docs(tool_use): add Opus 4.6 server-side compaction guidance to context compaction cookbook (anthropics#369)

Adds a callout recommending server-side compaction for Opus 4.6 users,
clarifying that this cookbook covers SDK-based compaction for older models
or alternative summarization model use cases.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: PedramNavid

tool_use/automatic-context-compaction.ipynb

@@ -44,6 +44,12 @@
     "- Anthropic SDK >= 0.74.1"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "id": "6j8bv0fnlqm",
+   "source": "> **Using Opus 4.6?** We recommend using [server-side compaction](https://docs.anthropic.com/en/docs/build-with-claude/compaction), which handles context management automatically without any SDK-level configuration.\n>\n> This cookbook covers **SDK-based compaction**, which is useful if you're using an older model or want to use a different (cheaper) model for summarization.",
+   "metadata": {}
+  },
   {
    "cell_type": "markdown",
    "id": "004e3b52",
@@ -1239,4 +1245,4 @@
  },
  "nbformat": 4,
  "nbformat_minor": 5
-}
+}