fix(desktop): mark the truncated head of a bot group-chat turn delta

apps/desktop/src/plugins/hermes-bots/group-round-members.ts

@@ -3,7 +3,6 @@ import { recordGroupActivity } from './group-activity'
 import {
   $groupChats,
   appendGroupChatEntry,
-  GROUP_CHAT_HISTORY_LIMIT,
   GROUP_CHAT_MAX_CONTINUATIONS,
   GROUP_CHAT_MAX_MESSAGES,
   groupThreadOf,
@@ -12,7 +11,7 @@ import {
 } from './group-chat'
 import type { GroupChatRoom } from './group-chat'
 import { groupMemberKey } from './group-membership'
-import { buildGroupChatTurnPrompt, formatGroupChatLine } from './group-round-prompt'
+import { buildGroupChatTurnPrompt, formatGroupDeltaLines } from './group-round-prompt'
 import { isGroupPassText, runGroupChatMemberTurn } from './group-turns'
 import type { Attachment, GroupMember, GroupMessage } from './types'
 
@@ -94,7 +93,7 @@ function prepareGroupRoundMember(context: GroupRoundMemberContext, member: Group
     groupName: context.group,
     members,
     viewer: member,
-    deltaLines: delta.slice(-GROUP_CHAT_HISTORY_LIMIT).map((e: GroupMessage) => formatGroupChatLine(e, member, context.group))
+    deltaLines: formatGroupDeltaLines(delta, member, context.group)
   })
 
   // Images riding this delta (user attachments — member entries don't

apps/desktop/src/plugins/hermes-bots/group-round-prompt.ts

@@ -1,5 +1,5 @@
 import { botMentionTag } from './data'
-import { groupSpeakerLabel } from './group-chat'
+import { GROUP_CHAT_HISTORY_LIMIT, groupSpeakerLabel } from './group-chat'
 import { groupMemberKey } from './group-membership'
 import type { GroupMember, GroupMessage, GroupMessageAuthor } from './types'
 
@@ -50,6 +50,23 @@ export function formatGroupChatLine(entry: GroupMessage, viewer: GroupChatLineVi
   return `${groupSpeakerLabel(entry.from.name, group)}${suffix}${source}: ${relabelMemberControlFrames(entry.text)}${attached}`
 }
 
+/** #114341: a member's turn renders only the last GROUP_CHAT_HISTORY_LIMIT
+ *  delta lines while the watermark commit advances past the whole tail, so
+ *  the head of an over-long delta is never delivered on any later turn
+ *  either. Mark the cut — without it a member has no way to know its view
+ *  of the room is partial (typically missing the very user instruction
+ *  that started the exchange). */
+export function formatGroupDeltaLines(delta: GroupMessage[], viewer: GroupChatLineViewer, group?: null | string) {
+  const omitted = delta.length - GROUP_CHAT_HISTORY_LIMIT
+  const lines = delta.slice(-GROUP_CHAT_HISTORY_LIMIT).map(entry => formatGroupChatLine(entry, viewer, group))
+
+  if (omitted > 0) {
+    lines.unshift(`… ${omitted} earlier room message${omitted === 1 ? '' : 's'} omitted since your last turn`)
+  }
+
+  return lines
+}
+
 function viewerNameOf(viewer: GroupChatLineViewer): string {
   return typeof viewer === 'string' ? viewer : viewer?.name || ''
 }

apps/desktop/src/plugins/hermes-bots/group-rounds.test.ts

@@ -625,6 +625,49 @@ describe('turn prompt', () => {
     expect(prompt).toMatch(/never thin out real content/i)
     expect(prompt).toMatch(/Keep chatter short/i)
   })
+
+  // #114341: the rendered window is capped at GROUP_CHAT_HISTORY_LIMIT while
+  // the watermark commit advances past the whole tail — the head of an
+  // over-long delta is never delivered on any later turn either, so the cut
+  // has to be visible in the prompt.
+  it('marks the head of an over-long delta as omitted', async () => {
+    await loadRoom()
+    const { formatGroupDeltaLines } = await import('./group-round-prompt')
+    const { GROUP_CHAT_HISTORY_LIMIT } = await import('./group-chat')
+
+    const delta: GroupMessage[] = Array.from({ length: GROUP_CHAT_HISTORY_LIMIT + 6 }, (_, i) => ({
+      at: i,
+      from: { kind: 'user', name: 'User' },
+      id: `m${i}`,
+      text: `line ${i}`
+    }))
+
+    const lines = formatGroupDeltaLines(delta, 'builder', null)
+
+    expect(lines).toHaveLength(GROUP_CHAT_HISTORY_LIMIT + 1)
+    expect(lines[0]).toBe('… 6 earlier room messages omitted since your last turn')
+    expect(lines[1]).toContain('line 6')
+    expect(lines.at(-1)).toContain(`line ${GROUP_CHAT_HISTORY_LIMIT + 5}`)
+  })
+
+  it('adds no omission marker when the delta fits the window', async () => {
+    await loadRoom()
+    const { formatGroupDeltaLines } = await import('./group-round-prompt')
+    const { GROUP_CHAT_HISTORY_LIMIT } = await import('./group-chat')
+
+    const delta: GroupMessage[] = Array.from({ length: GROUP_CHAT_HISTORY_LIMIT }, (_, i) => ({
+      at: i,
+      from: { kind: 'user', name: 'User' },
+      id: `m${i}`,
+      text: `line ${i}`
+    }))
+
+    const lines = formatGroupDeltaLines(delta, 'builder', null)
+
+    expect(lines).toHaveLength(GROUP_CHAT_HISTORY_LIMIT)
+    expect(lines.every(line => !line.includes('omitted'))).toBe(true)
+    expect(lines[0]).toContain('line 0')
+  })
 })
 
 describe('attachments', () => {