🤖 fix: delete partial in interruptStream when abandonPartial=true

Critical fix: interruptStream now deletes the partial when abandonPartial=true,
mirroring the IPC handler pattern. Without this, the partial would be committed
by streamWithHistory's unconditional commitToHistory call, reintroducing the
cancelled assistant response into history.

This completes the fix for editing compacting messages - now the cancelled
output is truly discarded instead of being appended after truncation.

Author: ethanndickson

src/node/services/agentSession.ts

@@ -376,6 +376,15 @@ export class AgentSession {
       return Err(stopResult.error);
     }
 
+    // Delete partial when abandoning to prevent commitToHistory from reintroducing it
+    // Mirrors the IPC handler pattern (ipcMain.ts:1108-1110)
+    if (abandonPartial) {
+      const deleteResult = await this.partialService.deletePartial(this.workspaceId);
+      if (!deleteResult.success) {
+        return Err(deleteResult.error);
+      }
+    }
+
     return Ok(undefined);
   }