test: integrate code-block copy regression into existing copy test suite

Address PR review:
- Drop standalone codeBlockMarkdown.test.ts; add `codeBlockFullContent` and
  `codeBlockPartialSelection` cases to copyTestInstances.ts and snapshot
  text/plain markdown for all copy test instances via a new
  `Copy tests (Markdown)` describe block (mirrors the export test pattern).
- Trim verbose comments in copyExtension and serializeBlocksExternalHTML.
- copyPasteEquality executor now passes the actual markdown payload as the
  text/plain MIME instead of a literal "text" placeholder, so paste handlers
  that prefer text/plain (e.g. inside code blocks) round-trip correctly.
- Update mixedInParagraph snapshots: prettify's `ignore: ["code"]` preserves
  trailing whitespace inside `<code>` spans, which is the actual HTML output.

Author: nperez0111

packages/core/src/api/clipboard/toClipboard/copyExtension.ts

@@ -27,16 +27,13 @@ function fragmentToExternalHTML<
   selectedFragment: Fragment,
   editor: BlockNoteEditor<BSchema, I, S>,
 ) {
-  const isWithinTable = view.state.selection instanceof CellSelection;
-
-  // Whether the selection is inline-only inside a single block whose content
-  // can be cleanly represented as standalone HTML (i.e. not a code block).
-  // For such "transparent" parents we strip the wrapper so pasting plain text
-  // into another app doesn't get a `<p>` around it. For code blocks we keep
-  // the wrapper so the block's own `toExternalHTML` runs.
   let isWithinBlockContent = false;
+  const isWithinTable = view.state.selection instanceof CellSelection;
 
   if (!isWithinTable) {
+    // Checks whether block ancestry should be included when creating external
+    // HTML. If the selection is within a block content node, the block ancestry
+    // is excluded as we only care about the inline content.
     const fragmentWithoutParents = view.state.doc.slice(
       view.state.selection.from,
       view.state.selection.to,
@@ -48,22 +45,13 @@ function fragmentToExternalHTML<
       children.push(fragmentWithoutParents.child(i));
     }
 
-    const isFullyInline =
+    isWithinBlockContent =
       children.find(
         (child) =>
           child.type.isInGroup("bnBlock") ||
           child.type.name === "blockGroup" ||
           child.type.spec.group === "blockContent",
       ) === undefined;
-
-    // Only use the inline-only path when the parent block isn't a code-content
-    // block. Code blocks need their `<pre><code>` wrapper to keep `\n` as
-    // literal newlines (instead of `<br>`) and to make the markdown converter
-    // emit a fenced block instead of escaping each newline as `\`.
-    const parentIsCode =
-      view.state.selection.$from.parent.type.spec.code === true;
-
-    isWithinBlockContent = isFullyInline && !parentIsCode;
     if (isWithinBlockContent) {
       selectedFragment = fragmentWithoutParents;
     }
@@ -152,7 +140,18 @@ export function selectedFragmentToHTML<
     editor,
   );
 
-  const markdown = cleanHTMLToMarkdown(externalHTML);
+  // Code blocks are treated differently for copying: text/plain is the raw
+  // selected text instead of markdown.
+  const { $from, $to } = view.state.selection;
+  const parentBlockType = $from.parent.type.name;
+  const parentBlockSpec = editor.blockImplementations[parentBlockType as any];
+  const isPurelyInsideCodeBlock =
+    $from.sameParent($to) &&
+    parentBlockSpec?.implementation.meta?.code === true;
+
+  const markdown = isPurelyInsideCodeBlock
+    ? view.state.doc.textBetween($from.pos, $to.pos)
+    : cleanHTMLToMarkdown(externalHTML);
 
   return { clipboardHTML, externalHTML, markdown };
 }

packages/core/src/api/exporters/html/util/serializeBlocksExternalHTML.ts

@@ -45,11 +45,6 @@ export function serializeInlineContentExternalHTML<
   if (!blockContent) {
     throw new Error("blockContent is required");
   } else if (typeof blockContent === "string") {
-    // Pass `blockType` so `inlineContentToNodes` keeps `\n` as text for
-    // code-content blocks instead of splitting into `hardBreak` nodes —
-    // otherwise the exported HTML for a code block contains `<br>` separators
-    // inside `<pre><code>` instead of literal newlines. Mirrors the internal
-    // HTML serializer, which already plumbs this through.
     nodes = inlineContentToNodes(
       [blockContent],
       editor.pmSchema,

tests/src/unit/core/clipboard/copy/__snapshots__/text/html/codeBlockFullContent.html

@@ -0,0 +1,3 @@
+const a = 1;
+<br />
+const b = 2;

tests/src/unit/core/clipboard/copy/__snapshots__/text/html/codeBlockPartialSelection.html

@@ -0,0 +1,3 @@
+onst a = 1;
+<br />
+const b = 2

tests/src/unit/core/clipboard/copy/__snapshots__/text/plain/basicBlocks.md

@@ -0,0 +1,24 @@
+Paragraph 1
+
+# Heading 1
+
+1. Numbered List Item 1
+
+* Bullet List Item 1
+* [ ] Check List Item 1
+* Toggle List Item 1
+
+```text
+console.log("Hello World");
+```
+
+|              |              |
+| ------------ | ------------ |
+| Table Cell 1 | Table Cell 2 |
+| Table Cell 3 | Table Cell 4 |
+
+
+
+***
+
+Paragraph 2

tests/src/unit/core/clipboard/copy/__snapshots__/text/plain/basicBlocksWithProps.md

@@ -0,0 +1,24 @@
+Paragraph 1
+
+## Heading 1
+
+2. Numbered List Item 1
+
+* Bullet List Item 1
+* [x] Check List Item 1
+* Toggle List Item 1
+
+```typescript
+console.log("Hello World");
+```
+
+|              |              |
+| ------------ | ------------ |
+| Table Cell 1 | Table Cell 2 |
+| Table Cell 3 | Table Cell 4 |
+
+<figure><img alt="1280px-Placeholder_view_vector.svg.png" src="https://upload.wikimedia.org/wikipedia/commons/thumb/3/3f/Placeholder_view_vector.svg/1280px-Placeholder_view_vector.svg.png"><figcaption>Placeholder</figcaption></figure>
+
+***
+
+Paragraph 2

tests/src/unit/core/clipboard/copy/__snapshots__/text/plain/childToParent.md

@@ -0,0 +1,3 @@
+Paragraph 1
+
+Nested Paragraph 1

tests/src/unit/core/clipboard/copy/__snapshots__/text/plain/childrenToNextParent.md

@@ -0,0 +1,7 @@
+Nested Paragraph 1
+
+Nested Paragraph 2
+
+Nested Paragraph 3
+
+Paragraph 2

tests/src/unit/core/clipboard/copy/__snapshots__/text/plain/childrenToNextParentsChildren.md

@@ -0,0 +1,13 @@
+Nested Paragraph 1
+
+Nested Paragraph 2
+
+Nested Paragraph 3
+
+Paragraph 2
+
+Nested Paragraph 4
+
+Nested Paragraph 5
+
+Nested Paragraph 6

tests/src/unit/core/clipboard/copy/__snapshots__/text/plain/codeBlockFullContent.md

@@ -0,0 +1,2 @@
+const a = 1;
+const b = 2;