fix(compaction): validate recovered agent config state

Retry compaction recovery when model or tool state is still incomplete, and treat reasoning or tool-only assistant progress as valid output so no-text tail recovery does not misfire.

src/hooks/compaction-context-injector/tail-monitor.ts

@@ -0,0 +1,52 @@
+const MEANINGFUL_ASSISTANT_PART_TYPES = new Set([
+  "reasoning",
+  "tool",
+  "tool_use",
+])
+
+export type TailMonitorState = {
+  currentMessageID?: string
+  currentHasOutput: boolean
+  consecutiveNoTextMessages: number
+  lastCompactedAt?: number
+  lastRecoveryAt?: number
+}
+
+export function finalizeTrackedAssistantMessage(
+  state: TailMonitorState,
+): number {
+  if (!state.currentMessageID) {
+    return state.consecutiveNoTextMessages
+  }
+
+  state.consecutiveNoTextMessages = state.currentHasOutput
+    ? 0
+    : state.consecutiveNoTextMessages + 1
+  state.currentMessageID = undefined
+  state.currentHasOutput = false
+
+  return state.consecutiveNoTextMessages
+}
+
+export function shouldTreatAssistantPartAsOutput(part: {
+  type?: string
+  text?: string
+}): boolean {
+  if (part.type === "text") {
+    return !!part.text?.trim()
+  }
+
+  return typeof part.type === "string" && MEANINGFUL_ASSISTANT_PART_TYPES.has(part.type)
+}
+
+export function trackAssistantOutput(
+  state: TailMonitorState,
+  messageID?: string,
+): void {
+  if (messageID && !state.currentMessageID) {
+    state.currentMessageID = messageID
+  }
+
+  state.currentHasOutput = true
+  state.consecutiveNoTextMessages = 0
+}