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>

src/AcDream.Launcher.Core/AcDream.Launcher.Core.csproj

@@ -5,6 +5,12 @@
     <Nullable>enable</Nullable>
     <LangVersion>latest</LangVersion>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+    <!-- Required by the LibraryImportAttribute source generator (F3's
+         Linux SIGINT P/Invoke in Launching/ILauncherChildProcess.cs):
+         the generated marshalling stub calls through an unmanaged
+         function pointer, which the compiler only allows in an unsafe
+         context. -->
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
   <ItemGroup>
     <ProjectReference Include="..\AcDream.Platform\AcDream.Platform.csproj" />

src/AcDream.Launcher.Core/Launching/ILauncherChildProcess.cs

@@ -1,4 +1,5 @@
 using System.Diagnostics;
+using System.Runtime.InteropServices;
 
 namespace AcDream.Launcher.Core.Launching;
 
@@ -28,6 +29,26 @@ public interface ILauncherChildProcess : IDisposable
 
     void Start();
 
+    /// <summary>
+    /// Attempts a graceful stop signal appropriate to the platform,
+    /// tried BEFORE <see cref="CloseMainWindow"/> (Campaign LA plan §LA3
+    /// review finding F3): a no-window console host (e.g.
+    /// <c>AcDream.Headless</c>) never has a main window for
+    /// <see cref="CloseMainWindow"/> to close, so without this step
+    /// <see cref="LauncherProcessSupervisor.Stop"/> always degraded
+    /// straight to a timeout + hard <see cref="Kill"/> — and a hard kill
+    /// leaves the ACE account session stuck for several minutes (a
+    /// documented project landmine; see CLAUDE.md
+    /// "Logout-before-reconnect"). On Linux this sends SIGINT (K4 proved
+    /// the headless host's SIGINT handler produces an ACE-confirmed
+    /// graceful logout). On Windows there is no reliable cross-console
+    /// mechanism for an arbitrary no-window child process today — see
+    /// <c>docs/ISSUES.md</c> for the tracked gap and fix direction; this
+    /// returns false there. Returns true only when the signal was
+    /// actually delivered; never throws.
+    /// </summary>
+    bool TryRequestGracefulStop();
+
     /// <summary>Mirrors <see cref="Process.CloseMainWindow"/> — requests
     /// a graceful close via WM_CLOSE. Returns false for a console/no-
     /// window process (never throws), matching the real API.</summary>
@@ -54,8 +75,16 @@ public sealed class SystemChildProcessFactory : ILauncherChildProcessFactory
         new SystemChildProcess(spec);
 }
 
-internal sealed class SystemChildProcess : ILauncherChildProcess
+internal sealed partial class SystemChildProcess : ILauncherChildProcess
 {
+    // SIGINT's numeric value (POSIX-stable across Linux distributions).
+    // K4/Slice K already proved the headless host's SIGINT handler
+    // produces an ACE-confirmed graceful logout.
+    private const int Sigint = 2;
+
+    [LibraryImport("libc", SetLastError = true)]
+    private static partial int kill(int pid, int sig);
+
     private readonly Process _process;
     private bool _raisingEnabled;
 
@@ -99,6 +128,31 @@ internal sealed class SystemChildProcess : ILauncherChildProcess
         _process.Start();
     }
 
+    public bool TryRequestGracefulStop()
+    {
+        if (!OperatingSystem.IsLinux())
+        {
+            // No reliable cross-console mechanism exists for an
+            // arbitrary no-window Windows child process — tracked gap,
+            // see docs/ISSUES.md.
+            return false;
+        }
+
+        try
+        {
+            return kill(_process.Id, Sigint) == 0;
+        }
+        catch
+        {
+            // Matches CloseMainWindow's "never throws" contract — the
+            // process may not have started yet, may have already exited
+            // (ESRCH), or the platform may lack libc under an unusual
+            // Linux runtime; any of these degrade to "signal not sent"
+            // rather than an exception out of Stop().
+            return false;
+        }
+    }
+
     public bool CloseMainWindow() => _process.CloseMainWindow();
 
     public void Kill() => _process.Kill(entireProcessTree: true);

src/AcDream.Launcher.Core/Launching/LauncherProcessSupervisor.cs

@@ -56,9 +56,11 @@ public sealed class LauncherProcessSupervisor : IDisposable
 
         SetState(LauncherSessionState.Starting);
 
+        bool started = false;
         try
         {
             process.Start();
+            started = true;
 
             if (password is not null)
             {
@@ -77,6 +79,28 @@ public sealed class LauncherProcessSupervisor : IDisposable
                 _process = null;
             }
 
+            // A failure after the child actually started (e.g. the stdin
+            // pipe breaks while feeding the password) must not leave a
+            // live, unsupervised, undisposable child running (Campaign LA
+            // plan §LA3 review finding F8) — kill the whole process tree
+            // and release the handle before propagating the original
+            // failure.
+            if (started)
+            {
+                try
+                {
+                    process.Kill();
+                }
+                catch
+                {
+                    // Best-effort — the ORIGINAL failure, rethrown below,
+                    // is what the caller needs to see; a failed cleanup
+                    // kill must not replace it.
+                }
+            }
+
+            process.Dispose();
+
             throw;
         }
 
@@ -84,10 +108,22 @@ public sealed class LauncherProcessSupervisor : IDisposable
     }
 
     /// <summary>
-    /// Requests a graceful stop (CloseMainWindow), falling back to Kill
-    /// if the process has not exited within <paramref name="timeout"/>.
-    /// A no-op if <see cref="Start"/> was never called or the process has
-    /// already exited.
+    /// Requests a graceful stop — first
+    /// <see cref="ILauncherChildProcess.TryRequestGracefulStop"/> (SIGINT
+    /// on Linux; a no-op on Windows today, see
+    /// <see cref="ILauncherChildProcess.TryRequestGracefulStop"/>'s docs),
+    /// then <see cref="ILauncherChildProcess.CloseMainWindow"/> — falling
+    /// back to <see cref="ILauncherChildProcess.Kill"/> if the process has
+    /// not exited within <paramref name="timeout"/>. A no-op if
+    /// <see cref="Start"/> was never called or the process has already
+    /// exited.
+    /// <para>
+    /// BLOCKS THE CALLING THREAD for up to <paramref name="timeout"/>
+    /// (via the real child's <c>WaitForExit</c>) — callers on a UI thread
+    /// must dispatch this off-thread rather than calling it directly (a
+    /// binding requirement for the LA4 Avalonia UI, which will call this
+    /// method from a "stop session" action).
+    /// </para>
     /// </summary>
     public void Stop(TimeSpan timeout)
     {
@@ -102,6 +138,7 @@ public sealed class LauncherProcessSupervisor : IDisposable
             return;
         }
 
+        process.TryRequestGracefulStop();
         process.CloseMainWindow();
         if (!process.WaitForExit(timeout) && !process.HasExited)
         {
@@ -121,10 +158,28 @@ public sealed class LauncherProcessSupervisor : IDisposable
         SetState(LauncherSessionState.Exited);
     }
 
+    /// <summary>
+    /// Applies a state transition, or silently ignores it (Campaign LA
+    /// plan §LA3 review finding F9): once <see cref="State"/> reaches the
+    /// terminal <see cref="LauncherSessionState.Exited"/>, no later call
+    /// may move it anywhere else, and <see cref="StateChanged"/> only
+    /// fires for a transition that was actually applied. This matters
+    /// because <see cref="Start"/>'s trailing
+    /// <c>SetState(LauncherSessionState.Running)</c> can race a
+    /// synchronous <see cref="OnProcessExited"/> callback fired from
+    /// inside <see cref="Start"/> itself (a child that dies immediately)
+    /// — without this guard, "Running" would silently resurrect a
+    /// process that has already reported its exit.
+    /// </summary>
     private void SetState(LauncherSessionState state)
     {
         lock (_gate)
         {
+            if (State == LauncherSessionState.Exited)
+            {
+                return;
+            }
+
             State = state;
         }
 

src/AcDream.Launcher.Core/Launching/SessionConfigComposer.cs

@@ -52,13 +52,7 @@ public static class SessionConfigComposer
         ArgumentNullException.ThrowIfNull(paths);
         ArgumentException.ThrowIfNullOrWhiteSpace(sessionId);
 
-        string sessionDirectory = Path.Combine(
-            paths.CacheDirectory,
-            "launcher",
-            "sessions",
-            sessionId);
-        string configFilePath = Path.Combine(sessionDirectory, "session.json");
-        string statusFilePath = Path.Combine(sessionDirectory, "status.jsonl");
+        (string configFilePath, string statusFilePath) = BuildSessionPaths(paths, sessionId);
 
         SessionCharacterSelector? selector = character.LaunchMode == LaunchMode.GuiSelect
             ? null
@@ -92,7 +86,69 @@ public static class SessionConfigComposer
         {
             Process = new SessionProcessSettings
             {
-                Paths = new SessionPathOverrides(),
+                Content = new SessionContentDescriptor
+                {
+                    DatDirectory = install.DatDirectory,
+                    PreparedAssetPath = install.PreparedAssetPath,
+                },
+            },
+            Sessions = [descriptor],
+        };
+
+        return new ComposedSessionConfig(
+            sessionId,
+            configFilePath,
+            statusFilePath,
+            document);
+    }
+
+    /// <summary>
+    /// Builds a probe session-config document (Campaign LA plan §LA2/
+    /// §LA3 review finding F2): the session carries <c>mode: "probe"</c>,
+    /// no <c>character</c> selector, and no <c>policy</c> — the host
+    /// reports the account's character roster over the status stream and
+    /// exits without entering the world. <c>plugins</c>/<c>loginCommands</c>
+    /// don't apply to a probe and are always omitted, exactly like an
+    /// empty configured set on a normal session.
+    /// </summary>
+    public static ComposedSessionConfig ComposeProbe(
+        ServerProfile server,
+        AccountProfile account,
+        LauncherInstallRecord install,
+        ApplicationPathSet paths,
+        string sessionId)
+    {
+        ArgumentNullException.ThrowIfNull(server);
+        ArgumentNullException.ThrowIfNull(account);
+        ArgumentNullException.ThrowIfNull(install);
+        ArgumentNullException.ThrowIfNull(paths);
+        ArgumentException.ThrowIfNullOrWhiteSpace(sessionId);
+
+        (string configFilePath, string statusFilePath) = BuildSessionPaths(paths, sessionId);
+
+        var descriptor = new SessionDescriptor
+        {
+            Id = sessionId,
+            Mode = "probe",
+            Endpoint = new SessionEndpointDescriptor
+            {
+                Host = server.Host,
+                Port = server.Port,
+            },
+            Account = account.Account,
+            Character = null,
+            Policy = null,
+            Credential = new SessionCredentialDescriptor(),
+            Plugins = null,
+            LoginCommands = null,
+            LoginCommandDelayMs = null,
+            StatusFile = statusFilePath,
+        };
+
+        var document = new SessionConfigDocument
+        {
+            Process = new SessionProcessSettings
+            {
                 Content = new SessionContentDescriptor
                 {
                     DatDirectory = install.DatDirectory,
@@ -149,9 +205,28 @@ public static class SessionConfigComposer
     public static string Serialize(SessionConfigDocument document) =>
         JsonSerializer.Serialize(document, SerializerOptions);
 
+    private static (string ConfigFilePath, string StatusFilePath) BuildSessionPaths(
+        ApplicationPathSet paths,
+        string sessionId)
+    {
+        string sessionDirectory = Path.Combine(
+            paths.CacheDirectory,
+            "launcher",
+            "sessions",
+            sessionId);
+
+        return (
+            Path.Combine(sessionDirectory, "session.json"),
+            Path.Combine(sessionDirectory, "status.jsonl"));
+    }
+
     private static SessionCharacterSelector BuildSelector(CharacterProfile character)
     {
-        if (CharacterIdFormat.TryParse(character.Id, out uint id))
+        // A parsed id of 0 is not a usable selector — both host loaders
+        // (App/Headless) reject `id: 0` outright, so falling through to
+        // the name selector here is the only shape that reaches a real
+        // character (Campaign LA plan §LA3 review finding F10).
+        if (CharacterIdFormat.TryParse(character.Id, out uint id) && id != 0)
         {
             return new SessionCharacterSelector { Id = id };
         }

src/AcDream.Launcher.Core/Launching/SessionConfigDocument.cs

@@ -29,7 +29,18 @@ public sealed class SessionConfigDocument
 
 public sealed class SessionProcessSettings
 {
-    public SessionPathOverrides Paths { get; init; } = new();
+    /// <summary>
+    /// PINNED CONTRACT (Campaign LA plan §LA3 review, finding F1): the
+    /// <c>paths</c> KEY is entirely OMITTED from the written JSON unless
+    /// a caller explicitly supplies overrides — never an empty object.
+    /// The App-side loader parses with strict
+    /// <c>UnmappedMemberHandling.Disallow</c> and has no <c>paths</c>
+    /// member of its own, so an emitted <c>"paths":{}</c> is a null-
+    /// omission artifact (the object's own members are all optional and
+    /// omit cleanly, but the containing property was never null itself)
+    /// that would fail every gui/guiSelect launch at config load.
+    /// </summary>
+    public SessionPathOverrides? Paths { get; init; }
 
     public SessionContentDescriptor Content { get; init; } = new();
 }
@@ -65,6 +76,13 @@ public sealed class SessionDescriptor
 {
     public string Id { get; init; } = string.Empty;
 
+    /// <summary>Present only for a probe session (<c>"probe"</c>,
+    /// Campaign LA plan §LA2/§LA3) — the host reports the account's
+    /// character roster and exits without entering the world. OMITTED
+    /// entirely for a normal gui/guiSelect/headless play session.
+    /// </summary>
+    public string? Mode { get; init; }
+
     public SessionEndpointDescriptor Endpoint { get; init; } = new();
 
     public string Account { get; init; } = string.Empty;

src/AcDream.Launcher.Core/Profiles/CharacterIdFormat.cs

@@ -13,6 +13,15 @@ public static class CharacterIdFormat
     public static string ToHexString(uint id) =>
         "0x" + id.ToString("X8", CultureInfo.InvariantCulture);
 
+    /// <summary>
+    /// Parses <paramref name="text"/> as a hex character id — the
+    /// <c>0x</c> prefix (case-insensitive) is REQUIRED (Campaign LA plan
+    /// §LA3 review finding F10). Every all-digit id is ALSO a valid hex
+    /// number (e.g. <c>"12345678"</c>), so accepting a bare unprefixed
+    /// string as hex silently reinterprets a hand-typed decimal id and
+    /// selects the wrong character; requiring the prefix makes "this is
+    /// hex" an explicit, unambiguous signal instead of a guess.
+    /// </summary>
     public static bool TryParse(string? text, out uint id)
     {
         id = 0;
@@ -20,8 +29,10 @@ public static class CharacterIdFormat
             return false;
 
         ReadOnlySpan<char> span = text.AsSpan().Trim();
-        if (span.StartsWith("0x", StringComparison.OrdinalIgnoreCase))
-            span = span[2..];
+        if (!span.StartsWith("0x", StringComparison.OrdinalIgnoreCase))
+            return false;
+
+        span = span[2..];
 
         return uint.TryParse(
             span,

src/AcDream.Launcher.Core/Profiles/LauncherProfileStore.cs

@@ -66,6 +66,13 @@ public sealed class LauncherProfileStore
     /// </summary>
     public bool Load()
     {
+        // Opportunistic cleanup of a stale ".tmp" left behind by a Save()
+        // that crashed between creating the temp file and the atomic
+        // rename (Campaign LA plan §LA3 review finding F4) — a stray
+        // temp file carries the same plaintext credentials as the real
+        // store and should not linger.
+        DeleteStaleTempFile(FilePath + ".tmp");
+
         if (!File.Exists(FilePath))
         {
             Document = new LauncherProfileDocument();
@@ -108,9 +115,16 @@ public sealed class LauncherProfileStore
     /// <summary>
     /// Persists <see cref="Document"/> to <see cref="FilePath"/> via a
     /// write-then-atomic-rename so a crash mid-write never leaves a
-    /// truncated credentials file. On Linux, restricts the final file to
-    /// owner read/write (0600) per Campaign LA's plaintext-credential
-    /// decision (spec §5, decisions log).
+    /// truncated credentials file. On Linux, the temp file is chmod'd to
+    /// owner read/write (0600) immediately after creation — BEFORE any
+    /// plaintext credential is serialized into it — so there is no window
+    /// where the temp file carries the process umask's (potentially
+    /// world/group-readable) default permissions while holding a
+    /// password; the final path gets the same restriction after the
+    /// rename (Campaign LA's plaintext-credential decision, spec §5,
+    /// decisions log; the temp-file window itself is review finding F4).
+    /// A failure between temp-file creation and the rename deletes the
+    /// stale temp file rather than leaving it behind.
     /// </summary>
     public void Save()
     {
@@ -121,12 +135,27 @@ public sealed class LauncherProfileStore
         }
 
         string tempPath = FilePath + ".tmp";
-        using (FileStream stream = File.Create(tempPath))
+        try
         {
-            JsonSerializer.Serialize(stream, Document, SerializerOptions);
-        }
+            using (FileStream stream = File.Create(tempPath))
+            {
+                if (OperatingSystem.IsLinux())
+                {
+                    File.SetUnixFileMode(
+                        tempPath,
+                        UnixFileMode.UserRead | UnixFileMode.UserWrite);
+                }
 
-        File.Move(tempPath, FilePath, overwrite: true);
+                JsonSerializer.Serialize(stream, Document, SerializerOptions);
+            }
+
+            File.Move(tempPath, FilePath, overwrite: true);
+        }
+        catch
+        {
+            DeleteStaleTempFile(tempPath);
+            throw;
+        }
 
         if (OperatingSystem.IsLinux())
         {
@@ -136,6 +165,23 @@ public sealed class LauncherProfileStore
         }
     }
 
+    private static void DeleteStaleTempFile(string tempPath)
+    {
+        try
+        {
+            if (File.Exists(tempPath))
+            {
+                File.Delete(tempPath);
+            }
+        }
+        catch
+        {
+            // Best-effort cleanup only — the caller's own exception (a
+            // failed Save()) or the fresh Load() already in progress is
+            // what matters; a cleanup failure must not mask either.
+        }
+    }
+
     // --- Server CRUD -----------------------------------------------
 
     public ServerProfile AddServer(string name, string host, int port)
@@ -312,16 +358,26 @@ public sealed class LauncherProfileStore
         foreach (CharacterRosterEntry entry in roster)
         {
             string idText = CharacterIdFormat.ToHexString(entry.Id);
-            CharacterProfile? existing = profile.Characters.Find(
-                character => string.Equals(
-                    character.Id,
-                    idText,
-                    StringComparison.OrdinalIgnoreCase));
 
-            // Defensive fallback for a hand-edited file where a character
-            // row was added with a name but no id yet.
+            // Normalize BOTH sides through TryParse/ToHexString rather
+            // than a raw string compare (Campaign LA plan §LA3 review
+            // finding F10): a stored id that round-trips to the same
+            // uint (different case, or — before this fix — no "0x"
+            // prefix) must match even though its text isn't byte-
+            // identical to the canonical form this method itself always
+            // writes.
+            CharacterProfile? existing = profile.Characters.Find(
+                character => CharacterIdFormat.TryParse(character.Id, out uint existingId)
+                    && existingId == entry.Id);
+
+            // Defensive fallback for a row whose id is missing OR
+            // unparseable (e.g. a hand-edited id with no "0x" prefix,
+            // which TryParse now rejects outright) — match by name
+            // instead so a later merge self-heals the id into the
+            // canonical form rather than creating a permanent duplicate
+            // row.
             existing ??= profile.Characters.Find(
-                character => character.Id is null
+                character => !CharacterIdFormat.TryParse(character.Id, out _)
                     && string.Equals(
                         character.Name,
                         entry.Name,

src/AcDream.Launcher.Core/Status/StatusEvent.cs

@@ -26,7 +26,7 @@ public sealed record ConnectedStatusEvent : StatusEvent;
 public readonly record struct StatusCharacterEntry(
     uint Id,
     string Name,
-    int SecondsGreyedOut);
+    uint SecondsGreyedOut);
 
 public sealed record CharacterListStatusEvent : StatusEvent
 {
@@ -79,3 +79,18 @@ public sealed record UnknownStatusEvent : StatusEvent
 {
     public required string RawJson { get; init; }
 }
+
+/// <summary>
+/// A status line whose <c>e</c> value IS one of the recognized event
+/// names, but whose payload does not match that event's expected shape
+/// (a missing required field, or a field present with the wrong JSON
+/// kind). Distinguished from <see cref="UnknownStatusEvent"/> (Campaign
+/// LA plan §LA3 review finding F12) so a launcher can tell "a newer/older
+/// host sent an event I've never heard of" apart from "a host I recognize
+/// sent me garbage for an event I do know" — the two cases call for
+/// different diagnostics. The tailer never throws for either case.
+/// </summary>
+public sealed record MalformedStatusEvent : StatusEvent
+{
+    public required string Error { get; init; }
+}

src/AcDream.Launcher.Core/Status/StatusEventParser.cs

@@ -11,23 +11,40 @@ namespace AcDream.Launcher.Core.Status;
 /// "accountName":"...","slotCount":6,"characters":[...]}</c>.
 ///
 /// <para>
-/// Never throws: a line whose <c>e</c> is not one of the eight known
-/// values, or whose payload doesn't match that event's expected shape,
-/// or that isn't valid JSON at all, degrades to a typed
-/// <see cref="UnknownStatusEvent"/> rather than an exception — a
-/// launcher must keep tailing a session's status stream even against a
-/// host running a newer/older wire version.
+/// Never throws: a null/blank/malformed-JSON line, an unrecognized
+/// <c>e</c> value, or a recognized <c>e</c> whose payload doesn't match
+/// that event's expected shape, all degrade to a typed event
+/// (<see cref="UnknownStatusEvent"/> or <see cref="MalformedStatusEvent"/>
+/// — see each type's docs) rather than an exception — a launcher must
+/// keep tailing a session's status stream even against a host running a
+/// newer/older wire version, or a host that briefly writes a torn line.
 /// </para>
 /// </summary>
 public static class StatusEventParser
 {
     public static StatusEvent Parse(string line)
     {
-        ArgumentException.ThrowIfNullOrWhiteSpace(line);
+        if (string.IsNullOrWhiteSpace(line))
+        {
+            // Campaign LA plan §LA3 review finding F7: a blank/whitespace
+            // line is a normal "nothing complete here yet" degrade, not a
+            // caller error — the old ArgumentException.ThrowIfNullOrWhiteSpace
+            // guard ran BEFORE the try/catch below and escaped uncaught.
+            return UnknownEvent(line ?? string.Empty);
+        }
 
+        JsonDocument document;
         try
         {
-            using JsonDocument document = JsonDocument.Parse(line);
+            document = JsonDocument.Parse(line);
+        }
+        catch (JsonException)
+        {
+            return UnknownEvent(line);
+        }
+
+        using (document)
+        {
             JsonElement root = document.RootElement;
 
             int v = GetInt32OrDefault(root, "v");
@@ -35,51 +52,70 @@ public static class StatusEventParser
             DateTimeOffset t = GetDateTimeOffsetOrDefault(root, "t");
             string sessionId = GetStringOrDefault(root, "sessionId");
 
-            return e switch
+            try
             {
-                "started" =>
-                    new StartedStatusEvent { V = v, E = e, T = t, SessionId = sessionId },
-                "connected" =>
-                    new ConnectedStatusEvent { V = v, E = e, T = t, SessionId = sessionId },
-                "characterList" =>
-                    ParseCharacterList(root, v, e, t, sessionId),
-                "enteredWorld" =>
-                    ParseEnteredWorld(root, v, e, t, sessionId),
-                "pluginLoaded" =>
-                    ParsePluginLoaded(root, v, e, t, sessionId),
-                "pluginFailed" =>
-                    ParsePluginFailed(root, v, e, t, sessionId),
-                "disconnected" =>
-                    ParseDisconnected(root, v, e, t, sessionId),
-                "exited" =>
-                    ParseExited(root, v, e, t, sessionId),
-                _ =>
-                    new UnknownStatusEvent
-                    {
-                        V = v,
-                        E = e,
-                        T = t,
-                        SessionId = sessionId,
-                        RawJson = line,
-                    },
-            };
-        }
-        catch (Exception)
-        {
-            // JsonException (malformed JSON), FormatException (a
-            // required-field miss inside a Parse* helper) — all degrade
-            // the same way: never throw out of the tailer.
-            return new UnknownStatusEvent
+                return e switch
+                {
+                    "started" =>
+                        new StartedStatusEvent { V = v, E = e, T = t, SessionId = sessionId },
+                    "connected" =>
+                        new ConnectedStatusEvent { V = v, E = e, T = t, SessionId = sessionId },
+                    "characterList" =>
+                        ParseCharacterList(root, v, e, t, sessionId),
+                    "enteredWorld" =>
+                        ParseEnteredWorld(root, v, e, t, sessionId),
+                    "pluginLoaded" =>
+                        ParsePluginLoaded(root, v, e, t, sessionId),
+                    "pluginFailed" =>
+                        ParsePluginFailed(root, v, e, t, sessionId),
+                    "disconnected" =>
+                        ParseDisconnected(root, v, e, t, sessionId),
+                    "exited" =>
+                        ParseExited(root, v, e, t, sessionId),
+                    _ =>
+                        new UnknownStatusEvent
+                        {
+                            V = v,
+                            E = e,
+                            T = t,
+                            SessionId = sessionId,
+                            RawJson = line,
+                        },
+                };
+            }
+            catch (Exception ex) when (ex is FormatException or InvalidOperationException)
             {
-                V = 0,
-                E = string.Empty,
-                T = default,
-                SessionId = string.Empty,
-                RawJson = line,
-            };
+                // FormatException: a Require* helper found a missing
+                // field or a field of the wrong JSON kind (e.g.
+                // "secondsGreyedOut": true"). InvalidOperationException:
+                // a JsonElement API call (EnumerateArray, TryGetProperty)
+                // against an element of the wrong ValueKind (e.g.
+                // "characters" present but not an array). Both mean `e`
+                // WAS recognized but its payload wasn't — distinguished
+                // from UnknownStatusEvent (Campaign LA plan §LA3 review
+                // finding F12).
+                return new MalformedStatusEvent
+                {
+                    V = v,
+                    E = e,
+                    T = t,
+                    SessionId = sessionId,
+                    Error = ex.Message,
+                };
+            }
         }
     }
 
+    private static UnknownStatusEvent UnknownEvent(string rawLine) =>
+        new()
+        {
+            V = 0,
+            E = string.Empty,
+            T = default,
+            SessionId = string.Empty,
+            RawJson = rawLine,
+        };
+
     private static StatusEvent ParseCharacterList(
         JsonElement root,
         int v,
@@ -96,7 +132,7 @@ public static class StatusEventParser
         {
             uint id = RequireUInt32(item, "id");
             string name = RequireString(item, "name");
-            int secondsGreyedOut = RequireInt32(item, "secondsGreyedOut");
+            uint secondsGreyedOut = RequireUInt32(item, "secondsGreyedOut");
             characters.Add(new StatusCharacterEntry(id, name, secondsGreyedOut));
         }
 

src/AcDream.Launcher.Core/Status/StatusFileTailer.cs

@@ -33,10 +33,31 @@ public sealed class StatusFileTailer
     /// <summary>
     /// Reads and parses every complete line appended to the file since
     /// the last call. Returns an empty list (never null, never throws)
-    /// when the file doesn't exist yet or nothing new/complete has
-    /// arrived since the last poll.
+    /// when the file doesn't exist yet, has been deleted/rotated between
+    /// the existence check and the open (a TOCTOU window — Campaign LA
+    /// plan §LA3 review finding F7), or nothing new/complete has arrived
+    /// since the last poll.
     /// </summary>
     public IReadOnlyList<StatusEvent> ReadNewEvents()
+    {
+        try
+        {
+            return ReadNewEventsCore();
+        }
+        catch (Exception ex) when (
+            ex is FileNotFoundException or DirectoryNotFoundException or IOException)
+        {
+            // The host process deleted/rotated the file (or its
+            // directory) between File.Exists and the open below, or
+            // another transient I/O condition hit mid-read — degrade to
+            // "nothing new this poll" rather than throwing out of a
+            // method documented never to throw; the next poll picks up
+            // wherever the file (or its replacement) actually is.
+            return [];
+        }
+    }
+
+    private IReadOnlyList<StatusEvent> ReadNewEventsCore()
     {
         if (!File.Exists(_path))
         {