@@ -40,6 +40,9 @@ export class Subscription {
   private readonly abort = new AbortController()
   private readonly shellSnapshots = new Map<string, string>()
   private readonly toolStarts = new Set<string>()
+  // altimate_change start — ACP chunks cannot retract provisional compaction text
+  private readonly summaryMessages = new Set<string>()
+  // altimate_change end
   private readonly permission: ACPPermission.Handler
   private started = false
 
@@ -67,6 +70,15 @@ export class Subscription {
 
   async handle(event: Event) {
     switch (event.type) {
+      // altimate_change start — recovery clears summary before publishing its authoritative answer
+      case "message.updated": {
+        const message = event.properties.info
+        if (message.role !== "assistant") return
+        if (message.summary) this.summaryMessages.add(message.id)
+        else this.summaryMessages.delete(message.id)
+        return
+      }
+      // altimate_change end
       case "permission.asked":
         this.permission.handle(event)
         return
@@ -169,6 +181,9 @@ export class Subscription {
         : await this.fetchPartMetadata(session.id, session.cwd, props.messageID, props.partID)
     if (metadata?.role !== "assistant") return
     if (metadata.partType === "text" && props.field === "text" && metadata.ignored !== true) {
+      // altimate_change start — internal summaries may be removed or replaced after streaming
+      if (this.summaryMessages.has(props.messageID)) return
+      // altimate_change end
       await this.input.connection.sessionUpdate({
         sessionId: session.id,
         update: {
@@ -218,6 +233,9 @@ export class Subscription {
   }
 
   private async recordFetchedPart(sessionId: string, message: SessionMessageResponse, part: Part) {
+    // altimate_change start — cover subscriptions that join after the initial message update
+    if (message.info.role === "assistant" && message.info.summary) this.summaryMessages.add(message.info.id)
+    // altimate_change end
     return await Effect.runPromise(
       this.input.session.recordPartMetadata({
         sessionId,
 
@@ -1,4 +1,4 @@
-// altimate_change — what `altimate-code run --output <file>` writes.
+// altimate_change start — what `altimate-code run --output <file>` writes.
 //
 // The file is the answer, not the transcript. A model often narrates between tool
 // calls ("Mixed time formats. Let me check all formats.") and that text is superseded
@@ -14,10 +14,12 @@ export const NO_TEXT_OUTPUT = "(no text output — tool-only response)"
 // token when the deliverable is already complete; that acknowledgement is not a new reply.
 const ACKNOWLEDGEMENT = new RegExp(`^${DONE_TOKEN}\\.?$`, "i")
 
+type CollectedText = { text: string; partID?: string }
+
 export class OutputCollector {
-  private readonly all: string[] = []
-  private final: string[] = []
-  private previous: string[] = []
+  private all: CollectedText[] = []
+  private final: CollectedText[] = []
+  private previous: CollectedText[] = []
 
   /** A new model step starts; text before it is no longer the reply. Compaction steps do not count. */
   stepStart(compaction = false) {
@@ -27,16 +29,24 @@ export class OutputCollector {
   }
 
   /** Completed assistant text. Synthetic/compaction text is kept for the fallback only. */
-  text(text: string, opts: { synthetic?: boolean; compaction?: boolean } = {}) {
+  text(text: string, opts: { synthetic?: boolean; compaction?: boolean; partID?: string } = {}) {
     const trimmed = text.trim()
     if (!trimmed) return
-    this.all.push(trimmed)
+    const part = { text: trimmed, partID: opts.partID }
+    this.all.push(part)
     if (opts.synthetic || opts.compaction) return
     if (ACKNOWLEDGEMENT.test(trimmed) && this.final.length === 0) {
       this.final = this.previous
       return
     }
-    this.final.push(trimmed)
+    this.final.push(part)
+  }
+
+  /** Removed text must disappear from the reply and every fallback. */
+  remove(partID: string) {
+    this.all = this.all.filter((part) => part.partID !== partID)
+    this.final = this.final.filter((part) => part.partID !== partID)
+    this.previous = this.previous.filter((part) => part.partID !== partID)
   }
 
   private readonly notes: string[] = []
@@ -51,7 +61,12 @@ export class OutputCollector {
    * an answer and would read as one); otherwise everything that was said.
    */
   content(): string {
-    const chosen = this.final.length ? this.final : this.notes.length ? this.notes : this.all
+    const chosen = this.final.length
+      ? this.final.map((part) => part.text)
+      : this.notes.length
+        ? this.notes
+        : this.all.map((part) => part.text)
     return chosen.join("\n\n") || NO_TEXT_OUTPUT
   }
 }
+// altimate_change end
@@ -1028,6 +1028,11 @@ You are speaking to a non-technical business executive. Follow these rules stric
             toggles.set("start", true)
           }
 
+          // altimate_change start — discarded streamed text must not survive in --output fallbacks
+          if (event.type === "message.part.removed" && event.properties.sessionID === sessionID) {
+            outputParts.remove(event.properties.partID)
+          }
+          // altimate_change end
           if (event.type === "message.part.updated") {
             const part = event.properties.part
             if (part.sessionID !== sessionID) continue
@@ -1171,6 +1176,7 @@ You are speaking to a non-technical business executive. Follow these rules stric
               const text = part.text.trim()
               if (args.output && text) {
                 outputParts.text(text, {
+                  partID: part.id,
                   synthetic: part.synthetic === true,
                   compaction: accounting.isCompactionStep(part.messageID),
                 })
 
@@ -916,7 +916,9 @@ export namespace SessionPrompt {
       // Once the echo has started, this answer still belongs to the earlier request.
       // Publish it before the loop continues to any user request queued during generation.
       const storedText = MessageV2.parts(message.id).filter((part) => part.type === "text")
-      const first = deferredText[0] ?? storedText[0]
+      // Only buffered parts are safe to reuse: stored parts may already have
+      // streamed deltas, and a blank update does not reset client text.
+      const first = deferredText[0]
       const part: MessageV2.TextPart = {
         id: first?.id ?? PartID.ascending(),
         sessionID,