feat(agent-builder): add agent memory section (#1133)

## Overview
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## Type of change

**Type:** [Replace with: New documentation page / Update existing
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## Checklist
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- [ ] I have read the [contributing guidelines](README.md)
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Author: Palashio

src/langsmith/agent-builder.mdx

@@ -10,6 +10,14 @@ Agent Builder is in private preview. Sign up for the waitlist [today](https://ww
 
 Agent Builder lets you turn natural-language ideas into production agents. It's powered by [deep-agents](https://github.com/langchain-ai/deepagents), and is not <Tooltip tip="Predetermined code paths that are designed to operate in a certain order.">workflow based</Tooltip>.
 
+## Memory and updates
+
+Agent Builder includes persistent agent memory and supports self-updates. This lets agents adapt over time and refine how they work without manual edits.
+
+- Persistent memory: Agents retain relevant information across runs to inform future decisions.
+- What can be updated: Tools (add, remove, or reconfigure), and instructions/system prompts.
+- Agents cannot modify their name, description, and/or triggers attached.
+
 ## Triggers
 
 Triggers define when your agent should start running. You can connect your agent to external tools or time-based schedules, letting it respond automatically to messages, emails, or recurring events.