ci(#464): guard against em-dash characters in lib/ and test/

Add .github/scripts/check_no_emdash.py and run it as the first step of
the analyze job, so it fails in seconds before the flutter setup. It
rejects the em-dash character (U+2014) in lib/ and test/ source (comments
and string literals) plus app_en.arb, excluding generated files, non-
English ARB, and the lone "no data" glyph placeholder ('—' as an entire
quoted value). Stops the regression that #457 and #462 had to sweep by
hand.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/scripts/check_no_emdash.py

@@ -0,0 +1,91 @@
+#!/usr/bin/env python3
+"""Fail if an em-dash (U+2014) appears in source-authored text.
+
+The em-dash reads as an AI tell, so it is kept out of the public repo (#457,
+#462, #464). This guard runs in CI (the `analyze` job) and can also be wired
+into a local pre-commit hook.
+
+In scope:
+  - lib/**/*.dart and test/**/*.dart  (code comments + string literals)
+  - lib/l10n/app_en.arb               (English UI copy)
+
+Out of scope (never flagged):
+  - Generated files: *.g.dart, lib/l10n/app_localizations*.dart
+  - Non-English ARB (lib/l10n/app_*.arb except app_en.arb): an em-dash may be
+    legitimate target-language punctuation.
+  - The lone "no data / not available" glyph placeholder: a dash that is the
+    entire quoted value, e.g. `return '—';`, `"key": "—"`, `text: '—'`. That is
+    a deliberate UI element, not prose.
+
+Exit status: 0 when clean, 1 when any in-scope em-dash is found (each printed
+as file:line: <content>).
+"""
+
+from __future__ import annotations
+
+import os
+import sys
+
+EM_DASH = "—"
+ROOTS = ("lib", "test")
+
+
+def _has_prose_emdash(line: str) -> bool:
+    """True if the line has an em-dash that is NOT a lone glyph placeholder.
+
+    The lone "no data" glyph is a dash that is the entire quoted value (`'—'`
+    or `"—"`). Strip those tokens first, so a line carrying both a glyph and a
+    real prose em-dash is still flagged.
+    """
+    stripped = line.replace("'" + EM_DASH + "'", "").replace('"' + EM_DASH + '"', "")
+    return EM_DASH in stripped
+
+
+def _in_scope(path: str) -> bool:
+    base = os.path.basename(path)
+    if base.endswith(".g.dart") or base.startswith("app_localizations"):
+        return False
+    if base.endswith(".dart"):
+        return True
+    # ARB: only the English source is in scope.
+    return base == "app_en.arb"
+
+
+def find_violations(roots=ROOTS):
+    hits = []
+    for root in roots:
+        if not os.path.isdir(root):
+            continue
+        for dirpath, _dirs, filenames in os.walk(root):
+            for name in filenames:
+                if not (name.endswith(".dart") or name.endswith(".arb")):
+                    continue
+                path = os.path.join(dirpath, name)
+                if not _in_scope(path):
+                    continue
+                with open(path, encoding="utf-8") as fh:
+                    for lineno, line in enumerate(fh, 1):
+                        if _has_prose_emdash(line):
+                            hits.append((path.replace(os.sep, "/"), lineno, line.rstrip()))
+    return hits
+
+
+def main() -> int:
+    roots = tuple(sys.argv[1:]) or ROOTS
+    hits = find_violations(roots)
+    if not hits:
+        print("check_no_emdash: OK (no em-dash characters in source)")
+        return 0
+    print(
+        "check_no_emdash: found the em-dash character (U+2014) in source. "
+        "Replace it with a comma, colon, or period (see #464):",
+        file=sys.stderr,
+    )
+    for path, lineno, content in hits:
+        print(f"  {path}:{lineno}: {content}", file=sys.stderr)
+    print(f"\n{len(hits)} em-dash(es) found.", file=sys.stderr)
+    return 1
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())

.github/workflows/flutter_dart.yml

@@ -14,6 +14,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
+      - name: Guard against em-dash characters (#464)
+        run: python3 .github/scripts/check_no_emdash.py
+
       - name: Set up Flutter
         uses: subosito/flutter-action@v2
         with: