fix: browser tab title now uses real file name instead of content-derived auto-name

- Auto-naming from content scoped to Untitled.md files only
- Files with a real name always reflect it in the browser tab
- Fenced code block language tags (html-autorun etc) stripped before auto-name extraction
- First meaningful heading/line used for auto-name, not raw content start

Author: ijbo

changelogs/CHANGELOG-tab-title-fix.md

@@ -0,0 +1,32 @@
+# Tab Title Fix — Use File Name as Browser Tab
+
+- Fixed: browser tab showing garbled content-derived name (e.g. "htmlau") instead of actual file name
+- Auto-naming from content now only applies to files still named "Untitled.md" (or "Untitled N.md")
+- Files with a real name (disk files, user-named files) always use their filename as the tab title
+- Fixed: fenced code block language tags (e.g. `html-autorun`) no longer leak into auto-derived names
+- Auto-naming now scans for the first meaningful heading/line after stripping code blocks
+
+---
+
+## Summary
+The workspace auto-naming feature was overriding the browser tab title with a truncated, letter-only snippet of the document content. For documents starting with `\`\`\`html-autorun` blocks, this produced names like "htmlau". The fix scopes auto-naming exclusively to genuinely untitled files and ensures real file names are always respected.
+
+---
+
+## 1. Tab Title Uses Actual File Name
+**Files:** `js/workspace.js`
+**What:** Added an early-exit guard in `autoNameFromContent()` that checks whether the file's current name matches the "Untitled" pattern (`/^untitled(\s*\d*)?\.md$/i`). If the file already has a real name, the function returns immediately without modifying the title.
+**Impact:** The browser tab and header chip now always reflect the real workspace file name for any named file.
+
+## 2. Code Block Language Tags Stripped from Auto-Name
+**Files:** `js/workspace.js`
+**What:** Before extracting the auto-name candidate, fenced code blocks (` ```lang ... ``` `) are stripped from the content string. The first non-empty heading or line is then extracted from the remaining text.
+**Impact:** Prevents block language identifiers like `html-autorun`, `python`, or `bash` from becoming the file/tab name.
+
+---
+
+## Files Changed (1 total)
+
+| File | Lines Changed | Type |
+|------|:---:|------|
+| `js/workspace.js` | +15 −10 | Bug fix — auto-naming scoped to untitled files only |

js/workspace.js

@@ -1043,19 +1043,24 @@
         var file = findFileById(workspace.activeFileId);
         if (!file) return;
 
-        var content = M.markdownEditor.value || '';
-        var stripped = content.replace(/^#+\s*/, '').trim(); // strip leading # headings
+        // Only auto-name files that are still genuinely untitled.
+        // Any file with a real name (set by user or loaded from storage) keeps it.
+        var baseName = file.name.split('/').pop();
+        if (!/^untitled(\s*\d*)?\.md$/i.test(baseName)) return;
 
-        if (!stripped) {
-            // Empty content → revert to Untitled
-            if (file.name !== 'Untitled.md') {
-                file.name = 'Untitled.md';
-                saveWorkspace();
-                renderFileList();
-                updatePageTitle(file.name);
-            }
-            return;
+        var content = M.markdownEditor.value || '';
+        // Strip fenced code blocks so ```html-autorun doesn't leak into the name
+        var strippedContent = content.replace(/^```[^\n]*\n[\s\S]*?```\n?/gm, '').trim();
+        // Find first heading or non-empty line
+        var firstMeaningfulLine = '';
+        var lines = strippedContent.split('\n');
+        for (var li = 0; li < lines.length; li++) {
+            var l = lines[li].trim();
+            if (l) { firstMeaningfulLine = l; break; }
         }
+        var stripped = firstMeaningfulLine.replace(/^#+\s*/, '').trim();
+
+        if (!stripped) return; // No content yet — keep "Untitled.md"
 
         // Take first 10 chars, keep only ASCII letters and spaces
         var autoName = stripped.substring(0, 10).replace(/[^a-zA-Z ]/g, '').trim();