fix: prefer full decoration range (#2239)

* fix: prefer full decoration range

* fix: consider docChanged flag

* fix: add test/simplify logic with helper

* fix: remove dead restore fallback in #collectDesiredState

#resolveEffectiveRanges already calls restoreRangesFromPrevious with
the same arguments — the second call was guaranteed to return the same
empty result. Also adds the missing #setPreviousRanges call to clear
stale ranges on this path.

---------

Co-authored-by: Caio Pizzol <caio@harbourshare.com>

Author: VladaHarbour

packages/super-editor/src/core/presentation-editor/dom/DecorationBridge.test.ts

@@ -873,6 +873,94 @@ describe('DecorationBridge', () => {
       expect(ranges[0].from).toBe(13);
       expect(ranges[0].to).toBe(19);
     });
+
+    it('prefers full restored span when plugin returns partial (e.g. after applying mark in long selection)', () => {
+      const fullText = 'Hello world';
+      const plugin = mutableExternalPlugin('focus');
+      plugin.setDecorations([{ from: 1, to: 12, class: 'highlight-selection' }]);
+      const state = mockStateWithDocText([plugin.plugin], fullText);
+
+      const ranges1 = bridge.collectDecorationRanges(state);
+      expect(ranges1).toHaveLength(1);
+      expect(ranges1[0].to - ranges1[0].from).toBe(fullText.length);
+
+      // This behavior is only expected right after a doc-changing transaction (e.g. applying a mark)
+      bridge.recordTransaction({ docChanged: true, mapping: { map: (pos: number) => pos } } as unknown as Transaction);
+
+      // Simulate plugin returning only a prefix after mapping (e.g. mark applied in middle)
+      plugin.setDecorations([{ from: 1, to: 6, class: 'highlight-selection' }]);
+      const ranges2 = bridge.collectDecorationRanges(state);
+      expect(ranges2).toHaveLength(1);
+      // Full span restored by text so highlight does not partially vanish (not just partial 5 chars)
+      expect(ranges2[0].to - ranges2[0].from).toBeGreaterThan(5);
+      expect(ranges2[0].classes).toContain('highlight-selection');
+    });
+
+    it('sync applies full span when plugin returns partial so highlight does not vanish', () => {
+      const { index, addSpan, rebuild } = createIndex();
+      addSpan(1, 6, 'Hello');
+      const worldSpan = addSpan(6, 12, ' world');
+      rebuild();
+
+      const { plugin, setDecorations } = mutableExternalPlugin('focus');
+      const state = mockStateWithDocText([plugin], 'Hello world');
+      setDecorations([{ from: 1, to: 12, class: 'highlight-selection' }]);
+      bridge.collectDecorationRanges(state);
+      bridge.sync(state, index);
+      expect(worldSpan.classList.contains('highlight-selection')).toBe(true);
+
+      // Simulate mark application (doc change) that can cause mapping collapse for decorations
+      bridge.recordTransaction({ docChanged: true, mapping: { map: (pos: number) => pos } } as unknown as Transaction);
+
+      setDecorations([{ from: 1, to: 6, class: 'highlight-selection' }]);
+      bridge.sync(state, index);
+      expect(worldSpan.classList.contains('highlight-selection')).toBe(true);
+    });
+
+    it('returns narrow range as-is when plugin narrows after meta-only transaction (docChanged: false)', () => {
+      const fullText = 'Hello world';
+      const plugin = mutableExternalPlugin('focus');
+      plugin.setDecorations([{ from: 1, to: 12, class: 'highlight-selection' }]);
+      const state = mockStateWithDocText([plugin.plugin], fullText);
+
+      bridge.collectDecorationRanges(state);
+      expect(bridge.collectDecorationRanges(state)).toHaveLength(1);
+
+      // Meta-only (e.g. setFocus with smaller range): no doc change
+      bridge.recordTransaction({ docChanged: false, mapping: { map: (pos: number) => pos } } as unknown as Transaction);
+      plugin.setDecorations([{ from: 1, to: 6, class: 'highlight-selection' }]);
+
+      const ranges = bridge.collectDecorationRanges(state);
+      expect(ranges).toHaveLength(1);
+      // Must not expand: narrow range comes back as-is (from 1 to 6 = 5 chars)
+      expect(ranges[0].to - ranges[0].from).toBe(5);
+      expect(ranges[0].from).toBe(1);
+      expect(ranges[0].to).toBe(6);
+    });
+
+    it('sync applies narrow range only when plugin narrows after meta-only transaction', () => {
+      const { index, addSpan, rebuild } = createIndex();
+      const helloSpan = addSpan(1, 6, 'Hello');
+      const worldSpan = addSpan(6, 12, ' world');
+      rebuild();
+
+      const { plugin, setDecorations } = mutableExternalPlugin('focus');
+      const state = mockStateWithDocText([plugin], 'Hello world');
+      setDecorations([{ from: 1, to: 12, class: 'highlight-selection' }]);
+      bridge.collectDecorationRanges(state);
+      bridge.sync(state, index);
+      expect(helloSpan.classList.contains('highlight-selection')).toBe(true);
+      expect(worldSpan.classList.contains('highlight-selection')).toBe(true);
+
+      // Meta-only: user narrowed selection (e.g. setFocus(1, 6))
+      bridge.recordTransaction({ docChanged: false, mapping: { map: (pos: number) => pos } } as unknown as Transaction);
+      setDecorations([{ from: 1, to: 6, class: 'highlight-selection' }]);
+      bridge.sync(state, index);
+
+      // Narrow range only: first span keeps class, second loses it
+      expect(helloSpan.classList.contains('highlight-selection')).toBe(true);
+      expect(worldSpan.classList.contains('highlight-selection')).toBe(false);
+    });
   });
 
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