rpc: log pullOnce watermark divergence at debug level

The inline retry path in pullOnce silently recovers from a cross-
side watermark divergence by resetting cursors and retrying. A
one-shot divergence is normal (a wsd respawn under the same
WebSocket, mid-flight test harness state) and the recovery is the
intended behavior. A persistently broken remote, however, will
trip the retry on every pull and silently degrade to repeated
baseline re-syncs, with no operator-visible signal.

Add a console.debug() so the divergence shows up in logs without
creating noise on the well-behaved happy path. The fields capture
which cursor diverged and which got reset, so a developer chasing
"why does this workspace keep re-syncing" has enough context to
correlate with the remote's lifecycle.

Author: aron-cf

packages/rpc/src/sync-driver.ts

@@ -159,6 +159,22 @@ async function pullOnceImpl(
     // down before we get here.
     await fetchResult.stream.cancel().catch(() => {});
     maybeDispose(fetchResult);
+    // Surface the divergence at debug level so an operator with
+    // log access can spot a persistently broken remote. We do not
+    // throw: a one-shot divergence is normal after a wsd restart
+    // under the same WebSocket, and the inline reset + retry is
+    // the intended recovery. A persistently-lying remote will log
+    // this on every pull, which is the operational signal that
+    // something upstream is wedged.
+    console.debug("[pullOnce] cross-side watermark divergence; resetting and retrying", {
+      backend,
+      appliedPushRev,
+      localPushRev,
+      remoteRev,
+      sinceRev,
+      resetPushRev: appliedPushRev < localPushRev,
+      resetFetchRev: remoteRev < sinceRev,
+    });
     if (appliedPushRev < localPushRev) {
       writeWatermark(db, "pushRev", 0, backend);
     }