docs(runtime): close Slice J and activate Slice K

Record the shared graphical/no-window reset architecture, deterministic lifecycle evidence, exact rollback point, and synchronized project guidance before beginning the Linux headless host.

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

docs/plans/2026-07-25-modern-runtime-slice-j.md

@@ -1,6 +1,6 @@
 # Modern runtime Slice J — presentation-independent runtime
 
-**Status:** J0–J7 COMPLETE; J8 ACTIVE
+**Status:** COMPLETE 2026-07-27
 **Parent:** `2026-07-24-modern-runtime-architecture.md`, Slice J
 **Authorization:** the user approved Slices F–L, including the otherwise-frozen
 Slice J gameplay-owner moves, on 2026-07-24
@@ -416,7 +416,7 @@ git revert ce41efb9e5938f79a7580476b949d172f52a1e69
 
 **Detailed execution plan:**
 [`2026-07-26-modern-runtime-slice-j8.md`](2026-07-26-modern-runtime-slice-j8.md).
-Implementation is active after J7's 2026-07-27 physical-display acceptance.
+Completed at `a9a822f2` after J7's 2026-07-27 physical-display acceptance.
 
 - Build a transport/content test host that constructs Runtime directly.
 - Connect, enter world, receive chat/inventory/world updates, move, use,
@@ -433,6 +433,16 @@ integration, resource teardown, packet/order/timing parity, and the user visual
 matrix all pass. Slice K may then build the Linux multi-session host without
 another gameplay extraction.
 
+J8 passes 395 Runtime tests, 3,731 App tests / 3 skips, 8,696 complete-solution
+tests / 5 skips, the exact-binary lifecycle/reconnect route, and the canonical
+nine-stop route. Graphical and direct hosts share one `GameRuntime`, one
+retryable canonical-generation reset transaction, and the same gameplay-owner
+graph. Exact rollback:
+
+```text
+git revert a9a822f206cc6021bc099988144488f3bd7c397b
+```
+
 ## 5. Commit order
 
 1. `arch(runtime): establish presentation-independent boundary`