fix(deploy): the sidecars' downloads try again within the hour after a failed round

A failed BRouter segment or listing, a failed tile cut or an unwritable folder waited the whole refresh period, 30 days without routes or a map; they try again after an hour, doubling to a day. Photon's failed download backs off from a day to a week, and a dead Photon is noticed within a minute. The downloads' network is an ordinary bridge the three share, as the comments now say.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

deploy/brouter/segments.sh

@@ -3,7 +3,9 @@
 # every 5°×5° segment of BRouter's project whose south-west corner lies in
 # BROUTER_REGION (`west,south,east,north` in whole degrees, multiples of 5; Europe's
 # `-25,35,40,70` by default), downloaded where the project has a newer one than the
-# volume holds, then again every BROUTER_REFRESH_DAYS days (30). Each is written beside
+# volume holds, then again every BROUTER_REFRESH_DAYS days (30); after a round where the
+# listing or a segment didn't come, again in an hour, the wait doubling up to a day
+# while rounds keep failing. Each is written beside
 # its old self and moved over it, so BRouter never reads half a file. Segments of
 # the sea, which the project doesn't have, are skipped.
 set -eu
@@ -25,8 +27,9 @@ name() {
 }
 
 refresh() {
+  complete=0
   listing=$(curl -fsS "$base/") || { echo "The segments' listing didn't come." >&2; return 0; }
-  fetched=0 kept=0
+  fetched=0 kept=0 failed=0
   lon=$west
   while [ "$lon" -le "$east" ]; do
     lat=$south
@@ -36,8 +39,11 @@ refresh() {
         # Only where the project's is newer than ours (If-Modified-Since): a
         # current one comes back empty.
         if [ -e "$file" ]; then set -- -z "$file"; else set --; fi
-        if curl -fsS -R --retry 3 "$@" -o "$file.part" "$base/$file" &&
-          [ -s "$file.part" ]; then
+        if ! curl -fsS -R --retry 3 "$@" -o "$file.part" "$base/$file"; then
+          rm -f "$file.part"
+          echo "Segment $file didn't come." >&2
+          failed=$((failed + 1))
+        elif [ -s "$file.part" ]; then
           mv "$file.part" "$file"
           fetched=$((fetched + 1))
         else
@@ -49,10 +55,30 @@ refresh() {
     done
     lon=$((lon + 5))
   done
-  echo "Segments: $fetched fetched, $kept current, $(du -sh . | cut -f1) in all."
+  echo "Segments: $fetched fetched, $kept current, $failed failed, $(du -sh . | cut -f1) in all."
+  if [ "$failed" -eq 0 ]; then complete=1; fi
 }
 
+# Seconds to wait after the $1th incomplete round in a row: $2, doubling up to $3.
+backoff() {
+  pause=$2 n=1
+  while [ "$n" -lt "$1" ] && [ "$pause" -lt "$3" ]; do
+    pause=$((pause * 2)) n=$((n + 1))
+  done
+  if [ "$pause" -gt "$3" ]; then pause=$3; fi
+  echo "$pause"
+}
+
+failures=0
 while :; do
   refresh
-  sleep $((days * 86400))
+  if [ "$complete" -eq 1 ]; then
+    failures=0
+    sleep $((days * 86400))
+  else
+    failures=$((failures + 1))
+    pause=$(backoff "$failures" 3600 86400)
+    echo "The round wasn't complete; trying again in $((pause / 60)) minutes." >&2
+    sleep "$pause"
+  fi
 done