diff --git a/client/src/hooks/Artifacts/__tests__/useArtifactProps.test.ts b/client/src/hooks/Artifacts/__tests__/useArtifactProps.test.ts index 5ffd52879f..1f71e4c2c0 100644 --- a/client/src/hooks/Artifacts/__tests__/useArtifactProps.test.ts +++ b/client/src/hooks/Artifacts/__tests__/useArtifactProps.test.ts @@ -1,5 +1,6 @@ import { renderHook } from '@testing-library/react'; import useArtifactProps from '../useArtifactProps'; +import { TOOL_ARTIFACT_TYPES, wrapAsFencedCodeBlock } from '~/utils/artifacts'; import type { Artifact } from '~/common'; describe('useArtifactProps', () => { @@ -207,4 +208,206 @@ describe('useArtifactProps', () => { expect(result.current.template).toBe('static'); }); }); + + describe('CODE artifacts', () => { + /* The CODE bucket reuses the static markdown pipeline — `marked` + * renders the wrapped fenced block as `
…`.
+     * These tests pin the wrap-then-render shape end-to-end so a future
+     * highlighter swap-in or CDN bump can't silently break the panel
+     * for code files. */
+    it('routes CODE artifacts to content.md / static template (markdown pipeline)', () => {
+      const artifact = createArtifact({
+        type: TOOL_ARTIFACT_TYPES.CODE,
+        title: 'simple_graph.py',
+        content: 'import matplotlib\nplt.savefig("foo.png")',
+      });
+      const { result } = renderHook(() => useArtifactProps({ artifact }));
+      expect(result.current.fileKey).toBe('content.md');
+      expect(result.current.template).toBe('static');
+    });
+
+    it('wraps the source as a fenced block with the language hint from the filename', () => {
+      const artifact = createArtifact({
+        type: TOOL_ARTIFACT_TYPES.CODE,
+        title: 'simple_graph.py',
+        content: 'x = 1\nprint(x)',
+      });
+      const { result } = renderHook(() => useArtifactProps({ artifact }));
+      const md = result.current.files['content.md'] as string;
+      /* Marked outputs `
` from this fence. */
+      expect(md.startsWith('```python\n')).toBe(true);
+      expect(md.endsWith('\n```')).toBe(true);
+      expect(md).toContain('x = 1');
+      expect(md).toContain('print(x)');
+    });
+
+    it('falls back to the raw extension as language hint for unknown extensions', () => {
+      const artifact = createArtifact({
+        type: TOOL_ARTIFACT_TYPES.CODE,
+        title: 'thing.qwerty',
+        content: 'data',
+      });
+      const { result } = renderHook(() => useArtifactProps({ artifact }));
+      const md = result.current.files['content.md'] as string;
+      expect(md.startsWith('```qwerty\n')).toBe(true);
+    });
+
+    it('uses an empty language hint when the title has no extension', () => {
+      const artifact = createArtifact({
+        type: TOOL_ARTIFACT_TYPES.CODE,
+        title: 'Makefile-style',
+        content: 'all: build',
+      });
+      const { result } = renderHook(() => useArtifactProps({ artifact }));
+      const md = result.current.files['content.md'] as string;
+      /* Empty hint = bare ` ``` ` opener (no language token). */
+      expect(md.startsWith('```\n')).toBe(true);
+    });
+
+    it('renders an index.html via the markdown template (visual parity with .md artifacts)', () => {
+      const artifact = createArtifact({
+        type: TOOL_ARTIFACT_TYPES.CODE,
+        title: 'app.js',
+        content: 'console.log("hi");',
+      });
+      const { result } = renderHook(() => useArtifactProps({ artifact }));
+      const html = result.current.files['index.html'] as string;
+      expect(html).toContain('');
+      expect(html).toContain('marked.parse');
+    });
+
+    /* Codex review P3: when `fileToArtifact` resolved a language via
+     * MIME fallback (extensionless title, useful MIME), the resolved
+     * value is stored on `artifact.language`. The hook reads it
+     * directly so the fence still gets the right `language-` class. */
+    it('uses pre-resolved artifact.language (covers MIME fallback for extensionless titles)', () => {
+      const artifact = createArtifact({
+        type: TOOL_ARTIFACT_TYPES.CODE,
+        title: 'noext',
+        language: 'python',
+        content: 'print(1)',
+      });
+      const { result } = renderHook(() => useArtifactProps({ artifact }));
+      const md = result.current.files['content.md'] as string;
+      expect(md.startsWith('```python\n')).toBe(true);
+    });
+
+    it('falls back to title-derived language when artifact.language is unset', () => {
+      /* Older callers that don't populate `language` still get a
+       * sensible fence via title-based lookup. */
+      const artifact = createArtifact({
+        type: TOOL_ARTIFACT_TYPES.CODE,
+        title: 'app.js',
+        content: 'console.log("hi");',
+      });
+      const { result } = renderHook(() => useArtifactProps({ artifact }));
+      const md = result.current.files['content.md'] as string;
+      expect(md.startsWith('```javascript\n')).toBe(true);
+    });
+  });
+});
+
+describe('wrapAsFencedCodeBlock', () => {
+  it('wraps source with the supplied language hint', () => {
+    expect(wrapAsFencedCodeBlock('print(1)', 'python')).toBe('```python\nprint(1)\n```');
+  });
+
+  it('emits a bare ``` opener when language is empty', () => {
+    expect(wrapAsFencedCodeBlock('hello', '')).toBe('```\nhello\n```');
+  });
+
+  it('trims a single trailing newline so the closing fence stays flush', () => {
+    /* Extractor output often ends with a newline; without trimming, the
+     * closing ``` would appear on its own line after a blank gap and
+     * marked would render an extra 
. */
+    expect(wrapAsFencedCodeBlock('a\nb\n', 'go')).toBe('```go\na\nb\n```');
+    /* Only ONE trailing newline gets trimmed — preserves explicit blank
+     * lines at end-of-file in the output. */
+    expect(wrapAsFencedCodeBlock('a\nb\n\n', 'go')).toBe('```go\na\nb\n\n```');
+  });
+
+  it('handles empty source cleanly (renders an empty fenced block)', () => {
+    expect(wrapAsFencedCodeBlock('', 'python')).toBe('```python\n\n```');
+  });
+
+  /* Codex review P2: a hardcoded triple-backtick fence breaks when the
+   * source itself contains a line starting with ``` (e.g. a JS template
+   * literal embedding markdown). CommonMark closes the outer fence on
+   * a line whose backtick run matches-or-exceeds the opener, so we have
+   * to emit STRICTLY MORE backticks than any leading-backtick run in
+   * the payload. */
+  it('uses a 4-backtick fence when source has a triple-backtick line at column 0', () => {
+    const src = 'const md = `\n```\nhello\n```\n`;';
+    const wrapped = wrapAsFencedCodeBlock(src, 'js');
+    expect(wrapped.startsWith('````js\n')).toBe(true);
+    expect(wrapped.endsWith('\n````')).toBe(true);
+    /* The payload's ``` lines are preserved verbatim — no escaping. */
+    expect(wrapped).toContain('\n```\nhello\n```\n');
+  });
+
+  it('uses a 5-backtick fence when source has a quadruple-backtick line', () => {
+    const src = 'before\n````\ninside\n````\nafter';
+    const wrapped = wrapAsFencedCodeBlock(src, 'md');
+    expect(wrapped.startsWith('`````md\n')).toBe(true);
+    expect(wrapped.endsWith('\n`````')).toBe(true);
+  });
+
+  it('keeps the 3-backtick fence when source has no leading-backtick lines', () => {
+    /* Ordinary code (no markdown-style fences) gets the conventional
+     * triple-backtick fence — readable and matches `marked`'s default
+     * expectations. */
+    const wrapped = wrapAsFencedCodeBlock('x = 1\nprint(x)', 'python');
+    expect(wrapped.startsWith('```python\n')).toBe(true);
+    expect(wrapped.endsWith('\n```')).toBe(true);
+  });
+
+  it('does not escalate the fence for backticks that are NOT at start-of-line', () => {
+    /* Inline backticks within a line don't count against the closing-
+     * fence rule, so they don't need escalation. Keeps the fence
+     * minimal for the common case (e.g. a Python file that uses
+     * markdown ` `code` ` in a docstring). */
+    const src = 'x = `inline backticks ``` here`';
+    const wrapped = wrapAsFencedCodeBlock(src, 'python');
+    expect(wrapped.startsWith('```python\n')).toBe(true);
+    expect(wrapped.endsWith('\n```')).toBe(true);
+  });
+
+  it('escalates correctly when the source itself starts with a backtick run', () => {
+    /* Edge: backticks at column 0 of the very first line. The leading-
+     * run scan must catch this position (regex anchor allows
+     * start-of-string match too). */
+    const src = '```already-fenced\nbody\n```';
+    const wrapped = wrapAsFencedCodeBlock(src, 'md');
+    expect(wrapped.startsWith('````md\n')).toBe(true);
+  });
+
+  /* Codex review P2 follow-up: CommonMark allows fence closers indented
+   * up to 3 spaces. The fence-length scan must catch backtick runs at
+   * columns 0–3, not just column 0 — otherwise an indented `\`\`\``
+   * inside a JS/Python source still terminates our outer fence. */
+  it.each([
+    [' ```', 4],
+    ['  ```', 4],
+    ['   ```', 4],
+    [' ````', 5],
+    ['   `````', 6],
+  ])('escalates fence to %s+1 backticks for indented closer "%s"', (line, expectedFenceLen) => {
+    const src = 'before\n' + line + '\nafter';
+    const wrapped = wrapAsFencedCodeBlock(src, 'js');
+    /* Fence prefix is `expectedFenceLen` backticks (one more than the
+     * indented run inside the source). */
+    expect(wrapped.startsWith('`'.repeat(expectedFenceLen) + 'js\n')).toBe(true);
+    expect(wrapped.endsWith('\n' + '`'.repeat(expectedFenceLen))).toBe(true);
+  });
+
+  it('does NOT escalate for backticks indented 4+ spaces (CommonMark indented-code-block territory)', () => {
+    /* 4-space indentation makes the line an indented code block, not a
+     * fence closer. The CommonMark spec caps fence-closer indentation
+     * at 3 spaces, so backticks at column 4+ can't terminate an
+     * unindented opener. */
+    const src = 'before\n    ```\nafter';
+    const wrapped = wrapAsFencedCodeBlock(src, 'js');
+    /* No escalation — keeps the default 3-backtick fence. */
+    expect(wrapped.startsWith('```js\n')).toBe(true);
+  });
 });
diff --git a/client/src/hooks/Artifacts/useArtifactProps.ts b/client/src/hooks/Artifacts/useArtifactProps.ts
index ce5e30cf5a..3a7b17c24a 100644
--- a/client/src/hooks/Artifacts/useArtifactProps.ts
+++ b/client/src/hooks/Artifacts/useArtifactProps.ts
@@ -2,7 +2,15 @@ import { useContext, useMemo } from 'react';
 import { ThemeContext, isDark } from '@librechat/client';
 import { removeNullishValues } from 'librechat-data-provider';
 import type { Artifact } from '~/common';
-import { getKey, getProps, getTemplate, getArtifactFilename } from '~/utils/artifacts';
+import {
+  getKey,
+  getProps,
+  getTemplate,
+  getArtifactFilename,
+  languageForFilename,
+  wrapAsFencedCodeBlock,
+  TOOL_ARTIFACT_TYPES,
+} from '~/utils/artifacts';
 import { getMarkdownFiles } from '~/utils/markdown';
 import { getMermaidFiles } from '~/utils/mermaid';
 
@@ -18,6 +26,21 @@ export default function useArtifactProps({ artifact }: { artifact: Artifact }) {
       return ['diagram.mmd', getMermaidFiles(artifact.content ?? '', isDarkMode)];
     }
 
+    /* CODE bucket: source files render through the same static-markdown
+     * pipeline as .md artifacts, but the raw source is wrapped in a
+     * fenced code block first so `marked` outputs
+     * `
…
` instead of
+     * paragraph text. The language hint is computed once at artifact
+     * construction (`fileToArtifact` writes it to `artifact.language`)
+     * so the MIME fallback fires for extensionless-filename + useful-
+     * MIME inputs. Title-derived fallback covers older callers that
+     * didn't set `language`. */
+    if (type === TOOL_ARTIFACT_TYPES.CODE) {
+      const lang = artifact.language ?? languageForFilename(artifact.title);
+      const wrapped = wrapAsFencedCodeBlock(artifact.content ?? '', lang);
+      return ['content.md', getMarkdownFiles(wrapped)];
+    }
+
     if (type === 'text/markdown' || type === 'text/md' || type === 'text/plain') {
       return ['content.md', getMarkdownFiles(artifact.content ?? '')];
     }
@@ -27,7 +50,7 @@ export default function useArtifactProps({ artifact }: { artifact: Artifact }) {
       [fileKey]: artifact.content,
     });
     return [fileKey, files];
-  }, [artifact.type, artifact.content, artifact.language, isDarkMode]);
+  }, [artifact.type, artifact.content, artifact.language, artifact.title, isDarkMode]);
 
   const template = useMemo(
     () => getTemplate(artifact.type ?? '', artifact.language),
diff --git a/client/src/utils/__tests__/artifacts.test.ts b/client/src/utils/__tests__/artifacts.test.ts
index 2d1216995c..02e7494c15 100644
--- a/client/src/utils/__tests__/artifacts.test.ts
+++ b/client/src/utils/__tests__/artifacts.test.ts
@@ -2,6 +2,7 @@ import {
   buildSandpackOptions,
   detectArtifactTypeFromFile,
   fileToArtifact,
+  languageForFilename,
   TOOL_ARTIFACT_TYPES,
 } from '../artifacts';
 
@@ -132,6 +133,246 @@ describe('detectArtifactTypeFromFile', () => {
       detectArtifactTypeFromFile({ filename: '.env', type: 'text/plain', text: 'KEY=value' }),
     ).toBeNull();
   });
+
+  describe('CODE bucket (programming-language source files)', () => {
+    /* `.py` and other code files were previously inline-only — PR #12832
+     * intentionally left them out of the side-panel pipeline. This bucket
+     * routes them through the markdown template with the source pre-
+     * wrapped as a fenced code block (`useArtifactProps`). */
+    it.each([
+      ['simple_graph.py', 'text/x-python'],
+      ['app.js', 'text/javascript'],
+      ['main.go', 'text/x-go'],
+      ['lib.rs', 'text/x-rust'],
+      ['style.css', 'text/css'],
+      ['build.sh', 'application/x-sh'],
+      ['query.sql', 'application/sql'],
+      ['Module.kt', 'text/x-kotlin'],
+    ])('routes %s (mime: %s) to the CODE bucket', (filename, type) => {
+      expect(detectArtifactTypeFromFile({ filename, type, text: 'x = 1' })).toBe(
+        TOOL_ARTIFACT_TYPES.CODE,
+      );
+    });
+
+    it('routes by extension even when MIME is generic octet-stream', () => {
+      /* file-type / inferMimeType sometimes can't classify code files
+       * (Python has no magic bytes); the extension map still wins. */
+      expect(
+        detectArtifactTypeFromFile({
+          filename: 'data.py',
+          type: 'application/octet-stream',
+          text: 'print(1)',
+        }),
+      ).toBe(TOOL_ARTIFACT_TYPES.CODE);
+    });
+
+    it('keeps jsx/tsx on the React (sandpack) bucket, not CODE', () => {
+      /* `.jsx` and `.tsx` are React component sources — the existing
+       * sandpack live-preview should win over the static CODE bucket. */
+      expect(detectArtifactTypeFromFile({ filename: 'App.jsx', type: '', text: 'x' })).toBe(
+        TOOL_ARTIFACT_TYPES.REACT,
+      );
+      expect(detectArtifactTypeFromFile({ filename: 'App.tsx', type: '', text: 'x' })).toBe(
+        TOOL_ARTIFACT_TYPES.REACT,
+      );
+    });
+
+    it('does NOT route data formats to CODE (CSV / JSON / YAML / TOML / XML)', () => {
+      /* These get dedicated viewers in follow-ups; for now they fall
+       * through to inline rendering (return null). */
+      expect(
+        detectArtifactTypeFromFile({ filename: 'data.csv', type: 'text/csv', text: 'a,b' }),
+      ).toBeNull();
+      expect(
+        detectArtifactTypeFromFile({ filename: 'data.json', type: 'application/json', text: '{}' }),
+      ).toBeNull();
+      expect(
+        detectArtifactTypeFromFile({
+          filename: 'config.yaml',
+          type: 'application/yaml',
+          text: 'a: 1',
+        }),
+      ).toBeNull();
+      expect(
+        detectArtifactTypeFromFile({
+          filename: 'pyproject.toml',
+          type: 'application/toml',
+          text: '',
+        }),
+      ).toBeNull();
+    });
+
+    it('does NOT route config dotfiles to CODE (.env / .ini)', () => {
+      expect(
+        detectArtifactTypeFromFile({ filename: 'app.env', type: 'text/plain', text: 'KEY=val' }),
+      ).toBeNull();
+      expect(
+        detectArtifactTypeFromFile({
+          filename: 'config.ini',
+          type: 'text/plain',
+          text: '[section]',
+        }),
+      ).toBeNull();
+    });
+
+    it('allows empty text for CODE files (an empty Python file is still a Python file)', () => {
+      expect(
+        detectArtifactTypeFromFile({ filename: 'empty.py', type: 'text/x-python', text: '' }),
+      ).toBe(TOOL_ARTIFACT_TYPES.CODE);
+    });
+
+    /* Codex review P2: extensionless build files like `Dockerfile` and
+     * `Makefile` have no `.` in their basename, so `extensionOf` returns
+     * `''` and the extension map can't match. Bare-name fallback
+     * recognizes the lowercased basename for these cases. */
+    it.each([
+      'Dockerfile',
+      'dockerfile',
+      'Makefile',
+      'makefile',
+      'Gemfile',
+      'Rakefile',
+      'Vagrantfile',
+      'Brewfile',
+    ])('routes extensionless build file %s to CODE via bare-name fallback', (filename) => {
+      expect(detectArtifactTypeFromFile({ filename, type: '', text: 'FROM alpine' })).toBe(
+        TOOL_ARTIFACT_TYPES.CODE,
+      );
+    });
+
+    it('still recognizes nested-path Dockerfile (path-preserving sanitizer output)', () => {
+      /* The path-preserving artifact sanitizer can ship `proj/Dockerfile`.
+       * Bare-name lookup must use the basename, not the full string. */
+      expect(
+        detectArtifactTypeFromFile({ filename: 'proj/Dockerfile', type: '', text: 'FROM alpine' }),
+      ).toBe(TOOL_ARTIFACT_TYPES.CODE);
+    });
+
+    it('does not bare-name match files that DO have an extension (no double-match)', () => {
+      /* `dockerfile.dev` has extension `dev` (not in the routing map),
+       * so it returns null. Bare-name lookup must skip files with a
+       * `.` so the extension path stays the source of truth for them. */
+      expect(
+        detectArtifactTypeFromFile({ filename: 'dockerfile.dev', type: '', text: 'x' }),
+      ).toBeNull();
+    });
+
+    it('does not bare-name match unknown extensionless filenames', () => {
+      expect(detectArtifactTypeFromFile({ filename: 'README', type: '', text: 'hi' })).toBeNull();
+      expect(detectArtifactTypeFromFile({ filename: 'LICENSE', type: '', text: 'MIT' })).toBeNull();
+    });
+
+    /* Codex review P3 companion: `extensionOf` used to consider the
+     * whole path string, so `pkg.v1/Dockerfile` yielded a path-laden
+     * "extension" that masked the bare-name fallback. The basename-
+     * first fix makes routing for these files work correctly. */
+    it('routes nested-path Dockerfile under dotted directory to CODE', () => {
+      expect(
+        detectArtifactTypeFromFile({ filename: 'pkg.v1/Dockerfile', type: '', text: 'FROM x' }),
+      ).toBe(TOOL_ARTIFACT_TYPES.CODE);
+    });
+
+    it('still routes file extensions correctly under dotted directory', () => {
+      expect(
+        detectArtifactTypeFromFile({ filename: 'pkg.v1/main.go', type: '', text: 'package main' }),
+      ).toBe(TOOL_ARTIFACT_TYPES.CODE);
+      expect(
+        detectArtifactTypeFromFile({
+          filename: 'a.b.c/script.py',
+          type: 'text/x-python',
+          text: 'x = 1',
+        }),
+      ).toBe(TOOL_ARTIFACT_TYPES.CODE);
+    });
+  });
+});
+
+describe('languageForFilename', () => {
+  it('returns the canonical language identifier for known extensions', () => {
+    expect(languageForFilename('foo.py')).toBe('python');
+    expect(languageForFilename('foo.ts')).toBe('typescript');
+    expect(languageForFilename('foo.go')).toBe('go');
+    expect(languageForFilename('foo.rs')).toBe('rust');
+    expect(languageForFilename('foo.kt')).toBe('kotlin');
+  });
+
+  it('falls back to the raw extension for unknown ones (renders monospace)', () => {
+    expect(languageForFilename('foo.qwerty')).toBe('qwerty');
+  });
+
+  it('returns the canonical language for extensionless build files (bare-name fallback)', () => {
+    /* Codex review P2 companion: language hint must follow the same
+     * bare-name fallback as the routing decision so the fenced block
+     * gets `language-dockerfile` / `language-makefile` etc. */
+    expect(languageForFilename('Dockerfile')).toBe('dockerfile');
+    expect(languageForFilename('Makefile')).toBe('makefile');
+    expect(languageForFilename('Gemfile')).toBe('ruby');
+    expect(languageForFilename('Rakefile')).toBe('ruby');
+  });
+
+  it('handles nested-path filenames (uses basename)', () => {
+    expect(languageForFilename('proj/Dockerfile')).toBe('dockerfile');
+    expect(languageForFilename('a/b/c.py')).toBe('python');
+  });
+
+  it('returns empty string for filenames with no extension and no recognized bare name', () => {
+    expect(languageForFilename('README')).toBe('');
+    expect(languageForFilename('')).toBe('');
+    expect(languageForFilename(undefined)).toBe('');
+  });
+
+  /* Codex review P3: `extensionOf` previously took `lastIndexOf('.')`
+   * across the FULL path, so `pkg.v1/Dockerfile` yielded the
+   * nonsensical "extension" `v1/dockerfile`. Since that's non-empty,
+   * `languageForFilename` returned it as the language hint instead of
+   * falling back to `bareNameOf`. The basename-first fix makes both
+   * helpers operate on the basename only. */
+  it('correctly falls back to bare-name when path has dotted directory components', () => {
+    expect(languageForFilename('pkg.v1/Dockerfile')).toBe('dockerfile');
+    expect(languageForFilename('a.b.c/Makefile')).toBe('makefile');
+    expect(languageForFilename('proj.beta/Gemfile')).toBe('ruby');
+  });
+
+  it('correctly identifies extension when path has dotted directory components', () => {
+    /* Dotted dir + dotted file: extension parsing should still find
+     * the file's extension, not concatenate dir+file fragments. */
+    expect(languageForFilename('pkg.v1/main.go')).toBe('go');
+    expect(languageForFilename('a.b.c/script.py')).toBe('python');
+  });
+
+  /* Codex review P3: when a file routes to CODE via MIME-only (e.g.
+   * `noext` filename + `text/x-python` MIME), we still want a language
+   * hint on the fenced block so the future highlighter swap-in can
+   * apply syntax colors. Without the MIME fallback, `language-` is
+   * empty and the highlighter can't engage. */
+  it('falls back to MIME when filename has no extension and no recognized bare name', () => {
+    expect(languageForFilename('noext', 'text/x-python')).toBe('python');
+    expect(languageForFilename('noext', 'text/x-go')).toBe('go');
+    expect(languageForFilename('noext', 'application/x-sh')).toBe('bash');
+    expect(languageForFilename(undefined, 'text/x-rust')).toBe('rust');
+  });
+
+  it('strips MIME parameters before lookup (charset, etc.)', () => {
+    expect(languageForFilename('noext', 'text/x-python; charset=utf-8')).toBe('python');
+    expect(languageForFilename('noext', 'TEXT/X-PYTHON;charset=utf-8')).toBe('python');
+  });
+
+  it('prefers extension over MIME when both are present (extension is more reliable)', () => {
+    /* `simple_graph.py` + a wrong/generic MIME → extension wins. */
+    expect(languageForFilename('simple_graph.py', 'application/octet-stream')).toBe('python');
+    expect(languageForFilename('main.go', 'text/x-python')).toBe('go');
+  });
+
+  it('prefers bare-name over MIME for build files', () => {
+    /* `Dockerfile` + a generic MIME → bare-name wins. */
+    expect(languageForFilename('Dockerfile', 'text/plain')).toBe('dockerfile');
+  });
+
+  it('returns empty string when no signal yields a hint (extensionless + unknown MIME)', () => {
+    expect(languageForFilename('noext', 'application/octet-stream')).toBe('');
+    expect(languageForFilename('noext', undefined)).toBe('');
+    expect(languageForFilename('noext')).toBe('');
+  });
 });
 
 describe('fileToArtifact', () => {
@@ -159,6 +400,101 @@ describe('fileToArtifact', () => {
     expect(fileToArtifact({ ...baseFile, filename: 'data.csv', type: 'text/csv' })).toBeNull();
   });
 
+  /* End-to-end test for the CODE bucket. The classification path is
+   * covered separately in `detectArtifactTypeFromFile`'s describe block;
+   * this asserts that the full `Artifact` object (id / type / title /
+   * content / messageId / lastUpdateTime) is constructed correctly for
+   * a typical Python file. Locks in the empty-text gate exception for
+   * CODE and the title pass-through that `useArtifactProps` reads to
+   * derive the language hint. */
+  it('builds a CODE-typed Artifact for a .py file with text', () => {
+    const artifact = fileToArtifact({
+      ...baseFile,
+      filename: 'simple_graph.py',
+      type: 'text/x-python',
+      text: 'import matplotlib.pyplot as plt\nplt.savefig("foo.png")',
+    });
+    expect(artifact).not.toBeNull();
+    expect(artifact!.type).toBe(TOOL_ARTIFACT_TYPES.CODE);
+    expect(artifact!.title).toBe('simple_graph.py');
+    expect(artifact!.content).toBe('import matplotlib.pyplot as plt\nplt.savefig("foo.png")');
+    expect(artifact!.id).toBe('tool-artifact-fid-1');
+    expect(artifact!.messageId).toBe('msg-1');
+  });
+
+  it('builds a CODE-typed Artifact for an empty .py file (empty-text exception applies)', () => {
+    /* CODE joins MARKDOWN/PLAIN_TEXT in the empty-text exception so an
+     * empty Python file still surfaces in the side panel rather than
+     * silently disappearing. */
+    const artifact = fileToArtifact({
+      ...baseFile,
+      filename: 'empty.py',
+      type: 'text/x-python',
+      text: '',
+    });
+    expect(artifact).not.toBeNull();
+    expect(artifact!.type).toBe(TOOL_ARTIFACT_TYPES.CODE);
+    expect(artifact!.content).toBe('');
+  });
+
+  it('builds a CODE-typed Artifact for an extensionless build file (Dockerfile)', () => {
+    const artifact = fileToArtifact({
+      ...baseFile,
+      filename: 'Dockerfile',
+      type: '',
+      text: 'FROM alpine\nRUN apk add curl',
+    });
+    expect(artifact).not.toBeNull();
+    expect(artifact!.type).toBe(TOOL_ARTIFACT_TYPES.CODE);
+    expect(artifact!.title).toBe('Dockerfile');
+    /* Bare-name resolved → `dockerfile` language hint stored on the
+     * artifact so `useArtifactProps` doesn't have to re-derive it. */
+    expect(artifact!.language).toBe('dockerfile');
+  });
+
+  /* Codex review P3: language is resolved AT CONSTRUCTION TIME so the
+   * MIME fallback fires for extensionless filenames. Without storing
+   * the language on the artifact, `useArtifactProps` would re-derive
+   * from `artifact.title` alone (which has no MIME context) and emit
+   * an empty `language-` class. */
+  it('stores the language hint on CODE artifacts (filename-derived)', () => {
+    const artifact = fileToArtifact({
+      ...baseFile,
+      filename: 'app.py',
+      type: 'text/x-python',
+      text: 'print(1)',
+    });
+    expect(artifact!.language).toBe('python');
+  });
+
+  it('stores the MIME-derived language on CODE artifacts when filename has no extension', () => {
+    const artifact = fileToArtifact({
+      ...baseFile,
+      filename: 'noext',
+      type: 'text/x-python',
+      text: 'print(1)',
+    });
+    expect(artifact).not.toBeNull();
+    expect(artifact!.type).toBe(TOOL_ARTIFACT_TYPES.CODE);
+    expect(artifact!.language).toBe('python');
+  });
+
+  it('does not set language on non-CODE artifacts', () => {
+    /* Markdown / HTML / etc. don't need a language hint — `useArtifactProps`
+     * uses different rendering paths for those. Keeping `language`
+     * undefined for them avoids confusing `getKey` which does include
+     * `language` in its cache key. */
+    const html = fileToArtifact(baseFile);
+    expect(html!.language).toBeUndefined();
+    const md = fileToArtifact({
+      ...baseFile,
+      filename: 'README.md',
+      type: 'text/markdown',
+      text: '# hi',
+    });
+    expect(md!.language).toBeUndefined();
+  });
+
   it('returns null when an HTML/React/Mermaid file has no text', () => {
     expect(fileToArtifact({ ...baseFile, text: '' })).toBeNull();
     expect(fileToArtifact({ ...baseFile, filename: 'App.tsx', type: '', text: '' })).toBeNull();
diff --git a/client/src/utils/artifacts.ts b/client/src/utils/artifacts.ts
index 88fe1f688a..3a17c843b2 100644
--- a/client/src/utils/artifacts.ts
+++ b/client/src/utils/artifacts.ts
@@ -24,6 +24,7 @@ const artifactFilename = {
 const artifactTemplate: Record<
   | keyof typeof artifactFilename
   | 'application/vnd.mermaid'
+  | 'application/vnd.code'
   | 'text/markdown'
   | 'text/md'
   | 'text/plain',
@@ -34,6 +35,12 @@ const artifactTemplate: Record<
   'application/vnd.ant.react': 'react-ts',
   'application/vnd.mermaid': 'react-ts',
   'application/vnd.code-html': 'static',
+  /* CODE bucket reuses the static markdown pipeline — `useArtifactProps`
+   * pre-wraps the content in a fenced block and hands it to
+   * `getMarkdownFiles`, so the rendered HTML uses the same `marked`
+   * pipeline as `.md` artifacts. Keeping `static` (vs. `react-ts`) means
+   * the panel doesn't pay the sandpack-React boot cost for source files. */
+  'application/vnd.code': 'static',
   'text/markdown': 'static',
   'text/md': 'static',
   'text/plain': 'static',
@@ -112,6 +119,7 @@ const mermaidDependencies = {
 const dependenciesMap: Record<
   | keyof typeof artifactFilename
   | 'application/vnd.mermaid'
+  | 'application/vnd.code'
   | 'text/markdown'
   | 'text/md'
   | 'text/plain',
@@ -122,6 +130,10 @@ const dependenciesMap: Record<
   'application/vnd.ant.react': standardDependencies,
   'text/html': standardDependencies,
   'application/vnd.code-html': standardDependencies,
+  /* CODE renders in the static markdown template; no React or other
+   * runtime deps. Empty map skips the sandpack `package.json` install
+   * step entirely (same as MARKDOWN/PLAIN_TEXT). */
+  'application/vnd.code': {},
   'text/markdown': {},
   'text/md': {},
   'text/plain': {},
@@ -163,12 +175,88 @@ export function buildSandpackOptions(
   };
 }
 
+/**
+ * Strip path separators so extension/bare-name lookups operate on the
+ * basename only. Artifact filenames can carry nested directories
+ * through the path-preserving sanitizer in the backend, and a dotted
+ * directory name (e.g. `pkg.v1/Dockerfile`) would otherwise produce a
+ * nonsensical "extension" like `v1/dockerfile`.
+ */
+const basenameOf = (filename: string): string => {
+  const slash = Math.max(filename.lastIndexOf('/'), filename.lastIndexOf('\\'));
+  return slash >= 0 ? filename.slice(slash + 1) : filename;
+};
+
+/**
+ * Internal: derive the lowercased extension from a pre-computed basename.
+ * Returns `''` for hidden-files (`.env` → `env` in legacy code, but we
+ * deliberately preserve that for backwards compatibility with the
+ * extension-list lookup; the bare-name fallback handles the
+ * extensionless case separately). The shared variant lets
+ * `detectArtifactTypeFromFile` compute the basename once and reuse it
+ * across the extension AND bare-name lookups.
+ */
+const extensionFromBasename = (base: string): string => {
+  const dot = base.lastIndexOf('.');
+  if (dot < 0 || dot === base.length - 1) {
+    return '';
+  }
+  return base.slice(dot + 1).toLowerCase();
+};
+
+/**
+ * Internal: derive the lowercased bare name for extensionless filenames
+ * from a pre-computed basename. Returns `''` for files that DO have an
+ * extension so `extensionOf` and `bareNameOf` are mutually exclusive.
+ */
+const bareNameFromBasename = (base: string): string => {
+  if (base.includes('.')) {
+    return '';
+  }
+  return base.toLowerCase();
+};
+
+/**
+ * Restrict the dot search to the basename — `pkg.v1/Dockerfile` should
+ * yield `''` (extensionless), not `v1/dockerfile`. Otherwise
+ * `languageForFilename` returns the path-laden string as the language
+ * hint and `marked` emits a `language-v1/dockerfile` class (broken).
+ * The bare-name fallback then can't fire because this returned
+ * non-empty.
+ */
+const extensionOf = (filename: string | undefined): string => {
+  if (!filename) return '';
+  return extensionFromBasename(basenameOf(filename));
+};
+
+/**
+ * Lowercased basename for extensionless filenames. Lets the routing map
+ * recognize `Dockerfile`, `Makefile`, `Gemfile`, etc. as code without
+ * a dotted extension. Returns `''` for files that DO have an extension
+ * (those go through `extensionOf`) so the two helpers don't double-match.
+ */
+const bareNameOf = (filename: string | undefined): string => {
+  if (!filename) return '';
+  return bareNameFromBasename(basenameOf(filename));
+};
+
+/** Strip charset / boundary parameters so we can do exact MIME comparisons. */
+const baseMime = (mime: string | undefined): string => {
+  if (!mime) {
+    return '';
+  }
+  const semi = mime.indexOf(';');
+  return (semi < 0 ? mime : mime.slice(0, semi)).trim().toLowerCase();
+};
+
 /**
  * Artifact MIME types we currently know how to render in the side panel
  * (or, for mermaid, inline). Plain text covers files we can show as raw
  * content even without a dedicated viewer (txt, docx-extracted text, …);
  * `useArtifactProps` routes `text/plain` through the markdown template
- * so the panel renders them cleanly.
+ * so the panel renders them cleanly. `CODE` is the same idea for source
+ * files — `useArtifactProps` wraps the content in a fenced code block
+ * with a language hint before handing it to the markdown viewer.
  */
 export const TOOL_ARTIFACT_TYPES = {
   HTML: 'text/html',
@@ -176,13 +264,236 @@ export const TOOL_ARTIFACT_TYPES = {
   MARKDOWN: 'text/markdown',
   MERMAID: 'application/vnd.mermaid',
   PLAIN_TEXT: 'text/plain',
+  CODE: 'application/vnd.code',
 } as const;
 
 export type ToolArtifactType = (typeof TOOL_ARTIFACT_TYPES)[keyof typeof TOOL_ARTIFACT_TYPES];
 
+/**
+ * Extension → fenced-code-block language hint for the CODE bucket. The
+ * key is the lowercased file extension (no dot); the value is the
+ * identifier `marked` reads off the fence (e.g. ```` ```python ```` ).
+ * The map drives BOTH the `EXTENSION_TO_TOOL_ARTIFACT_TYPE` routing
+ * (presence in this map = code file) and the fenced-block emit in
+ * `useArtifactProps`, so adding a new language is one place.
+ *
+ * Identifiers follow the GitHub / `highlight.js` convention so a future
+ * highlighter swap-in (currently the markdown template uses plain
+ * `marked`) picks up syntax colors automatically.
+ *
+ * Scope: programming languages + stylesheets + shell/SQL/build files.
+ * Pure data formats (CSV/TSV/JSON/YAML/TOML/XML) and config files
+ * (`.env`/`.ini`/`.conf`) are intentionally NOT routed to CODE in this
+ * pass — they're better served by dedicated viewers (CSV table view,
+ * etc.) or remain inline. Adding them later is a one-entry change.
+ */
+const CODE_EXTENSION_TO_LANGUAGE: Record = {
+  // Web / scripting
+  js: 'javascript',
+  mjs: 'javascript',
+  cjs: 'javascript',
+  ts: 'typescript',
+  py: 'python',
+  pyi: 'python',
+  rb: 'ruby',
+  php: 'php',
+  pl: 'perl',
+  pm: 'perl',
+  lua: 'lua',
+  // Compiled / systems
+  go: 'go',
+  rs: 'rust',
+  c: 'c',
+  h: 'c',
+  cc: 'cpp',
+  cpp: 'cpp',
+  hpp: 'cpp',
+  cs: 'csharp',
+  m: 'objectivec',
+  mm: 'objectivec',
+  swift: 'swift',
+  java: 'java',
+  kt: 'kotlin',
+  kts: 'kotlin',
+  scala: 'scala',
+  // Functional / data
+  r: 'r',
+  jl: 'julia',
+  dart: 'dart',
+  ex: 'elixir',
+  exs: 'elixir',
+  erl: 'erlang',
+  hs: 'haskell',
+  clj: 'clojure',
+  cljs: 'clojure',
+  fs: 'fsharp',
+  fsx: 'fsharp',
+  // Shell
+  sh: 'bash',
+  bash: 'bash',
+  zsh: 'bash',
+  fish: 'bash',
+  ps1: 'powershell',
+  bat: 'batch',
+  cmd: 'batch',
+  // Build / query languages. The bare-name `Dockerfile` / `Makefile` /
+  // etc. cases are documented on `bareNameOf`.
+  sql: 'sql',
+  graphql: 'graphql',
+  gql: 'graphql',
+  proto: 'protobuf',
+  dockerfile: 'dockerfile',
+  makefile: 'makefile',
+  gemfile: 'ruby',
+  rakefile: 'ruby',
+  vagrantfile: 'ruby',
+  brewfile: 'ruby',
+  gradle: 'groovy',
+  tf: 'hcl',
+  hcl: 'hcl',
+  patch: 'diff',
+  diff: 'diff',
+  // Stylesheets
+  css: 'css',
+  scss: 'scss',
+  sass: 'sass',
+  less: 'less',
+};
+
+/**
+ * MIME → fenced-block language hint. Used as a fallback for files whose
+ * filename has no extension AND no recognized bare name — without this,
+ * an attachment like `{ filename: 'noext', type: 'text/x-python' }`
+ * would route to CODE (via the MIME bucket map above) but render with
+ * an empty `language-` class, losing the syntax-hint metadata the
+ * future highlighter swap-in needs.
+ *
+ * Best-effort: covers the language MIMEs the codeapi backend actually
+ * emits (mirrors `MIME_TO_TOOL_ARTIFACT_TYPE`'s CODE entries). MIMEs
+ * without an entry here just fall through to the empty hint, same as
+ * unknown extensions.
+ */
+const MIME_TO_LANGUAGE: Record = {
+  'text/javascript': 'javascript',
+  'application/javascript': 'javascript',
+  'application/sql': 'sql',
+  'application/x-sh': 'bash',
+  'application/x-php': 'php',
+  'application/x-powershell': 'powershell',
+  'text/x-python': 'python',
+  'text/x-typescript': 'typescript',
+  'text/x-ruby': 'ruby',
+  'text/x-go': 'go',
+  'text/x-rust': 'rust',
+  'text/x-c': 'c',
+  'text/x-c++': 'cpp',
+  'text/x-csharp': 'csharp',
+  'text/x-java': 'java',
+  'text/x-kotlin': 'kotlin',
+  'text/x-scala': 'scala',
+  'text/x-perl': 'perl',
+  'text/x-r': 'r',
+  'text/x-lua': 'lua',
+  'text/x-swift': 'swift',
+  'text/css': 'css',
+};
+
+/**
+ * Look up the fenced-block language hint for an attachment, trying (in
+ * order): the filename's extension, the lowercased basename for
+ * extensionless build files, and the MIME type. Falls back to the raw
+ * extension if not in the map (so a `.foo` source still gets
+ * ```` ```foo ```` and renders monospace, even without highlighting).
+ * Empty string when no signal yields a hint — the fence emits as
+ * ```` ``` ```` with no language token.
+ *
+ * The MIME fallback covers the case where codeapi reports a code file
+ * with a stripped or extensionless name AND a useful Content-Type
+ * (e.g. `{ filename: 'noext', type: 'text/x-python' }`). Without it,
+ * such files would route to CODE but render without `language-python`
+ * on the `` element.
+ */
+export function languageForFilename(
+  filename: string | undefined,
+  mime?: string | undefined,
+): string {
+  const ext = extensionOf(filename);
+  if (ext) {
+    return CODE_EXTENSION_TO_LANGUAGE[ext] ?? ext;
+  }
+  /* Extensionless filename: try the basename. `Dockerfile` →
+   * `dockerfile` → `'dockerfile'` language hint. */
+  const bare = bareNameOf(filename);
+  if (bare && Object.prototype.hasOwnProperty.call(CODE_EXTENSION_TO_LANGUAGE, bare)) {
+    return CODE_EXTENSION_TO_LANGUAGE[bare];
+  }
+  /* MIME fallback for the extensionless-name + useful-MIME case. */
+  if (mime) {
+    const stripped = baseMime(mime);
+    if (Object.prototype.hasOwnProperty.call(MIME_TO_LANGUAGE, stripped)) {
+      return MIME_TO_LANGUAGE[stripped];
+    }
+  }
+  return '';
+}
+
+/**
+ * Find the longest run of backticks that could close a fenced code block
+ * inside `source`. CommonMark allows the closer to be indented up to 3
+ * spaces, so runs at columns 0–3 all qualify. The fence emitted by
+ * `wrapAsFencedCodeBlock` must have STRICTLY MORE backticks than any
+ * such run inside the payload — otherwise a markdown snippet inside a
+ * JS template literal (or any source containing ` ``` ` near
+ * column 0) closes the outer fence early and the rest renders as
+ * markdown, corrupting the artifact.
+ */
+export function longestLeadingBacktickRun(source: string): number {
+  let max = 0;
+  /* `^ {0,3}(`+)` matches lines whose leading whitespace is ≤ 3
+   * spaces (per CommonMark's fence-indent allowance) followed by one
+   * or more backticks. Tabs are not allowed — CommonMark expands them
+   * to 4 spaces, which is over the closer limit. The multiline + global
+   * flags scan every line in the payload. */
+  const re = /^ {0,3}(`+)/gm;
+  for (let m = re.exec(source); m !== null; m = re.exec(source)) {
+    if (m[1].length > max) max = m[1].length;
+  }
+  return max;
+}
+
+/**
+ * Wrap raw source as a fenced markdown code block so the CODE bucket
+ * can ride the existing markdown rendering pipeline — `marked` emits
+ * `
…
` and the future
+ * highlighter swap-in (currently the markdown template uses plain
+ * `marked` with no syntax colors) will pick up `language-`
+ * automatically. Pure; deterministic; safe on empty input (renders an
+ * empty fenced block which marked handles cleanly).
+ *
+ * Fence length is adaptive: 3 backticks by default, but bumped to
+ * (longest-leading-run-in-source + 1) when the source contains
+ * ` ``` ` (or longer) near the start of any line. This is the
+ * CommonMark-spec way to embed a fenced block inside another fenced
+ * block — see e.g. the markdown spec's nested-fence examples — and
+ * avoids the early-close attack on artifacts whose source is itself
+ * markdown-shaped.
+ */
+export function wrapAsFencedCodeBlock(source: string, lang: string): string {
+  const fenceLength = Math.max(3, longestLeadingBacktickRun(source) + 1);
+  const fence = '`'.repeat(fenceLength);
+  /* Trim a single trailing newline (common in extractor output) so the
+   * fence's closing ``` lands on its own line rather than after a blank
+   * gap that marked would render as an extra 
. */
+  const body = source.endsWith('\n') ? source.slice(0, -1) : source;
+  return fence + lang + '\n' + body + '\n' + fence;
+}
+
 const EXTENSION_TO_TOOL_ARTIFACT_TYPE: Record = {
   html: TOOL_ARTIFACT_TYPES.HTML,
   htm: TOOL_ARTIFACT_TYPES.HTML,
+  // jsx/tsx are React component sources — keep them on the React
+  // (sandpack) bucket rather than the new CODE bucket so the existing
+  // live-preview behavior survives. Plain JS/TS source goes through CODE.
   jsx: TOOL_ARTIFACT_TYPES.REACT,
   tsx: TOOL_ARTIFACT_TYPES.REACT,
   md: TOOL_ARTIFACT_TYPES.MARKDOWN,
@@ -199,25 +510,19 @@ const EXTENSION_TO_TOOL_ARTIFACT_TYPE: Record = {
   pptx: TOOL_ARTIFACT_TYPES.PLAIN_TEXT,
 };
 
-const extensionOf = (filename: string | undefined): string => {
-  if (!filename) {
-    return '';
-  }
-  const dot = filename.lastIndexOf('.');
-  if (dot < 0 || dot === filename.length - 1) {
-    return '';
-  }
-  return filename.slice(dot + 1).toLowerCase();
-};
-
-/** Strip charset / boundary parameters so we can do exact MIME comparisons. */
-const baseMime = (mime: string | undefined): string => {
-  if (!mime) {
-    return '';
-  }
-  const semi = mime.indexOf(';');
-  return (semi < 0 ? mime : mime.slice(0, semi)).trim().toLowerCase();
-};
+/* Append every entry in `CODE_EXTENSION_TO_LANGUAGE` to the routing map
+ * pointing at the CODE bucket. Keeping the language map as the source
+ * of truth means a new language is one entry away from being routable.
+ *
+ * Skip extensions already claimed by a non-CODE bucket — `jsx`/`tsx`
+ * belong to React (sandpack) for the live-preview, and a future
+ * contributor adding them to `CODE_EXTENSION_TO_LANGUAGE` (a natural
+ * mistake — they ARE source code) shouldn't silently break the React
+ * routing path. The explicit map entries above always win. */
+for (const ext of Object.keys(CODE_EXTENSION_TO_LANGUAGE)) {
+  if (ext in EXTENSION_TO_TOOL_ARTIFACT_TYPE) continue;
+  EXTENSION_TO_TOOL_ARTIFACT_TYPE[ext] = TOOL_ARTIFACT_TYPES.CODE;
+}
 
 const MIME_TO_TOOL_ARTIFACT_TYPE: Record = {
   'text/html': TOOL_ARTIFACT_TYPES.HTML,
@@ -227,6 +532,37 @@ const MIME_TO_TOOL_ARTIFACT_TYPE: Record = {
   'application/vnd.react': TOOL_ARTIFACT_TYPES.REACT,
   'application/vnd.ant.react': TOOL_ARTIFACT_TYPES.REACT,
   'application/vnd.mermaid': TOOL_ARTIFACT_TYPES.MERMAID,
+  // Code MIME types — codeapi serves these via Content-Type for source
+  // files (`text/x-python`, `text/x-typescript`, etc.) so a file whose
+  // extension was stripped or renamed upstream still routes to CODE.
+  // This is a best-effort COMMON-CASE list, not an exhaustive mirror of
+  // `CODE_EXTENSION_TO_LANGUAGE` — extension-based routing is the
+  // primary path, and the MIME table only matters when the filename is
+  // missing/extensionless AND the upstream supplied a useful MIME.
+  // Adding more here is harmless; missing entries fall through to inline
+  // rendering (the same as today).
+  'text/javascript': TOOL_ARTIFACT_TYPES.CODE,
+  'application/javascript': TOOL_ARTIFACT_TYPES.CODE,
+  'application/sql': TOOL_ARTIFACT_TYPES.CODE,
+  'application/x-sh': TOOL_ARTIFACT_TYPES.CODE,
+  'application/x-php': TOOL_ARTIFACT_TYPES.CODE,
+  'application/x-powershell': TOOL_ARTIFACT_TYPES.CODE,
+  'text/x-python': TOOL_ARTIFACT_TYPES.CODE,
+  'text/x-typescript': TOOL_ARTIFACT_TYPES.CODE,
+  'text/x-ruby': TOOL_ARTIFACT_TYPES.CODE,
+  'text/x-go': TOOL_ARTIFACT_TYPES.CODE,
+  'text/x-rust': TOOL_ARTIFACT_TYPES.CODE,
+  'text/x-c': TOOL_ARTIFACT_TYPES.CODE,
+  'text/x-c++': TOOL_ARTIFACT_TYPES.CODE,
+  'text/x-csharp': TOOL_ARTIFACT_TYPES.CODE,
+  'text/x-java': TOOL_ARTIFACT_TYPES.CODE,
+  'text/x-kotlin': TOOL_ARTIFACT_TYPES.CODE,
+  'text/x-scala': TOOL_ARTIFACT_TYPES.CODE,
+  'text/x-perl': TOOL_ARTIFACT_TYPES.CODE,
+  'text/x-r': TOOL_ARTIFACT_TYPES.CODE,
+  'text/x-lua': TOOL_ARTIFACT_TYPES.CODE,
+  'text/x-swift': TOOL_ARTIFACT_TYPES.CODE,
+  'text/css': TOOL_ARTIFACT_TYPES.CODE,
   // Office MIME types fall through to the plain-text bucket here too —
   // matches the extension map so a file whose extension was stripped
   // somewhere upstream still routes to the panel.
@@ -258,15 +594,30 @@ const MIME_TO_TOOL_ARTIFACT_TYPE: Record = {
 export function detectArtifactTypeFromFile(
   attachment: Partial>,
 ): ToolArtifactType | null {
-  const byExtension = EXTENSION_TO_TOOL_ARTIFACT_TYPE[extensionOf(attachment.filename)];
-  const type = byExtension ?? MIME_TO_TOOL_ARTIFACT_TYPE[baseMime(attachment.type)] ?? null;
+  /* Compute the basename once and reuse it across the extension AND
+   * bare-name lookups. Both `extensionOf(filename)` and
+   * `bareNameOf(filename)` would otherwise split path separators
+   * twice on the same input. */
+  const base = attachment.filename ? basenameOf(attachment.filename) : '';
+  const byExtension = EXTENSION_TO_TOOL_ARTIFACT_TYPE[extensionFromBasename(base)];
+  /* Bare-name fallback for extensionless build files (`Dockerfile`,
+   * `Makefile`, `Gemfile`, `Rakefile`, `Vagrantfile`, `Brewfile`). Only
+   * fires when the extension lookup missed AND the basename is in the
+   * routing map; everything else stays on the existing extension/MIME
+   * paths. */
+  const byBareName = byExtension
+    ? undefined
+    : EXTENSION_TO_TOOL_ARTIFACT_TYPE[bareNameFromBasename(base)];
+  const type =
+    byExtension ?? byBareName ?? MIME_TO_TOOL_ARTIFACT_TYPE[baseMime(attachment.type)] ?? null;
   if (type == null) {
     return null;
   }
   if (
     !attachment.text &&
     type !== TOOL_ARTIFACT_TYPES.PLAIN_TEXT &&
-    type !== TOOL_ARTIFACT_TYPES.MARKDOWN
+    type !== TOOL_ARTIFACT_TYPES.MARKDOWN &&
+    type !== TOOL_ARTIFACT_TYPES.CODE
   ) {
     return null;
   }
@@ -346,10 +697,23 @@ export function fileToArtifact(
   if (
     !attachment.text &&
     type !== TOOL_ARTIFACT_TYPES.PLAIN_TEXT &&
-    type !== TOOL_ARTIFACT_TYPES.MARKDOWN
+    type !== TOOL_ARTIFACT_TYPES.MARKDOWN &&
+    type !== TOOL_ARTIFACT_TYPES.CODE
   ) {
     return null;
   }
+  /* For CODE artifacts, resolve the language hint at construction time
+   * (rather than re-deriving from `artifact.title` in `useArtifactProps`)
+   * so the MIME fallback fires for extensionless filenames. Without
+   * this, `{ filename: 'noext', type: 'text/x-python' }` would route
+   * to CODE via the MIME bucket but render with an empty `language-`
+   * class because the title carries no extension to classify. The
+   * resolved language is stored on `artifact.language`, which the
+   * hook reads directly. */
+  const language =
+    type === TOOL_ARTIFACT_TYPES.CODE
+      ? languageForFilename(attachment.filename, attachment.type)
+      : undefined;
   return {
     id: toolArtifactKey(attachment),
     type,
@@ -360,6 +724,7 @@ export function fileToArtifact(
     // placeholder. Only `null`/`undefined` fall through to the
     // placeholder, matching "no extraction has run yet."
     content: attachment.text ?? options?.placeholder ?? '',
+    language,
     messageId: attachment.messageId ?? undefined,
     lastUpdateTime: toLastUpdate(attachment),
   };