VahterBanBot: cap ephemeral spam warning at SPAM_WARNING_MAX_SCORE (default 3.0)

src/VahterBanBot/Bot.fs

@@ -689,15 +689,23 @@ type BotService(
         // chat. Skipped if they were just total-banned above (a ban notice, not a warning, is
         // the right signal there) and restricted to the near-zero-false-positive text/LLM
         // verdicts — InvisibleMention/SpamTextCacheHit/ReactionSpam are deliberately excluded so
-        // a warning never teaches a spammer which signature tripped detection. Best-effort:
-        // delivery is not guaranteed and a failure must never fail the deletion, hence
-        // CallIgnore (never CallExn) — see AdminCommand's `confirm` helper for the same pattern.
+        // a warning never teaches a spammer which signature tripped detection. Further capped by
+        // SpamWarningMaxScore (strict <) so blatant spam (high score) is deleted silently — see
+        // BotConfiguration's doc comment. Best-effort: delivery is not guaranteed and a failure
+        // must never fail the deletion, hence CallIgnore (never CallExn) — see AdminCommand's
+        // `confirm` helper for the same pattern.
         if botConfig.Value.SpamWarningEnabled && not justBanned then
-            match reason with
-            | AutoDeleteReason.MlSpam _ | AutoDeleteReason.LlmSpam _ | AutoDeleteReason.ContentFilterSpam _ ->
+            let warnedReasonScore =
+                match reason with
+                | AutoDeleteReason.MlSpam x -> Some x.score
+                | AutoDeleteReason.LlmSpam x -> Some x.score
+                | AutoDeleteReason.ContentFilterSpam x -> Some x.score
+                | AutoDeleteReason.ReactionSpam _ | AutoDeleteReason.InvisibleMention | AutoDeleteReason.SpamTextCacheHit _ -> None
+            match warnedReasonScore with
+            | Some score when score < botConfig.Value.SpamWarningMaxScore ->
                 do! tg.CallIgnore(Req.SendMessage.Make(msg.ChatId, botConfig.Value.SpamWarningText, receiverUserId = msg.SenderId))
                 recordSpamWarningSent msg.ChatId msg.ChatUsername
-            | AutoDeleteReason.ReactionSpam _ | AutoDeleteReason.InvisibleMention | AutoDeleteReason.SpamTextCacheHit _ -> ()
+            | Some _ | None -> ()
     }
 
     /// Reports uncertain spam to potential spam channel with KILL/SPAM/NOT SPAM buttons for human triage.

src/VahterBanBot/Program.fs

@@ -165,7 +165,8 @@ let buildBotConf () =
                + "Модераторы видят все удаления и разберутся, если это ошибка.\n\n"
                + "⚠️ Your message was removed automatically because it looks like spam. Please do not "
                + "post it again — repeated removals may lead to a ban. Moderators can see all removals "
-               + "and will sort it out if this was a mistake.") }
+               + "and will sort it out if this was a mistake.")
+      SpamWarningMaxScore = getSettingOr "SPAM_WARNING_MAX_SCORE" "3.0" |> double }
 
 let ocrConfigOf (c: BotConfiguration) =
     { OcrEnabled          = c.OcrEnabled

src/VahterBanBot/Types.fs

@@ -518,7 +518,13 @@ type BotConfiguration =
       /// Fixed bilingual warning text, bot_setting-backed so it's tunable via POST
       /// /reload-settings without a redeploy. Deliberately generic — no scores, no ML/LLM
       /// distinction, no strike counts — so it doesn't teach spammers how detection works.
-      SpamWarningText: string }
+      SpamWarningText: string
+      /// Only warn when the deletion's ML score is below this cutoff (strict <), i.e. the
+      /// likely-false-positive band — blatant spam (high score) is deleted silently, no warning.
+      /// bot_setting-backed (not a constant) because the score scale drifts under daily ML
+      /// retraining. Default 3.0 is prod-data-derived (93.8% ham-deletion coverage, 43-point
+      /// spammer-warning reduction) — see Bot.fs's DeleteSpam.
+      SpamWarningMaxScore: float }
     member this.BotActor =
         Actor.Bot (Some {| botUserId = this.BotUserId; botUsername = this.BotUserName |})
 

tests/VahterBanBot.Tests/SpamWarningTests.fs

@@ -22,8 +22,10 @@ type SpamWarningMlTests(fixture: MlEnabledVahterTestContainers, _unused: MlAwait
 
         let user = Tg.user()
         do! fixture.ClearFakeCalls()
-        // "2222222" is a training-set spam word (see test_seed.sql); a single message never
-        // crosses the karma-autoban threshold on its own.
+        // "2222222" is a training-set spam word (see test_seed.sql), scoring 1.5686... under the
+        // fixture ML model (see MLScoreDeterminismTests) — comfortably below the default
+        // SPAM_WARNING_MAX_SCORE of 3.0. A single message never crosses the karma-autoban
+        // threshold on its own.
         let msgUpdate = Tg.quickMsg(chat = fixture.ChatsToMonitor[0], text = "2222222", from = user)
         let! _ = fixture.SendMessage msgUpdate
 
@@ -42,6 +44,72 @@ type SpamWarningMlTests(fixture: MlEnabledVahterTestContainers, _unused: MlAwait
         Assert.Contains("automatically", warnings[0].Body)
     }
 
+    [<Fact>]
+    let ``Flag ON: ML spam deletion scoring at/above SPAM_WARNING_MAX_SCORE sends no warning`` () = task {
+        do! setSpamWarning true
+
+        // Probe the exact ML score for this text under a deliberately permissive cutoff, then
+        // set SPAM_WARNING_MAX_SCORE just below it — robust against the underlying ML model
+        // (and its score scale) changing under retraining, unlike hardcoding a score value.
+        do! fixture.SetBotSetting("SPAM_WARNING_MAX_SCORE", "999")
+        do! fixture.ReloadSettings()
+        let probeMsg = Tg.quickMsg(chat = fixture.ChatsToMonitor[0], text = "2222222", from = Tg.user())
+        let! _ = fixture.SendMessage probeMsg
+        let! scoreOpt = fixture.GetMlScore probeMsg.Message.Value
+        let score =
+            match scoreOpt with
+            | Some s -> s
+            | None -> failwith "Sanity: probe message should have been ML-scored"
+
+        do! fixture.SetBotSetting("SPAM_WARNING_MAX_SCORE", string (score - 0.5))
+        do! fixture.ReloadSettings()
+        let user = Tg.user()
+        do! fixture.ClearFakeCalls()
+        let msgUpdate = Tg.quickMsg(chat = fixture.ChatsToMonitor[0], text = "2222222", from = user)
+        let! _ = fixture.SendMessage msgUpdate
+
+        let! msgDeleted = fixture.MessageIsAutoDeleted msgUpdate.Message.Value
+        Assert.True(msgDeleted, "Sanity: message should still be auto-deleted regardless of the warning cutoff")
+
+        let! calls = fixture.GetFakeCalls "sendMessage"
+        Assert.False(
+            calls |> Array.exists (fun c -> c.Body.Contains $"\"receiver_user_id\":{user.Id}"),
+            "a deletion scoring at/above SPAM_WARNING_MAX_SCORE must not send the ephemeral warning")
+    }
+
+    [<Fact>]
+    let ``Flag ON: boundary — score exactly equal to SPAM_WARNING_MAX_SCORE sends no warning`` () = task {
+        do! setSpamWarning true
+
+        // Same probe-then-pin approach as the at/above-cutoff test, but this time the cutoff is
+        // pinned to the *exact* observed score (round-trippable via .NET's default double
+        // ToString()), exercising the strict `<` boundary rather than a margin below it.
+        do! fixture.SetBotSetting("SPAM_WARNING_MAX_SCORE", "999")
+        do! fixture.ReloadSettings()
+        let probeMsg = Tg.quickMsg(chat = fixture.ChatsToMonitor[0], text = "2222222", from = Tg.user())
+        let! _ = fixture.SendMessage probeMsg
+        let! scoreOpt = fixture.GetMlScore probeMsg.Message.Value
+        let score =
+            match scoreOpt with
+            | Some s -> s
+            | None -> failwith "Sanity: probe message should have been ML-scored"
+
+        do! fixture.SetBotSetting("SPAM_WARNING_MAX_SCORE", string score)
+        do! fixture.ReloadSettings()
+        let user = Tg.user()
+        do! fixture.ClearFakeCalls()
+        let msgUpdate = Tg.quickMsg(chat = fixture.ChatsToMonitor[0], text = "2222222", from = user)
+        let! _ = fixture.SendMessage msgUpdate
+
+        let! msgDeleted = fixture.MessageIsAutoDeleted msgUpdate.Message.Value
+        Assert.True(msgDeleted, "Sanity: message should still be auto-deleted at the boundary")
+
+        let! calls = fixture.GetFakeCalls "sendMessage"
+        Assert.False(
+            calls |> Array.exists (fun c -> c.Body.Contains $"\"receiver_user_id\":{user.Id}"),
+            "score == SPAM_WARNING_MAX_SCORE must not warn -- the cutoff is a strict less-than")
+    }
+
     [<Fact>]
     let ``Flag OFF (default): no warning is sent for the same scenario`` () = task {
         do! setSpamWarning false
@@ -84,11 +152,12 @@ type SpamWarningMlTests(fixture: MlEnabledVahterTestContainers, _unused: MlAwait
             "a deletion that triggers total-ban must not also send an ephemeral warning")
     }
 
-    // Restore the flag to its default after every test.
+    // Restore the flag and cutoff to their defaults after every test.
     interface IAsyncDisposable with
         member _.DisposeAsync() =
             ValueTask(task {
                 do! fixture.SetBotSetting("SPAM_WARNING_ENABLED", "false")
+                do! fixture.SetBotSetting("SPAM_WARNING_MAX_SCORE", "3.0")
                 do! fixture.ReloadSettings()
             } :> Task)