terminal: reschedule compression after page replacement

Compaction and capacity growth publish fresh page generations, so an
active incremental traversal can detect them. They did not update the
separate activity token, however, and a completed compressor could
remain idle after either operation restored or replaced a cold page.

Mark successful replacements as compression activity without resetting
the exact continuation marker. The next scheduled step can retain valid
progress or restart through the existing generation checks.

src/terminal/PageList.zig

@@ -3179,6 +3179,7 @@ pub fn compact(self: *PageList, node: *List.Node) Allocator.Error!?*List.Node {
     self.pages.insertBefore(node, new_node);
     self.pages.remove(node);
     self.destroyNode(node);
+    self.page_compression.markActivity();
 
     new_page.assertIntegrity();
     return new_node;
@@ -3722,6 +3723,7 @@ pub fn increaseCapacity(
     self.pages.insertBefore(node, new_node);
     self.pages.remove(node);
     self.destroyNode(node);
+    self.page_compression.markActivity();
 
     new_page.assertIntegrity();
     return new_node;
@@ -6765,6 +6767,34 @@ test "PageList owns incremental compression state" {
     );
 }
 
+test "PageList replacements preserve compression continuation and mark activity" {
+    const testing = std.testing;
+
+    var s = try init(testing.allocator, 80, 24, null);
+    defer s.deinit();
+
+    const state: IncrementalCompressionState = .{
+        .flags = .{ .verifying = true },
+        .activity_serial = 42,
+        .last_serial = 7,
+        .next_serial = 8,
+    };
+    const expected: IncrementalCompressionState = .{
+        .flags = .{ .verifying = true },
+        .activity_serial = 43,
+        .last_serial = 7,
+        .next_serial = 8,
+    };
+
+    s.page_compression = state;
+    const replacement = try s.increaseCapacity(s.pages.first.?, null);
+    try testing.expectEqual(expected, s.page_compression);
+
+    s.page_compression = state;
+    _ = (try s.compact(replacement)).?;
+    try testing.expectEqual(expected, s.page_compression);
+}
+
 test "PageList incremental compression bounds inspected pages" {
     const testing = std.testing;