Core concept: The ask has two halves: free up space, but keep the memory of the work. That rules out anything that deletes history outright. Summarize what happened, and keep future noise out of the main window.

Why A and C are correct:

A: /compact condenses rather than discards. Compaction "summarizes conversation history when approaching context limits", and you can steer it: "/compact Focus on code samples and API usage tells Claude what to preserve during summarization."
A: The thread therefore survives in shortened form, which is exactly the "don't lose what we worked on" constraint.
C: Delegation keeps new noise out: "Delegate these to subagents so the verbose output stays in the subagent's context while only a summary returns to your main conversation."
C: The scratchpad is the durable half. Structured note-taking has the agent write "notes persisted to memory outside of the context window", so findings outlive any later compaction.

Why the others are wrong:

B: /clear is for "when switching to unrelated work". It starts a fresh session and throws the history away, which is the memory you were told to keep.
D: Hand-truncating messages discards content instead of summarizing it. It can orphan tool results from their tool calls and it breaks the cached prefix, so it costs more and remembers less.

Remember: Compact and delegate to keep the memory. Clear and truncate throw it away.

Question 190