diff --git a/packages/ui/src/components/message-section.tsx b/packages/ui/src/components/message-section.tsx
index a4900c8a..baa012b9 100644
--- a/packages/ui/src/components/message-section.tsx
+++ b/packages/ui/src/components/message-section.tsx
@@ -103,6 +103,42 @@ export default function MessageSection(props: MessageSectionProps) {
   let deleteMenuRef: HTMLDivElement | undefined
   let deleteMenuButtonRef: HTMLButtonElement | undefined
 
+  // Deletion is only allowed for messages/tool parts that occur AFTER the most
+  // recent compaction. Compaction effectively resets the stored context; deleting
+  // earlier items would not reliably reflect what the model sees.
+  const messageIndexById = createMemo(() => {
+    const ids = messageIds()
+    const map = new Map<string, number>()
+    for (let i = 0; i < ids.length; i++) {
+      map.set(ids[i], i)
+    }
+    return map
+  })
+
+  const lastCompactionIndex = createMemo(() => {
+    // Depend on a single session revision signal (not every message/part read)
+    // to keep reactive overhead small.
+    sessionRevision()
+    return untrack(() => store().getLastCompactionMessageIndex(props.sessionId))
+  })
+
+  const deletableStartIndex = createMemo(() => {
+    const idx = lastCompactionIndex()
+    return idx === -1 ? 0 : idx + 1
+  })
+
+  const deletableMessageIds = createMemo(() => {
+    const ids = messageIds()
+    const start = deletableStartIndex()
+    return new Set(ids.slice(start))
+  })
+
+  const isMessageDeletable = (messageId: string): boolean => {
+    const idx = messageIndexById().get(messageId)
+    if (idx === undefined) return false
+    return idx >= deletableStartIndex()
+  }
+
   // Build the message group for a segment.
   // Tool calls belong to the same assistant turn (between user messages).
   // Only assistant badges trigger group selection; user/tool badges are standalone.
@@ -132,12 +168,17 @@ export default function MessageSection(props: MessageSectionProps) {
   }
 
   const handleToggleTimelineSelection = (id: string) => {
-    setLastSelectionAnchorId(id)
     const segments = timelineSegments()
     const segmentIndex = segments.findIndex((s) => s.id === id)
     if (segmentIndex === -1) return
     const segment = segments[segmentIndex]
 
+    if (!isMessageDeletable(segment.messageId)) {
+      return
+    }
+
+    setLastSelectionAnchorId(id)
+
     if (selectionMode() === "tools" && segment.type !== "tool") {
       return
     }
@@ -177,11 +218,16 @@ export default function MessageSection(props: MessageSectionProps) {
   }
 
   const handleLongPressTimelineSelection = (segment: TimelineSegment) => {
-    setLastSelectionAnchorId(segment.id)
     const segments = timelineSegments()
     const segmentIndex = segments.findIndex((s) => s.id === segment.id)
     if (segmentIndex === -1) return
 
+    if (!isMessageDeletable(segment.messageId)) {
+      return
+    }
+
+    setLastSelectionAnchorId(segment.id)
+
     if (selectionMode() === "tools" && segment.type !== "tool") {
       return
     }
@@ -227,8 +273,8 @@ export default function MessageSection(props: MessageSectionProps) {
     const end = Math.max(anchorIndex, targetIndex)
 
     const rangeSegments = selectionMode() === "tools"
-      ? segments.slice(start, end + 1).filter((s) => s.type === "tool")
-      : segments.slice(start, end + 1)
+      ? segments.slice(start, end + 1).filter((s) => s.type === "tool" && isMessageDeletable(s.messageId))
+      : segments.slice(start, end + 1).filter((s) => isMessageDeletable(s.messageId))
     // Range selection replaces current selection so it can grow or shrink.
     setSelectedTimelineIds(new Set(rangeSegments.map((segment) => segment.id)))
   }
@@ -242,7 +288,11 @@ export default function MessageSection(props: MessageSectionProps) {
     setSelectionMode(mode)
     if (mode !== "tools") return
     const segments = timelineSegments()
-    const toolIds = new Set(segments.filter((segment) => segment.type === "tool").map((segment) => segment.id))
+    const toolIds = new Set(
+      segments
+        .filter((segment) => segment.type === "tool" && isMessageDeletable(segment.messageId))
+        .map((segment) => segment.id),
+    )
     setSelectedTimelineIds((prev) => {
       if (prev.size === 0) return prev
       const next = new Set([...prev].filter((id) => toolIds.has(id)))
@@ -345,7 +395,8 @@ export default function MessageSection(props: MessageSectionProps) {
   const deleteMessageIds = createMemo(() => selectedForDeletion())
   const deleteToolParts = createMemo(() => {
     const messageIds = deleteMessageIds()
-    return selectedToolParts().filter((entry) => !messageIds.has(entry.messageId))
+    const allowed = deletableMessageIds()
+    return selectedToolParts().filter((entry) => allowed.has(entry.messageId) && !messageIds.has(entry.messageId))
   })
   const isDeleteMode = createMemo(() => deleteMessageIds().size > 0 || deleteToolParts().length > 0)
   const selectedDeleteCount = createMemo(() => deleteMessageIds().size + deleteToolParts().length)
@@ -410,6 +461,7 @@ export default function MessageSection(props: MessageSectionProps) {
 
   const setMessageSelectedForDeletion = (messageId: string, selected: boolean) => {
     if (!messageId) return
+    if (!isMessageDeletable(messageId)) return
     setSelectedForDeletion((prev) => {
       const next = new Set(prev)
       if (selected) {
@@ -440,18 +492,20 @@ export default function MessageSection(props: MessageSectionProps) {
     const affectedMessageIds = new Set<string>()
     for (const segId of timelineIds) {
       const segment = segmentById.get(segId)
-      if (segment && segment.type !== "tool") affectedMessageIds.add(segment.messageId)
+      if (segment && segment.type !== "tool" && isMessageDeletable(segment.messageId)) {
+        affectedMessageIds.add(segment.messageId)
+      }
     }
     setSelectedForDeletion(affectedMessageIds)
   })
 
   const selectAllForDeletion = () => {
-    const allMessageIds = messageIds()
+    const allMessageIds = [...deletableMessageIds()]
     setSelectedForDeletion(new Set<string>(allMessageIds))
     // Also select all timeline segments — tool visibility is handled by
     // isSelectionActive() in isHidden(), no expand/collapse needed.
     const segments = timelineSegments()
-    setSelectedTimelineIds(new Set(segments.map((s) => s.id)))
+    setSelectedTimelineIds(new Set(segments.filter((s) => isMessageDeletable(s.messageId)).map((s) => s.id)))
   }
 
   const deleteSelectedMessages = async () => {
@@ -459,11 +513,13 @@ export default function MessageSection(props: MessageSectionProps) {
     const toolParts = deleteToolParts()
     if (selected.size === 0 && toolParts.length === 0) return
 
+    const allowed = deletableMessageIds()
+
     const idsInSessionOrder = messageIds()
     const toDelete: string[] = []
     for (let idx = idsInSessionOrder.length - 1; idx >= 0; idx -= 1) {
       const id = idsInSessionOrder[idx]
-      if (selected.has(id)) {
+      if (allowed.has(id) && selected.has(id)) {
         toDelete.push(id)
       }
     }
@@ -473,6 +529,7 @@ export default function MessageSection(props: MessageSectionProps) {
         await deleteMessage(props.instanceId, props.sessionId, messageId)
       }
       for (const { messageId, partId } of toolParts) {
+        if (!allowed.has(messageId)) continue
         await deleteMessagePart(props.instanceId, props.sessionId, messageId, partId)
       }
       clearDeleteMode()
@@ -1457,6 +1514,7 @@ export default function MessageSection(props: MessageSectionProps) {
               onClearSelection={handleClearTimelineSelection}
               selectedIds={selectedTimelineIds}
               expandedMessageIds={expandedMessageIds}
+              deletableMessageIds={deletableMessageIds}
               activeSegmentId={activeSegmentId()}
               instanceId={props.instanceId}
               sessionId={props.sessionId}
diff --git a/packages/ui/src/components/message-timeline.tsx b/packages/ui/src/components/message-timeline.tsx
index f5da1ab5..27f82e8b 100644
--- a/packages/ui/src/components/message-timeline.tsx
+++ b/packages/ui/src/components/message-timeline.tsx
@@ -36,6 +36,9 @@ interface MessageTimelineProps {
   onClearSelection?: () => void
   selectedIds?: Accessor<Set<string>>
   expandedMessageIds?: Accessor<Set<string>>
+  // Optional: restrict histogram/xray overlay to only show for these message ids.
+  // Used to hide ribs for messages before the last compaction.
+  deletableMessageIds?: Accessor<Set<string>>
   activeSegmentId?: string | null
   instanceId: string
   sessionId: string
@@ -319,6 +322,12 @@ const MessageTimeline: Component<MessageTimelineProps> = (props) => {
   const showTools = () => props.showToolSegments ?? true
   const deleteHover = () => props.deleteHover?.() ?? { kind: "none" as const }
 
+  const isHistogramEligible = (segment: TimelineSegment): boolean => {
+    const allowed = props.deletableMessageIds?.()
+    if (!allowed) return true
+    return allowed.has(segment.messageId)
+  }
+
   const registerButtonRef = (segmentId: string, element: HTMLButtonElement | null) => {
     if (element) {
       buttonRefs.set(segmentId, element)
@@ -396,6 +405,14 @@ const MessageTimeline: Component<MessageTimelineProps> = (props) => {
   // --- Selection & histogram rib state ---
   const isSelectionActive = createMemo(() => (props.selectedIds?.().size ?? 0) > 0)
 
+  // Segments eligible for xray ribs. We intentionally exclude messages before
+  // the last compaction (when provided by the parent) to avoid misleading token
+  // weights for content that's no longer in context.
+  const xraySegments = createMemo(() => {
+    if (!isSelectionActive()) return [] as TimelineSegment[]
+    return props.segments.filter((segment) => isHistogramEligible(segment))
+  })
+
   // Stable layout offsets per badge (relative to scroll content), recomputed only
   // on activation, resize, or expansion — NOT on every scroll frame.
   const [badgeOffsets, setBadgeOffsets] = createSignal<Record<string, { layoutTop: number; height: number }>>({})
@@ -495,7 +512,7 @@ const MessageTimeline: Component<MessageTimelineProps> = (props) => {
 
     // O(n) pre-pass: group segments by messageId for O(1) lookups below.
     const segmentsByMessageId = new Map<string, TimelineSegment[]>()
-    for (const s of props.segments) {
+    for (const s of xraySegments()) {
       let list = segmentsByMessageId.get(s.messageId)
       if (!list) {
         list = []
@@ -540,7 +557,7 @@ const MessageTimeline: Component<MessageTimelineProps> = (props) => {
   const aggregateTokensByMessageId = createMemo(() => {
     const chars = liveSegmentChars()
     const result: Record<string, number> = {}
-    for (const s of props.segments) {
+    for (const s of xraySegments()) {
       result[s.messageId] = (result[s.messageId] ?? 0) + (chars[s.id] ?? s.totalChars)
     }
     for (const id of Object.keys(result)) {
@@ -574,7 +591,7 @@ const MessageTimeline: Component<MessageTimelineProps> = (props) => {
 
   const maxTokens = createMemo(() => {
     let max = 0
-    for (const s of props.segments) {
+    for (const s of xraySegments()) {
       const tokens = getSegmentTokens(s)
       if (tokens > max) max = tokens
     }
@@ -881,7 +898,7 @@ const MessageTimeline: Component<MessageTimelineProps> = (props) => {
       <Portal>
         <Show when={isSelectionActive()}>
           <div class="message-timeline-xray-overlay" style={{ "--max-rib-width": `${maxRibWidth()}px`, "clip-path": `inset(${clipBounds().top}px 0 ${(typeof window !== "undefined" ? window.innerHeight : 0) - clipBounds().bottom}px 0)` }}>
-            <For each={props.segments}>
+            <For each={xraySegments()}>
               {(segment) => {
                 // Derive screen position from stable layout offset + scroll state.
                 // Only arithmetic — no DOM reads per segment per scroll frame.
diff --git a/packages/ui/src/stores/message-v2/instance-store.ts b/packages/ui/src/stores/message-v2/instance-store.ts
index c7ed2f93..bc2bb1f3 100644
--- a/packages/ui/src/stores/message-v2/instance-store.ts
+++ b/packages/ui/src/stores/message-v2/instance-store.ts
@@ -218,6 +218,9 @@ export interface InstanceMessageStore {
   getScrollSnapshot: (sessionId: string, scope: string) => ScrollSnapshot | undefined
   getSessionRevision: (sessionId: string) => number
   getSessionMessageIds: (sessionId: string) => string[]
+  // Index of the most recent message in the session that contains a compaction part.
+  // Returns -1 if there has been no compaction.
+  getLastCompactionMessageIndex: (sessionId: string) => number
   getMessage: (messageId: string) => MessageRecord | undefined
   getLatestTodoSnapshot: (sessionId: string) => LatestTodoSnapshot | undefined
   clearSession: (sessionId: string) => void
@@ -231,6 +234,24 @@ export function createInstanceMessageStore(instanceId: string, hooks?: MessageSt
 
   const messageInfoCache = new Map<string, MessageInfo>()
 
+  function getLastCompactionMessageIndex(sessionId: string): number {
+    if (!sessionId) return -1
+    const ids = state.sessions[sessionId]?.messageIds ?? []
+    // Scan from the end: we only care about the most recent compaction.
+    for (let i = ids.length - 1; i >= 0; i--) {
+      const messageId = ids[i]
+      const record = state.messages[messageId]
+      if (!record || !Array.isArray(record.partIds) || record.partIds.length === 0) continue
+      for (const partId of record.partIds) {
+        const part = record.parts[partId]?.data
+        if ((part as any)?.type === "compaction") {
+          return i
+        }
+      }
+    }
+    return -1
+  }
+
   function isCompletedTodoPart(part: ClientPart | undefined): boolean {
     if (!part || (part as any).type !== "tool") {
       return false
@@ -1138,8 +1159,8 @@ export function createInstanceMessageStore(instanceId: string, hooks?: MessageSt
  
    function clearInstance() {
      messageInfoCache.clear()
-     setState(reconcile(createInitialState(instanceId)))
-   }
+      setState(reconcile(createInitialState(instanceId)))
+    }
  
     return {
 
@@ -1172,10 +1193,11 @@ export function createInstanceMessageStore(instanceId: string, hooks?: MessageSt
      setScrollSnapshot,
      getScrollSnapshot,
      getSessionRevision: getSessionRevisionValue,
-      getSessionMessageIds: (sessionId: string) => state.sessions[sessionId]?.messageIds ?? [],
-      getMessage: (messageId: string) => state.messages[messageId],
-      getLatestTodoSnapshot: (sessionId: string) => state.latestTodos[sessionId],
-      clearSession,
-      clearInstance,
+       getSessionMessageIds: (sessionId: string) => state.sessions[sessionId]?.messageIds ?? [],
+       getLastCompactionMessageIndex,
+       getMessage: (messageId: string) => state.messages[messageId],
+       getLatestTodoSnapshot: (sessionId: string) => state.latestTodos[sessionId],
+       clearSession,
+       clearInstance,
     }
   }