feat: add agent fallback and preemptive-compaction restoration

- Add agent visibility fallback for first-run scenarios
- Restore preemptive-compaction hook
- Update migration and schema for preemptive-compaction restoration

src/hooks/preemptive-compaction.ts

@@ -0,0 +1,103 @@
+const ANTHROPIC_ACTUAL_LIMIT =
+  process.env.ANTHROPIC_1M_CONTEXT === "true" ||
+  process.env.VERTEX_ANTHROPIC_1M_CONTEXT === "true"
+    ? 1_000_000
+    : 200_000
+
+const PREEMPTIVE_COMPACTION_THRESHOLD = 0.78
+
+interface AssistantMessageInfo {
+  role: "assistant"
+  providerID: string
+  modelID?: string
+  tokens: {
+    input: number
+    output: number
+    reasoning: number
+    cache: { read: number; write: number }
+  }
+}
+
+interface MessageWrapper {
+  info: { role: string } & Partial<AssistantMessageInfo>
+}
+
+type PluginInput = {
+  client: {
+    session: {
+      messages: (...args: any[]) => any
+      summarize: (...args: any[]) => any
+    }
+    tui: {
+      showToast: (...args: any[]) => any
+    }
+  }
+  directory: string
+}
+
+export function createPreemptiveCompactionHook(ctx: PluginInput) {
+  const compactionInProgress = new Set<string>()
+  const compactedSessions = new Set<string>()
+
+  const toolExecuteAfter = async (
+    input: { tool: string; sessionID: string; callID: string },
+    _output: { title: string; output: string; metadata: unknown }
+  ) => {
+    const { sessionID } = input
+    if (compactedSessions.has(sessionID) || compactionInProgress.has(sessionID)) return
+
+    try {
+      const response = await ctx.client.session.messages({
+        path: { id: sessionID },
+      })
+      const payload = response as { data?: MessageWrapper[] } | MessageWrapper[]
+      const messages = Array.isArray(payload) ? payload : (payload.data ?? [])
+      const assistantMessages = messages
+        .filter((m) => m.info.role === "assistant")
+        .map((m) => m.info as AssistantMessageInfo)
+
+      if (assistantMessages.length === 0) return
+
+      const lastAssistant = assistantMessages[assistantMessages.length - 1]
+      if (lastAssistant.providerID !== "anthropic") return
+
+      const lastTokens = lastAssistant.tokens
+      const totalInputTokens = (lastTokens?.input ?? 0) + (lastTokens?.cache?.read ?? 0)
+      const usageRatio = totalInputTokens / ANTHROPIC_ACTUAL_LIMIT
+
+      if (usageRatio < PREEMPTIVE_COMPACTION_THRESHOLD) return
+
+      const modelID = lastAssistant.modelID
+      if (!modelID) return
+
+      compactionInProgress.add(sessionID)
+
+      await ctx.client.session.summarize({
+        path: { id: sessionID },
+        body: { providerID: lastAssistant.providerID, modelID, auto: true } as never,
+        query: { directory: ctx.directory },
+      })
+
+      compactedSessions.add(sessionID)
+    } catch {
+      // best-effort; do not disrupt tool execution
+    } finally {
+      compactionInProgress.delete(sessionID)
+    }
+  }
+
+  const eventHandler = async ({ event }: { event: { type: string; properties?: unknown } }) => {
+    if (event.type !== "session.deleted") return
+    const props = event.properties as Record<string, unknown> | undefined
+    const sessionInfo = props?.info as { id?: string } | undefined
+    if (sessionInfo?.id) {
+      compactionInProgress.delete(sessionInfo.id)
+      compactedSessions.delete(sessionInfo.id)
+    }
+  }
+
+  return {
+    "tool.execute.after": toolExecuteAfter,
+    event: eventHandler,
+  }
+}