@@ -1,4 +1,5 @@
 import { getFileExtension } from '@/lib/uploads/utils/file-utils'
+import { normalizeMimeType } from '@/lib/uploads/utils/mime'
 import { SUPPORTED_CODE_EXTENSIONS } from '@/lib/uploads/utils/validation'
 
 const TEXT_EDITABLE_MIME_TYPES = new Set([
@@ -132,6 +133,7 @@ export type FileCategory =
   | 'unsupported'
 
 export function resolveFileCategory(mimeType: string | null, filename: string): FileCategory {
+  mimeType = normalizeMimeType(mimeType)
   if (mimeType && TEXT_EDITABLE_MIME_TYPES.has(mimeType)) return 'text-editable'
   if (mimeType && IFRAME_PREVIEWABLE_MIME_TYPES.has(mimeType)) return 'iframe-previewable'
   if (mimeType && IMAGE_PREVIEWABLE_MIME_TYPES.has(mimeType)) return 'image-previewable'
@@ -140,9 +142,11 @@ export function resolveFileCategory(mimeType: string | null, filename: string):
   if (mimeType && DOCX_PREVIEWABLE_MIME_TYPES.has(mimeType)) return 'docx-previewable'
   if (mimeType && PPTX_PREVIEWABLE_MIME_TYPES.has(mimeType)) return 'pptx-previewable'
   if (mimeType && XLSX_PREVIEWABLE_MIME_TYPES.has(mimeType)) return 'xlsx-previewable'
+  if (mimeType?.startsWith('text/')) return 'text-editable'
 
   const ext = getFileExtension(filename)
-  const nameKey = ext || filename.toLowerCase()
+  const sourceName = filename.replace(/\.(example|template|sample|dist|default)$/i, '')
+  const nameKey = getFileExtension(sourceName) || sourceName.toLowerCase()
   if (TEXT_EDITABLE_EXTENSIONS.has(nameKey)) return 'text-editable'
   if (IFRAME_PREVIEWABLE_EXTENSIONS.has(ext)) return 'iframe-previewable'
   if (IMAGE_PREVIEWABLE_EXTENSIONS.has(ext)) return 'image-previewable'
@@ -151,6 +155,8 @@ export function resolveFileCategory(mimeType: string | null, filename: string):
   if (DOCX_PREVIEWABLE_EXTENSIONS.has(ext)) return 'docx-previewable'
   if (PPTX_PREVIEWABLE_EXTENSIONS.has(ext)) return 'pptx-previewable'
   if (XLSX_PREVIEWABLE_EXTENSIONS.has(ext)) return 'xlsx-previewable'
+  if (/^\.?env(?: \(\d+\))*(?:\.[\w.-]+)?$/i.test(filename)) return 'text-editable'
+  if (/^dockerfile\.[\w.-]+$/i.test(filename)) return 'text-editable'
 
   return 'unsupported'
 }
@@ -4,6 +4,10 @@ import { memo, useCallback, useEffect, useMemo, useRef, useState } from 'react'
 import { Music } from '@sim/emcn/icons'
 import dynamic from 'next/dynamic'
 import type { FileDownloadSource } from '@/lib/uploads/client/download'
+import {
+  MAX_TEXT_PREVIEW_BYTES,
+  TEXT_PREVIEW_SIZE_MESSAGE,
+} from '@/lib/uploads/client/text-content'
 import type { WorkspaceFileRecord } from '@/lib/uploads/contexts/workspace'
 import { resolveMediaMimeType } from '@/lib/uploads/utils/file-utils'
 import {
@@ -51,12 +55,19 @@ const RichMarkdownEditor = dynamic(
  */
 const CSV_INLINE_EDIT_MAX_BYTES = 5 * 1024 * 1024
 
-export function isTextEditable(file: { type: string; name: string }): boolean {
-  return resolveFileCategory(file.type, file.name) === 'text-editable'
+export function isTextEditable(file: {
+  type: string
+  name: string
+  size?: number | null
+}): boolean {
+  return (
+    resolveFileCategory(file.type, file.name) === 'text-editable' &&
+    (file.size ?? 0) <= MAX_TEXT_PREVIEW_BYTES
+  )
 }
 
-export function isPreviewable(file: { type: string; name: string }): boolean {
-  return resolvePreviewType(file.type, file.name) !== null
+export function isPreviewable(file: { type: string; name: string; size?: number | null }): boolean {
+  return resolvePreviewType(file.type, file.name) !== null && isTextEditable(file)
 }
 
 /**
@@ -180,13 +191,17 @@ function FileViewerContent({
   const category = resolveFileCategory(file.type, file.name)
 
   if (category === 'text-editable') {
+    if (isCsvStreamOnly(file)) {
+      return readOnly ? (
+        <UnsupportedPreview name={file.name} />
+      ) : (
+        <CsvTablePreview key={file.id} file={file} workspaceId={workspaceId} />
+      )
+    }
+    if (!isTextEditable(file)) {
+      return <UnsupportedPreview name={file.name} reason={TEXT_PREVIEW_SIZE_MESSAGE} />
+    }
     if (readOnly) {
-      // ReadOnlyTextPreview loads the whole file as text; a large CSV would OOM the
-      // browser. CsvTablePreview's streamed fallback is workspace-only, so on the
-      // read-only public path a large CSV is download-only.
-      if (isCsvStreamOnly(file)) {
-        return <UnsupportedPreview name={file.name} />
-      }
       // Markdown renders through the inline rich editor (non-editable) so the public share
       // surface matches the in-app reading experience; canEdit={false} disables autosave,
       // the bubble menu, and every other editing affordance.
@@ -203,12 +218,6 @@ function FileViewerContent({
       }
       return <ReadOnlyTextPreview file={file} workspaceId={workspaceId} />
     }
-    // A large CSV can't be loaded whole into the editor (the browser OOMs on the full text).
-    // Render a streamed, read-only preview of the first rows + an "Import as a table" path instead.
-    if (isCsvStreamOnly(file)) {
-      return <CsvTablePreview key={file.id} file={file} workspaceId={workspaceId} />
-    }
-
     if (isMarkdownFile(file)) {
       return (
         <RichMarkdownEditor
 
@@ -6,6 +6,7 @@ import { useTheme } from 'next-themes'
 import '@sim/emcn/components/code/code.css'
 import { CSV_PREVIEW_MAX_ROWS } from '@/lib/api/contracts/workspace-file-table'
 import { getFileExtension } from '@/lib/uploads/utils/file-utils'
+import { normalizeMimeType } from '@/lib/uploads/utils/mime'
 import {
   SIM_ARTIFACT_SHELL,
   SIM_ARTIFACT_STYLESHEET,
@@ -50,6 +51,7 @@ const PREVIEWABLE_EXTENSIONS: Record<string, PreviewType> = {
 export const RICH_PREVIEWABLE_EXTENSIONS = new Set(Object.keys(PREVIEWABLE_EXTENSIONS))
 
 export function resolvePreviewType(mimeType: string | null, filename: string): PreviewType {
+  mimeType = normalizeMimeType(mimeType)
   if (mimeType && PREVIEWABLE_MIME_TYPES[mimeType]) return PREVIEWABLE_MIME_TYPES[mimeType]
   const ext = getFileExtension(filename)
   return PREVIEWABLE_EXTENSIONS[ext] ?? null
 
@@ -8,21 +8,29 @@ import { getFileExtension } from '@/lib/uploads/utils/file-utils'
 
 const logger = createLogger('FilePreview')
 
+interface UnsupportedPreviewProps {
+  name: string
+  reason?: string
+}
+
 /**
  * Terminal fallback for a file this app cannot render — either the format has no
  * viewer at all, or a viewer that was expected to work failed (e.g. a HEIC whose
  * server-side derivative could not be produced).
  */
-export const UnsupportedPreview = memo(function UnsupportedPreview({ name }: { name: string }) {
+export const UnsupportedPreview = memo(function UnsupportedPreview({
+  name,
+  reason,
+}: UnsupportedPreviewProps) {
   const ext = getFileExtension(name)
 
   return (
     <div className='flex flex-1 flex-col items-center justify-center gap-[8px]'>
       <p className='text-[14px] text-[var(--text-primary)]'>
-        Preview not available{ext ? ` for .${ext} files` : ' for this file'}
+        Preview not available{reason ? '' : ext ? ` for .${ext} files` : ' for this file'}
       </p>
       <p className='text-[var(--text-muted)] text-small'>
-        Use the download button to view this file
+        {reason ?? 'Use the download button to view this file'}
       </p>
     </div>
   )
 
@@ -3,30 +3,51 @@
  */
 import { Editor } from '@tiptap/core'
 import { afterEach, describe, expect, it } from 'vitest'
-import { createMarkdownContentExtensions } from './extensions'
-import { findHeadingPos } from './heading-anchors'
+import { createMarkdownContentExtensions } from '@/app/workspace/[workspaceId]/files/components/file-viewer/rich-markdown-editor/extensions'
+import { scrollToHeading } from '@/app/workspace/[workspaceId]/files/components/file-viewer/rich-markdown-editor/heading-anchors'
 
 let editor: Editor | null = null
 afterEach(() => {
   editor?.destroy()
   editor = null
 })
 
-/** A ProseMirror doc parsed from markdown, for the position-resolution tests. */
-function docOf(markdown: string) {
+function editorOf(markdown: string) {
   editor = new Editor({ extensions: createMarkdownContentExtensions() })
   editor.commands.setContent(markdown, { contentType: 'markdown' })
-  return editor.state.doc
+  return editor
 }
 
-describe('findHeadingPos', () => {
-  it('disambiguates duplicate slugs GitHub-style (foo, foo-1, foo-2)', () => {
-    const doc = docOf('# Notes\n\na\n\n# Notes\n\nb\n\n# Notes\n\nc')
-    const first = findHeadingPos(doc, 'notes')
-    const second = findHeadingPos(doc, 'notes-1')
-    const third = findHeadingPos(doc, 'notes-2')
-    expect(first).toBeGreaterThanOrEqual(0)
-    expect(second).toBeGreaterThan(first)
-    expect(third).toBeGreaterThan(second)
+describe('Markdown heading navigation', () => {
+  it.each([
+    ['Unicode headings', '# Café 你好', 'café-你好', 0],
+    ['punctuation spacing', '# Network & data', 'network--data', 0],
+    ['existing suffixes', '# Notes\n\n# Notes-1\n\n# Notes', 'notes-2', 2],
+  ] as const)('scrolls to GitHub fragments for %s', (_name, markdown, slug, index) => {
+    const editor = editorOf(markdown)
+    const headings = editor.view.dom.querySelectorAll<HTMLElement>('h1, h2, h3, h4, h5, h6')
+    let scrolledTo: HTMLElement | null = null
+    for (const heading of headings) {
+      heading.scrollIntoView = () => {
+        scrolledTo = heading
+      }
+    }
+    expect(scrollToHeading(editor.view, `#${encodeURIComponent(slug)}`)).toBe(true)
+    expect(scrolledTo).toBe(headings[index])
+  })
+
+  it('scrolls to duplicate headings in document order', () => {
+    const editor = editorOf('# Notes\n\na\n\n# Notes\n\nb\n\n# Notes\n\nc')
+    const headings = editor.view.dom.querySelectorAll<HTMLElement>('h1, h2, h3, h4, h5, h6')
+    let scrolledTo: HTMLElement | null = null
+    for (const heading of headings) {
+      heading.scrollIntoView = () => {
+        scrolledTo = heading
+      }
+    }
+    for (const [index, fragment] of ['#notes', '#notes-1', '#notes-2'].entries()) {
+      expect(scrollToHeading(editor.view, fragment)).toBe(true)
+      expect(scrolledTo).toBe(headings[index])
+    }
   })
 })
@@ -1,36 +1,32 @@
 import type { Node as ProseMirrorNode } from '@tiptap/pm/model'
+import type { EditorView } from '@tiptap/pm/view'
+import GithubSlugger from 'github-slugger'
 
-/**
- * Slugify heading text GitHub-style (lowercase, drop punctuation, collapse whitespace to hyphens) so
- * that `[label](#slug)` fragment links — written against how GitHub renders the same markdown —
- * resolve to the matching heading. Mirrors what `rehype-slug` produced in the old preview.
- */
-export function slugifyHeading(text: string): string {
-  return text
-    .toLowerCase()
-    .trim()
-    .replace(/[^\w\s-]/g, '')
-    .replace(/\s+/g, '-')
-    .replace(/-+/g, '-')
-}
-
-/**
- * The document position of the heading a `#slug` fragment link targets, or -1 if none matches.
- * Computed on demand (at click time) rather than maintained as per-keystroke decorations. Duplicate
- * slugs are disambiguated GitHub-style: `intro`, `intro-1`, `intro-2`, …
- */
-export function findHeadingPos(doc: ProseMirrorNode, slug: string): number {
-  const seen = new Map<string, number>()
+/** Resolves GitHub heading fragments, including Unicode and collisions with existing suffixes. */
+function findHeadingPos(doc: ProseMirrorNode, slug: string): number {
+  const slugger = new GithubSlugger()
   let found = -1
   doc.descendants((node, pos) => {
     if (found >= 0) return false
     if (node.type.name !== 'heading') return true
-    const base = slugifyHeading(node.textContent)
-    if (!base) return true
-    const n = seen.get(base) ?? 0
-    seen.set(base, n + 1)
-    if ((n === 0 ? base : `${base}-${n}`) === slug) found = pos
-    return found < 0
+    if (slugger.slug(node.textContent) === slug) found = pos
+    return false
   })
   return found
 }
+
+/** Scrolls within this editor without navigating the page or changing the document selection. */
+export function scrollToHeading(view: EditorView, fragment: string): boolean {
+  let slug: string
+  try {
+    slug = decodeURIComponent(fragment.slice(1))
+  } catch {
+    return false
+  }
+  const pos = slug ? findHeadingPos(view.state.doc, slug) : 0
+  if (pos < 0) return false
+  const target = slug ? view.nodeDOM(pos) : view.dom
+  if (!(target instanceof HTMLElement)) return false
+  target.scrollIntoView({ behavior: 'smooth', block: 'start' })
+  return true
+}
@@ -5,6 +5,7 @@ import { Check, Duplicate, Pencil, Unlink } from '@sim/emcn/icons'
 import { getMarkRange } from '@tiptap/core'
 import { type Editor, useEditorState } from '@tiptap/react'
 import { createPortal } from 'react-dom'
+import { scrollToHeading } from '@/app/workspace/[workspaceId]/files/components/file-viewer/rich-markdown-editor/heading-anchors'
 import { normalizeLinkHref } from '@/app/workspace/[workspaceId]/files/components/file-viewer/rich-markdown-editor/markdown-fidelity'
 import {
   applyLink,
@@ -38,8 +39,8 @@ function resolveLinkRange(editor: Editor, el: HTMLElement): LinkRange | null {
 
 /**
  * Floating card shown when hovering a link, so the destination is visible even when the link text
- * differs from the URL. The URL opens in a new tab; Copy is always available, while Edit (inline) and
- * Remove require an editable document. Positioned with Floating UI against the hovered anchor; a short
+ * differs from the URL. Heading links scroll within the editor; other URLs open in a new tab.
+ * Copy is always available, while Edit (inline) and Remove require an editable document. Positioned with Floating UI against the hovered anchor; a short
  * close delay plus the card's own hover bridge let the pointer travel from the link into the card.
  */
 export function LinkHoverCard({ editor }: LinkHoverCardProps) {
@@ -208,7 +209,13 @@ export function LinkHoverCard({ editor }: LinkHoverCardProps) {
           {safeHref ? (
             <a
               href={safeHref}
-              target='_blank'
+              target={safeHref.startsWith('#') ? undefined : '_blank'}
+              onClick={(event) => {
+                if (!safeHref.startsWith('#')) return
+                event.preventDefault()
+                if (!editor.isDestroyed) scrollToHeading(editor.view, safeHref)
+                dismiss()
+              }}
               rel='noopener noreferrer'
               title={rawHref}
               className='max-w-[260px] truncate px-2 text-[var(--text-body)] text-small hover:underline'