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# "Help a friend" (built 2026-10-29)
A person with a disability in a risk zone asks for help → 3 closest volunteer helpers by **flood-aware travel time** get an offer → first to accept gets a route + turn-by-turn steps.
## Design decisions (chosen by the user)
| Question | Choice |
|---|---|
| Routing | Own router (`roads.rs`): OSM roads from Geofabrik extracts, Dijkstra; edges with EFAS depth > 0.3 m (scenario, default rp100) get +5 s per flooded metre (same for every mode), so used only if unavoidable → `flooded_m` |
| Sign-up | On demand only; no pre-registry of disabled people |
| Deep water | `water_now: true` → status `escalated`, "call 112", no volunteer |
| Demo | Synthetic, EMSR517 AOI15 (`code/help_demo.py`) |
## API (`flood_api/src/help.rs`, SQLite `out/help.sqlite`)
`POST /help/zones {name,bbox}` · `POST /helpers {zone,lon,lat,mode:walk|bike|car}` · `PATCH /helpers/{id}` · `POST /help-requests {zone,lon,lat,need,urgent?,scenario?,water_now?}` · `POST /help-requests/{id}/accept {helper_id}` · `GET /help-requests/{id}` · `POST /help-requests/{id}/close`
- Tables: zones, helpers, help_requests, assignments. Status: open / assigned / done / escalated / unmatched.
- Privacy: no names; need ∈ mobility/visual/hearing/other; requests + helpers purged after 72 h.
- Zone graph in memory, rebuilt lazily from the stored bbox after a restart.
## Demo result (AOI15, 806 km², 273k nodes, 7,810 km roads)
- Zone build ~30–35 s; a request after that takes < 1 s.
- Request in a cell 3.0 m deep at RP100: best helper by car 1.2 km, 12 min, 319 m of it on roads flooded in the scenario (unavoidable last stretch).
- Escalation and error paths tested.
## Assumptions / limits (for brief + AI sheet)
- 0.3 m flooded threshold, 5 s/m flood penalty, car speeds per road type: assumptions, not sourced.
- EFAS = scenario max depth, not live water levels; OSM = today's roads, not 2021.
- `in_risk_zone` = EFAS depth > 0 at the point (not the ML risk score).
- No authentication, no helper vetting, no notifications (demo). Health data = GDPR Art. 9 → real use needs a DPIA, consent, an official operator.
- Volunteers add to 112 / civil protection; they don't replace them.
## Shelters (added 2026-10-29)
- OSM kinds (`osm::shelter_kind`): `shelter` = `social_facility=shelter`, `emergency=assembly_point`; `candidate_shelter` = schools, sports halls / centres (assumption, not designated; capacity unknown). Bus/picnic `amenity=shelter` excluded.
- Also in `/region` facilities. OSM cache now `osm_v2_*` (old caches lack shelters).
- `GET /help/zones/{zone}/shelters?scenario=` → list + `dry` (EFAS depth = 0).
- `GET /help-requests/{id}/shelter?mode=&scenario=&candidates=` → nearest dry shelter by flood-aware route (forward Dijkstra); mode default = accepted helper's, else walk.
- AOI15: 164 shelters (11 OSM shelters, 153 candidates); 30 flood at RP100 (18 %), excluded from routing.
## Fixes after the API test (2026-10-29)
- Points (helper, person, helper move) must be inside the zone bbox and ≤ 500 m from a road usable by the mode → else 422.
- `eta_s` = real travel time; `cost_s` = eta + flood penalty, used for ranking. Was ×20 time, which pushed a walker 259 m away below a bike 5.9 km away.
- 404 unknown zone / helper / request (no raw SQL errors); 409 busy helper, request already assigned/done.
- accept: helper must be available (atomic check); close frees the helper only if it has no other assigned request.
- `/help-requests/{id}/shelter` defaults to the request's own scenario.
- Re-POST `/help/zones` = upsert (helpers and requests kept).
- `POST /help/zones`: name must be `[A-Za-z0-9_-]+` (empty name was accepted before); bbox goes through `region_check` (inverted / zero / > 3000 km² / outside study hull → 422 in < 5 ms) BEFORE the 30 s – 2 min graph build.
- 2026-10-29 (cems-efas-72): `DELETE /helpers/{id}` (an accepted request goes back to `open`, returns `requests_reopened`) and `DELETE /help-requests/{id}` (frees its helper unless assigned elsewhere): delete on demand, not only after 72 h. CORS allows DELETE.
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