End the hint prompt in a full stop: an unterminated list made Whisper drop punctuation and loop

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server-py/sidecar.py

@@ -65,9 +65,15 @@ def normalize_hint(raw):
     return ", ".join(part for part in parts if part)
 
 
+def _prompt_sentence(text):
+    return " " + text if re.search(r"[.?!]$", text) else " " + text + "."
+
+
 def fit_prompt_ids(hint, encode, budget=PROMPT_TOKEN_BUDGET):
     """Prompt token ids for `hint`, cut to `budget` tokens at a whole word.
 
+    The prompt is a space-led sentence ending in a full stop (unless it ends
+    in . ? ! already) - an unterminated list drops punctuation and loops.
     The start of the list is kept and the end dropped; a dangling ","/";" is
     removed; a first word longer than the budget is cut at the budget.
     `encode` must add no special tokens.
@@ -75,13 +81,13 @@ def fit_prompt_ids(hint, encode, budget=PROMPT_TOKEN_BUDGET):
     text = normalize_hint(hint)
     if not text:
         return []
-    full = encode(" " + text)
+    full = encode(_prompt_sentence(text))
     if len(full) <= budget:
         return full
     words = text.split(" ")
 
     def encode_prefix(count):
-        return encode(" " + re.sub(r"[,;]+$", "", " ".join(words[:count])))
+        return encode(_prompt_sentence(re.sub(r"[,;]+$", "", " ".join(words[:count]))))
 
     low, high = 0, len(words) - 1
     while low < high: