Fix bot kwargs and scoot over unread button to middle

app/fanout/bot_exec.py

@@ -85,25 +85,38 @@ def _analyze_bot_signature(bot_func_or_sig) -> BotCallPlan:
         )
 
     positional_capacity = len(positional_params)
-    if not has_varargs and positional_capacity < 8:
-        raise ValueError(
-            "Bot function must accept at least 8 positional parameters before optional extras"
-        )
-
     base_args = [object()] * 8
+    base_keyword_args: dict[str, object] = {
+        "sender_name": object(),
+        "sender_key": object(),
+        "message_text": object(),
+        "is_dm": object(),
+        "channel_key": object(),
+        "channel_name": object(),
+        "sender_timestamp": object(),
+        "path": object(),
+    }
     candidate_specs: list[tuple[str, list[object], dict[str, object]]] = []
-    if has_kwargs or explicit_optional_names:
+    keyword_args = dict(base_keyword_args)
+    if has_kwargs or "is_outgoing" in params:
+        keyword_args["is_outgoing"] = False
+    if has_kwargs or "path_bytes_per_hop" in params:
+        keyword_args["path_bytes_per_hop"] = 1
+    candidate_specs.append(("keyword", [], keyword_args))
+
+    if not has_kwargs and explicit_optional_names:
         kwargs: dict[str, object] = {}
         if has_kwargs or "is_outgoing" in params:
             kwargs["is_outgoing"] = False
         if has_kwargs or "path_bytes_per_hop" in params:
             kwargs["path_bytes_per_hop"] = 1
-        candidate_specs.append(("keyword", base_args, kwargs))
-    else:
-        if has_varargs or positional_capacity >= 10:
-            candidate_specs.append(("positional_10", base_args + [False, 1], {}))
-        if has_varargs or positional_capacity >= 9:
-            candidate_specs.append(("positional_9", base_args + [False], {}))
+        candidate_specs.append(("mixed_keyword", base_args, kwargs))
+
+    if has_varargs or positional_capacity >= 10:
+        candidate_specs.append(("positional_10", base_args + [False, 1], {}))
+    if has_varargs or positional_capacity >= 9:
+        candidate_specs.append(("positional_9", base_args + [False], {}))
+    if has_varargs or positional_capacity >= 8:
         candidate_specs.append(("legacy", base_args, {}))
 
     for call_style, args, kwargs in candidate_specs:
@@ -111,7 +124,7 @@ def _analyze_bot_signature(bot_func_or_sig) -> BotCallPlan:
             sig.bind(*args, **kwargs)
         except TypeError:
             continue
-        if call_style == "keyword":
+        if call_style in {"keyword", "mixed_keyword"}:
             return BotCallPlan(call_style="keyword", keyword_args=tuple(kwargs.keys()))
         return BotCallPlan(call_style=call_style)
 
@@ -141,6 +154,7 @@ def execute_bot_code(
 
     The code should define a function:
     `bot(sender_name, sender_key, message_text, is_dm, channel_key, channel_name, sender_timestamp, path, is_outgoing, path_bytes_per_hop)`
+    or use named parameters / `**kwargs`.
     that returns either None (no response), a string (single response message),
     or a list of strings (multiple messages sent in order).
 
@@ -221,21 +235,27 @@ def execute_bot_code(
             )
         elif call_plan.call_style == "keyword":
             keyword_args: dict[str, Any] = {}
+            if "sender_name" in call_plan.keyword_args:
+                keyword_args["sender_name"] = sender_name
+            if "sender_key" in call_plan.keyword_args:
+                keyword_args["sender_key"] = sender_key
+            if "message_text" in call_plan.keyword_args:
+                keyword_args["message_text"] = message_text
+            if "is_dm" in call_plan.keyword_args:
+                keyword_args["is_dm"] = is_dm
+            if "channel_key" in call_plan.keyword_args:
+                keyword_args["channel_key"] = channel_key
+            if "channel_name" in call_plan.keyword_args:
+                keyword_args["channel_name"] = channel_name
+            if "sender_timestamp" in call_plan.keyword_args:
+                keyword_args["sender_timestamp"] = sender_timestamp
+            if "path" in call_plan.keyword_args:
+                keyword_args["path"] = path
             if "is_outgoing" in call_plan.keyword_args:
                 keyword_args["is_outgoing"] = is_outgoing
             if "path_bytes_per_hop" in call_plan.keyword_args:
                 keyword_args["path_bytes_per_hop"] = path_bytes_per_hop
-            result = bot_func(
-                sender_name,
-                sender_key,
-                message_text,
-                is_dm,
-                channel_key,
-                channel_name,
-                sender_timestamp,
-                path,
-                **keyword_args,
-            )
+            result = bot_func(**keyword_args)
         else:
             result = bot_func(
                 sender_name,

frontend/src/components/MessageList.tsx

@@ -835,45 +835,43 @@ export function MessageList({
       </div>
 
       {/* Scroll to bottom button */}
-      {(showJumpToUnread || showScrollToBottom) && (
-        <div className="absolute bottom-4 right-4 flex items-center gap-2">
-          {showJumpToUnread && (
-            <button
-              type="button"
-              onClick={() => {
-                unreadMarkerRef.current?.scrollIntoView?.({ block: 'center' });
-                setShowJumpToUnread(false);
-              }}
-              className="h-9 rounded-full bg-card hover:bg-accent border border-border px-3 text-sm font-medium shadow-lg transition-all hover:scale-105 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring"
-            >
-              Jump to unread
-            </button>
-          )}
-          {showScrollToBottom && (
-            <button
-              onClick={scrollToBottom}
-              className="w-9 h-9 rounded-full bg-card hover:bg-accent border border-border flex items-center justify-center shadow-lg transition-all hover:scale-105 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring"
-              title="Scroll to bottom"
-              aria-label="Scroll to bottom"
-            >
-              <svg
-                xmlns="http://www.w3.org/2000/svg"
-                width="18"
-                height="18"
-                viewBox="0 0 24 24"
-                fill="none"
-                stroke="currentColor"
-                strokeWidth="2"
-                strokeLinecap="round"
-                strokeLinejoin="round"
-                className="text-muted-foreground"
-              >
-                <polyline points="6 9 12 15 18 9" />
-              </svg>
-            </button>
-          )}
+      {showJumpToUnread && (
+        <div className="pointer-events-none absolute bottom-4 left-1/2 -translate-x-1/2">
+          <button
+            type="button"
+            onClick={() => {
+              unreadMarkerRef.current?.scrollIntoView?.({ block: 'center' });
+              setShowJumpToUnread(false);
+            }}
+            className="pointer-events-auto h-9 rounded-full bg-card hover:bg-accent border border-border px-3 text-sm font-medium shadow-lg transition-all hover:scale-105 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring"
+          >
+            Jump to unread
+          </button>
         </div>
       )}
+      {showScrollToBottom && (
+        <button
+          onClick={scrollToBottom}
+          className="absolute bottom-4 right-4 w-9 h-9 rounded-full bg-card hover:bg-accent border border-border flex items-center justify-center shadow-lg transition-all hover:scale-105 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring"
+          title="Scroll to bottom"
+          aria-label="Scroll to bottom"
+        >
+          <svg
+            xmlns="http://www.w3.org/2000/svg"
+            width="18"
+            height="18"
+            viewBox="0 0 24 24"
+            fill="none"
+            stroke="currentColor"
+            strokeWidth="2"
+            strokeLinecap="round"
+            strokeLinejoin="round"
+            className="text-muted-foreground"
+          >
+            <polyline points="6 9 12 15 18 9" />
+          </svg>
+        </button>
+      )}
 
       {/* Path modal */}
       {selectedPath && (

tests/test_bot.py

@@ -373,6 +373,30 @@ def bot(sender_name, sender_key, message_text, is_dm, channel_key, channel_name,
         )
         assert result == "bytes=2"
 
+    def test_pure_kwargs_bot_receives_core_fields_and_optional_extras(self):
+        """Pure **kwargs bots are first-class and receive the full payload by keyword."""
+        code = """
+def bot(**kwargs):
+    return (
+        f"{kwargs.get('sender_name')}|{kwargs.get('message_text')}|"
+        f"{kwargs.get('is_outgoing')}|{kwargs.get('path_bytes_per_hop')}"
+    )
+"""
+        result = execute_bot_code(
+            code=code,
+            sender_name="Alice",
+            sender_key="abc123",
+            message_text="Hi",
+            is_dm=True,
+            channel_key=None,
+            channel_name=None,
+            sender_timestamp=None,
+            path="aabb",
+            is_outgoing=True,
+            path_bytes_per_hop=2,
+        )
+        assert result == "Alice|Hi|True|2"
+
     def test_channel_message_with_none_sender_key(self):
         """Channel messages correctly pass None for sender_key."""
         code = """
@@ -489,6 +513,12 @@ class TestBotCodeValidation:
             }
         )
 
+    def test_pure_kwargs_code_passes(self):
+        """Pure **kwargs bots are valid."""
+        from app.routers.fanout import _validate_bot_config
+
+        _validate_bot_config({"code": "def bot(**kwargs):\n    return kwargs.get('message_text')"})
+
     def test_syntax_error_raises(self):
         """Syntax error in code raises HTTPException."""
         from fastapi import HTTPException