Clear the open minors: lost marking and overrun logging, form teardown guard, line breaks and ERANGE in config, probe strength

The E-1608 source marks every restart as lost and logs each overrun; its form stops touching
siblings after the chooser destroys them; the link skips command id 0, retries a full-buffer
discover send and ignores a zero-length scan read. Session files escape \n and \r; get_int and
get_double reject out-of-range values; the UDPS port spin reports changes; a skipped source panel
says why on stderr. The E-1608 probe now checks the signal names and the reconnect itself.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/source/e1608/e1608_link.cpp

@@ -199,9 +199,16 @@ std::vector<DeviceInfo> discover(const std::vector<std::string>& targets, int po
     } catch (const LinkError&) {
       continue;
     }
-    // A sweep may hit unreachable hosts; those sends fail and are simply skipped.
-    (void)::sendto(u.get(), &probe, 1, MSG_NOSIGNAL, reinterpret_cast<const sockaddr*>(&a),
-                   sizeof a);
+    // A sweep may hit unreachable hosts; those sends fail and are simply skipped. A full send
+    // buffer is not that: wait for room once and retry, so a large sweep does not lose probes.
+    const auto send_probe = [&] {
+      return ::sendto(u.get(), &probe, 1, MSG_NOSIGNAL, reinterpret_cast<const sockaddr*>(&a),
+                      sizeof a);
+    };
+    if (send_probe() < 0 && (errno == EAGAIN || errno == ENOBUFS)) {
+      wait_fd(u.get(), POLLOUT, 20);
+      (void)send_probe();
+    }
   }
   const auto deadline = Clock::now() + std::chrono::milliseconds(wait_ms);
   for (;;) {
@@ -288,7 +295,8 @@ std::vector<std::uint8_t> Link::command(std::uint8_t cmd, const std::vector<std:
     while (::recv(cmd_.get(), junk, sizeof junk, MSG_DONTWAIT) > 0) {
     }
   }
-  const std::uint8_t id = ++next_id_;
+  if (++next_id_ == 0) next_id_ = 1;  // id 0 is never used, in case a board treats it specially
+  const std::uint8_t id = next_id_;
   std::vector<std::uint8_t> f;
   f.reserve(7 + payload.size());
   f.push_back(0xDB);
@@ -349,6 +357,7 @@ void Link::send_filler() {
 
 std::size_t Link::read_scan(std::uint8_t* buf, std::size_t cap, int timeout_ms) {
   if (!scan_.valid()) throw LinkError(Kind::Io, "the scan socket is not open");
+  if (cap == 0) return 0;  // recv would return 0 and read as a close
   if (!wait_fd(scan_.get(), POLLIN, timeout_ms)) return 0;
   const ssize_t n = ::recv(scan_.get(), buf, cap, MSG_DONTWAIT);
   if (n > 0) return static_cast<std::size_t>(n);