Meeting point

Fairness objective: minimize the MAXIMUM per-person travel time to the
venue ("no one gets screwed"), tie-broken by the smaller spread
(max - min across everyone), then by the smaller total. This is
deliberately not "minimize the average" — that objective can strand
one person with a long trip so two others get a short one.

origins is 2-5 points, each a {"lat": ..., "lon": ..., "mode": ...}
dict, a GERS id, or a free-text place name, mixed freely — mode is
"walk", "cycle", or "drive", defaulting to "walk" when omitted (a
string origin always gets the default mode; give a dict with "mode" to
pick otherwise), and can differ per person (e.g. one driving, one
walking). An id/name that failed to resolve returns an indexed error
(origins[i]: ...) with candidates on ambiguity. Any origin given by
id/name adds "resolved": [{"index", "name", "id", "lat", "lon",
"matched_by"}, ...] for just those origins; absent when every origin
was already coordinates. category optionally filters candidate venues
to an Overture taxonomy slug (e.g. 'coffee_shop'); a wrong or
unrecognized slug is a silent zero-match, not an error.

Method: a seed center is computed from each origin's implied
straight-line travel time (not raw distance, so a walking participant
pulls the center toward them more than a driving one at the same
distance), venues are searched for near that seed, and each
candidate's real per-person times come from routing.route() — the
exact routed number, not the seed's approximation. The total routed
(candidate, origin) fan-out is capped at 16 pairs, regardless of
`limit` — 8 candidates at 2 origins, down to 3 candidates at 5.

Returns {"center": {"lat", "lon"}, "candidates": [{"id", "name",
"category", "lat", "lon", "per_person": [{"origin_idx", "mode",
"travel_time_min", "distance_m"}, ...], "max_travel_time_min",
"spread_min"}, ...]}, ranked fairest-first, capped at `limit` (default
3, max 5). per_person entries carry origin_idx aligned to the input
origins list, one entry per origin — a candidate that can't be routed
from every origin (no street graph nearby, or genuinely disconnected)
is dropped from the ranking entirely rather than ranked on a partial,
unfair comparison. A per_person leg whose street graph hit its
internal size cap carries "truncated": true (as does its candidate,
and the answer carries a note) — that leg's time may be off. An empty
"candidates" list is a valid answer (nothing matched the category
nearby, or nothing routed from every origin) — it carries a "note"
explaining which, including when every pair was over the mode's
straight-line routing cap (try a faster mode).

confirm=true after the user agreed to wait for a first-time
street-graph build (about 5–25 seconds; see `route`). Without it, a
fan-out that would need a cold graph build returns {"error":
"needs_confirm"} instead of silently blocking. Omit confirm unless you
just asked and they said yes.

A non-empty result also carries "map" (#369) — a render-ready payload,
keyword-splattable straight into this server's map-rendering tool (its
keys are exactly that tool's keyword arguments): pins every origin, the
fairest candidate picked out by class, the rest, and the fairness seed
center, plus a one-line summary naming the fairest venue and its
numbers. Absent when "candidates" is empty.

Returns a structured {"error": "bad_request", ...} if origins has
fewer than 2 or more than 5 points, a point is missing/non-numeric
lat or lon, or a mode isn't walk/cycle/drive; {"error": "bad_request",
...} with the offending coordinate if lat/lon is out of range; or a
structured {"error": ...} if the upstream places or transportation
dataset is unavailable or missing columns this tool depends on.