fix: address link tracker clear decref imbalance (#803)

LinkTracker tracked one pool ref per link ID, but clear() decremented
once per cell reference count. For links repeated across many cells this
could cause one valid decref followed by many failing decref calls
during buffer clear.

---------

Co-authored-by: Simon Klee <hello@simonklee.dk>

Author: aarcamp

packages/core/src/zig/link.zig

@@ -264,11 +264,7 @@ pub const LinkTracker = struct {
         var it = self.used_ids.iterator();
         while (it.next()) |entry| {
             const id = entry.key_ptr.*;
-            const count = entry.value_ptr.*;
-            var i: u32 = 0;
-            while (i < count) : (i += 1) {
-                self.pool.decref(id) catch {};
-            }
+            self.pool.decref(id) catch {};
         }
     }
 

packages/core/src/zig/tests/link_test.zig

@@ -121,6 +121,33 @@ test "LinkTracker - clear releases tracked IDs" {
     try std.testing.expectEqual(@as(u32, 0), try pool.getRefcount(id2));
 }
 
+test "LinkTracker - clear only decrefs once per ID with multiple cell refs" {
+    var pool = LinkPool.init(std.testing.allocator);
+    defer pool.deinit();
+
+    const id = try pool.alloc("https://example.com/shared");
+
+    var tracker_a = LinkTracker.init(std.testing.allocator, &pool);
+    defer tracker_a.deinit();
+
+    var tracker_b = LinkTracker.init(std.testing.allocator, &pool);
+    defer tracker_b.deinit();
+
+    tracker_a.addCellRef(id);
+    tracker_a.addCellRef(id);
+    tracker_a.addCellRef(id);
+
+    tracker_b.addCellRef(id);
+
+    try std.testing.expectEqual(@as(u32, 2), try pool.getRefcount(id));
+
+    // Clear tracker A should decref once (2 -> 1).
+    tracker_a.clear();
+
+    try std.testing.expectEqual(@as(u32, 1), try pool.getRefcount(id));
+    try std.testing.expectEqualSlices(u8, "https://example.com/shared", try pool.get(id));
+}
+
 test "LinkPool - leak repro: alloc-only IDs accumulate live slots" {
     var pool = LinkPool.init(std.testing.allocator);
     defer pool.deinit();