diff --git a/src/node/services/agentSession.ts b/src/node/services/agentSession.ts
index adbe96ee30..df98d9b477 100644
--- a/src/node/services/agentSession.ts
+++ b/src/node/services/agentSession.ts
@@ -271,6 +271,15 @@ export class AgentSession {
     }
 
     if (options?.editMessageId) {
+      // Interrupt an existing stream or compaction, if active
+      if (this.aiService.isStreaming(this.workspaceId)) {
+        // MUST use abandonPartial=true to prevent handleAbort from performing partial compaction
+        // with mismatched history (since we're about to truncate it)
+        const stopResult = await this.interruptStream(/* abandonPartial */ true);
+        if (!stopResult.success) {
+          return Err(createUnknownSendMessageError(stopResult.error));
+        }
+      }
       const truncateResult = await this.historyService.truncateAfterMessage(
         this.workspaceId,
         options.editMessageId
@@ -362,6 +371,16 @@ export class AgentSession {
       return Ok(undefined);
     }
 
+    // Delete partial BEFORE stopping to prevent abort handler from committing it
+    // The abort handler in aiService.ts runs immediately when stopStream is called,
+    // so we must delete first to ensure it finds no partial to commit
+    if (abandonPartial) {
+      const deleteResult = await this.partialService.deletePartial(this.workspaceId);
+      if (!deleteResult.success) {
+        return Err(deleteResult.error);
+      }
+    }
+
     const stopResult = await this.aiService.stopStream(this.workspaceId, abandonPartial);
     if (!stopResult.success) {
       return Err(stopResult.error);
diff --git a/src/node/services/ipcMain.ts b/src/node/services/ipcMain.ts
index 519a55ee58..a9c22f8338 100644
--- a/src/node/services/ipcMain.ts
+++ b/src/node/services/ipcMain.ts
@@ -1104,12 +1104,6 @@ export class IpcMain {
             return { success: false, error: stopResult.error };
           }
 
-          // If abandonPartial is true, delete the partial instead of committing it
-          if (options?.abandonPartial) {
-            log.debug("Abandoning partial for workspace:", workspaceId);
-            await this.partialService.deletePartial(workspaceId);
-          }
-
           return { success: true, data: undefined };
         } catch (error) {
           const errorMessage = error instanceof Error ? error.message : String(error);