Make Markdown typing shortcuts work everywhere in the editor

Tiptap's built-in bold/italic input rules only fire after whitespace,
so **bold** typed after punctuation (an em dash, an open paren, a
colon) never converted, and [text](url) had no input rule at all. A
small extension adds punctuation-tolerant bold/italic rules (using
lookbehinds so the preceding character isn't swallowed by the rule's
range deletion) and a link rule that fires on the closing parenthesis.
Link URLs pass the same validator as navigation links, so javascript:
URLs stay as plain text, and mid-word patterns like 2**3** are left
alone.

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

src/components/admin/RichTextEditor.tsx

@@ -7,6 +7,7 @@ import type { Editor } from "@tiptap/react";
 import { EditorContent, useEditor, useEditorState } from "@tiptap/react";
 import StarterKit from "@tiptap/starter-kit";
 import { useEffect, useId, useRef, useState } from "react";
+import { MarkdownInputRules } from "@/components/admin/markdown-input-rules";
 import { ErrorText, Label, cx } from "@/components/ui";
 import { renderMarkdown } from "@/lib/markdown";
 import { uploadImageFile } from "@/lib/upload-client";
@@ -126,6 +127,7 @@ export function RichTextEditor({
       Image.configure({ allowBase64: false }),
       TableKit.configure({ table: { resizable: false } }),
       Placeholder.configure({ placeholder: "Write your story…" }),
+      MarkdownInputRules,
     ],
     content: initialHTML,
     editorProps: {

src/components/admin/markdown-input-rules.ts

@@ -0,0 +1,69 @@
+import { Extension, InputRule, markInputRule } from "@tiptap/core";
+import { isValidLinkUrl } from "@/lib/validation";
+
+/**
+ * Extra Markdown typing shortcuts on top of tiptap's built-ins.
+ *
+ * Tiptap's own bold/italic input rules only fire when the opening
+ * marker sits at the start of a line or after whitespace, so typing
+ * `dash—**bold**` or `(**bold**)` never converts. These variants also
+ * accept punctuation before the marker. The lookbehind (instead of a
+ * consumed prefix) matters: `markInputRule` deletes everything in the
+ * match around the content group, so a consumed prefix character would
+ * be swallowed with the asterisks.
+ *
+ * `[text](url)` has no built-in rule at all; the custom rule below
+ * inserts a link mark when the closing parenthesis is typed. URLs are
+ * checked with the same validator used for navigation links, so
+ * `javascript:` and friends never become clickable (the text is simply
+ * left as typed).
+ *
+ * The word-ish guard `[^\w*_\x60]` (not a word character, backtick, or
+ * marker) keeps rules from firing mid-word: `2**3**` stays math.
+ */
+const BOLD_STAR = /(?<=^|[^\w*_`])(?:\*\*(?![\s*])([^*]+)\*\*)$/;
+const BOLD_UNDERSCORE = /(?<=^|[^\w*_`])(?:__(?![\s_])([^_]+)__)$/;
+const ITALIC_STAR = /(?<=^|[^\w*_`])(?:\*(?![\s*])([^*]+?)\*)$/;
+const ITALIC_UNDERSCORE = /(?<=^|[^\w*_`])(?:_(?![\s_])([^_]+?)_)$/;
+const LINK = /\[([^\]]+)\]\(([^()\s]+)\)$/;
+
+export const MarkdownInputRules = Extension.create({
+  name: "markdownInputRules",
+
+  addInputRules() {
+    const { bold, italic, link } = this.editor.schema.marks;
+    const rules: InputRule[] = [];
+
+    if (bold) {
+      rules.push(
+        markInputRule({ find: BOLD_STAR, type: bold }),
+        markInputRule({ find: BOLD_UNDERSCORE, type: bold }),
+      );
+    }
+    if (italic) {
+      rules.push(
+        markInputRule({ find: ITALIC_STAR, type: italic }),
+        markInputRule({ find: ITALIC_UNDERSCORE, type: italic }),
+      );
+    }
+    if (link) {
+      rules.push(
+        new InputRule({
+          find: LINK,
+          handler: ({ state, range, match }) => {
+            const [, text, href] = match;
+            if (!isValidLinkUrl(href)) return;
+            state.tr.replaceWith(
+              range.from,
+              range.to,
+              state.schema.text(text, [link.create({ href })]),
+            );
+            // Don't keep writing inside the link after it's inserted.
+            state.tr.removeStoredMark(link);
+          },
+        }),
+      );
+    }
+    return rules;
+  },
+});