fix: correct padEditor author-attribute test off-by-one; run backend on PRs (#36)

Two linked problems surfaced when backend-tests finally ran on a main push:

1. Test off-by-one (the actual failure). The "inserts carry an author
   attribute even when authorId is empty" spec walked atext.attribs and
   required every op past the insert point to carry an author. But
   applyEdit splices the new text in *before* the pad's trailing '\n', so
   that original, AI-untouched newline is shifted to the document tail and
   correctly stays unattributed. The check skipped the seed prefix but had
   no upper bound, so it wrongly asserted on that trailing newline. Bound
   the check to [insertStart, insertEnd) — the span the AI actually wrote.
   The surgical-attribution code was right; only the assertion over-reached.

2. Why nobody noticed for ~2.5 weeks. backend-tests was skipped for
   same-repo PRs (it ran only on pushes or fork PRs), and the parent
   workflow only triggers push on main/master. So same-repo feature-branch
   PRs got no backend run, and this failure only ever showed up post-merge
   on main, where nothing blocks on it. Drop the guard so backend runs on
   every PR; it needs no secrets, so this is safe for forks too.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: JohnMcLear

.github/workflows/backend-tests.yml

@@ -6,11 +6,14 @@ on:
 
 jobs:
   withplugins:
-    # run on pushes to any branch
-    # run on PRs from external forks
-    if: |
-      (github.event_name != 'pull_request')
-      || (github.event.pull_request.head.repo.id != github.event.pull_request.base.repo.id)
+    # Always run. The previous guard skipped this job for same-repo pull
+    # requests (it only ran on pushes or fork PRs), but the parent workflow
+    # only triggers `push` on main/master — so same-repo feature-branch PRs
+    # got NO backend run at all, and failures only surfaced post-merge on
+    # main where nothing blocks on them. A genuine padEditor regression sat
+    # red on main for weeks as a result. Backend tests need no secrets, so
+    # running them on every PR (incl. forks) is safe and is what actually
+    # guards the branch before merge.
     name: with Plugins
     runs-on: ubuntu-latest
     steps:

static/tests/backend/specs/padEditor.ts

@@ -362,7 +362,8 @@ describe('ep_ai_chat - padEditor', function () {
 
           const pad = await padManager.getPad(padId);
           const baseLen = pad.text().length; // includes trailing '\n'
-          const result = await padEditor.applyEdit(pad, {appendText: '\nMore'});
+          const appendText = '\nMore';
+          const result = await padEditor.applyEdit(pad, {appendText});
           assert.ok(result.success,
               `append should succeed without authorId; got: ${JSON.stringify(result)}`);
 
@@ -388,13 +389,19 @@ describe('ep_ai_chat - padEditor', function () {
           // createPad API before this PR's invariant existed.
           let cursor = 0;
           // applyEdit inserts at currentText.length - 1, i.e. before the
-          // trailing '\n'. So the new span starts at baseLen - 1.
+          // trailing '\n'. So the new span starts at baseLen - 1 and spans
+          // exactly the inserted characters. The pad's original trailing '\n'
+          // is pushed to the very end of the document and is intentionally
+          // left unattributed — the AI never wrote it, so only [insertStart,
+          // insertEnd) is the AI's work and must carry an author attribute.
           const insertStart = baseLen - 1;
+          const insertEnd = insertStart + appendText.length;
           for (const op of Changeset.deserializeOps(updated.atext.attribs)) {
             const opStart = cursor;
             const opEnd = cursor + op.chars;
             cursor = opEnd;
-            if (opEnd <= insertStart) continue; // entirely in the seed
+            if (opEnd <= insertStart) continue; // entirely in the seed prefix
+            if (opStart >= insertEnd) continue; // seed's trailing '\n', shifted past our insert
             let hasAuthor = false;
             for (const [key] of attribsFromString(op.attribs, pool)) {
               if (key === 'author') hasAuthor = true;