multi-attach: say who else is watching, and where you are

A small tag in each client's own top-right corner when several
terminals share the session: the viewer count, and on a view that is
a crop being panned by somebody else's cursor, the crop's offset into
the shared screen ("2 clients +12+4") -- which is exactly the moment
a screen moving on its own needs explaining. Stamped per client after
projection, because every terminal has its own count of others and
its own offset; the shared status bar is composed once and can be
cropped out of a panned view anyway. attach_indicator false hides
it.

1 files changed, 17 insertions, 1 deletions

diff --git a/tests/test_session.py b/tests/test_session.py
index 5878945..4a5c7e7 100644
--- a/tests/test_session.py
+++ b/tests/test_session.py
@@ -208,9 +208,14 @@ def main():
 
     # --- multiple attached clients share one session --------------------
     pid3, fd3 = attach(name, cols=50, rows=12)
-    drain(fd3)
+    out3 = drain(fd3)
     tail = drain(fd2, idle=0.2, limit=2.0)
     check(
+        "both clients are told about each other",
+        b"2 clients" in tail and b"2 clients" in out3,
+        repr((tail[-80:], out3[-80:])),
+    )
+    check(
         "a second client leaves the first attached",
         b"replaced" not in tail and running(pid2),
         repr(tail[-60:]),
@@ -245,6 +250,17 @@ def main():
     )
     check("the last client to type owns the size", screen_size(name) == (80, 24))
 
+    # Push the shared cursor below the small client's 12 rows: its view has
+    # to pan down to follow, and the tag must say where it went.
+    os.write(fd2, b"\n" * 20)
+    drain(fd2)
+    panned = drain(fd3)
+    check(
+        "a cropped view names its offset into the shared screen",
+        b"clients +" in panned,
+        repr(panned[-100:]),
+    )
+
     resize(pid3, fd3, 40, 10)
     drain(fd3)
     check(