docs(architecture): reconcile GameWindow extraction program

Close the completed M3 and portal observer gates, make the behavior-preserving GameWindow ownership campaign the explicit M4 prerequisite, and replace the stale extraction sketch with an implementation-audited sequence.

Co-authored-by: OpenAI Codex <codex@openai.com>

docs/architecture/acdream-architecture.md

@@ -829,12 +829,18 @@ Current movement/collision ownership:
 - **G.3 is shipped**: dungeon streaming, portal-space presentation, collision,
   lighting, doors, and the full round-trip gate landed. The separate far-
   teleport unstreamed-edge residual is issue #153, not unfinished G.3.
-- **M3** owns current connected magic/portal acceptance; Track LH is the future
-  presentation-independent Linux/headless extraction.
+- **M3 landed 2026-07-21** with connected magic/portal acceptance and the final
+  two-client observer gate; Track LH is the future presentation-independent
+  Linux/headless extraction.
+- **The behavior-preserving thin-`GameWindow` ownership campaign is the active
+  prerequisite before new M4 subsystem bodies.** Its reconciled ledger and
+  sequence live in `docs/architecture/code-structure.md`. This decision does
+  not reclassify the remaining L.2 conformance work or Track LH.
 
-The GameEntity / thin GameWindow refactor remains a valid target architecture,
-but it is not a prerequisite for L.2. Do not resurrect old R1-R8 phase numbers
-for new work; add or update roadmap phases instead.
+Full `GameEntity` type aggregation remains a separate, higher-risk target after
+the thin-`GameWindow` campaign. The current campaign reuses canonical
+`LiveEntityRuntime` rather than introducing another entity owner. Do not
+resurrect old R1-R8 phase numbers for new work; update the roadmap instead.
 
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