You are building a customer support resolution agent using the Claude Agent SDK.

The agent must preserve durable state for several concurrently open issues without keeping every conversational turn in the active context window. Option D creates a structured issue ledger containing identifiers, issue type, requested action, current status, completed steps, unresolved questions, and relevant tool outputs.

Anthropic recommends structured note-taking for long-horizon agents. In this pattern, critical state is written outside the context window and retrieved later, allowing the agent to preserve dependencies and progress across dozens of tool calls. Anthropic also describes compaction as retaining critical details while discarding redundant raw messages and historical tool output. ( https://www.anthropic.com/engineering/effective-context-engineering-for-ai-agents )

Option A is better than retaining the entire transcript, but a narrative summary can merge separate issues or obscure exact identifiers and statuses. Option B will discard the refund conversation because it occurred outside the most recent 30 turns. Option C may recover current backend facts, but it cannot reconstruct conversational commitments, prior explanations, or why a particular action remains pending.

A structured context layer should maintain one record per issue and be updated after every material action. The active prompt can include compact summaries of all open issues and expanded details only for the issue currently being discussed.

Official references/topics: Structured note-taking, external agent memory, context compaction, multi-issue state management.