build(steam): stage steam_api64.dll beside the exe — one file, not the whole SDK

The SDK zip is 24 MB of headers, examples and tools we never build. The runtime
dependency is one native library, so scripts/steam-sdk.sh extracts exactly
sdk/redistributable_bin/win64/steam_api64.dll into steam/ (gitignored, like ffmpeg/ —
the script is the audit trail) and writes steam_appid.txt = 480, Valve's Spacewar app,
so SteamAPI.Init() resolves an app id locally before LlamaCasty has one of its own.

Two csproj details that would have cost a debugging session:
- Link="steam_api64.dll" puts it BESIDE the exe; without Link, None items keep their
  relative path and it lands in steam/, where the loader does not look.
- ExcludeFromSingleFile, for the same reason ffmpeg needed it: a native DLL otherwise
  gets swallowed into the single-file bundle and cannot be loaded at runtime.

steam_appid.txt is Debug-only — Valve's guidance is not to ship it — and the publish
output confirms it: dll present at the root, no appid file, exe still 127 MB (proof the
DLL was not bundled).

Also queued, as asked: preview undo (Ctrl+Z / Ctrl+Shift+Z) in edit mode, noted as the
partner to the defaults-vs-current split — undo covers the slip, defaults cover the mess.

.gitignore

@@ -21,3 +21,7 @@ CREDENTIALS.md
 .aider*
 ffmpeg/
 BuildCounter.txt
+
+# Steamworks runtime (steam_api64.dll, 312 KB) — extracted from the SDK zip, never committed;
+# scripts/steam-sdk.sh documents which file and why. Same rule as ffmpeg/: the pin is the audit trail.
+steam/

Distribution.md

@@ -46,9 +46,12 @@ dotnet publish ytLive.csproj -c Release -r win-x64 --self-contained true \
    the DLC app ID is what the app passes to `BIsDlcInstalled`.
 3. **Depot.** One depot holding the publish output; the base app and the DLC share the install
    directory, and the DLC package grants no files of its own — it is entitlement only.
-4. **Steamworks SDK.** Drop `steam_api64.dll` (+ `steam_appid.txt` for local runs) into the publish
-   output; the managed side is a thin wrapper (`Steamworks.NET` or hand-written interop) behind
-   `IEntitlement`.
+4. **Steamworks SDK.** `./scripts/steam-sdk.sh ~/Downloads/steamworks_sdk_165.zip` extracts
+   `steam_api64.dll` from `sdk/redistributable_bin/win64/` into `steam/` (gitignored) and stages
+   `steam_appid.txt` = 480 — Valve's Spacewar app, so `SteamAPI.Init()` works locally before
+   LlamaCasty has an App ID. The csproj copies the DLL **beside the exe** (`Link`) with
+   `ExcludeFromSingleFile`, and copies `steam_appid.txt` in Debug only — never into a depot. The
+   managed side is the `Steamworks.NET` package (`SteamApps.BIsDlcInstalled`).
 5. **Store page** configured and made public **two weeks before release** — Valve's rule, and it is
    the window where wishlists accumulate.
 

TASKS.md

@@ -42,6 +42,7 @@ Dog test.
 | 34 | ☐ | Scheduled streams (Text-drawer version) | [`task-34`](TASKS/task-34-scheduled-streams.md) |
 | 35 | ☐ | Scene-linked audio | [`task-35`](TASKS/task-35-scene-linked-audio.md) |
 | 37 | ☐ | Defaults vs current layout split (build-id); enables one-click revert to defaults | [`task-37`](TASKS/task-37-defaults-current-split.md) |
+| — | ☐ | **Preview undo (Ctrl+Z / Ctrl+Shift+Z)** — in edit mode, revert the last preview change (drag, resize, add, remove, property edit); bounded stack, cleared on scene change or layout load. The natural partner to 37: undo covers the slip, defaults cover the mess | this line |
 | 39·2 | ☐ | YPP slice 2: Analytics scopes, watch-hours/Shorts velocity + ETA | [`task-39`](TASKS/task-39-ypp-journey-tracker.md) |
 | 49 | ☐ | Chat profanity filter: local, opt-in, **non-persistent**, user-supplied word list | [`task-49`](TASKS/task-49-chat-profanity-filter.md) |
 | 50 | ☐ | One-button publish of the local recording (resumable upload) | [`task-50`](TASKS/task-50-publish-recording.md) |

scripts/steam-sdk.sh

@@ -0,0 +1,45 @@
+#!/usr/bin/env bash
+# steam-sdk.sh — extract the one file the app needs from the Steamworks SDK, and stage the
+# local-only app id.
+#
+# Why not unzip the whole SDK: it is ~24 MB of C++ headers, examples and tools we never build.
+# The runtime dependency is exactly one native library, and the release tooling (ContentBuilder)
+# is only needed on the machine that uploads a depot.
+#
+#   ./scripts/steam-sdk.sh ~/Downloads/steamworks_sdk_165.zip
+#
+# steam_api64.dll is Valve's redistributable — shipping it beside a Steam-published exe is
+# permitted by the Steamworks terms. It is NOT committed: steam/ is gitignored, like ffmpeg/.
+
+set -euo pipefail
+
+ZIP="${1:-$HOME/Downloads/steamworks_sdk_165.zip}"
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+
+[ -f "$ZIP" ] || { echo "❌ SDK zip not found: $ZIP" >&2; echo "   Download it from partner.steamgames.com/downloads/steamworks_sdk.zip while signed in." >&2; exit 1; }
+
+mkdir -p "$ROOT/steam"
+
+python3 - "$ZIP" "$ROOT" <<'PY'
+import sys, zipfile, pathlib
+
+zip_path, root = sys.argv[1], pathlib.Path(sys.argv[2])
+want = "sdk/redistributable_bin/win64/steam_api64.dll"
+dest = root / "steam" / "steam_api64.dll"
+
+with zipfile.ZipFile(zip_path) as z:
+    with z.open(want) as src, open(dest, "wb") as out:
+        out.write(src.read())
+
+print(f"✓ {dest.relative_to(root)} ({dest.stat().st_size // 1024} KB)")
+PY
+
+# steam_appid.txt is a LOCAL TESTING affordance: it lets SteamAPI.Init() resolve an app id
+# without going through the Steam client. 480 is Valve's public Spacewar test app, so the app
+# can be exercised before LlamaCasty has an app id of its own. It is Debug-only in the csproj
+# and must never ship in a depot — Valve's guidance is to remove it from release builds.
+printf '480\n' > "$ROOT/steam/steam_appid.txt"
+echo "✓ steam/steam_appid.txt = 480 (Spacewar, local Debug testing only)"
+
+echo ""
+echo "Next: the entitlement seam (IEntitlement + SteamApps.BIsDlcInstalled)."

ytLive.csproj

@@ -100,6 +100,21 @@
     <Compile Remove="Controls\DeveloperPanel.xaml.cs" />
   </ItemGroup>
 
+  <!-- Steamworks runtime (scripts/steam-sdk.sh extracts it; steam/ is gitignored).
+       ⛔ Link puts it BESIDE the exe rather than under steam/, because the loader looks there.
+       ⛔ ExcludeFromSingleFile matters for the same reason as ffmpeg: a native DLL otherwise
+       gets swallowed into the single-file bundle and the app cannot load it at runtime. -->
+  <ItemGroup>
+    <None Remove="steam\**" />
+    <None Include="steam\steam_api64.dll" Link="steam_api64.dll"
+          CopyToOutputDirectory="PreserveNewest" CopyToPublishDirectory="Always"
+          ExcludeFromSingleFile="true" />
+    <!-- Local-only: lets SteamAPI.Init() resolve an app id outside the Steam client (480 =
+         Valve's Spacewar test app). Never published — Valve's guidance is to omit it. -->
+    <None Include="steam\steam_appid.txt" Link="steam_appid.txt" Condition="'$(Configuration)' == 'Debug'"
+          CopyToOutputDirectory="PreserveNewest" />
+  </ItemGroup>
+
   <ItemGroup>
     <None Include="THIRD-PARTY-NOTICES.txt" CopyToOutputDirectory="PreserveNewest" />
     <!-- The EULA and privacy policy travel with every copy: they are what the About screen and