test: stats file-count residual, --threads coverage, deterministic delete timing

- Output parity: add `File list size` to the strict --stats differential and
  document the row-#3 residual with test_stats_file_count_breakdown_residual
  (rsync's `Number of files`/`Number of created files` type breakdown is not
  reproducible from what the sender knows: no directory accounting and no
  per-entry destination-created state).  The row stays a caveat.
- Add --threads variants for the --stats and --progress/-P differentials.
  The `-n --delete --threads` variant is a documented xfail: the threaded
  dry-run path does not consume the receiver's STATUS_STATS delete list yet.
- Replace the 0.2s sleep flake in the delete-timing proxy with a socket
  barrier: the hook now fires only after the server sends a reply (proving it
  processed the preceding per-directory delete plan), using --incremental +
  --ignore-times to guarantee a mid-transfer handshake reply.

.probe.sh

@@ -1,15 +0,0 @@
-B=/workspace/build-ci
-D=/workspace/.probe
-rm -rf $D && mkdir -p $D/src $D/dst
-head -c 200000 /dev/urandom > $D/src/f.bin
-$B/server -p 45995 --allow-unauthenticated >$D/srv.log 2>&1 &
-SRV=$!; sleep 0.7
-for flags in "" "--incremental" "--incremental --delta"; do
-  rm -rf $D/dst; mkdir -p $D/dst
-  echo "=== fastsync flags='$flags' fresh: %b %c %l %n ==="
-  $B/client --source-dir $D/src --dest-dir $D/dst --server-port 45995 --save-to-disk -a $flags --out-format="%b %c %l %n" 2>&1 | grep -v ERROR
-done
-echo "=== rsync whole-file: ==="
-rm -rf $D/rsrc $D/rdst; mkdir -p $D/rsrc $D/rdst; head -c 200000 /dev/urandom > $D/rsrc/f.bin
-rsync -a --out-format="%b %c %l %n" $D/rsrc/ $D/rdst/
-kill $SRV 2>/dev/null || true

tests/integration/test_delete_timing_parity.py

@@ -101,15 +101,24 @@ class _SlicingProxy:
     """Forward the client stream to a server, optionally cutting it or invoking a
     hook after a byte threshold.  ``forward_limit`` mode resets both ends after
     that many client bytes (a mid-transfer failure).  ``hook`` mode calls the
-    hook once and keeps forwarding to completion."""
+    hook once and keeps forwarding to completion.
+
+    With ``wait_for_reply`` the hook is a real barrier, not a timing guess: it
+    fires only after the server has sent *any* reply, which the receiver does
+    only after it has consumed the frames that precede the payload (the
+    per-directory delete plan for ``--delete-delay``).  The caller pairs it with
+    ``--incremental`` so a per-file handshake reply is guaranteed mid-transfer.
+    """
 
     def __init__(self, target_port, forward_limit=None, hook=None, hook_after=0,
-                 throttle=0.0):
+                 throttle=0.0, wait_for_reply=False):
         self.target = ("127.0.0.1", target_port)
         self.forward_limit = forward_limit
         self.hook = hook
         self.hook_after = hook_after
         self.throttle = throttle
+        self.wait_for_reply = wait_for_reply
+        self.server_replied = threading.Event()
         self.hook_called = threading.Event()
         self.listener = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
         self.listener.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
@@ -158,15 +167,7 @@ class _SlicingProxy:
                             data = data[:room]
                         backend.sendall(data)
                         forwarded += len(data)
-                        if (self.hook is not None and not self.hook_called.is_set()
+                        self._maybe_hook(forwarded)
-                                and forwarded >= self.hook_after):
-                            # Give the receiver time to process the (tiny) plan
-                            # frames that precede this offset before the hook
-                            # mutates the destination.
-                            if self.throttle > 0:
-                                time.sleep(0.2)
-                            self.hook()
-                            self.hook_called.set()
                         if self.forward_limit is not None and forwarded >= self.forward_limit:
                             socks = []
                             break
@@ -174,6 +175,10 @@ class _SlicingProxy:
                             time.sleep(self.throttle)
                     else:
                         client.sendall(data)
+                        # Any server reply proves the receiver consumed the
+                        # frames that precede it, so the hook barrier is met.
+                        self.server_replied.set()
+                        self._maybe_hook(forwarded)
         except OSError:
             pass
         for sock in (client, backend):
@@ -190,6 +195,19 @@ class _SlicingProxy:
         except OSError:
             pass
 
+    def _maybe_hook(self, forwarded):
+        """Fire the one-shot hook once its barrier is satisfied: enough client
+        bytes have been forwarded and, when ``wait_for_reply`` is set, the
+        server has sent a reply proving it processed the preceding frames."""
+        if self.hook is None or self.hook_called.is_set():
+            return
+        if forwarded < self.hook_after:
+            return
+        if self.wait_for_reply and not self.server_replied.is_set():
+            return
+        self.hook()
+        self.hook_called.set()
+
     def finish(self):
         self._thread.join(30)
         try:
@@ -317,8 +335,16 @@ class TestDeleteDelayVsAfterSnapshot:
                     # after the directory's plan (delay) has been processed.
                     _write(new_extra, b"created mid-transfer\n")
 
-                proxy = _SlicingProxy(server.port, hook=hook, hook_after=MID_TRANSFER_BYTES, throttle=PROXY_THROTTLE)
+                # --incremental gives the receiver a mid-transfer handshake
-                flags = [timing] + (["--threads"] if mt else [])
+                # reply; the proxy waits for it (wait_for_reply) so the hook is
+                # causally after the plan frame, never a timing guess.
+                # --ignore-times forces the big file to transfer on the second
+                # timing too (the first run already installed it), keeping the
+                # mid-transfer reply present in both iterations.
+                proxy = _SlicingProxy(server.port, hook=hook,
+                                      hook_after=MID_TRANSFER_BYTES,
+                                      throttle=PROXY_THROTTLE, wait_for_reply=True)
+                flags = [timing, "--incremental", "--ignore-times"] + (["--threads"] if mt else [])
                 result, _ = run_client(source, dest, flags=flags, port=proxy.port)
                 proxy.finish()
                 assert result.returncode == 0, (

tests/integration/test_output_parity.py

@@ -5,6 +5,7 @@ differential tests run the SAME transfer with real ``rsync 3.4.1`` and with
 fastsync and compare stdout, so they are skipped when rsync is unavailable.
 """
 import os
+import re
 import shutil
 import subprocess
 import sys
@@ -383,19 +384,22 @@ class TestWireStatsParity:
 
     @requires_rsync
     @pytest.mark.ci
-    def test_progress_first_frame_matches_rsync(self, shared_server):
+    @pytest.mark.parametrize("mt", [False, True])
-        """For a sub-32 KiB file the first --progress frame is deterministic
+    @pytest.mark.parametrize("progress_flag", ["--progress", "-P"])
-        (0.00 kB/s, 0:00:00) and must be byte-identical to rsync's."""
+    def test_progress_first_frame_matches_rsync(self, shared_server, progress_flag, mt):
+        """For a sub-32 KiB file the first --progress/-P frame is deterministic
+        (0.00 kB/s, 0:00:00) and must be byte-identical to rsync's, in both the
+        single-threaded and --threads send paths."""
         source = os.path.join(TEST_DATA_DIR, "wire_pg_src")
         dest = os.path.join(TEST_DATA_DIR, "wire_pg_dst")
         rdst = os.path.join(TEST_DATA_DIR, "wire_pg_rdst")
         _make_one_file(source, "f.bin", 100)
         clean_dir(dest)
         clean_dir(rdst)
-        rsync_result = _rsync(["-a", "--progress", source + "/", rdst + "/"])
+        rsync_result = _rsync(["-a", progress_flag, source + "/", rdst + "/"])
         assert rsync_result.returncode == 0, rsync_result.stderr
-        result, _ = run_client(source, dest, flags=["-a", "--progress"],
+        flags = ["-a", progress_flag] + (["--threads"] if mt else [])
-                               port=shared_server.port)
+        result, _ = run_client(source, dest, flags=flags, port=shared_server.port)
         assert result.returncode == 0, result.stderr[:300]
 
         def frames(text):
@@ -410,8 +414,10 @@ class TestWireStatsParity:
 
     @requires_rsync
     @pytest.mark.ci
-    def test_stats_selected_lines_match_rsync(self, shared_server):
+    @pytest.mark.parametrize("mt", [False, True])
-        """The protocol-independent --stats lines must match rsync exactly."""
+    def test_stats_selected_lines_match_rsync(self, shared_server, mt):
+        """The protocol-independent --stats lines must match rsync exactly, in
+        both the single-threaded and --threads (multithreaded) send paths."""
         source = os.path.join(TEST_DATA_DIR, "wire_st_src")
         dest = os.path.join(TEST_DATA_DIR, "wire_st_dst")
         rdst = os.path.join(TEST_DATA_DIR, "wire_st_rdst")
@@ -420,8 +426,8 @@ class TestWireStatsParity:
         clean_dir(rdst)
         rsync_result = _rsync(["-a", "--stats", source + "/", rdst + "/"])
         assert rsync_result.returncode == 0, rsync_result.stderr
-        result, _ = run_client(source, dest, flags=["-a", "--stats"],
+        flags = ["-a", "--stats"] + (["--threads"] if mt else [])
-                               port=shared_server.port)
+        result, _ = run_client(source, dest, flags=flags, port=shared_server.port)
         assert result.returncode == 0, result.stderr[:300]
         keys = (
             "Number of regular files transferred",
@@ -430,6 +436,7 @@ class TestWireStatsParity:
             "Literal data",
             "Matched data",
             "Number of deleted files",
+            "File list size",
         )
 
         def pick(text):
@@ -446,8 +453,68 @@ class TestWireStatsParity:
 
     @requires_rsync
     @pytest.mark.ci
-    def test_dry_run_delete_lines_match_rsync(self):
+    def test_stats_file_count_breakdown_residual(self, shared_server):
-        """-n --delete emits transfer-relative `*deleting` lines like rsync."""
+        """Residual (row #3): rsync prints the `Number of files` and
+        `Number of created files` lines with a per-type breakdown
+        (`(reg: X, dir: Y, link: Z)`).
+
+        FastSync cannot reproduce it from what the sender currently knows: the
+        scanner does not put directory entries in the transfer list (directories
+        are created implicitly), and without a per-entry destination-probe the
+        sender cannot tell which entries the receiver newly created.  So FastSync
+        prints the bare transferred-entry count.  This test pins the divergence
+        explicitly -- the row must not be marked ✅.
+        """
+        source = os.path.join(TEST_DATA_DIR, "wire_stc_src")
+        dest = os.path.join(TEST_DATA_DIR, "wire_stc_dst")
+        rdst = os.path.join(TEST_DATA_DIR, "wire_stc_rdst")
+        _make_one_file(source, "f.bin", 6000)
+        clean_dir(dest)
+        clean_dir(rdst)
+        rsync_result = _rsync(["-a", "--stats", source + "/", rdst + "/"])
+        assert rsync_result.returncode == 0, rsync_result.stderr
+        result, _ = run_client(source, dest, flags=["-a", "--stats"],
+                               port=shared_server.port)
+        assert result.returncode == 0, result.stderr[:300]
+
+        def stats_line(text, key):
+            for line in text.splitlines():
+                if line.startswith(key + ":"):
+                    return line
+            return None
+
+        r_files = stats_line(rsync_result.stdout, "Number of files")
+        r_created = stats_line(rsync_result.stdout, "Number of created files")
+        f_files = stats_line(result.stdout, "Number of files")
+        f_created = stats_line(result.stdout, "Number of created files")
+
+        # rsync always carries the type breakdown (the source root counts as a
+        # directory; the single regular file as reg).
+        assert re.match(r"Number of files: 2 \(reg: 1, dir: 1\)$", r_files), r_files
+        assert re.match(r"Number of created files: 1 \(reg: 1\)$", r_created), r_created
+        # FastSync prints only the bare count: no directory accounting and no
+        # per-entry "created" knowledge.
+        assert re.fullmatch(r"Number of files: 1", f_files), f_files
+        assert re.fullmatch(r"Number of created files: 1", f_created), f_created
+
+    @requires_rsync
+    @pytest.mark.ci
+    @pytest.mark.parametrize("mt", [
+        False,
+        pytest.param(
+            True,
+            marks=pytest.mark.xfail(
+                reason="known gap: the --threads dry-run delete path does not "
+                       "consume the receiver's STATUS_STATS delete list yet, so "
+                       "`-n --delete` emits no *deleting lines (tracked by the "
+                       "parity-blockers STATUS_STATS fix)",
+                strict=False,
+            ),
+        ),
+    ])
+    def test_dry_run_delete_lines_match_rsync(self, mt):
+        """-n --delete emits transfer-relative `*deleting` lines like rsync
+        (single-threaded; the --threads variant is a documented xfail)."""
         source = os.path.join(TEST_DATA_DIR, "wire_del_src")
         dest = os.path.join(TEST_DATA_DIR, "wire_del_dst")
         rdst = os.path.join(TEST_DATA_DIR, "wire_del_rdst")
@@ -483,10 +550,10 @@ class TestWireStatsParity:
             line for line in rsync_result.stdout.splitlines() if line.startswith("*deleting")
         )
         # The shared session server refuses deletion; start one that allows it.
+        flags = ["-a", "-n", "--delete", "-i"] + (["--threads"] if mt else [])
         with ServerManager() as server:
             server.start(extra_args=["--allow-delete"])
-            result, _ = run_client(source, dest, flags=["-a", "-n", "--delete", "-i"],
+            result, _ = run_client(source, dest, flags=flags, port=server.port)
-                                   port=server.port)
         assert result.returncode == 0, result.stderr[:300]
         fast_del = sorted(
             line for line in result.stdout.splitlines() if line.startswith("*deleting")