test(6194): match the head<=1 post-compact contract

Tests previously asserted head=0 exactly after compaction; the
temp-pad-swap path lands at head=1 (one seed rev plus one content
rev) matching the shape of a freshly-imported pad. Relax the
assertions to  and derive the removed-count from
before-head minus after-head, so the tests still catch regressions in
text-preservation, saved-revision cleanup, and append-after-compact
without being tied to the exact implementation shape.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: JohnMcLear

src/tests/backend/specs/compactPad.ts

@@ -15,13 +15,15 @@ describe(__filename, function () {
   });
 
   describe('pad.compactHistory()', function () {
-    it('no-ops an empty (head <= 0) pad', async function () {
+    it('no-ops a pad that is already at head <= 1', async function () {
       const pad = await padManager.getPad(padId);
+      // Fresh pads land at head=0 (just the defaultText rev); compactHistory
+      // has nothing useful to do on a pad that short.
       const removed = await pad.compactHistory();
       assert.strictEqual(removed, 0);
     });
 
-    it('collapses all history into rev 0 while preserving text', async function () {
+    it('collapses history to head<=1 while preserving text', async function () {
       const pad = await padManager.getPad(padId);
       await pad.appendText('line 1\n');
       await pad.appendText('line 2\n');
@@ -32,49 +34,57 @@ describe(__filename, function () {
 
       const removed = await pad.compactHistory();
 
-      assert.strictEqual(removed, before);
-      assert.strictEqual(pad.getHeadRevisionNumber(), 0);
+      // The collapsed pad matches the shape of a freshly-imported pad
+      // (head=1: a seed rev + the full-content rev). Exact count depends
+      // on whether the defaultText-init counted as rev 0, but the
+      // invariant is `head <= 1`.
+      const afterHead = pad.getHeadRevisionNumber();
+      assert.ok(afterHead <= 1, `expected head<=1 after compact, got ${afterHead}`);
+      assert.strictEqual(removed, before - afterHead);
+      assert.strictEqual(pad.atext.text, expectedText);
       // Reload from DB to confirm the collapse actually landed.
       const reloaded = await padManager.getPad(padId);
-      assert.strictEqual(reloaded.getHeadRevisionNumber(), 0);
+      assert.strictEqual(reloaded.getHeadRevisionNumber(), afterHead);
       assert.strictEqual(reloaded.atext.text, expectedText);
     });
 
     it('drops saved-revision bookmarks', async function () {
       const pad = await padManager.getPad(padId);
-      await pad.appendText('content\n');
-      // Push a fake savedRevision pointer — the real API would call
-      // addSavedRevision but we avoid coupling the test to that API
-      // surface; any non-empty array reaches the same codepath.
+      await pad.appendText('content line 1\n');
+      await pad.appendText('content line 2\n');
       // @ts-ignore — savedRevisions is private but set from JSON on load.
       pad.savedRevisions.push({revNum: pad.getHeadRevisionNumber()});
       await pad.compactHistory();
       // @ts-ignore
       assert.deepStrictEqual(pad.savedRevisions, []);
     });
 
-    it('leaves subsequent edits appending to the collapsed base', async function () {
+    it('leaves subsequent edits appending cleanly on top of the collapsed base', async function () {
       const pad = await padManager.getPad(padId);
       await pad.appendText('first\n');
       await pad.appendText('second\n');
-      await pad.compactHistory();
-      assert.strictEqual(pad.getHeadRevisionNumber(), 0);
       await pad.appendText('third\n');
-      assert.strictEqual(pad.getHeadRevisionNumber(), 1);
-      assert.ok(pad.atext.text.includes('third'));
+      await pad.compactHistory();
+      const postCompactHead = pad.getHeadRevisionNumber();
+      await pad.appendText('fourth\n');
+      assert.strictEqual(pad.getHeadRevisionNumber(), postCompactHead + 1);
+      assert.ok(pad.atext.text.includes('fourth'),
+          `expected "fourth" in post-compact text: ${pad.atext.text}`);
     });
   });
 
   describe('API.compactPad()', function () {
-    it('returns the removed-revision count and mutates the pad in place',
+    it('reports the number of revisions removed and compacts the pad',
         async function () {
           const pad = await padManager.getPad(padId);
           await pad.appendText('alpha\n');
           await pad.appendText('beta\n');
+          await pad.appendText('gamma\n');
           const before = pad.getHeadRevisionNumber();
           const result = await api.compactPad(padId);
-          assert.strictEqual(result.removed, before);
-          assert.strictEqual(pad.getHeadRevisionNumber(), 0);
+          const afterHead = pad.getHeadRevisionNumber();
+          assert.ok(afterHead <= 1);
+          assert.strictEqual(result.removed, before - afterHead);
         });
   });
 });