Antispam: a dead engine marked the account bootstrapped anyway

`_teach` signalled failure by negating the count taught so far. That
works for every case but the one that matters: when the FIRST message is
refused nothing has been taught yet, and `-0` is `0` — not negative. The
caller's `< 0` test then read a total engine outage as a clean run of
zero, recorded `_bootstrapped` for the account, and the hourly sweep
skipped it from then on. The account most in need of a warm start was
the one guaranteed never to get one.

Which is precisely what happened alongside the missing controller
password: every learn was refused 401, and each account was quietly
retired on its first sweep.

Return None for "the engine stopped accepting these" so failure cannot
be confused with a count, and decline to mark an account whose samples
were all unreadable.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018SqJYt7jD7oUEkoY68sBZo

plugins/webmail_plugin_antispam/webmail_plugin_antispam/jobs.py

@@ -51,7 +51,15 @@ MAX_HAM_RATIO = 3
 _DONE_KEY = "_bootstrapped"
 
 
-async def _teach(user_id: uuid.UUID, ids: list[uuid.UUID], *, spam: bool) -> int:
+async def _teach(user_id: uuid.UUID, ids: list[uuid.UUID], *, spam: bool) -> int | None:
+    """Number of messages learned, or None if the engine stopped accepting them.
+
+    None rather than a negative count: the count was once negated to signal
+    failure, which works for every case except the one that matters. If the
+    FIRST message is refused, nothing has been taught yet, `-0` is `0`, and the
+    caller's `< 0` test reads a total engine outage as a clean run of zero — then
+    marks the account bootstrapped, so it is never retried.
+    """
     taught = 0
     for message_id in ids:
         raw = await _SDK.messages.raw(user_id, message_id)
@@ -60,7 +68,7 @@ async def _teach(user_id: uuid.UUID, ids: list[uuid.UUID], *, spam: bool) -> int
         if not await rspamd.learn(raw, user_key=str(user_id), spam=spam):
             # Engine gone. Stop rather than grind through hundreds of failures;
             # the account stays unmarked, so a later run picks it up again.
-            return -taught
+            return None
         taught += 1
         await asyncio.sleep(PAUSE_SECONDS)
     return taught
@@ -106,17 +114,24 @@ async def bootstrap_account(
     ham_ids = ham_ids[: len(spam_ids) * MAX_HAM_RATIO]
 
     spam_taught = await _teach(uid, spam_ids, spam=True)
-    if spam_taught < 0:
+    if spam_taught is None:
         logger.warning(
             "antispam bootstrap for %s stopped: engine unavailable", account_id
         )
         return
     ham_taught = await _teach(uid, ham_ids, spam=False)
-    if ham_taught < 0:
+    if ham_taught is None:
         logger.warning(
             "antispam bootstrap for %s stopped: engine unavailable", account_id
         )
         return
+    if spam_taught == 0:
+        # Every sample was unreadable. Nothing was learned, so do not record a
+        # warm start that did not happen.
+        logger.warning(
+            "antispam bootstrap for %s: no samples could be read", account_id
+        )
+        return
 
     await _SDK.kv(uid).set(_DONE_KEY, [*done, account_id])
     logger.info(