OhMyWind

    For the questions about a place rather than a passage: how hard it
    blows at Groix this afternoon, when the thermal breeze fills in, when
    the mistral eases, whether the models agree, what the swell does at a
    harbour entrance tonight.

    Args:
        lat: latitude in degrees.
        lon: longitude in degrees.
        start: ISO-8601 datetime with the user's UTC offset (e.g.
            "2026-05-01T08:00:00+02:00"). Every time in the answer comes
            back in that offset.
        end: ISO-8601 datetime, timezone-aware.
        models: optional list of model names. Leave it unset for the
            automatic choice: AROME (1.3 km) wherever it reaches the
            window, and the next model that reaches its end when the
            window runs past two days. Name several models (``["arome",
            "icon_eu", "ecmwf", "gfs"]``) only when the user asks whether
            the models agree: each one costs a request.

    Returns hourly ``wind`` per model (speed, direction it comes from,
    gusts, in knots), ``sea`` (wave height, period, direction), and, only
    where they are material, ``current`` (speed in knots, direction it
    flows to, from a tidal atlas where one covers the point) and ``tide``
    (height around mean sea level: read the range and the times of high
    and low water from it, not a depth over chart datum). Each series is
    a table: ``columns`` names the fields once, each of ``rows`` is one
    hour. Also ``openwind_url``, the OhMyWind map centred on the point.

    No widget comes with this tool. The values are a model forecast,
    not a measurement of what is blowing right now.

    Pass a point at sea. Open-Meteo Marine answers from the nearest sea
    cell: a few kilometres inland the ``sea`` values are the open coast's
    (Guipavas, inland of Brest, gets the waves of the rade), further
    inland they come back null, the ``sea`` array present and empty of
    information rather than absent. Wind is always the point's own.

    Note: the first request after inactivity may incur ~5s of cold-start.

    For the questions about a pass or a harbour entrance: when to be at
    the Raz de Sein to carry the stream, when the Fromveur turns, how
    hard it runs at Port-Navalo tomorrow, when high water is at Chausey.
    Costs no weather request: harmonic predictions from the atlases this
    server ships (SHOM, MARC and others), the same ones ``plan_passage``
    applies leg by leg.

    Args:
        lat: latitude in degrees, at sea, in the pass itself.
        lon: longitude in degrees.
        start: ISO-8601 datetime with the user's UTC offset; every time
            in the answer comes back in that offset.
        end: ISO-8601 datetime, timezone-aware. At most 400 steps.
        heading_deg: optional course through the point (true degrees,
            the direction you head to). With it, each step gets
            ``along_kn`` (positive: the stream carries you, negative: it
            stems you) and the answer lists the ``favourable`` and
            ``adverse`` windows.
        step_minutes: 5 to 180, default 30.

    Returns ``covered``, ``source``, ``confidence``, ``points`` (a table:
    ``columns`` time, ``speed_kn``, ``direction_to_deg`` it flows to,
    ``along_kn``, ``height_m`` around mean sea level; one row per step),
    ``slack`` (the moments the stream nearly
    stops), ``high_waters`` / ``low_waters``, ``favourable`` /
    ``adverse`` when a heading is given, ``tide_coefficient`` (French
    national coefficient, Brest, on French atlases), a ``warning`` when
    the atlas does not resolve the pass, and ``openwind_url``.

    Outside every atlas (most of the Mediterranean, the open sea)
    ``covered`` is false; ``get_marine_forecast`` returns the global
    model's current there, where it matters.

    Astronomical tide only: no surge, no wind-driven current. The windows
    are facts about the stream, not a recommendation: weigh them against
    the wind (``get_marine_forecast``) and the whole passage
    (``plan_passage``). No widget comes with this tool.
    

    The LLM (or user) maps a commercial model (e.g. "Sun Odyssey 32") to one
    of these archetypes from the metadata — there is no server-side mapping.
    ``voile_aviron_16ft`` is for open sail-and-oar dinghies only (no cabin,
    rowed as well as sailed); a small cabin cruiser maps to ``cruiser_20ft``.
    

    ## Tool routing: read this first

    Before calling, classify the user's question:

    1. **Pure weather lookup at a point** ("y aura-t-il du vent à Cassis
       samedi à 14h ?", "quelles vagues dimanche au cap Sicié ?"): call
       ``get_marine_forecast``. Do NOT call
       ``plan_passage``: there's no route to plan.

    2. **Trajet question with a flexible date** ("Marseille → Porquerolles
       ce week-end", "demain ou après-demain", "dans les prochains jours"):
       call ``plan_passage`` in **compare-windows mode**, passing
       ``latest_departure`` (e.g. earliest+48h) and ``sweep_interval_hours``
       (3 or 6 typically) so the user sees several departure scenarios
       side-by-side.
       This is the **default** for trajet planning: same API cost as a
       single passage thanks to cache prewarm, much more value.

    3. **Trajet with a precise hour pinned by the user** ("je pars demain
       à 8h", "départ Saturday 9am"): call ``plan_passage`` in single
       mode (no ``latest_departure``). Used for the final "show me the
       detailed plan for THIS departure" view, often after step 2.

    4. **Two ways to go** ("nord ou sud du Fromveur pour Ouessant ?",
       "par l'intérieur ou l'extérieur des Glénan ?", "Ré ou Aix
       demain ?"): one ``plan_passage`` call, the first route in
       ``waypoints`` and the others in ``alternatives`` (two at most),
       each with a short ``label`` saying how it goes ("Par le nord du
       Fromveur"). Every route is computed for the same departures, so
       the widget compares them cell by cell. Do not make one call per
       route.

    5. **When to be at a pass** ("à quelle heure au Raz de Sein ?",
       "quand renverse le courant au Fromveur ?"): ``get_tidal_stream``
       at the pass, with the course you will steer, and ``plan_passage``
       comparing departures, both in the same turn; then pick the
       departure that brings you there in the favourable window.

    6. **Methodology question** ("comment c'est calculé ?",
       "quelle efficacité par défaut ?"): call ``read_me``.

    Rule of thumb: if the user does NOT give an exact hour, prefer
    compare-windows. The widget renders one of the windows by default
    and the chat lets the user pick another.

    ## Waypoints must stay in the water

    This server runs a coarse land check before anything else: a leg
    that runs a couple of kilometres over land, or a waypoint inland, gets
    the call refused before any forecast request, with the leg and the
    place named. Redraw it and call again: a route over land is not one
    the boat can sail. The shoreline is coarse (about 1 km, the coast widened by
    2 km so harbours stay at sea, and any water a fine current atlas
    resolves counts as sea): a spit narrower than about 4 km, or a
    leg that shaves a headland, passes the check and is timed as drawn,
    too short, too fast, and scored on conditions the boat would never
    meet.

    So the route is still yours to draw. Between every consecutive pair of
    waypoints the straight line must stay at sea. Add intermediate
    waypoints to round anything the direct line would cut: headlands,
    peninsulas, islands, shoals.

    - Toulon to Saint-Tropez: the direct line crosses the Massif des
      Maures. Pass south of the presqu'île de Giens, then round cap Bénat
      and cap Camarat before turning north into the gulf.
    - Brest to Douarnenez: the direct line crosses the presqu'île de
      Crozon. Exit the goulet, round the cap de la Chèvre, then head east
      into the bay.

    Keep about 1 NM of clearance off headlands, more with onshore wind or
    swell, and do not shave the inside of islands. Extra waypoints are
    close to free: the cap is 50, and sampling cost follows
    ``segment_length_nm`` and total distance, not the waypoint count. When
    in doubt, add the waypoint.

    A waypoint that lands ashore has a second effect. Open-Meteo returns
    no sea state over land, so those samples carry a null wave height and
    the complexity score silently falls back to wind only, dropping the
    axis that would have flagged a rough passage.

    ## Returned payload

    Every time comes back in the UTC offset of ``departure``: send the
    user's own (``+02:00`` for France in summer) and read the times as
    their clock.

    Single mode:

    - ``passage``: per-segment timing report (distance_nm, duration_h,
      model used, segments[] with TWS/TWA/boat_speed/Hs, warnings).
    - ``complexity``: 1-5 difficulty score with wind/sea breakdown and a
      human-readable rationale.
    - ``openwind_url``: deep-link to ohmywind.fr/plan that renders the
      same passage in the standalone web app.
    - ``waypoints``: the route as you sent it, which the widget draws on
      a map.
    - ``route_label`` and ``alternatives[]``, only when you passed
      alternatives: each alternative has its ``label``, ``waypoints``,
      ``passage``, ``complexity`` and ``openwind_url``.
    - ``disclaimer``: usage warning intended for the user
      (decision-support tool, not a navigation instrument).

    Compare-windows mode (``latest_departure`` set):

    - ``mode``: ``"multi_window"``.
    - ``sweep``: ``earliest`` / ``latest`` / ``interval_hours`` /
      ``window_count``.
    - ``windows[]``: each entry has ``departure``, its ``weekday``,
      ``arrival``, ``duration_h``, ``distance_nm``, ``complexity`` (level
      + label + rationale), ``conditions_summary`` (tws_min/max,
      predominant sail angle, hs_min/max), ``warnings`` (the difficulty
      first), ``openwind_url``.
    - ``meta_warnings``: notes about the whole sweep or the route ("3
      fenêtres ignorées …", a long route sampled more sparsely).
    - ``waypoints``: the route as you sent it, once for all windows.
    - ``route_label`` and ``alternatives[]``, only when you passed
      alternatives: each alternative has its ``label``, ``waypoints``
      and its own ``windows[]``, same departures.
    - ``disclaimer``: usage warning intended for the user
      (decision-support tool, not a navigation instrument).

    ``openwind_url`` opens this plan in the web app, where the route,
    departure and boat can be edited and the plan shared. It points at
    the environment this server is configured for, so it is the one to
    use rather than a URL composed by hand.

    ## How it renders

    On hosts that support MCP Apps (Claude, Claude Desktop, ChatGPT, VS
    Code Copilot, Goose, Postman, MCPJam), the response is automatically
    accompanied by an interactive widget served via the
    ``ui://openwind/plan-passage`` resource declared on this tool's
    ``_meta``. In compare-windows mode it lists the departures; the one
    the user selects (the earliest at first) drives a map of the route
    you drew, coloured by its wind, and its per-leg detail. In single
    mode it shows the figures, the map and the per-leg detail. The user
    sees your waypoints on that map, one more reason to keep every leg at
    sea.

    On hosts without MCP Apps support (Cursor, Le Chat, terminal), no
    widget renders; the payload and ``openwind_url`` carry the plan.

    ## Args

        waypoints: list of ``{"lat": ..., "lon": ...}`` dicts, 2 to 50.
            Used exactly as drawn. Read "Waypoints must stay in the
            water" above before building it.
        departure: ISO-8601 datetime, timezone-aware.
        archetype: the boat. Pick it yourself from what the user sails,
            among these (``list_boat_archetypes`` returns the same list):
            - ``cruiser_20ft``: 20 ft (6 m) monohull, slow (Beneteau First 210, Catalina 22, Jeanneau Tonic 23)
            - ``cruiser_25ft``: 25 ft (8 m) monohull, slow (Beneteau First 25, Catalina 25, Jeanneau Sun Odyssey 24)
            - ``cruiser_30ft``: 30 ft (9 m) monohull, slow (Sun Odyssey 32, Bavaria 31, Beneteau Oceanis 31)
            - ``cruiser_40ft``: 40 ft (12 m) monohull, average (Sun Odyssey 410, Bavaria 41 Cruiser, Hanse 418)
            - ``cruiser_50ft``: 50 ft (15 m) monohull, fast (Sun Odyssey 519, Bavaria C50, Hanse 508)
            - ``catamaran_40ft``: 40 ft (12 m) catamaran, fast-reach (Lagoon 40, Bali 4.1, Fountaine Pajot Lucia 40)
            - ``racer_cruiser``: 40 ft (12 m) monohull, very-fast (J/122, Pogo 12.50, Solaris 40)
            - ``voile_aviron_16ft``: 16 ft (5 m) monohull, slow (Vivier Ilur, Vivier Aven, Vivier Aber)
            ``voile_aviron_16ft`` is an open sail-and-oar dinghy only; a small cabin cruiser is ``cruiser_20ft``.
        efficiency: multiplier on polar speed. ``0.85`` racing, ``0.75``
            cruising (default), ``0.65`` loaded family cruising, ``0.55``
            heavy seas / fouled hull.
        segment_length_nm: target sub-segment length. Default 10 nm
            balances precision vs Open-Meteo budget; drop to 5 for tight
            coastal work, raise to 20 for long offshore legs.
        model: wind model. Default ``"auto"`` tries AROME (≤48 h) →
            ICON-EU (≤5 d) → ECMWF IFS 0.25° (≤10 d) → GFS (≤16 d).
            Pass ``arome``, ``icon_eu``, ``ecmwf`` or ``gfs`` to bypass.
        max_hs_m: optional max significant wave height (meters) over the
            route: pass it if you have a sea-state estimate from
            ``get_marine_forecast`` and want it factored into the score.
            Defaults to wind-only scoring.
        motor_threshold_kn: optional sail-speed floor (knots) under which
            the simulator switches to engine power. Must be paired with
            ``motor_speed_kn`` (either alone is ignored). Typical value
            2 kn: sailors fire up the engine rather than crawl in light
            wind. Leave unset for 100% sail. Range (0, 10].
        motor_speed_kn: optional speed under engine (knots) applied to
            segments where the sail estimate falls under
            ``motor_threshold_kn``. Typical 5-6 kn for a cruising boat.
            Range (0, 12].
        min_upwind_twa_deg: optional minimum sailable TWA (degrees)
            overriding the archetype's own value (42-50 deg depending on
            the boat). Pass it when you know the boat points better or
            worse than the archetype suggests. Range [25, 70].
        route_label: optional short name for the main route, shown in
            the widget when you pass alternatives ("Par le nord").
        alternatives: optional other routes for the same trip, at most
            two: ``[{"label": "Par le sud", "waypoints": [...]}, ...]``.
            Same departures, same boat, same rules for the waypoints
            (stay at sea). Each route costs its own forecast requests:
            pass them only when the user weighs two ways to go.
        inland_waterway: true only when the user sails up a river or a
            canal the coarse shoreline counts as land (the Seine to
            Rouen, the Loire to Nantes): it turns the land check off for
            this call. Never set it to get past a refusal at sea; redraw
            the route instead.

    ## Compare-windows mode (latest_departure set)

    When ``latest_departure`` is provided, the tool switches into a
    window-comparison call: it walks departure times from ``departure``
    up to ``latest_departure`` every ``sweep_interval_hours`` (default
    1 h). Returns ``{"mode": "multi_window", "sweep": {...}, "windows":
    [...]}`` instead of the single-passage payload. Each window contains
    ``departure``, ``arrival``, ``duration_h``, ``distance_nm``,
    ``complexity``, ``conditions_summary``, ``warnings``, and its own
    ``openwind_url``.

    ``target_eta``: optional ISO-8601 datetime. When set, only windows that
    arrive within ±2 h of the target are returned. If none match, all
    windows are returned with a ``meta_warnings`` note.

    ## Failure modes

    Raises ``ForecastHorizonError`` if the chosen model's horizon doesn't
    cover the passage and ``model != "auto"``. The error message names the
    failing model and suggests longer-range alternatives.

    Call this when the user asks how passage timing, complexity, or
    boat speed are computed (e.g. "comment c'est calculé ?",
    "what assumptions does the model use?", "is tacking modelled?").

    The returned text covers: polar lookup, default efficiency 0.75,
    VMG / tacking correction, wave derate, single-pass timing,
    compare-windows mode semantics, regional defaults, wind against
    current, short-period chop, what is intentionally not modelled, and
    the data attributions.