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@@ -1096,6 +1096,10 @@ per-session incremental memory given a numeric ceiling at gate time.
 
 ### Slice L — Linux graphical host and evidence-gated GPU work
 
+**Prepared execution plan:**
+[`2026-07-26-modern-runtime-slice-l.md`](2026-07-26-modern-runtime-slice-l.md).
+Implementation begins after Slice K closes.
+
 **Purpose:** Finish platform portability and only then pursue remaining GPU
 opportunities.
 
diff --git a/docs/plans/2026-07-26-modern-runtime-slice-l.md b/docs/plans/2026-07-26-modern-runtime-slice-l.md
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+# Modern runtime Slice L — Linux graphical host and evidence-gated GPU work
+
+**Status:** PREPARED — BEGINS AFTER SLICE K CLOSEOUT
+**Parent:** `2026-07-24-modern-runtime-architecture.md`, Slice L
+**Authorization:** the user approved Slices F–L on 2026-07-24
+**Purpose:** ship the existing modern OpenGL client on supported Linux drivers
+with identical Runtime behavior and accepted visual presentation, then make
+only GPU changes whose measured bottleneck and visual equivalence are proven.
+
+## 1. Entry contract
+
+Slice L begins only after Slice K proves Linux Runtime/Core.Net/Content,
+portable paths/config/credentials, one production headless host, deterministic
+wire timing, shared immutable content, and a clean 30-session stress gate.
+
+L does not fork the game client into a second Linux implementation. The same
+`AcDream.App`, `GameRuntime`, retained UI, rendering pipeline, shaders, and
+resource owners run on both platforms. Platform-specific behavior is confined
+to typed host services selected once at startup.
+
+## 2. Mandatory renderer boundary
+
+The modern path remains mandatory:
+
+- OpenGL 4.3 core;
+- `GL_ARB_bindless_texture`;
+- `GL_ARB_shader_draw_parameters`;
+- the current bindless texture/SSBO/MDI layouts and shaders.
+
+There is no legacy renderer, texture-unit fallback, reduced-distance mode, or
+platform-specific gameplay/render path. An unsupported driver fails startup
+with a precise capability report.
+
+Driver acceptance begins with a committed matrix:
+
+- AMD Mesa/RadeonSI on X11;
+- AMD Mesa/RadeonSI on Wayland;
+- NVIDIA proprietary driver on X11;
+- NVIDIA proprietary driver on Wayland where Silk's backend is supported;
+- Intel only if the hardware/driver exposes every mandatory extension.
+
+Each row records distribution/kernel, display protocol, compositor, GPU,
+driver, OpenGL vendor/renderer/version, extension presence, swap interval,
+monitor refresh, and audio backend. A row may be “unsupported” only because a
+mandatory capability is absent or the native window backend cannot create the
+required context—not because a visual mismatch was waived.
+
+## 3. Initial platform inventory
+
+Portable foundations already exist:
+
+- Silk.NET owns window/input/OpenGL APIs;
+- OpenAL Soft is designed for PulseAudio/PipeWire/CoreAudio as well as Windows;
+- shader and UI asset paths use `AppContext.BaseDirectory`/`Path.Combine`;
+- `BitmapFont.TryLoadSystemMonospaceFont` already includes common Linux font
+  paths;
+- Runtime/Core.Net/Content are presentation-independent after J/K.
+
+Known Linux blockers and audit targets:
+
+- `FramePacingController` unconditionally constructs
+  `WindowsHighResolutionFramePacingWaiter`, which throws off Windows.
+- The OpenAL Soft native package/runtime assets must be verified for each
+  Linux RID rather than assumed.
+- Silk window backend/native dependency publication is not packaged or tested.
+- the smoke-plugin MSBuild copy target uses Windows path separators;
+- key bindings, cursor creation, clipboard, relative mouse, monitor refresh,
+  window-state callbacks, and high-DPI scaling need live X11/Wayland evidence;
+- settings, layouts, keymaps, logs, screenshots, and diagnostics must use the
+  portable path owner established in K rather than `%LOCALAPPDATA%` wording or
+  ad hoc paths;
+- no Linux graphical CI/smoke environment exists;
+- no Linux driver timer-query validation or screenshot baseline exists;
+- no package/install/uninstall contract exists.
+
+## 4. Platform-service contracts
+
+### Frame pacing
+
+Keep the existing display-aware policy:
+
+- VSync uses the driver's swap wait.
+- VSync-off normal play uses a refresh-matched low-CPU software deadline.
+- explicit uncapped diagnostics perform no wait.
+
+Replace direct Windows construction with `IFramePacingWaiterFactory`.
+Windows retains the high-resolution waitable timer. Linux uses an
+absolute-monotonic deadline wait (`clock_nanosleep` or a proven equivalent)
+with cancellation-safe disposal. Neither path busy-spins for the normal wait.
+The same missed-deadline rebase rule prevents catch-up bursts.
+
+Gate both waiters for deadline error, CPU usage, cancellation, disposal, missed
+deadlines, monitor changes, and long stalls.
+
+### Paths and persistence
+
+Reuse K's portable path owner for:
+
+- settings and key bindings;
+- retained UI layouts;
+- logs and diagnostic captures;
+- screenshots and automation artifacts;
+- plugins;
+- prepared assets and DAT location overrides.
+
+No feature reads a Windows-only environment variable/path at its call site.
+
+### Input/window
+
+Test the exact retained-input pipeline on X11 and Wayland:
+
+- keyboard keys, modifiers, text input, repeat, and configurable bindings;
+- mouse buttons, wheel, press-time selection, dragging, resizing, and cursors;
+- relative mouse capture, recenter/release, and focus loss;
+- clipboard;
+- window move/resize/minimize/restore/close and monitor transition;
+- DPI/framebuffer size versus logical size.
+
+Retail input behavior remains the acceptance oracle; Linux key/scancode
+adaptation cannot alter action semantics.
+
+### Audio
+
+OpenAL initialization remains fail-open only for the existing explicit
+no-audio mode or unavailable device. Package the correct OpenAL Soft native
+asset, identify PulseAudio/PipeWire device/context selection, and prove
+source/buffer/context teardown. Audio absence must not stall the frame or
+change Runtime/VFX timing.
+
+## 5. Packaging contract
+
+Produce repeatable `linux-x64` artifacts first; add `linux-arm64` only after
+the complete native dependency and GL extension matrix passes.
+
+Artifacts contain:
+
+- the App and managed dependency closure;
+- Silk window/input/OpenGL native dependencies;
+- OpenAL Soft;
+- shaders and retained-UI XML;
+- plugin directory/manifest support;
+- a launch entry point and version/provenance record.
+
+DATs, account credentials, and the machine-local `acdream.pak` are not bundled.
+Startup diagnostics identify their configured paths without exposing secrets.
+
+Provide:
+
+- framework-dependent development publish;
+- self-contained release publish if native/runtime size and licenses are
+  acceptable;
+- desktop entry/icon/install documentation;
+- package validation on a clean Linux user account.
+
+## 6. Execution
+
+### L0 — platform services and Linux build
+
+- Add Linux App build/publish jobs to CI after K's non-graphical Linux jobs.
+- Add typed platform capability, path, pacing, and native-dependency owners.
+- Implement the Linux monotonic frame waiter and factory selection.
+- Correct cross-platform MSBuild paths and packaging assumptions.
+- Add source/dependency guards against platform checks outside platform-owner
+  classes.
+
+Gate: App restores/builds/publishes for `linux-x64`; unit tests prove both
+frame waiters and portable paths; no Windows P/Invoke executes on Linux.
+
+### L1 — context, extensions, and native backends
+
+- Create a Linux window and OpenGL 4.3 core context under X11 and Wayland.
+- Capture the full capability record before renderer construction.
+- Verify mandatory bindless and shader-draw-parameter calls, MDI, SSBOs,
+  persistent resource ownership, timer queries, framebuffer sRGB/depth/stencil,
+  and swap behavior.
+- Initialize input and OpenAL Soft.
+- Fail unsupported rows with one actionable diagnostic.
+
+Gate: a packaged smoke scene opens, renders, accepts input, plays optional
+audio, captures a screenshot, and shuts down with zero GL/OpenAL/window debt on
+each supported matrix row.
+
+### L2 — complete graphical connected route
+
+- Run the same exact-binary lifecycle/reconnect route used on Windows.
+- Run the canonical nine-stop route with movement, jump, combat, portal,
+  revisit, and graceful shutdown.
+- Verify radar, retained UI, inventory paperdoll, Use/approach, combat facing,
+  spell effects, portal tunnel/materialization/exit, cursors, chat, and audio.
+- Compare pinned-camera images against accepted Windows references using the
+  existing per-channel tolerance and differing-pixel-fraction rule.
+- Record CPU/GPU frame history, allocation, managed/native/GPU residency,
+  handles, threads, and driver facts.
+
+Gate: lifecycle/resource invariants and retail behavior match; screenshot
+differences are within the committed driver-aware threshold and individually
+inspected; no resource growth survives repeated portals.
+
+### L3 — packaging and clean-machine gate
+
+- Publish versioned Linux artifacts.
+- Test install, first launch, configuration discovery, plugin discovery,
+  upgrade, and uninstall on a clean user account.
+- Prove no implicit write occurs beside a read-only installed binary.
+- Prove missing DAT/pak/driver/audio conditions produce actionable,
+  credential-safe errors.
+
+Gate: a clean machine reaches world, completes the route, exits gracefully,
+and preserves settings/layout/key bindings under XDG paths.
+
+### L4 — accurate Linux profiling
+
+- Validate GL timer-query attribution on each accepted driver.
+- Capture capped and uncapped canonical route, dense-town, portal-window, and
+  long-duration profiles on a physical local display.
+- Attribute CPU update, render submission, GPU passes, allocations, upload,
+  particle, light, culling, and command-compaction costs.
+- Compare Windows and Linux without mixing RDP/display protocol populations.
+
+Gate: the dominant remaining CPU/GPU stages are named with reliable samples.
+If no GPU stage is material, do not migrate work merely because the roadmap
+lists candidates.
+
+### L5 — evidence-gated GPU changes
+
+For each candidate independently:
+
+1. show it is a dominant stage in L4 evidence;
+2. write a focused plan with ownership, synchronization, fallback/error, and
+   teardown contracts;
+3. implement one bisectable change;
+4. run deterministic/Release/connected/resource gates;
+5. publish CPU and GPU before/after plus visual equivalence;
+6. keep the change only if the intended metric materially improves without
+   regressions.
+
+Candidate order, only when evidence supports it:
+
+- GPU visibility culling;
+- indirect command compaction;
+- particle simulation;
+- bounded light selection.
+
+No candidate changes server authority, physics, animation ordering, DAT effect
+semantics, retained UI, or visible draw range.
+
+### L6 — closeout
+
+- Repeat the accepted Linux driver, packaging, connected, screenshot,
+  resource, and performance matrices.
+- Run Windows regression gates.
+- Audit every GPU migration and exact rollback.
+- Update architecture, milestones, roadmap, issues/divergences,
+  AGENTS/CLAUDE, and durable memory.
+
+Gate: supported Linux graphical artifacts ship the same intended client
+behavior; every retained GPU change has measured evidence and visual parity;
+all teardown ledgers converge.
+
+## 7. Adversarial matrix
+
+- X11 versus Wayland, compositor on/off where practical;
+- AMD versus NVIDIA extension/function-pointer behavior;
+- mandatory extension advertised but call returns invalid handle/error;
+- no display, no audio device, missing font, missing clipboard service;
+- monitor hotplug, refresh change, DPI change, minimize, suspend/resume, focus
+  loss, and close during portal;
+- VSync ignored, adaptive sync, software pacing stall, timer interruption, and
+  clock discontinuity;
+- read-only install directory and XDG paths with spaces/non-ASCII;
+- missing/corrupt pak, DAT mismatch, plugin failure, shader compile failure;
+- GL context loss/failure during construction and teardown;
+- audio context/buffer/source partial construction failure;
+- screenshot differences from gamma, texture filtering, precision, clip
+  origin, or driver shader compilation;
+- GPU migration overflow, indirect count mismatch, fence delay, stale
+  generation, device reset, and visibility false-negative;
+- Windows regression after each platform abstraction.
+
+## 8. Non-goals
+
+- No legacy renderer or extension fallback.
+- No reduced visual distance or Linux-specific quality default.
+- No renderer rewrite solely for portability.
+- No GPU migration without measured dominance.
+- No macOS graphical support in Slice L; the portable Runtime/headless work and
+  typed platform services should make a later macOS plan smaller, but Apple
+  OpenGL capability constraints require a separate decision.
+- No bundled DAT files, credentials, or local server.
+
+## 9. Commit and rollback discipline
+
+Land L0–L6 as separate buildable commits. Record the full production SHA and
+exact `git revert <sha>` after each focused/Linux/Windows/connected/visual
+gate. GPU candidates each receive their own plan, commit, measurement, visual
+gate, and rollback; rejected experiments are reverted rather than hidden
+behind dormant alternate paths.