fix: nltk_check() now catches LookupError for missing punkt_tab data

nltk_check() only caught ImportError (package not installed) but missed
LookupError (package installed, data not downloaded). Users with nltk
present via transitive deps (rouge_score) got an unhelpful ValueError
instead of install instructions when punkt_tab was missing.

Also adds punkt_tab download to CI workflow — same pattern as Ollama
model pulls.

Author: planetf1

.github/workflows/quality.yml

@@ -41,6 +41,8 @@ jobs:
       - name: Send failure message pre-commit
         if: failure() # This step will only run if a previous step failed
         run: echo "The quality verification failed. Please run precommit "
+      - name: Download NLTK data
+        run: uv run python -m nltk.downloader punkt_tab
       - name: Install Ollama
         run: curl -fsSL https://ollama.com/install.sh | sh
       - name: Start serving ollama

mellea/formatters/granite/base/optional.py

@@ -49,8 +49,10 @@ def nltk_check(feature_name: str):
         feature_name: Name of the feature that requires NLTK, used in the error message.
 
     Raises:
-        ImportError: If the ``nltk`` package is not installed, re-raised with
-            a descriptive message and installation instructions.
+        ImportError: If the ``nltk`` package is not installed or required
+            NLTK data (e.g. ``punkt_tab``) has not been downloaded,
+            re-raised with a descriptive message and installation
+            instructions.
     """
     try:
         yield
@@ -60,3 +62,8 @@ def nltk_check(feature_name: str):
             f"{feature_name} in the 'granite_io' library."
             f"{_NLTK_INSTALL_INSTRUCTIONS}"
         ) from err
+    except LookupError as err:
+        raise ImportError(
+            f"NLTK data required for {feature_name} is not installed."
+            f"{_NLTK_INSTALL_INSTRUCTIONS}"
+        ) from err

mellea/formatters/granite/base/util.py

@@ -60,8 +60,10 @@ def nltk_check(feature_name: str):
         feature_name: Name of the feature that requires NLTK, used in the error message.
 
     Raises:
-        ImportError: If the ``nltk`` package is not installed, re-raised with
-            a descriptive message and installation instructions.
+        ImportError: If the ``nltk`` package is not installed or required
+            NLTK data (e.g. ``punkt_tab``) has not been downloaded,
+            re-raised with a descriptive message and installation
+            instructions.
     """
     try:
         yield
@@ -71,6 +73,11 @@ def nltk_check(feature_name: str):
             f"{feature_name} in the 'granite_io' library."
             f"{NLTK_INSTALL_INSTRUCTIONS}"
         ) from err
+    except LookupError as err:
+        raise ImportError(
+            f"NLTK data required for {feature_name} is not installed."
+            f"{NLTK_INSTALL_INSTRUCTIONS}"
+        ) from err
 
 
 def find_substring_in_text(substring: str, text: str) -> list[dict]: