fix(core): ensure compaction is more reliable, add reserve token buffer to ensure that input window has enough room to compact (#12924)

Co-authored-by: James Lal <james@littlebearlabs.io>

packages/sdk/js/src/v2/gen/types.gen.ts

@@ -203,6 +203,7 @@ export type AssistantMessage = {
   summary?: boolean
   cost: number
   tokens: {
+    total?: number
     input: number
     output: number
     reasoning: number
@@ -418,6 +419,7 @@ export type StepFinishPart = {
   snapshot?: string
   cost: number
   tokens: {
+    total?: number
     input: number
     output: number
     reasoning: number
@@ -1822,6 +1824,10 @@ export type Config = {
      * Enable pruning of old tool outputs (default: true)
      */
     prune?: boolean
+    /**
+     * Token buffer for compaction. Leaves enough window to avoid overflow during compaction.
+     */
+    reserved?: number
   }
   experimental?: {
     disable_paste_summary?: boolean