fix(launcher): Campaign LA LA3 review fixes — contract paths omission, probe composition, graceful stop, hygiene

Opus review of LA3 returned FIX FIRST; this addresses every finding in
scope (F1-F5, F7-F12; F6 CI-lane addition excluded per instructions):

- F1 (CRITICAL): SessionProcessSettings.Paths is now nullable and left
  null by SessionConfigComposer unless a caller supplies overrides, so
  the JSON key is entirely absent instead of "paths":{} — the App-side
  loader's strict UnmappedMemberHandling.Disallow would otherwise reject
  every gui/guiSelect session-config document at load.
- F2: added SessionConfigComposer.ComposeProbe and a nullable
  SessionDescriptor.Mode field ("probe", omitted for normal play) per
  the pinned contract — no character/policy/plugins/loginCommands.
- F3: LauncherProcessSupervisor.Stop now tries
  ILauncherChildProcess.TryRequestGracefulStop (Linux: libc SIGINT via
  LibraryImport, K4-proven graceful headless logout) before
  CloseMainWindow. Windows has no reliable no-window-console equivalent
  today; filed docs/ISSUES.md #397 with the CREATE_NEW_PROCESS_GROUP +
  CTRL_BREAK fix direction. Stop()'s blocking-timeout contract is now
  documented for LA4.
- F4: LauncherProfileStore.Save chmods the Linux temp file to 0600
  immediately after creation, before any credential is serialized;
  failure paths and Load() clean up a stale .tmp.
- F5: added LauncherCoreDependencyBoundaryTests asserting Launcher.Core
  references exactly AcDream.Platform and no packages.
- F7: StatusEventParser.Parse no longer throws on a whitespace/null
  line; StatusFileTailer.ReadNewEvents swallows the File.Exists/open
  TOCTOU window (FileNotFoundException/DirectoryNotFoundException/
  IOException) instead of throwing.
- F8: Start() now kills (entire process tree) and disposes a child that
  started successfully but failed while being fed its stdin password,
  instead of orphaning it.
- F9: SetState is monotonic — once Exited, no later transition applies
  or fires StateChanged, closing a Start()-path race where a
  synchronously-exiting child could be "resurrected" to Running.
- F10: CharacterIdFormat.TryParse now requires the "0x" prefix (an
  unprefixed hand-typed decimal id is also valid hex and was silently
  misread); a parsed id of 0 is treated as unusable and falls back to
  the name selector; LauncherProfileStore.MergeRoster normalizes both
  sides through TryParse/ToHexString instead of raw string equality, so
  a legacy unprefixed-hex row self-heals via name match instead of
  duplicating.
- F11: StatusCharacterEntry.SecondsGreyedOut is now uint, matching
  CharacterRosterEntry and the host writer.
- F12: added MalformedStatusEvent, returned for a recognized `e` whose
  payload doesn't match its shape, distinguished from UnknownStatusEvent
  (an unrecognized `e`).

AllowUnsafeBlocks was added to AcDream.Launcher.Core.csproj — required
by the LibraryImport source generator's function-pointer marshalling
stub for F3's Linux SIGINT P/Invoke.

Verification: dotnet build AcDream.slnx -c Release green (0 errors);
dotnet test tests/AcDream.Launcher.Core.Tests -c Release green at 94/94
on native Windows and under WSL (Ubuntu, verified across multiple runs
for the timing-sensitive SIGINT/sharing-violation tests, no flakes
observed).

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

tests/AcDream.Launcher.Core.Tests/LauncherCoreDependencyBoundaryTests.cs

@@ -0,0 +1,79 @@
+using System.Runtime.CompilerServices;
+using System.Xml.Linq;
+
+namespace AcDream.Launcher.Core.Tests;
+
+// Campaign LA plan §LA3 review finding F5: AcDream.Launcher.Core's entire
+// premise (spec §LA3, SessionConfigDocument.cs's "PINNED CONTRACT" remarks)
+// is being the BCL-plus-Platform-only assembly the external Avalonia
+// launcher (LA4) can reference without pulling in any game-solution
+// dependency. That contract is what this guard enforces — the csproj must
+// declare exactly one ProjectReference (AcDream.Platform) and zero
+// PackageReference entries, forever, in the same spirit as Platform's,
+// Runtime's, and Headless's dependency-boundary guards.
+public sealed class LauncherCoreDependencyBoundaryTests
+{
+    [Fact]
+    public void LauncherCoreProjectReferencesOnlyPlatformAndDeclaresNoPackages()
+    {
+        string repositoryRoot = FindRepositoryRoot();
+        string projectPath = Path.Combine(
+            repositoryRoot,
+            "src",
+            "AcDream.Launcher.Core",
+            "AcDream.Launcher.Core.csproj");
+        var project = XDocument.Load(projectPath);
+
+        var projectReferences = project.Descendants("ProjectReference")
+            .Select(element => element.Attribute("Include")?.Value)
+            // The csproj is authored with Windows-style "..\Foo\Foo.csproj"
+            // separators; Path.GetFileName only recognizes the platform's
+            // own separator, so on Linux it would return the whole
+            // relative path unchanged instead of just the filename.
+            // Normalizing to '/' first keeps this assertion
+            // platform-agnostic (this project's tests run under both
+            // native Windows and WSL — see Campaign LA plan §LA3 review
+            // finding F5's acceptance).
+            .Select(include => include is null
+                ? null
+                : Path.GetFileName(include.Replace('\\', '/')))
+            .ToList();
+
+        Assert.Equal(["AcDream.Platform.csproj"], projectReferences);
+        Assert.Empty(project.Descendants("PackageReference"));
+    }
+
+    private static string FindRepositoryRoot(
+        [CallerFilePath] string sourcePath = "")
+    {
+        string[] starts =
+        {
+            Path.GetDirectoryName(sourcePath) ?? string.Empty,
+            Directory.GetCurrentDirectory(),
+            AppContext.BaseDirectory,
+        };
+        foreach (string start in starts)
+        {
+            if (string.IsNullOrEmpty(start))
+            {
+                continue;
+            }
+
+            var directory = new DirectoryInfo(start);
+            while (directory is not null)
+            {
+                if (File.Exists(Path.Combine(
+                        directory.FullName,
+                        "AcDream.slnx")))
+                {
+                    return directory.FullName;
+                }
+
+                directory = directory.Parent;
+            }
+        }
+
+        throw new DirectoryNotFoundException(
+            "Could not find AcDream.slnx above the source, working, or output directory.");
+    }
+}