docs(agent-memory): polish hero opener for clarity

Drop the self-referential "by default" qualifier (the non-default mode it
implied is Agent Memory itself, making the phrase quietly circular).
Make the cold-start problem more concrete by spelling out that prior
runs' learnings are lost \u2014 strengthens the value framing the page is
trying to build for the waitlist CTA.

Co-Authored-By: Oz <oz-agent@warp.dev>

Author: hongyi-chen

src/content/docs/agent-platform/capabilities/agent-memory/index.mdx

@@ -10,7 +10,7 @@ sidebar:
 Agent Memory is in **research preview** and is enabled per workspace for design partners. [Join the waitlist](https://warp.dev/oz/agent-memory#waitlist) to request access for your workspace.
 :::
 
-Every cloud agent run starts cold by default — it knows your codebase only as far as it can see in a single conversation. Agent Memory changes that. It captures durable knowledge from finished cloud runs and surfaces it at the start of future runs, so each run picks up where the last one left off.
+Every cloud agent run starts cold — it knows your codebase only as far as it can see in a single conversation, and anything the last run figured out is gone. Agent Memory changes that. It captures durable knowledge from finished cloud runs and surfaces it at the start of future runs, so each run picks up where the last one left off.
 
 Agent Memory is a persistent, cross-harness memory layer that lives on Oz. The same knowledge is available whether your next run uses Warp Agent, Claude Code, Codex, or another supported harness. [Request early access](https://warp.dev/oz/agent-memory#waitlist) to try it with your team.