v2.1.0-provider-picker: BooCoder systemd migration + provider picker

- BooCoder moves from Docker to host systemd service (boocoder.service)
- Agent dispatch (ACP + PTY) switches from SSH to direct spawn/exec
- SSH helpers marked @deprecated (kept for one release cycle)
- Provider registry (5 providers: boocode, opencode, goose, claude, qwen)
- Agent probe with direct which/exec + model discovery (qwen settings, static claude models)
- GET /api/providers route with installed status, models, transport fallback
- ProviderPicker frontend component in CoderPane header
- External provider messages route through tasks row instead of inference enqueue
- Smart scroll: MessageList only auto-scrolls when near bottom (150px threshold)
- DB: available_agents gets models, label, transport columns
- Bug fix: loadContext SELECT includes allowed_read_paths
- Bug fix: cap hit sentinel inserted before buildMessagesPayload
- docker-compose.yml: boocoder service commented out, BOOCODER_URL env var added
- CLAUDE.md: updated docs for systemd, provider registry, JSONB gotcha, loadContext

apps/web/src/components/MessageList.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useMemo, useRef } from 'react';
+import { useCallback, useEffect, useMemo, useRef } from 'react';
 import type { Chat, Message } from '@/api/types';
 import { MessageBubble } from './MessageBubble';
 import { ToolCallGroup } from './ToolCallGroup';
@@ -142,13 +142,26 @@ function stampCapHits(items: RenderItem[]): RenderItem[] {
   });
 }
 
+const SCROLL_THRESHOLD_PX = 150;
+
 export function MessageList({ messages, sessionChats }: Props) {
   const endRef = useRef<HTMLDivElement>(null);
+  const scrollContainerRef = useRef<HTMLDivElement>(null);
+  const isNearBottomRef = useRef(true);
 
   const renderItems = useMemo(() => stampCapHits(group(flatten(messages))), [messages]);
 
+  const handleScroll = useCallback(() => {
+    const el = scrollContainerRef.current;
+    if (!el) return;
+    isNearBottomRef.current =
+      el.scrollHeight - el.scrollTop - el.clientHeight < SCROLL_THRESHOLD_PX;
+  }, []);
+
   useEffect(() => {
-    endRef.current?.scrollIntoView({ block: 'end' });
+    if (isNearBottomRef.current) {
+      endRef.current?.scrollIntoView({ block: 'end' });
+    }
   }, [messages]);
 
   if (messages.length === 0) {
@@ -160,7 +173,7 @@ export function MessageList({ messages, sessionChats }: Props) {
   }
 
   return (
-    <div className="flex-1 overflow-y-auto">
+    <div className="flex-1 overflow-y-auto" ref={scrollContainerRef} onScroll={handleScroll}>
       <div className="max-w-[1000px] mx-auto w-full px-6 py-4 space-y-4">
         {renderItems.map((item) => {
           if (item.kind === 'message') {