test: group examples into per-category folders

Move examples/*.sx and their expected/ snapshots into per-category
subfolders (examples/<category>/...). Folder = leading filename token,
with ffi-objc/ffi-jni kept whole; filenames are unchanged. The corpus
runner and LSP sweep now discover each category's expected/ dir, while
issues/ stays flat. Example 1058's repo-root-relative companion import
is made file-relative. Path strings embedded in 164 snapshots were
regenerated (path-only changes). Test-layout docs in CLAUDE.md updated.

examples/event/1632-event-loop.sx

@@ -0,0 +1,71 @@
+// std.event (PLAN-HTTPZ S5): the OS-neutral Loop — idle timeout costs
+// nothing, read readiness carries the registration's udata, write
+// interest reports an empty send buffer immediately, EOF is a flag not
+// an errno, and the deadline helpers do monotonic timeout math.
+#import "modules/std.sx";
+
+main :: () -> i32 {
+    pair : [2]i32 = ---;
+    if socket.socketpair(socket.AF_UNIX, socket.SOCK_STREAM, 0, @pair[0]) != 0 {
+        print("socketpair failed\n");
+        return 1;
+    }
+    a := pair[0];
+    b := pair[1];
+
+    loop, ie := event.Loop.init();
+    if ie { print("loop init failed\n"); return 1; }
+    are := false;
+    loop.add_read(a, 41) catch { are = true; };
+    if are { print("add_read failed\n"); return 1; }
+
+    evs : [8]event.Event = ---;
+
+    // Idle: a bounded wait returns 0 events, and roughly honors the bound.
+    t0 := event.deadline_in(40);
+    n, we := loop.wait(.{ ptr = @evs[0], len = 8 }, 40);
+    if we { print("wait failed\n"); return 1; }
+    if n != 0 { print("idle wait: expected 0 events, got {}\n", n); return 1; }
+    if !event.expired(t0) { print("idle wait returned before its timeout\n"); return 1; }
+    print("idle wait: 0 events, deadline expired\n");
+
+    // Readable: the event carries fd, udata, and the pending byte count.
+    msg := "ping";
+    socket.write(b, msg.ptr, 4);
+    n2, we2 := loop.wait(.{ ptr = @evs[0], len = 8 }, 1000);
+    if we2 { print("wait failed\n"); return 1; }
+    if n2 != 1 { print("after write: expected 1 event, got {}\n", n2); return 1; }
+    if !evs[0].readable { print("event not readable\n"); return 1; }
+    if evs[0].fd != a { print("event names the wrong fd\n"); return 1; }
+    if evs[0].udata != 41 { print("udata did not round-trip\n"); return 1; }
+    if evs[0].nbytes != 4 { print("expected 4 pending bytes, got {}\n", evs[0].nbytes); return 1; }
+    print("readable: fd/udata/nbytes all correct\n");
+
+    // Write interest on an empty send buffer reports writable at once.
+    awe := false;
+    loop.add_write(b, 42) catch { awe = true; };
+    if awe { print("add_write failed\n"); return 1; }
+    buf : [16]u8 = ---;
+    socket.read(a, @buf[0], 16);   // drain so only the WRITE event fires
+    n3, we3 := loop.wait(.{ ptr = @evs[0], len = 8 }, 1000);
+    if we3 { print("wait failed\n"); return 1; }
+    if n3 != 1 { print("write interest: expected 1 event, got {}\n", n3); return 1; }
+    if !evs[0].writable { print("event not writable\n"); return 1; }
+    if evs[0].udata != 42 { print("write udata did not round-trip\n"); return 1; }
+    print("writable: immediate, udata correct\n");
+    loop.del_write(b);
+
+    // Peer close: readable with the eof flag set.
+    socket.close(b);
+    n4, we4 := loop.wait(.{ ptr = @evs[0], len = 8 }, 1000);
+    if we4 { print("wait failed\n"); return 1; }
+    if n4 != 1 { print("after close: expected 1 event, got {}\n", n4); return 1; }
+    if !evs[0].eof { print("after close: eof flag not set\n"); return 1; }
+    print("peer close: eof flagged\n");
+
+    loop.del_read(a);
+    socket.close(a);
+    loop.close();
+    print("event loop ok\n");
+    return 0;
+}

examples/event/expected/1632-event-loop.exit

@@ -0,0 +1 @@
+0

examples/event/expected/1632-event-loop.stderr

@@ -0,0 +1 @@
+

examples/event/expected/1632-event-loop.stdout

@@ -0,0 +1,5 @@
+idle wait: 0 events, deadline expired
+readable: fd/udata/nbytes all correct
+writable: immediate, udata correct
+peer close: eof flagged
+event loop ok