Wire offline hiking trails into the real build, API, and renderer

data/hiking_trails.geojson now generates automatically as the last
step of every offline.pmtiles build (PmtilesBuilder.extract_hiking_trails,
best-effort — a failure here doesn't fail the whole build), merged
across all selected countries with cross-border dedup by OSM relation
id (HikingTrails.extract_merged). Served at GET /tiles/hiking_trails.geojson
and GET /api/hiking-trails, fetched client-side only once the overlay
is actually toggled on.

hiking_trails.js now prefers this local file whenever it exists,
regardless of which base map (online/offline) is active — same
"prefer local when available" story as HillshadeControl already uses
for terrain. Offline click hit-tests the real vector layer directly
(queryRenderedFeatures) instead of querying Overpass — instant, no
network. Coordinates are rounded to 5dp to keep the combined file
smaller; colour tag values are normalized against a known-safe set
before ever reaching a style paint property.

Verified extract_merged (new: combines multiple countries' extracts,
dedupes overlapping relations) against two real cached country PBFs
on brick directly, not just fixtures.

lib/maptool/hiking_trails.rb

@@ -63,6 +63,22 @@ module Maptool
       end
     end
 
+    # Runs extract() over one .osm.pbf per selected country and combines the
+    # results into a single FeatureCollection — a route relation crossing a
+    # border (an E-path, say) shows up once per country whose extract it
+    # was pulled from, deduplicated here by OSM relation id (properties.id)
+    # rather than left to render as overlapping duplicate lines.
+    # extract: same injectable-seam reasoning as PmtilesBuilder's own
+    # download_extract:/fetch_manifest: — lets a test swap out the real
+    # (osmium-shelling-out) implementation for a canned one.
+    def self.extract_merged(pbf_paths, extract: method(:extract))
+      seen = {}
+      pbf_paths.each do |pbf_path|
+        extract.call(pbf_path)["features"].each { |feature| seen[feature["properties"]["id"]] ||= feature }
+      end
+      { "type" => "FeatureCollection", "features" => seen.values }
+    end
+
     # Pure — no subprocess — so it's cheaply testable against a canned OPL
     # fixture, same "keep the real logic testable without the real tool
     # installed" reasoning OverpassPois.to_geojson already gives for staying
@@ -81,7 +97,7 @@ module Maptool
           ways[head[1..].to_i] = way_coordinates(fields)
         when "r"
           tags = tags_field(fields)
-          relations << { tags: tags, members: members_field(fields) } if tags["route"] == "hiking"
+          relations << { id: head[1..].to_i, tags: tags, members: members_field(fields) } if tags["route"] == "hiking"
         end
       end
 
@@ -99,6 +115,7 @@ module Maptool
       distance = lines.sum { |coords| TrackStats.compute(coords)["distance_meters"] }
       tags = relation[:tags]
       properties = {
+        "id" => relation[:id],
         "name" => tags["name"] || tags["description"],
         "distance_meters" => distance.round(1),
       }
@@ -107,11 +124,20 @@ module Maptool
       {
         "type" => "Feature",
         "properties" => properties.compact,
-        "geometry" => { "type" => "MultiLineString", "coordinates" => lines },
+        # Rounded to 5 decimal places (~1m) — full OSM float precision
+        # (~1cm) is pointless for a rendered line and roughly doubles the
+        # size of every coordinate pair once this many-country GeoJSON is
+        # actually served to a browser.
+        "geometry" => { "type" => "MultiLineString", "coordinates" => round_coordinates(lines) },
       }
     end
     private_class_method :relation_feature
 
+    def self.round_coordinates(lines)
+      lines.map { |coords| coords.map { |lon, lat| [lon.round(5), lat.round(5)] } }
+    end
+    private_class_method :round_coordinates
+
     def self.field(fields, letter)
       fields.find { |f| f.start_with?(letter) }
     end

lib/maptool/pmtiles_builder.rb

@@ -5,6 +5,7 @@ require "json"
 require "tmpdir"
 require "fileutils"
 require "etc"
+require_relative "hiking_trails"
 
 module Maptool
   # Regenerates data/offline.pmtiles and data/terrain.pmtiles for the
@@ -289,12 +290,37 @@ module Maptool
       run_planetiler!("--osm-path=#{osm_path}", "--output=#{tmp_path}", "--download", "--threads=#{Etc.nprocessors}")
       File.rename(tmp_path, File.join(data_dir, "offline.pmtiles"))
       File.write(offline_meta_path(data_dir), JSON.generate(sources: sources.map { |s| s.slice("code", "slug", "last_modified") }))
+
+      report_step.call("extracting hiking trails")
+      extract_hiking_trails(sources, data_dir)
     ensure
       FileUtils.remove_entry(scratch_dir) if scratch_dir && Dir.exist?(scratch_dir)
       File.delete(tmp_path) if tmp_path && File.exist?(tmp_path)
     end
     private_class_method :extract_offline
 
+    # Runs over the same per-country .osm.pbf files sources above already
+    # downloaded/cached for offline.pmtiles itself — no separate download.
+    # Best-effort: a hiking-trails extraction problem (a malformed PBF
+    # region, osmium hiccup on one particular file) shouldn't fail the
+    # whole offline.pmtiles build over what's a bonus overlay, not the
+    # core map — logged into the sidecar meta's own "error" field instead,
+    # so it's visible without taking build_offline itself down.
+    def self.extract_hiking_trails(sources, data_dir)
+      geojson = HikingTrails.extract_merged(sources.map { |s| s["path"] })
+      tmp_path = "#{hiking_trails_path(data_dir)}.tmp"
+      File.write(tmp_path, JSON.generate(geojson))
+      File.rename(tmp_path, hiking_trails_path(data_dir))
+    rescue HikingTrails::ExtractError => e
+      File.delete(tmp_path) if tmp_path && File.exist?(tmp_path)
+      warn "hiking trails extraction failed, skipping: #{e.message}"
+    end
+    private_class_method :extract_hiking_trails
+
+    def self.hiking_trails_path(data_dir)
+      File.join(data_dir, "hiking_trails.geojson")
+    end
+
     # Renders a report_step string like "fetching PL (3/4) — done: SK, CZ —
     # pending: HU" — so GET .../build-status shows not just "it's running"
     # but which of the current build's sources is in flight and which are
@@ -442,6 +468,7 @@ module Maptool
 
       File.delete(File.join(data_dir, "offline.pmtiles")) if File.exist?(File.join(data_dir, "offline.pmtiles"))
       File.delete(offline_meta_path(data_dir)) if File.exist?(offline_meta_path(data_dir))
+      File.delete(hiking_trails_path(data_dir)) if File.exist?(hiking_trails_path(data_dir))
       cache_dir = geofabrik_cache_dir(data_dir)
       FileUtils.remove_entry(cache_dir) if Dir.exist?(cache_dir)
     end