These work

CLAUDE.md

@@ -72,7 +72,7 @@ Python + Polars. Two phases:
    - `poi_proximity.py` — Counts POIs within 2km per postcode using 0.05° spatial grid
    - `crime.py` — Aggregates crime CSVs into yearly averages by LSOA
 
-**Critical: column renaming in `merge.py`** — The pipeline renames columns from snake_case to human-readable names before writing `wide.parquet`. The Rust server auto-discovers features from whatever column names exist in the parquet. Key renames:
+**Critical: column renaming in `merge.py`** — The pipeline renames columns from snake_case to human-readable names before writing `wide.parquet`. The Rust server and frontend use **only** these human-readable names — there are no fallbacks to snake_case. Key renames:
 - `pp_address` → `Address per Property Register`
 - `postcode` → `Postcode`
 - `latest_price` → `Last known price`
@@ -80,7 +80,7 @@ Python + Polars. Two phases:
 - `total_floor_area` → `Total floor area (sqm)`
 - `current_energy_rating` → `Current energy rating`
 
-The server and frontend must handle these human-readable names. See the full rename map in `merge.py`.
+The server requires these exact column names at startup (will error if missing). See the full rename map in `merge.py`.
 
 ### Backend (`server-rs/`)
 
@@ -127,7 +127,7 @@ React 18 + TypeScript. deck.gl `H3HexagonLayer` over MapLibre GL. TailwindCSS. N
   - `useUrlSync` — URL state synchronization
 
 **Key patterns:**
-- URL encodes view/filters/POI categories/active tab as query params for shareable links
+- URL encodes view/filters/POI categories/active tab as query params for shareable links. Only the current format is supported — no legacy parameter parsing (old `v=`, `f=`, or tab abbreviations are not handled).
 - AbortControllers cancel in-flight requests on new queries (150ms debounce)
 - Zoom → H3 resolution defined in `consts.ts` `ZOOM_TO_RESOLUTION_THRESHOLDS`: `<7.5→5, <9.5→6, <10.5→8, <12→9, ≥12→10`
 - `POSTCODE_ZOOM_THRESHOLD = 15`: below 15 shows H3 hexagons, at/above 15 shows postcode polygons
@@ -153,7 +153,7 @@ React 18 + TypeScript. deck.gl `H3HexagonLayer` over MapLibre GL. TailwindCSS. N
 - `api.ts` — `apiUrl(endpoint, params?)` builds API URLs. `logNonAbortError(label, err)` and `isAbortError(err)` for error handling.
 - `features.ts` — `groupFeaturesByCategory(features)` groups FeatureMeta[] by their `group` field.
 - `format.ts` — `formatNumber(value, decimals)` for number formatting. `calculateHistogramMean(histogram)` for weighted mean calculation.
-- `property-fields.ts` — `getNum(property, ...keys)` for getting numeric property values with fallback field names.
+- `property-fields.ts` — `getNum(property, key)` for getting a single numeric property value. Takes exactly one key — no fallback names.
 
 When adding new UI, prefer using these shared components over inline implementations to maintain consistency.
 
@@ -271,6 +271,7 @@ Every UI element must use the correct token from this table. Do not invent new p
 
 ## Coding Preferences
 
+- **No backwards compatibility, no silent fallbacks**: Never add fallback codepaths for old data formats, legacy URL parameters, or alternate field names. Never silently swallow errors — always error loudly (return an error, panic, or at minimum log). If something is wrong, the code should fail visibly. One canonical name per field, one format per API, one way to do things.
 - **Unified data models over special-casing**: Prefer storing different data types uniformly (e.g., enums as f32 indices alongside numeric features) rather than maintaining separate code paths
 - **Terse tests**: Test what matters in as few tests as possible — don't overcomplicate with excessive setup or edge cases that don't add value
 - **Extract and organize**: Group related utilities into proper modules (e.g., `utils/`, `parsing/`) rather than leaving helpers scattered
@@ -313,6 +314,8 @@ Follow these conventions in all Rust code:
 - **Startup precomputation**: Static responses (like `/api/features`) are computed once at startup and cached in `AppState`
 - **POI transform validation**: Fails if any OSM category is unmapped — guarantees exhaustive coverage
 - **Fuzzy join**: Groups by postcode, uses `thefuzz.token_sort_ratio` with numeric token compatibility, greedy assignment from highest score
+- **Filter parsing is strict**: `parse_filters()` returns `Result` — malformed entries, unknown feature names, and unparseable numbers all return 400 Bad Request. No silent skipping of invalid filters.
+- **Data loading is strict**: `extract_string_col` and `lookup_enum_value` take a single column name (no fallback names). H3 precomputation panics on invalid coordinates. Required parquet columns must exist at startup.
 - **Filter bounds format**: `south,west,north,east` (not standard bbox order)
 - **Server-side AABB filtering**: Both `/api/hexagons` and `/api/postcodes` filter results by bounding-box intersection with query bounds. Hexagons use `h3_cell_bounds()` (h3o returns degrees, not radians). Postcodes compute polygon AABB from vertices. See `bounds_intersect()` in `parsing/bounds.rs`.
 - **GridIndex returns slightly more than requested**: The 0.01° grid cells mean properties up to ~1km outside the viewport may be returned. The AABB filter in the route handlers catches these extras.