fix(quickadapter): catch UnicodeDecodeError in journal tail probe

Codex inline review (P2) on PR #102 flagged that
`_optuna_journal_has_corrupt_tail` catches only
`json.JSONDecodeError` from `json.loads(last_line)`, but
`json.loads` raises `UnicodeDecodeError` (subclass of
`ValueError`, NOT of `JSONDecodeError`) when the trailing record
contains invalid UTF-8 bytes — a common crash pattern when
`fsync` is interrupted mid-multibyte. The exception escapes the
helper, propagates out of `optuna_create_storage` (the helper
runs BEFORE the recoverable try/except), reaches
`optuna_create_study`'s broad outer handler, and reproduces the
silent-HPO-skip symptom under a different corruption class.

Empirically reproduced:

  >>> json.loads(b'\\xc3\\x28')
  UnicodeDecodeError: 'utf-8' codec can't decode byte 0xc3 in
  position 0: invalid continuation byte

Broaden the except clause from `json.JSONDecodeError` to
`ValueError` — the common parent of both `JSONDecodeError` and
`UnicodeDecodeError` — so the helper treats any
`json.loads`-unparseable trailing record as corruption and routes
it through the same quarantine path. Other `ValueError` subclasses
are not plausibly raised by `json.loads` on bytes input.

Reproducer at `/tmp/quickadapter-tests/test_optuna_journal_quarantine.py`
extended from 17 to 19 scenarios (Class C4 detection + end-to-end
quarantine on invalid UTF-8). All pass.

diff --git a/quickadapter/user_data/freqaimodels/QuickAdapterRegressorV3.py b/quickadapter/user_data/freqaimodels/QuickAdapterRegressorV3.py
index 6a0311e2b451c35188bc3fb0b9d9361fc9ecbb70..399120f55c57ffbe8667b5f81afd3212cf3dfff7 100644 (file)
--- a/quickadapter/user_data/freqaimodels/QuickAdapterRegressorV3.py
+++ b/quickadapter/user_data/freqaimodels/QuickAdapterRegressorV3.py
@@ -4274,8 +4274,10 @@ class QuickAdapterRegressorV3(BaseRegressionModel):
         Bounded tail probe (last ``_OPTUNA_JOURNAL_TAIL_PROBE_BYTES``).
         Return True iff the file is non-empty AND its trailing record
         is (a) missing the newline, (b) empty (bare ``\\n``), or
-        (c) malformed JSON. Fail-open when the probe window cuts a
-        single line larger than the window; defer to the
+        (c) ``json.loads``-unparseable (malformed JSON, ``ValueError``,
+        or invalid UTF-8, ``UnicodeDecodeError`` — both are
+        ``ValueError`` subclasses). Fail-open when the probe window
+        cuts a single line larger than the window; defer to the
         post-construction handler.
         """
         if not journal_path.exists():
@@ -4307,7 +4309,7 @@ class QuickAdapterRegressorV3(BaseRegressionModel):
             return True
         try:
             json.loads(last_line)
-        except json.JSONDecodeError:
+        except ValueError:
             return True
         return False