test: stub the clipboard transport in the excel spec for CI determinism

Headless CI runners deny real clipboard access (focus/permission), so the
realPress Ctrl+C/Ctrl+V test now stubs navigator.clipboard while keeping
the real keystroke pipeline; the real-hardware path stays a manual check.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: 6pac-ai

cypress/e2e/clipboard-api.cy.ts

@@ -11,9 +11,11 @@
  * The spec is SELF-HOSTING (harness served via cy.intercept; no example page)
  * and stubs navigator.clipboard for determinism — the same pattern
  * slickgrid-universal uses in its unit tests. The stub also captures the exact
- * serialized text, which real-clipboard tests cannot assert. The end-to-end
- * path through the REAL clipboard (realPress Ctrl+C / Ctrl+V in Electron) is
- * covered by example-excel-compatible-spreadsheet.cy.ts.
+ * serialized text, which real-clipboard tests cannot assert. The full realPress
+ * Ctrl+C / Ctrl+V keystroke path is covered by
+ * example-excel-compatible-spreadsheet.cy.ts with the same transport stub —
+ * headless CI runners deny real clipboard access (focus/permission), so the
+ * real-hardware path is a manual check.
  *
  * Grid A pastes through column editors (editor.applyValue); grid B has no
  * editors, covering the raw field-assignment path plus both override hooks.

cypress/e2e/example-excel-compatible-spreadsheet.cy.ts

@@ -6,6 +6,20 @@ describe('Example - Excel-compatible spreadsheet and Cell Selection', { retries:
   });
 
   it('should click on cell B2, copy value, ArrowDown, paste value, ArrowRight, and expect to be in column C', () => {
+    // stub the Clipboard API transport: headless CI runners deny real clipboard
+    // access (focus/permission), so realPress drives the full keystroke path
+    // while the transport stays deterministic
+    cy.window().then((win: any) => {
+      const store = { text: '' };
+      Object.defineProperty(win.navigator, 'clipboard', {
+        configurable: true,
+        value: {
+          writeText: (t: string) => { store.text = t; return Promise.resolve(); },
+          readText: () => Promise.resolve(store.text),
+        },
+      });
+    });
+
     cy.getCell(2, 2, '', { parentSelector: '#myGrid', rowHeight: cellHeight })
       .as('cell_B2')
       .click();