docs: Campaign LA Linux posture — full launcher stack Linux-tested; GUI waits for Slice L

User decision 2026-08-14: everything the launcher does ships Linux-tested
in this campaign (launcher UI, install/update with manual DAT picker,
headless launches with plugins + login commands, probe, per-slice Linux
test runs, Linux connected-gate section at LA11). GUI client launches
stay Windows-only until Slice L resumes later; the launcher renders GUI
modes disabled on Linux with an explicit note, and the host-agnostic
session-config contract means Slice L lights them up with no launcher
changes.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/plans/2026-08-14-launcher-campaign.md

@@ -51,6 +51,32 @@ Parallelism guide: LA3/LA4 (launcher side) proceed alongside LA5–LA8 (client
 side) — different assemblies, no shared files. LA9/LA10 close the launcher
 side; LA11 closes the campaign.
 
+## Linux posture (binding — user decision 2026-08-14)
+
+Everything the launcher does must WORK ON LINUX in this campaign, except
+GUI client launches: the Linux graphical client is Slice L, parked at L1,
+resuming later ("ok we will do it later"). Concretely:
+
+- **Linux-shipping in LA:** the Avalonia launcher UI, profile CRUD +
+  0600-permission file, installer (manual DAT picker — the auto-detect
+  paths are Windows-only; `acdream-bake` is GL-free and runs on Linux),
+  updater (staged swap; Linux can replace a running binary but keep the
+  same staged-atomic flow), headless launches with plugins + login
+  commands, and the character probe.
+- **Launcher UX on Linux:** the `gui` / `guiSelect` launch modes render
+  disabled with an explicit "requires the Linux graphical client (Slice
+  L)" note — never a silent failure.
+- **Per-slice enforcement:** every slice touching Launcher.Core, Headless,
+  Runtime, Bake, or Platform runs its test projects on Linux (native
+  Ubuntu or WSL, matching the K-slice practice) before the slice is DONE;
+  LA4/LA9/LA10 additionally prove a real `linux-x64` self-contained
+  publish. LA11's connected-gate script gets a Linux section: launcher on
+  Ubuntu doing CRUD, probe, headless launch with plugin + login commands,
+  first-run install with a manual DAT path, and an update swap.
+- When Slice L later ships, the launcher's Linux GUI modes light up with
+  NO launcher changes (the session-config contract is host-agnostic) —
+  that expectation is part of LA's design acceptance.
+
 ## LA0 — `AcDream.Platform` extraction
 
 New BCL-only project `src/AcDream.Platform/` holding `ApplicationPathSet` +