chore(deps): update marked to v18

.changeset/update-marked-v18.md

@@ -0,0 +1,7 @@
+---
+"streamdown": patch
+---
+
+Update `marked` from `^17.0.1` to `^18.0.11`.
+
+marked v18 no longer folds a block token's trailing blank line(s) into its own `raw`; that whitespace now surfaces as a separate `space` token immediately following the block (e.g. after `html`, `heading`, and `table` tokens). This changed the token stream shape that `parseMarkdownIntoBlocks` consumes, causing a dangling `space` token after a closed custom-tag HTML block to be emitted as its own standalone block. `parseMarkdownIntoBlocks` now folds a `space` token into the preceding block instead of pushing it as a new one, restoring v17-identical block boundaries and counts. The lossless `token.raw` concatenation invariant is preserved.

packages/streamdown/__tests__/custom-tag-markdown.test.tsx

@@ -149,4 +149,27 @@ Content for snippet 2
     expect(blocks[0]).toContain("</ai-thinking>");
     expect(blocks[1]).toContain("# Outside");
   });
+
+  it("does not create a standalone block from a trailing blank-line space token (marked v18)", () => {
+    // marked v18 no longer folds a block token's trailing blank line(s) into
+    // its own `raw`; it now emits that whitespace as a separate `space`
+    // token. Block boundaries/count must stay identical to marked v17.
+    const md = `<ai-thinking>
+
+**bold**
+
+</ai-thinking>
+
+# Outside`;
+
+    const blocks = parseMarkdownIntoBlocks(md);
+
+    expect(blocks.length).toBe(2);
+    // Lossless concat invariant: joining blocks must reconstruct the input.
+    expect(blocks.join("")).toBe(md);
+    // No block should be pure whitespace.
+    for (const block of blocks) {
+      expect(block.trim().length).toBeGreaterThan(0);
+    }
+  });
 });

packages/streamdown/lib/parse-blocks.tsx

@@ -156,6 +156,16 @@ export const parseMarkdownIntoBlocks = (markdown: string): string[] => {
       }
     }
 
+    // marked v18 no longer absorbs a block token's trailing blank line(s) into
+    // its own `raw`; instead that whitespace surfaces as a separate `space`
+    // token immediately after (e.g. html/heading/table blocks). A bare space
+    // token is never meaningful content on its own, so fold it into the
+    // previous block to keep block boundaries/counts identical to v17.
+    if (token.type === "space" && mergedBlocksLen > 0) {
+      mergedBlocks[mergedBlocksLen - 1] += currentBlock;
+      continue;
+    }
+
     // Math block merging logic
     // If previous block has unclosed math (odd number of $$), merge current block into it.
     // This handles cases where marked's Lexer splits math blocks (e.g. = on its own line

packages/streamdown/package.json

@@ -40,7 +40,7 @@
     "clsx": "^2.1.1",
     "hast-util-to-jsx-runtime": "^2.3.6",
     "html-url-attributes": "^3.0.1",
-    "marked": "^17.0.1",
+    "marked": "^18.0.11",
     "rehype-harden": "^1.1.8",
     "rehype-raw": "^7.0.0",
     "rehype-sanitize": "^6.0.0",