fix: Improve autoscroll to bottom

toju-app/src/app/domains/chat/README.md

@@ -14,7 +14,8 @@ chat/
 ├── domain/
 │   └── rules/
 │       ├── message.rules.ts                     canEditMessage, normaliseDeletedMessage, getMessageTimestamp
-│       └── message-sync.rules.ts               Inventory-based sync: chunkArray, findMissingIds, limits
+│       ├── message-sync.rules.ts               Inventory-based sync: chunkArray, findMissingIds, limits
+│       └── auto-scroll.rules.ts                resolveAutoScrollBehavior: instant on channel switch, smooth for live msgs
 │
 ├── feature/
 │   ├── chat-messages/                       Main chat view (orchestrates composer, list, overlays)

toju-app/src/app/domains/chat/domain/rules/auto-scroll.rules.spec.ts

@@ -0,0 +1,50 @@
+import { resolveAutoScrollBehavior } from './auto-scroll.rules';
+
+describe('resolveAutoScrollBehavior', () => {
+  const base = {
+    newMessages: true,
+    forceLocalSend: false,
+    distanceFromBottom: 0,
+    withinInitialGrace: false
+  };
+
+  it('does nothing when no new messages arrived', () => {
+    expect(resolveAutoScrollBehavior({ ...base, newMessages: false })).toBe('none');
+  });
+
+  it('jumps instantly for the local user own send regardless of grace', () => {
+    expect(resolveAutoScrollBehavior({ ...base, forceLocalSend: true })).toBe('instant');
+    expect(
+      resolveAutoScrollBehavior({ ...base, forceLocalSend: true, withinInitialGrace: true })
+    ).toBe('instant');
+  });
+
+  it('jumps instantly when near bottom while settling after a channel switch', () => {
+    expect(
+      resolveAutoScrollBehavior({ ...base, distanceFromBottom: 40, withinInitialGrace: true })
+    ).toBe('instant');
+  });
+
+  it('animates smoothly for live messages once settled and near bottom', () => {
+    expect(
+      resolveAutoScrollBehavior({ ...base, distanceFromBottom: 40, withinInitialGrace: false })
+    ).toBe('smooth');
+  });
+
+  it('shows the indicator (no scroll) when far from the bottom', () => {
+    expect(resolveAutoScrollBehavior({ ...base, distanceFromBottom: 800 })).toBe('none');
+    expect(
+      resolveAutoScrollBehavior({ ...base, distanceFromBottom: 800, withinInitialGrace: true })
+    ).toBe('none');
+  });
+
+  it('honours a custom sticky threshold', () => {
+    expect(
+      resolveAutoScrollBehavior({ ...base, distanceFromBottom: 150, stickyThreshold: 100 })
+    ).toBe('none');
+
+    expect(
+      resolveAutoScrollBehavior({ ...base, distanceFromBottom: 80, stickyThreshold: 100 })
+    ).toBe('smooth');
+  });
+});

toju-app/src/app/domains/chat/domain/rules/auto-scroll.rules.ts

@@ -0,0 +1,44 @@
+/** Behaviour the message list should apply when new messages arrive. */
+export type AutoScrollBehavior = 'smooth' | 'instant' | 'none';
+
+export interface AutoScrollDecisionInput {
+  /** Whether the message count grew since the last render. */
+  readonly newMessages: boolean;
+  /** Forced jump for the local user's own just-sent message. */
+  readonly forceLocalSend: boolean;
+  /** Pixels from the bottom of the scroll container. */
+  readonly distanceFromBottom: number;
+  /**
+   * True while the conversation is still settling after a channel/server
+   * switch (initial scroll + async embed/image height changes). During this
+   * window we jump instantly so we never animate to the wrong position.
+   */
+  readonly withinInitialGrace: boolean;
+  /** Distance threshold under which the list is considered stuck to bottom. */
+  readonly stickyThreshold?: number;
+}
+
+/**
+ * Decides how the message list should react when the message count changes.
+ *
+ * - No new messages -> `none`.
+ * - Local user's own send -> `instant` (never animate your own message).
+ * - Near bottom during the post-switch settle window -> `instant` (so loading
+ *   a channel always lands at the bottom without a mid-chat smooth animation).
+ * - Near bottom afterwards -> `smooth` (live messages animate into view).
+ * - Far from bottom -> `none` (show the new-messages indicator instead).
+ */
+export function resolveAutoScrollBehavior(input: AutoScrollDecisionInput): AutoScrollBehavior {
+  if (!input.newMessages)
+    return 'none';
+
+  if (input.forceLocalSend)
+    return 'instant';
+
+  const threshold = input.stickyThreshold ?? 300;
+
+  if (input.distanceFromBottom > threshold)
+    return 'none';
+
+  return input.withinInitialGrace ? 'instant' : 'smooth';
+}

toju-app/src/app/domains/chat/feature/chat-messages/components/message-list/chat-message-list.component.ts

@@ -16,6 +16,7 @@ import {
 } from '@angular/core';
 import { Store } from '@ngrx/store';
 import { Attachment } from '../../../../../attachment';
+import { resolveAutoScrollBehavior } from '../../../../domain/rules/auto-scroll.rules';
 import { getMessageTimestamp } from '../../../../domain/rules/message.rules';
 import { Message, User } from '../../../../../../shared-kernel';
 import {
@@ -264,14 +265,22 @@ export class ChatMessageListComponent implements AfterViewChecked, OnDestroy {
     const forceLocalSendScroll = this.shouldForceLocalSendScroll();
 
     if (newMessages) {
-      if (forceLocalSendScroll || distanceFromBottom <= 300) {
+      const behavior = resolveAutoScrollBehavior({
+        newMessages,
+        forceLocalSend: forceLocalSendScroll,
+        distanceFromBottom,
+        withinInitialGrace: this.isWithinInitialScrollGrace()
+      });
+
+      if (behavior === 'instant') {
         if (forceLocalSendScroll) {
           this.clearLocalSendScrollPending();
-          this.scheduleScrollToBottomAfterRender(true);
-        } else {
-          this.scheduleScrollToBottomSmooth();
         }
 
+        this.scheduleScrollToBottomAfterRender(true);
+        this.showNewMessagesBar.set(false);
+      } else if (behavior === 'smooth') {
+        this.scheduleScrollToBottomSmooth();
         this.showNewMessagesBar.set(false);
       } else {
         queueMicrotask(() => this.showNewMessagesBar.set(true));
@@ -301,8 +310,12 @@ export class ChatMessageListComponent implements AfterViewChecked, OnDestroy {
         this.showNewMessagesBar.set(false);
         this.lastMessageCount = this.messages().length;
         this.scheduleCodeHighlight();
-      } else if (!this.loading()) {
-        this.initialScrollPending = false;
+      } else {
+        // No messages rendered yet for this conversation. Stay armed so the
+        // very first batch (cached or async-loaded) anchors to the bottom.
+        // For a genuinely empty conversation this flag simply stays true and
+        // is harmless: onMessagesChanged is gated on it, and the next
+        // ngAfterViewChecked with messages will perform the initial scroll.
         this.lastMessageCount = 0;
       }
 
@@ -560,6 +573,18 @@ export class ChatMessageListComponent implements AfterViewChecked, OnDestroy {
     return !!latestMessage && latestMessage.senderId === this.currentUserId();
   }
 
+  /**
+   * True while the conversation is still settling after a channel/server
+   * switch. The bottom-scroll watch is active during this window (initial
+   * scroll + async embed/image height changes), so we jump instantly instead
+   * of animating to avoid landing in the middle of the chat. The watch ends
+   * after the timeout or as soon as the user scrolls, after which live
+   * messages animate smoothly again.
+   */
+  private isWithinInitialScrollGrace(): boolean {
+    return this.bottomScrollObserver !== null;
+  }
+
   private getMessageDateTimestamp(message: Message): number {
     return message.timestamp || getMessageTimestamp(message);
   }