KamadoPool/ckpool/patches/0004-dump-pending-block-for-fallback.patch

diff --git a/src/generator.c b/src/generator.c
index 22e2e08..438b199 100644
--- a/src/generator.c
+++ b/src/generator.c
@@ -351,11 +351,25 @@ bool generator_submitblock(ckpool_t *ckp, const char *buf)
 	server_instance_t *si;
 	bool warn = false;
 	connsock_t *cs;
+	/* Bound the wait for current_si so a permanently-down primary
+	 * bitcoind does not pin the caller forever. After this many 10ms
+	 * sleeps (~3s), return false so the caller (in our fork:
+	 * local_block_submit) can hand off to kamado-api's fallback
+	 * broadcaster instead of blocking the stratifier on a dead RPC.
+	 * Original upstream behavior was to spin indefinitely; we trade
+	 * that for predictable latency. */
+	const int max_no_si_iters = 300;
+	int no_si_iters = 0;
 
 	while (unlikely(!(si = gdata->current_si))) {
 		if (!warn)
-			LOGWARNING("No live current server in generator_blocksubmit! Resubmitting indefinitely!");
+			LOGWARNING("No live current server in generator_blocksubmit! Waiting up to ~3s before giving up so fallback can take over...");
 		warn = true;
+		if (++no_si_iters > max_no_si_iters) {
+			LOGWARNING("generator_submitblock: no live primary server after %d ms, returning false",
+				   no_si_iters * 10);
+			return false;
+		}
 		cksleep_ms(10);
 	}
 	cs = &si->cs;
diff --git a/src/stratifier.c b/src/stratifier.c
index 52da790..7caf179 100644
--- a/src/stratifier.c
+++ b/src/stratifier.c
@@ -2069,16 +2069,75 @@ process_block(const workbase_t *wb, const char *coinbase, const int cblen,
 	return gbt_block;
 }
 
-/* Submit block data locally, absorbing and freeing gbt_block */
+/* Write the raw block hex to a sidecar file under <logdir>/pending-blocks/
+ * so the external watcher (kamado-api) can re-broadcast via fallback RPC
+ * nodes. Best-effort: any error here is logged at INFO and never blocks
+ * the caller. Called only after the primary submit fails so the happy
+ * path stays disk-free. */
+static void kamado_dump_pending_block(ckpool_t *ckp, const char *gbt_block,
+				      const char *rhash, int height,
+				      char *out_path, size_t out_path_len)
+{
+	char dir[512] = {};
+	int fd;
+	size_t blen;
+	ssize_t w;
+
+	out_path[0] = '\0';
+	if (!ckp || !ckp->logdir || !gbt_block)
+		return;
+	snprintf(dir, sizeof(dir), "%spending-blocks", ckp->logdir);
+	if (mkdir(dir, 0750) < 0 && errno != EEXIST) {
+		LOGINFO("kamado: mkdir %s failed: %s", dir, strerror(errno));
+		return;
+	}
+	snprintf(out_path, out_path_len, "%s/%d-%.16s.hex", dir, height, rhash);
+	fd = open(out_path, O_WRONLY | O_CREAT | O_TRUNC, 0640);
+	if (fd < 0) {
+		LOGINFO("kamado: open %s failed: %s", out_path, strerror(errno));
+		out_path[0] = '\0';
+		return;
+	}
+	blen = strlen(gbt_block);
+	w = write(fd, gbt_block, blen);
+	close(fd);
+	if (w != (ssize_t)blen) {
+		LOGINFO("kamado: short write to %s (%zd/%zu)", out_path, w, blen);
+		unlink(out_path);
+		out_path[0] = '\0';
+		return;
+	}
+	LOGNOTICE("kamado: dumped pending block height %d to %s (%zu bytes) for fallback broadcast",
+		  height, out_path, blen);
+}
+
+/* Submit block data locally, absorbing and freeing gbt_block.
+ *
+ * Order matters: we always try ckp's primary bitcoind FIRST so the
+ * happy path adds zero latency or disk I/O. Only when the primary
+ * rejects (or generator_submitblock returns false for any other
+ * reason) do we dump the raw hex to <logdir>/pending-blocks/ so the
+ * kamado-api watcher can re-broadcast via fallback RPC nodes. */
 static bool local_block_submit(ckpool_t *ckp, char *gbt_block, const uchar *flip32, int height)
 {
-	bool ret = generator_submitblock(ckp, gbt_block);
 	char heighthash[68] = {}, rhash[68] = {};
+	char pending_path[512] = {};
 	uchar swap256[32];
+	bool ret;
 
-	free(gbt_block);
 	swap_256(swap256, flip32);
 	__bin2hex(rhash, swap256, 32);
+
+	/* Primary submit first — this is the latency-critical path. */
+	ret = generator_submitblock(ckp, gbt_block);
+
+	/* Only touch disk if the primary didn't accept. */
+	if (!ret) {
+		kamado_dump_pending_block(ckp, gbt_block, rhash, height,
+					  pending_path, sizeof(pending_path));
+	}
+
+	free(gbt_block);
 	generator_preciousblock(ckp, rhash);
 
 	/* Check failures that may be inconclusive but were submitted via other
@@ -2099,6 +2158,10 @@ static bool local_block_submit(ckpool_t *ckp, char *gbt_block, const uchar *flip
 				   height, ret ? "ACCEPTED" : "REJECTED");
 		}
 	}
+	/* Block ended up on chain (either initial submit or precious-block
+	 * recovery): the dump file is no longer needed. */
+	if (ret && pending_path[0])
+		unlink(pending_path);
 	return ret;
 }