docs(headless): close K0 and activate K1

Pin the tested Windows/Linux portability boundary, exact rollback, dependency audit, and synchronized architecture and roadmap state before starting the production single-session host.

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

docs/plans/2026-07-26-modern-runtime-slice-k.md

@@ -1,6 +1,6 @@
 # Modern runtime Slice K — Linux headless and multi-session host
 
-**Status:** ACTIVE 2026-07-27 — SLICE J ENTRY GATE PASSED
+**Status:** K0 COMPLETE; K1 ACTIVE 2026-07-27
 **Parent:** `2026-07-24-modern-runtime-architecture.md`, Slice K
 **Authorization:** the user approved Slices F–L on 2026-07-24
 **Purpose:** run efficient automated clients on Linux without a display, GPU,
@@ -212,6 +212,14 @@ soon as session teardown begins.
 
 ### K0 — portability boundary and Linux CI
 
+**Complete at `aada8a37`.** The dedicated `AcDream.Headless` executable and
+test project reference only Runtime, strict no-connect configuration validation
+runs on Windows and Linux, dependency/loaded-assembly guards forbid graphical
+and audio backends, and the Windows/Ubuntu workflow builds/tests only the
+portable closure. Local Ubuntu 24.04 gates pass 600 Core.Net, 119 Content, 395
+Runtime, and 12 Headless tests. The exact Windows Release solution passes
+8,708 tests / 5 intentional skips.
+
 - Add `AcDream.Headless` and `AcDream.Headless.Tests`.
 - Add dependency-closure and loaded-assembly guards.
 - Add a normal GitHub Actions matrix for Windows and Ubuntu.
@@ -333,3 +341,9 @@ Land K0–K4 as separate buildable commits. Record the full production SHA and
 exact `git revert <sha>` after each complete focused/Release/Linux/connected
 gate. No later sub-slice begins while the prior exact rollback is absent from
 this plan.
+
+K0 exact rollback:
+
+```text
+git revert aada8a37c1e933f9f0a3f41dc4f05615b01023bc
+```