Updates: a download that breaks is carried on

When the connection breaks during a release download (issue #54), the
device waits up to a minute for Wi-Fi, asks for the rest of the file
with a Range request and carries on: the slot and the hash so far are
kept. It gives up after three tries in a row that bring nothing.
Nothing is kept across a restart.

Carrying on asks for 64 KB free, not 80: between two connections of an
install 78 KB is free, and the first attempt on the device was refused
for that. update damage cut now breaks every connection after n bytes.

Tried on the device: v0.23.0 installed over four connections, and a
download that brought nothing given up with nothing switched.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0162FokPdvY2KsS4NBfwyWPk

src/services/update_service.h

@@ -71,6 +71,7 @@ class UpdateService : public Service {
     // (is its certificate accepted?), and a download cut short or with one byte flipped.
     void requestProbe(const std::string& host, const std::string& path) { probeHost_ = host; probePath_ = path; probeResult_ = "..."; request_ = Request::Probe; }
     std::string probeResult() const { return probeResult_; }
+    int lastResumes() const { return resumes_; }  // how often the last download from Gitea was carried on (issue #54)
     void damageNextDownload(long cutAfter, long flipAt) { damageCut_ = cutAfter; damageFlip_ = flipAt; }
     void forgetToday() { store_.putInt("rel_day", 0); nextCheckMs_ = 0; announced_.clear(); }  // the daily check runs at the next tick
 
@@ -115,6 +116,7 @@ class UpdateService : public Service {
     uint32_t nextCheckMs_ = 90000;  // not before the device has settled
     std::string probeHost_, probePath_;
     volatile long damageCut_ = -1, damageFlip_ = -1;
+    volatile int resumes_ = 0;
     std::string probeResult_;
 };