Lint reStructuredText prose with Vale to ban em dashes

.gitignore

@@ -112,3 +112,6 @@ src/*/_setuptools_scm_version.py
 
 # Nix
 result
+
+# Vale styles downloaded by ``vale sync``
+styles/

.pre-commit-config.yaml

@@ -309,6 +309,36 @@ repos:
           - *uv_version
         stages: [pre-commit]
 
+      # Vale enforces prose style rules, such as banning em dashes, in
+      # reStructuredText files.
+      # The rules come from the ``ClearProse`` package pinned in ``.vale.ini``,
+      # which ``vale sync`` downloads into the (gitignored) ``styles``
+      # directory.
+      # Vale needs ``rst2html`` from Docutils on the ``PATH`` to parse
+      # reStructuredText.
+      # ``vale sync`` also runs when ``.vale.ini`` changes, so a package
+      # bump takes effect without waiting for the next reStructuredText
+      # change.
+      - id: vale-sync
+        name: vale sync
+        entry: uv run --extra=dev vale sync
+        language: python
+        pass_filenames: false
+        files: (\.rst$|^\.vale\.ini$)
+        additional_dependencies:
+          - *uv_version
+        stages: [pre-commit]
+
+      - id: vale
+        name: vale
+        entry: uv run --extra=dev vale
+        language: python
+        types_or: [rst]
+        require_serial: true
+        additional_dependencies:
+          - *uv_version
+        stages: [pre-commit]
+
       - id: doc8
         name: doc8
         entry: uv run --extra=dev -m doc8

.vale.ini

@@ -0,0 +1,7 @@
+StylesPath = styles
+MinAlertLevel = error
+
+Packages = https://github.com/adamtheturtle/vale-style-clear-prose/releases/download/v1.1.0/ClearProse.zip
+
+[*.rst]
+BasedOnStyles = ClearProse

pyproject.toml

@@ -88,6 +88,7 @@ optional-dependencies.dev = [
     "towncrier==25.8.0",
     "ty==0.0.65",
     "types-pyyaml==6.0.12.20260724",
+    "vale==3.13.0.0",
     "vulture==2.16",
     "vws-python-mock==2026.2.22.3",
     "vws-test-fixtures==2023.3.5",
@@ -297,6 +298,7 @@ ignore = [
     ".git_archival.txt",
     ".pre-commit-config.yaml",
     ".prettierrc",
+    ".vale.ini",
     ".yamlfmt",
     "bin",
     "bin/*",