terminal: handle style ID overflow

src/terminal/PageList.zig

@@ -1573,6 +1573,18 @@ pub fn adjustCapacity(
     return new_page;
 }
 
+/// Compact a page, reallocating to minimize the amount of memory
+/// required for the page. This is useful when we've overflowed ID
+/// spaces, are archiving a page, etc.
+///
+/// Note today: this doesn't minimize the memory usage, but it does
+/// fix style ID overflow. A future update can shrink the memory
+/// allocation.
+pub fn compact(self: *PageList, page: *List.Node) !*List.Node {
+    // Adjusting capacity with no adjustments forces a reallocation.
+    return try self.adjustCapacity(page, .{});
+}
+
 /// Create a new page node. This does not add it to the list and this
 /// does not do any memory size accounting with max_size/page_size.
 fn createPage(self: *PageList, cap: Capacity) !*List.Node {

src/terminal/Screen.zig

@@ -971,26 +971,36 @@ pub fn manualStyleUpdate(self: *Screen) !void {
     const md = page.styles.upsert(
         page.memory,
         self.cursor.style,
-    ) catch |err| switch (err) {
+    ) catch |err| md: {
+        switch (err) {
             // Our style map is full. Let's allocate a new page by doubling
             // the size and then try again.
-        error.OutOfMemory => md: {
+            error.OutOfMemory => {
                 const node = try self.pages.adjustCapacity(
                     self.cursor.page_pin.page,
                     .{ .styles = page.capacity.styles * 2 },
                 );
 
+                page = &node.data;
+            },
+
+            // We've run out of style IDs. This is fixed by doing a page
+            // compaction.
+            error.Overflow => {
+                const node = try self.pages.compact(
+                    self.cursor.page_pin.page,
+                );
+                page = &node.data;
+            },
+        }
+
         // Since this modifies our cursor page, we need to reload
         self.cursorReload();
 
-            page = &node.data;
         break :md try page.styles.upsert(
             page.memory,
             self.cursor.style,
         );
-        },
-
-        error.Overflow => return err, // TODO
     };
     self.cursor.style_id = md.id;
     self.cursor.style_ref = &md.ref;