docs(research): record POC-3 outcome — phase 0 gates all pass

- pocs.md: POC-3 marked complete/proceed with result summary; sequencing
  status updated
- alk-stack.md: verify item 2 (HTTP smart protocol shape) resolved,
  pointing at poc3-findings.md

docs/research/pocs.md

@@ -81,6 +81,15 @@ whole pack in memory for large repos — record memory behavior for a
 
 ## POC-3: smart-http shape through alkhttp
 
+**Status**: complete (2026-09-21) — **proceed**. See `poc3-findings.md`.
+Real git 2.43 clones/fetches/tag-checkouts over `http://` through the full
+alkcall → alkhttp path (`Connection::from_bidi(http/1.1)` → `HttpAdapter`
+→ axum custom routes); request bodies stream (measured via dribble probe +
+git's forced-chunked path), pack responses stream under back pressure with
+O(counts) memory on a 60k-object clone. Key protocol correction: http V2
+responses end at the flush — the `0002` response-end pkt is synthesized by
+the client's transport helper, never sent on the wire.
+
 **Hypothesis**: alkhttp can serve `GET /info/refs` and stream a POST body
 (ingest without full buffering) for `git-receive-pack`.
 
@@ -99,8 +108,8 @@ POC-1 first (the BiStream/packetline fit is the load-bearing assumption).
 POC-2 next (the crux of fetch). POC-3 last (http shape). Each POC updates
 the corresponding research doc with results and a proceed/pivot/block note.
 
-**Status**: POC-1 and POC-2 complete and proceed; POC-3 is the remaining
-gate for phase 0 completion.
+**Status**: POC-1, POC-2, and POC-3 complete and proceed — phase 0 gates
+all pass.
 
 ## Modes applied to these POCs