fix: remove ineffective duplicate attachment cleanup

Keep deletion on the existing IPC attachment cleanup path; remove an unused callback wired to the wrong coordinator and a nonexistent blob-store method. Verified focused conversation deletion test and git diff --check.

desktop/src/workspace/local-workspace-conversations.cjs

@@ -23,7 +23,6 @@ class LocalWorkspaceConversations {
     this.isGroupBusy = options.isGroupBusy
     this.clearSessionState = options.clearSessionState
     this.runLedger = options.runLedger
-    this.discardAttachments = options.discardAttachments
     this.agentLabel = options.agentLabel
     this.createId = options.createId
     this.now = options.now
@@ -153,17 +152,11 @@ class LocalWorkspaceConversations {
     if (!state.groups.some(group => group.id === groupId)) {
       throw new Error('LOCAL_GROUP_NOT_FOUND')
     }
-    const attachmentIds = [...new Set(state.messages
-      .filter(message => message.groupId === groupId)
-      .flatMap(message => Array.isArray(message.attachments) ? message.attachments : [])
-      .map(attachment => attachment?.id)
-      .filter(id => typeof id === 'string'))]
     this.commit(() => {
       this.clearSessionState(groupId)
       state.groups = state.groups.filter(group => group.id !== groupId)
       state.messages = state.messages.filter(message => message.groupId !== groupId)
     }, () => this.runLedger?.deleteGroup?.(groupId))
-    this.discardAttachments?.(attachmentIds)
   }
 
   deleteMessage(groupId, messageId) {

desktop/src/workspace/local-workspace.cjs

@@ -217,13 +217,6 @@ class LocalWorkspace extends EventEmitter {
     })
     this.runLedgerCoordinator = new LocalWorkspaceRunLedger({
       runLedger: this.runLedger,
-      discardAttachments: ids => {
-        const referenced = new Set(this.state.messages.flatMap(message => (
-          Array.isArray(message.attachments) ? message.attachments : []
-        )).map(attachment => attachment?.id).filter(Boolean))
-        const orphaned = ids.filter(id => !referenced.has(id))
-        if (orphaned.length) this.contentBlobStore.discard(orphaned)
-      },
       state: () => this.state,
       save: () => this.save(),
       createId: () => this.createId(),