Audit code cells for unwrappable lines; fix three offenders + safety net

User-flagged: /examples/testing showed a horizontal scrollbar inside
a walkthrough code cell. Root cause: white-space: pre-wrap wraps at
spaces, but the line

    suite = unittest.defaultTestLoader.loadTestsFromTestCase(AddTests)

contains a 58-char run after the first space that pre-wrap can't
break. Same pattern in two other examples.

TDD:

  RED — Contract 12 in tests/test_example_content.py
  (CellCodeWrappingContract) flags any \\S-run > 50 chars in
  walkthrough cell code. Pre-fix output:

    logging cell 0 line 6: 68-char run
      handler.setFormatter(logging.Formatter("%(levelname)s:%(message)s"))
    testing cell 2 line 2: 58-char run
      unittest.defaultTestLoader.loadTestsFromTestCase(AddTests)
    datetime cell 2 line 1: 51-char run
      datetime.fromisoformat("2026-05-04T12:30:00+00:00")

  GREEN — introduce intermediate names so each line wraps cleanly:

    testing.md
      loader = unittest.defaultTestLoader
      suite = loader.loadTestsFromTestCase(AddTests)
      ...
      runner = unittest.TextTestRunner(stream=stream, verbosity=0)
      result = runner.run(suite)

    logging.md
      formatter = logging.Formatter("%(levelname)s:%(message)s")
      handler.setFormatter(formatter)

    datetime.md
      iso_text = "2026-05-04T12:30:00+00:00"
      parsed = datetime.fromisoformat(iso_text)

  Each :::program block and the matching :::cell block updated
  together so the runnable code and the walkthrough stay in sync.

CSS safety net (public/site.css): added `overflow-wrap: anywhere`
to `.cell-source pre, .cell-source .shiki-block, .cell-output pre`.
A future long URL, long string literal, or long encoded blob will
break mid-run instead of pushing a horizontal scrollbar onto the
page. Code that's authored to wrap cleanly (the rule above keeps it
authored well) will still wrap at spaces because pre-wrap takes
precedence over overflow-wrap when both apply.

59 tests pass; SEO/cache lint clears 110 pages.

Author: claude

public/site.f9a6740c684b.css public/site.1452cc5609f2.csspublic/site.f9a6740c684b.css renamed to public/site.1452cc5609f2.css

@@ -1,3 +1,3 @@
 # Generated by scripts/fingerprint_assets.py. Do not edit by hand.
-ASSET_PATHS = {'SITE_CSS': '/site.f9a6740c684b.css', 'SYNTAX_JS': '/syntax-highlight.3b6c7f730d46.js', 'EDITOR_JS': '/editor.dd81f5171b14.js'}
-HTML_CACHE_VERSION = 'c48d15294056'
+ASSET_PATHS = {'SITE_CSS': '/site.1452cc5609f2.css', 'SYNTAX_JS': '/syntax-highlight.3b6c7f730d46.js', 'EDITOR_JS': '/editor.dd81f5171b14.js'}
+HTML_CACHE_VERSION = '54735cba7a40'

public/site.css

@@ -28,7 +28,8 @@ expires_at = created_at + timedelta(days=7, hours=2)
 print(expires_at.isoformat())
 
 print(created_at.strftime("%Y-%m-%d %H:%M %Z"))
-parsed = datetime.fromisoformat("2026-05-04T12:30:00+00:00")
+iso_text = "2026-05-04T12:30:00+00:00"
+parsed = datetime.fromisoformat(iso_text)
 print(parsed == created_at)
 ```
 :::
@@ -77,7 +78,8 @@ Use `strftime()` for human-facing formatting and `fromisoformat()` when reading
 
 ```python
 print(created_at.strftime("%Y-%m-%d %H:%M %Z"))
-parsed = datetime.fromisoformat("2026-05-04T12:30:00+00:00")
+iso_text = "2026-05-04T12:30:00+00:00"
+parsed = datetime.fromisoformat(iso_text)
 print(parsed == created_at)
 ```
 

src/asset_manifest.py

@@ -20,7 +20,8 @@ import sys
 logger = logging.getLogger("example")
 logger.setLevel(logging.INFO)
 handler = logging.StreamHandler(sys.stdout)
-handler.setFormatter(logging.Formatter("%(levelname)s:%(message)s"))
+formatter = logging.Formatter("%(levelname)s:%(message)s")
+handler.setFormatter(formatter)
 logger.handlers[:] = [handler]
 
 logger.debug("hidden")
@@ -39,7 +40,8 @@ import sys
 logger = logging.getLogger("example")
 logger.setLevel(logging.INFO)
 handler = logging.StreamHandler(sys.stdout)
-handler.setFormatter(logging.Formatter("%(levelname)s:%(message)s"))
+formatter = logging.Formatter("%(levelname)s:%(message)s")
+handler.setFormatter(formatter)
 logger.handlers[:] = [handler]
 
 logger.debug("hidden")

src/example_sources/datetime.md

@@ -47,9 +47,11 @@ class AddTests(unittest.TestCase):
         with self.assertRaises(ZeroDivisionError):
             divide(1, 0)
 
-suite = unittest.defaultTestLoader.loadTestsFromTestCase(AddTests)
+loader = unittest.defaultTestLoader
+suite = loader.loadTestsFromTestCase(AddTests)
 stream = io.StringIO()
-result = unittest.TextTestRunner(stream=stream, verbosity=0).run(suite)
+runner = unittest.TextTestRunner(stream=stream, verbosity=0)
+result = runner.run(suite)
 print(result.testsRun)
 print(result.wasSuccessful())
 ```
@@ -111,9 +113,11 @@ A runner executes the suite and records whether every assertion passed. Capturin
 ```python
 import io
 
-suite = unittest.defaultTestLoader.loadTestsFromTestCase(AddTests)
+loader = unittest.defaultTestLoader
+suite = loader.loadTestsFromTestCase(AddTests)
 stream = io.StringIO()
-result = unittest.TextTestRunner(stream=stream, verbosity=0).run(suite)
+runner = unittest.TextTestRunner(stream=stream, verbosity=0)
+result = runner.run(suite)
 print(result.testsRun)
 print(result.wasSuccessful())
 ```

src/example_sources/logging.md

@@ -76,5 +76,41 @@ def test_unsupported_prose_mentions_code(self):
         self.assertEqual(failures, [], "\n  " + "\n  ".join(failures))
 
 
+class CellCodeWrappingContract(unittest.TestCase):
+    """Contract 12: walkthrough cell code wraps inside the narrow
+    prose|code column without horizontal scroll.
+
+    The cells render in a column whose mono font fits roughly 55-60
+    characters at desktop widths and narrower on tablets. CSS sets
+    `white-space: pre-wrap` so lines wrap at SPACES, but a continuous
+    run with no space (a long dotted call, an import chain, a string
+    literal) overflows even after pre-wrap and triggers a horizontal
+    scrollbar inside the code block.
+
+    Heuristic: no \\S-run in any cell may exceed 50 characters. Hits
+    must be either shortened (introduce a temporary name and split
+    the call) or accepted with `overflow-wrap: anywhere` in CSS as a
+    safety net.
+    """
+
+    MAX_UNBREAKABLE_RUN = 50
+
+    def test_no_unwrappable_run_in_cell_code(self):
+        import re as _re
+
+        failures: list[str] = []
+        for ex in EXAMPLES:
+            for i, cell in enumerate(ex.get("cells", [])):
+                for j, line in enumerate(cell.get("code", "").splitlines()):
+                    longest = max(_re.findall(r"\S+", line) or [""], key=len)
+                    if len(longest) > self.MAX_UNBREAKABLE_RUN:
+                        failures.append(
+                            f"{ex['slug']} cell {i} line {j}: "
+                            f"{len(longest)}-char unbreakable run will overflow "
+                            f"the prose|code column → {longest[:60]!r}"
+                        )
+        self.assertEqual(failures, [], "\n  " + "\n  ".join(failures))
+
+
 if __name__ == "__main__":
     unittest.main()