Routing series/post4 topic weaving

_drafts/stash-replica-routing.md

@@ -85,3 +85,6 @@ The PID argument bites on the produce side only. The consume side works without
 TODO: link the Gemini doc from the weaving post: <https://docs.google.com/document/d/1ShcWeGuP1kMAzqFtEmjuIIAMJJre0Uy4bzkWm3bZbZ8/edit?usp=sharing>
 
 Point to make: KIP-939 (two-phase commit support) still does not fix this. If we went anywhere near it we would be in full distributed consensus pain. Not read or verified yet. Summarise from the doc before quoting, and check its claims against the KIP.
+
+## Topic ID is also temporal
+1. Topic IDs / UUIDs (KIP-516)At first glance, a Topic ID looks spatial (it’s just a coordinate for a topic). But it is actually a temporal lifecycle marker generated by the KRaft controller.The Semantics: If you delete a topic and recreate it with the same name, it gets a new UUID to prevent zombie delayed fetches from corrupting the new log.Why it breaks stateless math: You can mathematically fake a Node ID using $V = id + S \times t$ because Node IDs are predictable integers. You cannot mathematically derive a random backend UUID from a frontend virtual UUID.The Proxy Seam: To support API versions v13+ (where Produce and Fetch requests use UUIDs instead of strings), the proxy must maintain a stateful [Virtual Topic UUID -> Physical Topic UUID] mapping table in memory. If a proxy replica restarts and loses that map, it cannot route the frame. This is exactly why a proxy might intentionally cap PRODUCE API versions to v12—forcing clients to use string names—just to avoid handling cluster-specific Topic IDs.