }
]
```

Validation (POST/PATCH entries): only allowed when `type === 'flight'` (else 400); array of 1–8 objects; each needs `from` and `to` with `code` (2–4 uppercase alphanumerics); `name` optional ≤80 chars; `lat`/`lng` both-or-neither, same ranges as entry lat/lng; `flight_no` optional ≤12 chars; `dep_time`/`arr_time` optional `HH:MM`. PATCH with `segments: null` clears them.

**Route expansion**: an entry whose segments have coordinates contributes airport stops to `/route` instead of its own lat/lng — `from` of the first segment, then `to` of every segment, in order (airports without coords are skipped; consecutive duplicate coords are collapsed). Stops derived this way have `"kind": "airport"` and include `"code"`. So CNX-BKK-DXB-FRA yields 4 stops and 3 measured legs on the map.

### Airports lookup

`GET /api/airports?q=<query>` → `200 {results: [{code, name, city, country, lat, lng}]}` (max 8; requires auth).

Backed by a bundled dataset at `src/server/data/airports.json` generated from the public-domain OurAirports data (filter: has IATA code + scheduled service; keep code/name/municipality/iso_country/lat/lng). Matching: exact/prefix IATA code match first (case-insensitive), then name/city substring. This makes `CNX` → Chiang Mai Intl instant and offline.

### Cost semantics

- Only entries with non-null `price` count toward costs.
- **Effective participants** of an entry = its `entry_participants` rows, or **all current trip members** if it has none.
- `split_mode`:
  - `equal` — `price` is the TOTAL; split equally among effective participants ("rental car 50/50"). `paid_by` is credited with having paid the total.
  - `own` — `price` is PER PERSON; each effective participant owes and pays their own ("everyone pays their own flight"). No debt created. Effective total = price × participant count.
  - `payer` — personal expense: `paid_by` owes and pays the whole price alone (requires `paid_by`; validation error otherwise).

## Endpoints

### Auth (Mullvad-style account tokens)

| Method & path | Body | Response |
|---|---|---|
| `POST /api/auth/account` | `{}` (empty) | `201 {user: {id, display_name}, token: "XXXX-XXXX-XXXX-XXXX"}` — creates an account, logs it in. The raw token is returned ONLY here, never again. |
| `POST /api/auth/login` | `{token}` | `200 {user}`; `401` on unknown token |
| `POST /api/auth/logout` | — | `204` |
| `GET /api/auth/me` | — | `200 {user: {id, display_name}}` or `401` |
| `PATCH /api/auth/me` | `{display_name}` | `200 {user}`; validates 1–40 chars after trim |

Token rules:
- 16 chars from the unambiguous alphabet `ABCDEFGHJKMNPQRSTUVWXYZ23456789` (no I/L/O/0/1), generated with `crypto.randomBytes`, displayed grouped `XXXX-XXXX-XXXX-XXXX`.
- Login normalizes input: strip dashes/spaces, uppercase, then compare `sha256(token)` against `users.token_hash`. Only the hash is stored.
- `display_name` is auto-generated at account creation as `adjective-animal` (e.g. `brave-otter`) from two small built-in word lists; not unique; user-editable via PATCH.

User JSON shape everywhere: `{id, display_name}`.

### Trips

| Method & path | Body | Response |
|---|---|---|
| `GET /api/trips` | — | `200 {trips: [{id, name, start_date, end_date, owner_id, currency, role, sort_order, member_count, entry_count}]}` (trips where user is member, ordered by the caller's `trip_members.sort_order`, then newest first for ties) |
| `POST /api/trips` | `{name, start_date, end_date, currency?}` | `201 {trip}`; validates: name non-empty ≤120 chars, valid dates, `end_date >= start_date`, range ≤ 365 days, currency (if given) matches `^[A-Z]{3}$` (default `USD`). Creator becomes member with role `owner`. |
| `GET /api/trips/:id` | — | `200 {trip: {id, name, start_date, end_date, owner_id, currency, join_code}, members: [{id, display_name, role}], entries: [entry…]}` entries ordered by `(date, sort_order, id)` |
| `PATCH /api/trips/:id` | any of `{name, start_date, end_date, currency}` | `200 {trip}` (same validation; entries outside new range are kept) |
| `PATCH /api/trips/:id/order` | `{sort_order}` | `200 {sort_order}` — updates the CALLER's own `trip_members.sort_order` for this trip (any member; integer required, else 400). Per-user: does not affect other members' dashboard order. |
| `DELETE /api/trips/:id` | — | `204` — owner only, else `403`. Deletes members + entries too. |
| `POST /api/trips/join` | `{code}` | `200 {trip}` — joins the trip with that join_code as `editor` (idempotent: already a member → still `200 {trip}`); `404 {"error":"not found"}` on unknown code. Code normalized like tokens (strip dashes/spaces, uppercase). |
| `POST /api/trips/:id/join-code` | — | `200 {trip}` — regenerates join_code, owner only (`403` otherwise) |
| `DELETE /api/trips/:id/members/:userId` | — | `204` — owner only (owner cannot remove self) |

`join_code`: 8 chars, same alphabet as account tokens, generated at trip creation, displayed grouped `XXXX-XXXX`. Members see it in trip JSON (it's how they invite others); it is NOT a credential — it only grants membership of that one trip.

### Entries

| Method & path | Body | Response |
|---|---|---|
| `POST /api/trips/:id/entries` | `{date, end_date?, type, title, details?, start_time?, end_time?, location_name?, lat?, lng?, sort_order?, price?, paid_by?, split_mode?, participants?, segments?}` | `201 {entry}`; validates type enum, date format, end_date null or valid date ≥ date, title non-empty ≤200 chars; lat/lng must both be present or both absent, lat ∈ [-90,90], lng ∈ [-180,180]; price null or number ≥ 0; paid_by null or a trip member's user id; split_mode ∈ `equal\|own\|payer` (`payer` requires paid_by); participants null/[] (= all members) or array of trip-member user ids; segments per "Flight segments" above; transport_mode per "Transport entries" above (POSTing a stay may auto-create a transport entry, see same section) |
| `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, auto_ref, waypoints}` where `participants` is an array of user ids (`[]` = all members), `segments` is the parsed array or `null`, `auto_ref` is the parsed `{from,to}` object or `null`, and `waypoints` is the parsed `[{lat,lng,name?}]` array or `null`. `auto_ref` is server-managed (not accepted in POST/PATCH bodies; editing an auto transport keeps its `auto_ref`).

### Checklist (packing list & advice)

Each trip has one flat checklist whose items are grouped by a free-text `category` ("Documents", "Clothing", …). Items are either **shared** (`user_id` null — every member sees and can tick them, e.g. "First-aid kit") or **personal** (`user_id` = the owner — only that user sees them, e.g. their own medication). There is no separate list entity: `category` is the grouping.

`GET /api/trips/:id/checklist` → `200`

```json
{
  "items": [
    { "id": 7, "trip_id": 3, "text": "Passport (valid 6+ months)", "category": "Documents",
      "qty": null, "checked": true, "checked_by": 1, "personal": false,
      "user_id": null, "sort_order": 0, "suggestion_key": "doc-passport" },
    { "id": 9, "trip_id": 3, "text": "T-shirts", "category": "Clothing",
      "qty": 8, "checked": false, "checked_by": null, "personal": true,
      "user_id": 1, "sort_order": 1, "suggestion_key": "clothing-tshirts" }
  ],
  "progress": { "total": 2, "checked": 1, "byCategory": [ { "category": "Documents", "total": 1, "checked": 1 } ] }
}
```

- Returns shared items **plus the caller's own personal items** — never another member's personal items.
- Item JSON is always the full row plus the derived boolean `personal` (`user_id !== null`); `checked` is a real boolean (not 0/1) and `qty`/`checked_by`/`suggestion_key` are `null` when unset.
- Order: by `category` first (fixed order `Documents, Clothing, Toiletries, Health, Electronics, Extras`, then any other category alphabetically), then `(sort_order, id)`.
- `progress.byCategory` follows the same category order and covers only categories present in `items`.

| Method & path | Body | Response |
|---|---|---|
| `POST /api/trips/:id/checklist` | `{text, category?, qty?, personal?, checked?, sort_order?}` | `201 {item}` — validates: `text` non-empty ≤120 chars after trim; `category` ≤40 chars after trim (default `General`); `qty` null or integer 1–99; `personal` boolean (default `false`) → sets `user_id` to the caller; `checked` boolean (default `false`); `sort_order` integer (default: max within the trip's list + 1). Member of the trip required (else `404`). |
| `PATCH /api/checklist/:itemId` | any subset of `{text, category, qty, checked, personal, sort_order}` | `200 {item}` — same validation. Ticking (`checked: true`) sets `checked_by` to the caller; `checked: false` clears it. `personal: true` claims the item for the caller (`user_id` = caller), `personal: false` makes it shared (`user_id` null). |
| `DELETE /api/checklist/:itemId` | — | `204` |
| `POST /api/trips/:id/checklist/reset` | `{}` | `200 {unchecked: <count>}` — unticks every item **visible to the caller** (shared + own personal) and clears their `checked_by`. For re-using a list on the return trip. |

Item routes resolve the trip via the item, then require membership. A non-existent item, an item in a trip the caller is not a member of, **or another user's personal item** all return `404 {"error":"not found"}` (no leaking).

**Packing advice (suggestions)** — deterministic, offline rules derived from the trip itself (duration, months, entry types, destination latitudes/countries). No external service, no LLM.

`GET /api/trips/:id/checklist/suggestions` → `200`

```json
{
  "suggestions": [
    { "key": "doc-passport", "text": "Passport (valid 6+ months)", "category": "Documents",
      "qty": null, "reason": "You have 2 flights", "added": true },
    { "key": "clothing-tshirts", "text": "T-shirts", "category": "Clothing",
      "qty": 8, "reason": "9 nights", "added": false }
  ],
  "context": { "days": 10, "nights": 9, "months": [8], "countries": ["Thailand"],
               "climate": ["tropical"], "flights": 2, "rentals": 1, "transportModes": ["ferry"] }
}
```

- `key` is a stable identifier (kebab-case) — it is what `POST` takes and what gets stored in `checklist_items.suggestion_key`.
- `added` = an item with that `suggestion_key` already exists among the items visible to the caller (shared or own personal), so the UI can grey it out.
- `reason` is a short human string explaining why it was suggested ("9 nights", "Ferry crossing", "Thailand uses type A/B/C sockets"). Suggestions are ordered by category (same fixed order as items).
- Rules live in `src/server/util/packing.js` as a pure `buildSuggestions({trip, entries, days, nights})` so they are unit-testable and stable across calls with the same input. Rough rule set: always-on basics (ID/passport, cards+cash, medication, toothbrush, phone+charger, water bottle, day bag); nights-scaled clothing quantities (`qty = min(nights + 1, 10)` for t-shirts/underwear/socks, laundry kit over 7 nights); flight entries → liquids ≤100 ml, power bank in cabin, check-in done, plus neck pillow/compression socks on long-haul (any air leg > 5000 km); rental entries → driving licence, international driving permit, phone mount; transport modes → ferry ⇒ motion-sickness tablets, train ⇒ snacks + luggage lock; destination latitude/month → tropical (|lat| < 23.5) ⇒ sun cream, insect repellent, rain jacket, rehydration salts; cold (|lat| > 55 year-round, or |lat| ≥ 35 when the trip falls in that hemisphere's winter — the latitude floor stops a December trip to Bangkok being tagged both tropical and cold) ⇒ warm layers, hat + gloves; ≥3 stays ⇒ packing cubes; destination country → power-adapter suggestion naming the socket types (small built-in country table; unknown/mixed ⇒ "Universal travel adapter"). Countries come from the last comma-segment of `location_name` and from flight-segment airport codes. For flights only the **arrival** airport of each segment counts (for both climate and country): the first segment's departure airport is where the traveller starts out, not a destination — counting it would put "warm layers, hat & gloves" and a home-country plug adapter on a December Frankfurt→Bangkok beach trip. Flying back into a cold place later is still covered, since that arrival is a segment's `to`.

`POST /api/trips/:id/checklist/suggestions` `{keys: ["doc-passport", …], personal?: false}` → `201 {created: [item…], skipped: ["doc-passport"]}`

- Bulk-adds the given suggestions as checklist items (unchecked, `suggestion_key` set, appended in the current suggestion order). `keys` must be a non-empty array of ≤60 strings; an unknown key → `400 {"error":"unknown suggestion key: <key>"}`.
- Keys already present among the caller's visible items go to `skipped` instead of being duplicated.

### Route & summary (computed)

`GET /api/trips/:id/route` →

```json
{
  "stops": [ {"entryId": 1, "date": "2026-08-01", "type": "flight",
              "title": "BKK → CNX", "location_name": "Chiang Mai", "lat": 18.79, "lng": 98.98} ],
  "legs":  [ {"fromEntryId": 1, "toEntryId": 4, "km": 587.3, "mode": "ground",
              "waypoints": [{"lat": 46.5, "lng": 10.45, "name": "Stelvio Pass"}]} ],
  "totalKm": 587.3,
  "summary": {
    "days": 10, "nights": 9,
    "flights": 2, "flightSegments": 4, "transports": 1, "activities": 4,
    "rentals": 1, "includedKm": 1500,
    "stays": 2, "areas": [{"name": "Venice", "days": 3}, {"name": "Berlin", "days": 7}],
    "kmAir": 0, "kmDriven": 587.3,
    "locations": ["Bangkok", "Chiang Mai"]
  }
}
```

- `stops` = entries having lat/lng, ordered by `(date, sort_order, id)`; flight entries with coordinate-bearing segments are expanded into airport stops instead (see "Flight segments" — `kind: "airport"`, includes `code`). Stops also carry `transport_mode` (the entry's value, or null) so the map can show mode-specific icons.
- `legs` = consecutive stop pairs; skip zero-distance pairs (< 0.05 km) — still include the stop, just no leg.
- Each ground leg carries `waypoints`: the via-points of the transport entry that bridges it, or `[]`. Bridging entry = the earliest (by `date`, `id`) `transport` entry with a non-empty `waypoints` array whose `date` falls within `[fromStop.date, toStop.date]` inclusive. Air legs always have `waypoints: []`. The map passes these to the directions proxy's `via` so the drawn road route detours through them; `km` in `/route` stays great-circle regardless (the routed distance is computed client-side).
- Every leg has `mode`: `"air"` when BOTH endpoints are `kind:"airport"` stops expanded from the SAME flight entry (i.e. actual flight segments); `"ground"` for everything else (stay→airport transfers, city-to-city drives). `summary.kmAir` / `summary.kmDriven` are the per-mode sums (1 decimal). `kmDriven` is the rough rental-car figure: great-circle, so real road km will be somewhat higher.
- `days` = inclusive count from start_date to end_date; `nights = days - 1` (0 for single-day trips).
- `locations` = unique `location_name` values in stop order.
- km rounded to 1 decimal.

### Costs & splitting (computed)

`GET /api/trips/:id/costs` →

```json
{
  "currency": "USD",
  "totalCost": 1450.0,
  "byType": { "flight": 800.0, "transport": 300.0, "stay": 350.0 },
  "perUser": [
    { "userId": 1, "displayName": "brave-otter", "share": 725.0, "paid": 950.0, "net": 225.0 },
    { "userId": 2, "displayName": "calm-heron",  "share": 725.0, "paid": 500.0, "net": -225.0 }
  ],
  "settlements": [ { "fromUserId": 2, "toUserId": 1, "amount": 225.0 } ],
  "unassigned": 0.0
}
```

Computation (see Cost semantics above):

- `share` = what the user's part of the trip costs; `paid` = what they actually paid; `net = paid - share` (positive → others owe them).
- `equal` with `paid_by` null: the cost still counts into shares and `byType`, but nobody is credited as payer — accumulate that amount into `unassigned` (frontend shows a hint to assign payers).
- `own`: adds `price` to each participant's `share` AND `paid` (self-paid, no debt).
- `settlements`: minimal-transfer greedy — repeatedly match the largest debtor with the largest creditor until all nets are settled; amounts rounded to 2 decimals, drop transfers < 0.01.
- `totalCost` = sum of effective totals of all priced entries; `byType` groups the same by entry type.
- All money values rounded to 2 decimals in the response.

### Geocoding proxy

`GET /api/geocode?q=<query>` → `200 {results: [{name, lat, lng}]}` (max 5).

Proxies `https://nominatim.openstreetmap.org/search?format=jsonv2&limit=5&accept-language=en&q=…` server-side with header `User-Agent: trip-plan-app/0.1 (self-hosted)` (`accept-language=en` so results come back in Latin script, not the local language). Map Nominatim's `display_name`→`name`, parse lat/lon to numbers. On upstream failure return `502 {"error":"geocoding unavailable"}`. Cache identical queries in-memory for 10 minutes.

### Directions proxy (OSRM)

`GET /api/directions?from=<lat>,<lng>&to=<lat>,<lng>[&via=<lat>,<lng>|<lat>,<lng>…]` → `200 {km, geometry}` (requires auth).

- Optional `via` = up to 8 `lat,lng` pairs separated by `|`, routed in order between `from` and `to` (scenic waypoints). Each pair validated like from/to → any malformed/out-of-range pair or more than 8 → `400`. The cache key includes the via-points.
- Proxies `${OSRM_URL}/route/v1/driving/{fromLng},{fromLat};{viaLng},{viaLat};…;{toLng},{toLat}?overview=full&geometries=geojson` server-side. `OSRM_URL` env var, default `https://router.project-osrm.org` (the public demo server — fine for light personal use; self-hosters can point it at their own OSRM). Send the same `User-Agent` header as the geocode proxy.
- Validation: `from`/`to` must each be `lat,lng` with finite numbers in range (lat [-90,90], lng [-180,180]) → else `400`. Upstream failure, non-Ok OSRM code, or no route → `502 {"error":"directions unavailable"}`.
- Response `km` = route distance / 1000 rounded to 1 decimal; `geometry` = the GeoJSON coordinates converted to `[[lat,lng], …]` (Leaflet order).
- In-memory cache: key = both coord pairs rounded to 5 decimals, TTL 24 h, cap ~500 entries (evict oldest).

**Consumer contract (map)**: the frontend requests directions for each `mode: "ground"` route leg and, on success, draws the road-following polyline instead of the straight line and shows the routed km for that leg ("via road"); on 502/failure it keeps the straight great-circle line silently. Air legs stay straight/dashed. `/route` itself (and `summary.kmDriven`) remains great-circle — the server does not call OSRM during route computation.

## Frontend contract notes

- SPA served from `public/`; all non-`/api` GETs fall back to `public/index.html` is NOT required — a single `index.html` with hash-based routing (`#/login`, `#/trips`, `#/trip/:id`) is the expected design, so no server-side fallback is needed.
- Leaflet 1.9.x via unpkg CDN in `index.html`.
- Session cookie is httpOnly; frontend detects auth state via `GET /api/auth/me` on load.
- Checklist UI lives in `public/js/views/checklist.js`, rendered as a card in the trip detail side column (below Costs). It shows a progress bar, items grouped by category with a checkbox / qty / 🔒-personal marker per row, inline add, drag-reorder (`dragdrop.js` `enableReorder`, desktop-only like the rest), an "Uncheck all" action, and a "💡 Suggestions" modal listing the advice with per-item checkboxes and "Add selected". Ticking a box PATCHes optimistically and re-syncs on failure.