fix(advice): stale advice must not overwrite a correction

The review found a race between the background advice thread and the
brewer correcting a reading.

`set_reading_advice` wrote unconditionally by id.  The advice is
generated in the background, so if the brewer corrects a reading while
the advice for the OLD gravity is still being generated, the slow thread
lands afterwards and overwrites the fresh advice with advice about a
reading that no longer exists.  The reading ends up with the final
gravity from the correction and the advice from before it.

Reproduced against the live database:

    wrote advice for 1050
    wrote advice for 1020
    late stale write matched: 0
    final sg: 1020 | final advice: 'ADVICE FOR THE CORRECTION'

The write is now conditional on the reading still holding the gravity
the advice was generated for, so a late thread matches nothing.

Also
----
`finish_reason` is now checked.  A reply that stopped at the token
ceiling is incomplete - it may be advice that stops mid-sentence - and
it was being stored as if it were the whole answer.  It is now marked
as cut off.

173 tests (up from 171).

src/flask/brew_advice.py

@@ -198,11 +198,24 @@ def call_ollama(prompt: str, *, url: str | None = None, model: str | None = None
     if not choices:
         raise RuntimeError("the model returned no choices")
     message = choices[0].get("message") or {}
+
+    # Some models put their working in a separate field.  It is ignored -
+    # the advice is the content.
     content = message.get("content") or ""
     content = content.strip()
     if not content:
         raise RuntimeError("the model returned an empty response")
-    return _trim_advice(_strip_reasoning(content))
+
+    # A reply cut off at the token ceiling is INCOMPLETE.  It may be
+    # advice that stops mid-sentence, so it is marked as truncated rather
+    # than stored as if it were the whole answer.
+    finish_reason = choices[0].get("finish_reason") or body.get("done_reason")
+    truncated = finish_reason == "length"
+
+    advice = _trim_advice(_strip_reasoning(content))
+    if truncated:
+        advice = _trim_advice(advice + " (the reply was cut off)")
+    return advice
 
 
 def _trim_advice(text: str) -> str: