diag: let the node say what is wrong with it (#81)

* Bump to 1.2.11

One change, and it is the reason a node on Windows kept collecting peers it
could not hear.

FD_SETSIZE was never defined in this tree, so it defaulted to 64 and select()
could watch the listen socket plus 63 peers -- everything past that stayed
connected and was never read again. Windows FD_SET stops adding once its array
is full and says nothing, so there was no error to notice. Because new
connections go on the end of vNodes, it was always the newest connection that
starved, including the ones dialed to fix connectivity.

Measured on two nodes: 277 and 90 CNode objects against 93 and 90 live
sockets, 316 and 355 sockets in a bound-but-never-connected state, and a status
bar reporting hundreds of peers for a node really talking to thirty.

1.2.11 raises FD_SETSIZE to 1024 on Windows, caps connections at 125, drops a
node stuck undeliverable after 60 seconds instead of holding it forever, stops
answering a failed select() with POSIX code that has no meaning on Windows, and
warns when there are more peers than select can watch.

* diag: let the node say what is wrong with it

Every hard problem in this project so far was found from outside the node --
sockets read over WMI, committed memory compared against a README, a grep over
somebody debug.log. In each case the node knew and had no way to say so.

One report, rendered identically for the GUI panel and the log: peers held vs
peers actually watched by select(), blocks received and how many arrived without
a parent, proof-of-work mode with the live miner thread count, and per peer the
age of the last message in each direction plus anything stuck unsent.

1 files changed, 19 insertions, 0 deletions

diff --git a/src/net.h b/src/net.h
index 01f314d..bd4eb77 100644
--- a/src/net.h
+++ b/src/net.h
@@ -102,6 +102,25 @@ static const int          BTF_PING_INTERVAL_SECS   = 10 * 60;
 static const int          BTF_BEHIND_GRACE_SECS         = 5 * 60;
 static const int          BTF_BEHIND_WARN_INTERVAL_SECS = 5 * 60;
 
+// --- Self-diagnosis -------------------------------------------------------
+//
+// A node that has stopped working looks exactly like a node with nothing to
+// do. That has cost this project real time more than once: a node deaf to
+// most of its peers, a miner allocating one RandomX dataset per thread, a
+// third of arriving blocks missing their parent -- each was found from
+// outside, by reading the process's sockets or its memory from another
+// machine, because the node itself had no way to say so.
+//
+// These counters exist so it can. Cheap to keep, and they name the failures
+// that actually happened rather than the ones that sound impressive.
+extern int   nPeersWatched;        // peers in the last select() set
+extern int64 nBlocksReceived;      // blocks handed to ProcessBlock
+extern int64 nBlocksWithoutParent; // ...of those, how many arrived orphaned
+
+// One report, rendered the same way for the GUI panel and the log, so what a
+// user pastes into an issue is what a developer already knows how to read.
+string GetDiagnosticsText();
+
 // Defined in main.cpp. Declared here because CNode announces it in the version
 // message, and net.h is included before main.h.
 extern int nBestHeight;