wip: Campaign LA LA2 probe mode + idle policy — INCOMPLETE, stopped mid-task

Agent was stopped for token budget. Landed here: probe flag through
LiveSessionConnectOptions + the StartCore short-circuit, the mode field
with JsonRequired-to-semantic-validation move, host exit-code mapping,
and 34 passing tests including 3 new probe tests (agent last reported
green before the stop). NOT DONE: the idle-policy unit tests (next
step), full-suite verification, and the WSL run.

Build/test state UNVERIFIED at this commit. Next session: finish idle
policy tests, run Runtime+Headless Release suites Windows and WSL, then
dispatch the Opus dual-lens review.

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

src/AcDream.Headless/Configuration/HeadlessConfiguration.cs

@@ -46,11 +46,33 @@ internal sealed record HeadlessSessionDescriptor
     [JsonRequired]
     public string Account { get; init; } = string.Empty;
 
-    [JsonRequired]
+    /// <summary>
-    public HeadlessCharacterSelector Character { get; init; } = new();
+    /// Campaign LA slice LA2: ABSENT (<see langword="null"/>) for normal play
+    /// sessions; <see cref="HeadlessSessionMode.Probe"/> for the LA2 probe
+    /// (connect → characterList → graceful disconnect, never EnterWorld) —
+    /// the pinned launch-contract schema's <c>mode</c> field
+    /// (<c>docs/plans/2026-08-14-launcher-campaign.md</c> LA1/LA2).
+    /// <see cref="Character"/>/<see cref="Policy"/> requiredness depends on
+    /// this value, which is why their requiredness lives in
+    /// <see cref="HeadlessConfigurationLoader"/>'s semantic validation rather
+    /// than a <c>[JsonRequired]</c> attribute — that attribute fires during
+    /// deserialization, before <see cref="Mode"/> can be inspected at all.
+    /// </summary>
+    public HeadlessSessionMode? Mode { get; init; }
 
-    [JsonRequired]
+    /// <summary>
-    public HeadlessBotPolicyDescriptor Policy { get; init; } = new();
+    /// Required for play sessions (<see cref="Mode"/> absent); MUST be
+    /// omitted for probe sessions (<see cref="HeadlessSessionMode.Probe"/>) —
+    /// the pinned contract keeps the shape unambiguous by forbidding a probe
+    /// session from also declaring a selector. Enforced by
+    /// <see cref="HeadlessConfigurationLoader.ValidateSession"/>, not
+    /// <c>[JsonRequired]</c> (see this record's own doc on <see cref="Mode"/>).
+    /// </summary>
+    public HeadlessCharacterSelector? Character { get; init; }
+
+    /// <summary>Same mode-dependent requiredness as <see cref="Character"/>:
+    /// required for play sessions, forbidden for probe sessions.</summary>
+    public HeadlessBotPolicyDescriptor? Policy { get; init; }
 
     [JsonRequired]
     public HeadlessCredentialReference Credential { get; init; } = new();
@@ -140,6 +162,19 @@ internal sealed class HeadlessBotPolicyDescriptor
     public HeadlessBotPolicyRole? Role { get; init; }
 }
 
+/// <summary>
+/// Campaign LA slice LA2: see <see cref="HeadlessSessionDescriptor.Mode"/>.
+/// The pinned launch-contract schema defines exactly two states for a
+/// session — ABSENT (mapped to <see langword="null"/>, meaning "play") or
+/// the literal string <c>"probe"</c> — so <see cref="Probe"/> is the only
+/// member; there is no explicit "play" spelling.
+/// </summary>
+[JsonConverter(typeof(JsonStringEnumConverter<HeadlessSessionMode>))]
+internal enum HeadlessSessionMode
+{
+    Probe,
+}
+
 /// <summary>See <see cref="HeadlessBotPolicyDescriptor.Role"/>.</summary>
 [JsonConverter(typeof(JsonStringEnumConverter<HeadlessBotPolicyRole>))]
 internal enum HeadlessBotPolicyRole

src/AcDream.Headless/Configuration/HeadlessConfigurationLoader.cs

@@ -182,6 +182,57 @@ internal static class HeadlessConfigurationLoader
                 $"Session '{session.Id}' requires a non-empty account.");
         }
 
+        ValidateModeShape(session);
+
+        if (session.Credential is null
+            || string.IsNullOrWhiteSpace(session.Credential.Reference))
+        {
+            throw new HeadlessConfigurationException(
+                $"Session '{session.Id}' requires a credential reference.");
+        }
+
+        ValidateCharacterOptions(session);
+        ValidateLaunchContractFields(session);
+    }
+
+    /// <summary>
+    /// Campaign LA slice LA2: mode-dependent requiredness for
+    /// <see cref="HeadlessSessionDescriptor.Character"/>/
+    /// <see cref="HeadlessSessionDescriptor.Policy"/> — this REPLACES the
+    /// former `[JsonRequired]` attributes on both properties (which fired
+    /// unconditionally at deserialize time, before a probe session's
+    /// omission could ever be distinguished from a play session's mistake).
+    /// A play session (mode absent) keeps EXACTLY today's strictness: a
+    /// missing/malformed character selector or a missing policy id still
+    /// fails load, just via <see cref="HeadlessConfigurationException"/>
+    /// naming the field instead of a raw <see cref="JsonException"/> citing
+    /// "missing required properties" — same exit code (3,
+    /// <c>HeadlessExitCode.ConfigurationError</c>) either way, more specific
+    /// text now (an accepted improvement, not a contract change). A probe
+    /// session (mode "probe") must OMIT both fields entirely — the pinned
+    /// contract keeps the shape unambiguous by rejecting a probe session
+    /// that also declares a selector or a policy, rather than silently
+    /// ignoring them.
+    /// </summary>
+    private static void ValidateModeShape(HeadlessSessionDescriptor session)
+    {
+        if (session.Mode == HeadlessSessionMode.Probe)
+        {
+            if (session.Character is not null)
+            {
+                throw new HeadlessConfigurationException(
+                    $"Session '{session.Id}' has mode \"probe\" and must omit "
+                    + "'character' — a probe never selects a character.");
+            }
+            if (session.Policy is not null)
+            {
+                throw new HeadlessConfigurationException(
+                    $"Session '{session.Id}' has mode \"probe\" and must omit "
+                    + "'policy' — a probe never drives a bot policy.");
+            }
+            return;
+        }
+
         if (session.Character is null)
         {
             throw new HeadlessConfigurationException(
@@ -206,16 +257,6 @@ internal static class HeadlessConfigurationLoader
             throw new HeadlessConfigurationException(
                 $"Session '{session.Id}' requires a non-empty policy id.");
         }
-
-        if (session.Credential is null
-            || string.IsNullOrWhiteSpace(session.Credential.Reference))
-        {
-            throw new HeadlessConfigurationException(
-                $"Session '{session.Id}' requires a credential reference.");
-        }
-
-        ValidateCharacterOptions(session);
-        ValidateLaunchContractFields(session);
     }
 
     /// <summary>

src/AcDream.Headless/Hosting/HeadlessProcessHost.cs

@@ -200,6 +200,22 @@ internal sealed class HeadlessProcessHost : IDisposable
         foreach (HeadlessSessionHost session in _sessions)
         {
             RuntimeSessionStartResult started = session.Start();
+            // Campaign LA slice LA2: ProbeComplete is a SUCCESS variant, not
+            // a connection failure — the session already connected, reported
+            // its roster, and gracefully disconnected before EnterWorld (see
+            // LiveSessionController's probe short-circuit). Continue to the
+            // next configured session instead of returning ConnectionError,
+            // so a probe session sharing a process with play sessions never
+            // tears the others down. ProbeHeadlessBotPolicy already reports
+            // IsComplete, so the scheduler below skips this session entirely.
+            if (started.Status == RuntimeSessionStartStatus.ProbeComplete)
+            {
+                _diagnostics.Lifecycle(
+                    session.SessionId,
+                    "probed",
+                    session.Runtime);
+                continue;
+            }
             if (started.Status != RuntimeSessionStartStatus.Connected)
             {
                 if (started.Error is { } error)

src/AcDream.Headless/Hosting/HeadlessSessionHost.cs

@@ -319,7 +319,7 @@ internal sealed class HeadlessSessionHost : IDisposable
                             // doc). Gating on role keeps two sessions
                             // writing the SAME field from ever racing —
                             // only one role ever writes it.
-                            if (descriptor.Policy.Role
+                            if (descriptor.Policy?.Role
                                     == HeadlessBotPolicyRole.Recruit
                                 && gateCoordinator is not null)
                             {
@@ -366,13 +366,24 @@ internal sealed class HeadlessSessionHost : IDisposable
 
             hostLease = runtime.AcquireHostLease(
                 $"headless:{descriptor.Id}");
+            // Campaign LA slice LA2: a probe session's descriptor carries no
+            // `policy` at all (the loader rejects the opposite pairing) — a
+            // probe never reaches TrySelectCharacter/EnterWorld, so there is
+            // no policy id to switch on. ProbeHeadlessBotPolicy reports
+            // IsComplete unconditionally so HeadlessProcessScheduler treats
+            // this session as already finished the instant it is
+            // constructed, letting the scheduler's Run() loop return
+            // immediately for a probe-only process instead of waiting for
+            // SIGINT.
             policy = policyOverride
-                ?? HeadlessBotPolicyFactory.Create(
+                ?? (descriptor.Mode == HeadlessSessionMode.Probe
-                    descriptor.Policy,
+                    ? new ProbeHeadlessBotPolicy()
-                    runtime,
+                    : HeadlessBotPolicyFactory.Create(
-                    () => _pendingConfirmation,
+                        descriptor.Policy!,
-                    RespondToConfirmation,
+                        runtime,
-                    gateCoordinator);
+                        () => _pendingConfirmation,
+                        RespondToConfirmation,
+                        gateCoordinator));
             policySubscription = runtime.Subscribe(policy);
             diagnostics.Lifecycle(
                 descriptor.Id,
@@ -636,11 +647,18 @@ internal sealed class HeadlessSessionHost : IDisposable
                         _stoppedGeneration);
                     // Campaign LA slice LA1: "exited" = terminal — the sole
                     // point every disposal path (graceful and post-
-                    // quarantine) converges on.
+                    // quarantine) converges on. LA2: a probe session that
+                    // never faulted reports reason "probe" here instead of
+                    // "disposed" — the pinned contract's exit event for a
+                    // successful probe.
                     _statusWriter.Exited(
                         _descriptor.Id,
                         _faulted ? 1 : 0,
-                        _faulted ? "fault" : "disposed");
+                        _faulted
+                            ? "fault"
+                            : _descriptor.Mode == HeadlessSessionMode.Probe
+                                ? "probe"
+                                : "disposed");
                     _disposeStage++;
                     _disposed = true;
                     break;
@@ -717,7 +735,8 @@ internal sealed class HeadlessSessionHost : IDisposable
                 _descriptor.Endpoint.Port,
                 _descriptor.Account,
                 password,
-                MapCharacterSelector(_descriptor.Character));
+                MapCharacterSelector(_descriptor.Character),
+                Probe: _descriptor.Mode == HeadlessSessionMode.Probe);
             LiveSessionStartResult result = _liveSession.Start(options);
             if (result.Selection is { } selection)
                 _accountName = selection.AccountName;
@@ -964,12 +983,19 @@ internal sealed class HeadlessSessionHost : IDisposable
         return declared;
     }
 
-    private static LiveSessionCharacterSelector MapCharacterSelector(
+    /// <summary>Campaign LA slice LA2: <see langword="null"/> for a probe
-        HeadlessCharacterSelector selector) =>
+    /// session (the loader guarantees <c>Character</c> is omitted whenever
-        new(
+    /// <c>Mode</c> is <see cref="HeadlessSessionMode.Probe"/>) — a probe
-            selector.Index,
+    /// never reaches <c>TrySelectCharacter</c>, so "no selector configured"
-            selector.Id,
+    /// is the correct, harmless mapping.</summary>
-            selector.Name);
+    private static LiveSessionCharacterSelector? MapCharacterSelector(
+        HeadlessCharacterSelector? selector) =>
+        selector is null
+            ? null
+            : new(
+                selector.Index,
+                selector.Id,
+                selector.Name);
 
     private RuntimeSessionStartResult Convert(
         LiveSessionStartResult result)
@@ -988,6 +1014,8 @@ internal sealed class HeadlessSessionHost : IDisposable
                 RuntimeSessionStartStatus.Deferred,
             LiveSessionStartStatus.Failed =>
                 RuntimeSessionStartStatus.Failed,
+            LiveSessionStartStatus.ProbeComplete =>
+                RuntimeSessionStartStatus.ProbeComplete,
             _ => throw new ArgumentOutOfRangeException(
                 nameof(result),
                 result.Status,

src/AcDream.Headless/Policies/HeadlessBotPolicy.cs

@@ -100,6 +100,21 @@ internal static class HeadlessBotPolicyFactory
     }
 }
 
+/// <summary>
+/// Campaign LA slice LA2: the "idle" consumer policy id — the session enters
+/// world (unchanged <see cref="HeadlessSessionHost"/> start/select/EnterWorld
+/// path) and then does nothing actively: no chat, no movement, no combat.
+/// <see cref="IsComplete"/> is permanently <see langword="false"/>, so
+/// <see cref="HeadlessProcessScheduler"/> keeps ticking the session
+/// (harmlessly — <see cref="Tick"/> and every delta handler below are no-ops)
+/// until the process is stopped (SIGINT/cancellation) or disposed; teardown
+/// then rides <see cref="HeadlessSessionHost.Dispose"/>'s existing graceful
+/// stop/logout path — the same mechanism K4's endurance gate already proved.
+/// No <see cref="HeadlessBotPolicyDescriptor.Role"/> is required. This class
+/// predates LA2 (introduced at K1 as dev/test scaffolding); LA2 formalizes it
+/// as the documented headless "just sit in world" play policy and adds
+/// focused coverage in <c>HeadlessBotPolicyTests</c>.
+/// </summary>
 internal sealed class IdleHeadlessBotPolicy : IHeadlessBotPolicy
 {
     public bool IsComplete => false;
@@ -149,6 +164,70 @@ internal sealed class IdleHeadlessBotPolicy : IHeadlessBotPolicy
     }
 }
 
+/// <summary>
+/// Campaign LA slice LA2: the policy substituted (never selected via
+/// <see cref="HeadlessBotPolicyFactory.Create"/> — a probe session's
+/// descriptor carries no <c>policy</c> id at all) for a
+/// <see cref="HeadlessSessionMode.Probe"/> session. <see cref="IsComplete"/>
+/// is <see langword="true"/> from construction, BEFORE
+/// <see cref="HeadlessSessionHost.Start"/> even runs, so
+/// <see cref="HeadlessProcessScheduler"/> never dispatches a tick to this
+/// session — a probe session's <see cref="AcDream.Runtime.Session.WorldSession"/>
+/// is already gracefully torn down by
+/// <see cref="AcDream.Runtime.Session.LiveSessionController"/>'s probe
+/// short-circuit by the time the scheduler would otherwise look at it, and a
+/// single-session probe process's <c>Run()</c> loop returns immediately
+/// instead of waiting for SIGINT.
+/// </summary>
+internal sealed class ProbeHeadlessBotPolicy : IHeadlessBotPolicy
+{
+    public bool IsComplete => true;
+
+    public void Tick(
+        IGameRuntimeView view,
+        IGameRuntimeCommands commands)
+    {
+        ArgumentNullException.ThrowIfNull(view);
+        ArgumentNullException.ThrowIfNull(commands);
+    }
+
+    public void OnLifecycle(in RuntimeLifecycleDelta delta)
+    {
+    }
+
+    public void OnCommand(in RuntimeCommandDelta delta)
+    {
+    }
+
+    public void OnEntity(in RuntimeEntityDelta delta)
+    {
+    }
+
+    public void OnInventory(in RuntimeInventoryDelta delta)
+    {
+    }
+
+    public void OnChat(in RuntimeChatDelta delta)
+    {
+    }
+
+    public void OnMovement(in RuntimeMovementDelta delta)
+    {
+    }
+
+    public void OnPortal(in RuntimePortalDelta delta)
+    {
+    }
+
+    public void OnCombat(in RuntimeCombatDelta delta)
+    {
+    }
+
+    public void Dispose()
+    {
+    }
+}
+
 /// <summary>
 /// Explicit connected-gate policy: wait for the local player, issue one
 /// harmless local-speech command and one lifestone recall, reconnect after

src/AcDream.Runtime/GameRuntimeCommands.cs

@@ -27,6 +27,14 @@ public enum RuntimeSessionStartStatus
     Failed,
     Inactive,
     StaleGeneration,
+    /// <summary>
+    /// Campaign LA slice LA2: mirrors
+    /// <see cref="Session.LiveSessionStartStatus.ProbeComplete"/> — a probe
+    /// session connected, reported its roster, and gracefully disconnected
+    /// before EnterWorld. A SUCCESS outcome for the headless process host's
+    /// exit-code mapping, not a failure.
+    /// </summary>
+    ProbeComplete,
 }
 
 public readonly record struct RuntimeSessionStartResult(

src/AcDream.Runtime/Session/LiveSessionContracts.cs

@@ -13,7 +13,23 @@ public sealed record LiveSessionConnectOptions(
     int Port,
     string User,
     string Password,
-    LiveSessionCharacterSelector? Character = null);
+    LiveSessionCharacterSelector? Character = null,
+    /// <summary>
+    /// Campaign LA slice LA2: short-circuits
+    /// <see cref="LiveSessionController"/>'s connect transaction right after
+    /// the roster report (before <c>TrySelectCharacter</c>/
+    /// <c>ApplySelectedCharacter</c>/<c>EnterWorld</c>) — connect, receive
+    /// <c>CharacterList</c>, report the roster, gracefully disconnect via the
+    /// same <c>StopCore</c> teardown the <see cref="LiveSessionStartStatus.NoCharacters"/>
+    /// path already uses, and return
+    /// <see cref="LiveSessionStartStatus.ProbeComplete"/>. The pinned launch
+    /// contract (<c>docs/plans/2026-08-14-launcher-campaign.md</c> LA1's
+    /// <c>mode</c> field) requires a probe session to omit both
+    /// <see cref="Character"/> and its policy entirely, but the controller
+    /// itself does not enforce that pairing — the headless config loader
+    /// does, before a <see cref="LiveSessionConnectOptions"/> is ever built.
+    /// </summary>
+    bool Probe = false);
 
 public interface IRuntimeLiveSessionFramePhase
 {

src/AcDream.Runtime/Session/LiveSessionController.cs

@@ -13,6 +13,14 @@ public enum LiveSessionStartStatus
     Connected,
     Deferred,
     Failed,
+    /// <summary>
+    /// Campaign LA slice LA2: a <see cref="LiveSessionConnectOptions.Probe"/>
+    /// session connected, received (and reported) the character roster, and
+    /// gracefully disconnected BEFORE selection/EnterWorld — deliberately a
+    /// SUCCESS variant of the <see cref="NoCharacters"/> early-exit shape
+    /// (same <c>StopCore</c> teardown), not a failure.
+    /// </summary>
+    ProbeComplete,
 }
 
 public readonly record struct LiveSessionOwnershipSnapshot(
@@ -647,6 +655,24 @@ public sealed class LiveSessionController
                     return new LiveSessionStartResult(LiveSessionStartStatus.Deferred);
             }
 
+            // Campaign LA slice LA2: the probe short-circuit lands here —
+            // right after the roster report, before TrySelectCharacter ever
+            // runs — so a probe session never reaches selection,
+            // ApplySelectedCharacter, or EnterWorld. This mirrors the
+            // NoCharacters early-exit immediately below (same StopCore
+            // teardown), the deliberate difference being the returned status
+            // is a SUCCESS, not a failure. Non-probe callers (options.Probe
+            // is false by default) fall straight through to the unchanged
+            // selection/enter path below — byte-identical to pre-LA2
+            // behavior.
+            if (options.Probe)
+            {
+                Console.WriteLine(
+                    "live: probe complete — disconnecting before EnterWorld");
+                StopCore();
+                return new LiveSessionStartResult(LiveSessionStartStatus.ProbeComplete);
+            }
+
             if (characters is null
                 || !TrySelectCharacter(
                     characters,

src/AcDream.Runtime/Session/LiveSessionHost.cs

@@ -316,6 +316,8 @@ public sealed class LiveSessionHost : IRuntimeSessionCommands
                 RuntimeSessionStartStatus.Deferred,
             LiveSessionStartStatus.Failed =>
                 RuntimeSessionStartStatus.Failed,
+            LiveSessionStartStatus.ProbeComplete =>
+                RuntimeSessionStartStatus.ProbeComplete,
             _ => throw new ArgumentOutOfRangeException(
                 nameof(result),
                 result.Status,

tests/AcDream.Headless.Tests/HeadlessConfigurationLoaderTests.cs

@@ -208,6 +208,208 @@ public sealed class HeadlessConfigurationLoaderTests
         Assert.Empty(declared!);
     }
 
+    // ── Campaign LA slice LA2: probe-mode `mode` field shape validation ──
+
+    [Fact]
+    public void ProbeSessionOmittingCharacterAndPolicyLoads()
+    {
+        using TemporaryConfiguration file = TemporaryConfiguration.Create(
+            """
+            {
+              "version": 1,
+              "sessions": [
+                {
+                  "id": "probe-session",
+                  "endpoint": { "host": "127.0.0.1", "port": 9000 },
+                  "account": "account",
+                  "mode": "probe",
+                  "credential": { "provider": "environment", "reference": "PROBE_PASSWORD" }
+                }
+              ]
+            }
+            """);
+
+        HeadlessConfiguration configuration =
+            HeadlessConfigurationLoader.Load(file.Path);
+
+        HeadlessSessionDescriptor session = Assert.Single(configuration.Sessions)!;
+        Assert.Null(session.Character);
+        Assert.Null(session.Policy);
+    }
+
+    [Fact]
+    public void ProbeSessionDeclaringCharacterFailsLoadNamingTheField()
+    {
+        using TemporaryConfiguration file = TemporaryConfiguration.Create(
+            """
+            {
+              "version": 1,
+              "sessions": [
+                {
+                  "id": "probe-with-character",
+                  "endpoint": { "host": "127.0.0.1", "port": 9000 },
+                  "account": "account",
+                  "mode": "probe",
+                  "character": { "index": 0 },
+                  "credential": { "provider": "environment", "reference": "PROBE_PASSWORD" }
+                }
+              ]
+            }
+            """);
+
+        HeadlessConfigurationException exception = Assert.Throws<
+            HeadlessConfigurationException>(
+                () => HeadlessConfigurationLoader.Load(file.Path));
+
+        Assert.Contains("probe", exception.Message, StringComparison.Ordinal);
+        Assert.Contains("character", exception.Message, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void ProbeSessionDeclaringPolicyFailsLoadNamingTheField()
+    {
+        using TemporaryConfiguration file = TemporaryConfiguration.Create(
+            """
+            {
+              "version": 1,
+              "sessions": [
+                {
+                  "id": "probe-with-policy",
+                  "endpoint": { "host": "127.0.0.1", "port": 9000 },
+                  "account": "account",
+                  "mode": "probe",
+                  "policy": { "id": "idle" },
+                  "credential": { "provider": "environment", "reference": "PROBE_PASSWORD" }
+                }
+              ]
+            }
+            """);
+
+        HeadlessConfigurationException exception = Assert.Throws<
+            HeadlessConfigurationException>(
+                () => HeadlessConfigurationLoader.Load(file.Path));
+
+        Assert.Contains("probe", exception.Message, StringComparison.Ordinal);
+        Assert.Contains("policy", exception.Message, StringComparison.Ordinal);
+    }
+
+    /// <summary>
+    /// A play session (mode absent) missing `character` must still fail —
+    /// the LA2 change moved this requiredness from `[JsonRequired]` (a raw
+    /// <see cref="System.Text.Json.JsonException"/> at deserialize time) to
+    /// <see cref="HeadlessConfigurationLoader.ValidateSession"/>'s semantic
+    /// check (a <see cref="HeadlessConfigurationException"/> naming the
+    /// missing field). Exit-code parity (both map to
+    /// <c>HeadlessExitCode.ConfigurationError</c>) is proven at
+    /// <c>HeadlessEntryPointTests</c>; this test pins the loader-level
+    /// exception type/message.
+    /// </summary>
+    [Fact]
+    public void PlaySessionMissingCharacterStillFailsLoad()
+    {
+        using TemporaryConfiguration file = TemporaryConfiguration.Create(
+            """
+            {
+              "version": 1,
+              "sessions": [
+                {
+                  "id": "play-missing-character",
+                  "endpoint": { "host": "127.0.0.1", "port": 9000 },
+                  "account": "account",
+                  "policy": { "id": "idle" },
+                  "credential": { "provider": "environment", "reference": "PLAY_PASSWORD" }
+                }
+              ]
+            }
+            """);
+
+        HeadlessConfigurationException exception = Assert.Throws<
+            HeadlessConfigurationException>(
+                () => HeadlessConfigurationLoader.Load(file.Path));
+
+        Assert.Contains(
+            "requires a character selector",
+            exception.Message,
+            StringComparison.Ordinal);
+    }
+
+    /// <summary>Same parity claim as
+    /// <see cref="PlaySessionMissingCharacterStillFailsLoad"/> for the
+    /// `policy` field.</summary>
+    [Fact]
+    public void PlaySessionMissingPolicyStillFailsLoad()
+    {
+        using TemporaryConfiguration file = TemporaryConfiguration.Create(
+            """
+            {
+              "version": 1,
+              "sessions": [
+                {
+                  "id": "play-missing-policy",
+                  "endpoint": { "host": "127.0.0.1", "port": 9000 },
+                  "account": "account",
+                  "character": { "index": 0 },
+                  "credential": { "provider": "environment", "reference": "PLAY_PASSWORD" }
+                }
+              ]
+            }
+            """);
+
+        HeadlessConfigurationException exception = Assert.Throws<
+            HeadlessConfigurationException>(
+                () => HeadlessConfigurationLoader.Load(file.Path));
+
+        Assert.Contains(
+            "requires a non-empty policy id",
+            exception.Message,
+            StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void PlaySessionKeepsTodaysStrictCharacterSelectorAndPolicyValidation()
+    {
+        // Unrelated to `mode` — proves the LA2 refactor of ValidateSession
+        // did not loosen the existing selector-shape/policy-id checks for
+        // ordinary play sessions (mode absent).
+        using TemporaryConfiguration badSelector = TemporaryConfiguration.Create(
+            """
+            {
+              "version": 1,
+              "sessions": [
+                {
+                  "id": "bad-selector",
+                  "endpoint": { "host": "127.0.0.1", "port": 9000 },
+                  "account": "account",
+                  "character": { "index": 0, "name": "Two" },
+                  "policy": { "id": "idle" },
+                  "credential": { "provider": "environment", "reference": "A" }
+                }
+              ]
+            }
+            """);
+        using TemporaryConfiguration blankPolicy = TemporaryConfiguration.Create(
+            """
+            {
+              "version": 1,
+              "sessions": [
+                {
+                  "id": "blank-policy",
+                  "endpoint": { "host": "127.0.0.1", "port": 9000 },
+                  "account": "account",
+                  "character": { "index": 0 },
+                  "policy": { "id": "" },
+                  "credential": { "provider": "environment", "reference": "B" }
+                }
+              ]
+            }
+            """);
+
+        Assert.Throws<HeadlessConfigurationException>(
+            () => HeadlessConfigurationLoader.Load(badSelector.Path));
+        Assert.Throws<HeadlessConfigurationException>(
+            () => HeadlessConfigurationLoader.Load(blankPolicy.Path));
+    }
+
     private static string ConfigurationWith(params string[] sessions) =>
         $$"""{"version":1,"sessions":[{{string.Join(",", sessions)}}]}""";
 

tests/AcDream.Headless.Tests/HeadlessEntryPointTests.cs

@@ -191,6 +191,76 @@ public sealed class HeadlessEntryPointTests
         Assert.Contains(expected, error.ToString());
     }
 
+    /// <summary>
+    /// Campaign LA slice LA2: before this change, an omitted `character` or
+    /// `policy` field failed deserialization itself with a raw
+    /// <see cref="System.Text.Json.JsonException"/> ("missing required
+    /// properties") — this test pins that the LA2 move to semantic
+    /// validation (<see cref="AcDream.Headless.Configuration.HeadlessConfigurationException"/>
+    /// naming the exact missing field) preserves the SAME exit code
+    /// (3, <c>HeadlessExitCode.ConfigurationError</c>) end to end through
+    /// <see cref="HeadlessEntryPoint.Run(IReadOnlyList{string}, TextWriter, TextWriter)"/>.
+    /// The message text change (generic → field-naming) is a deliberate,
+    /// accepted improvement, not a contract break.
+    /// </summary>
+    [Theory]
+    [InlineData(
+        """
+        {"version":1,"sessions":[{"id":"s","endpoint":{"host":"127.0.0.1","port":9000},"account":"account","policy":{"id":"idle"},"credential":{"provider":"environment","reference":"X"}}]}
+        """,
+        "character selector")]
+    [InlineData(
+        """
+        {"version":1,"sessions":[{"id":"s","endpoint":{"host":"127.0.0.1","port":9000},"account":"account","character":{"index":0},"credential":{"provider":"environment","reference":"X"}}]}
+        """,
+        "policy id")]
+    public void PlaySessionMissingCharacterOrPolicyKeepsConfigurationErrorExitCode(
+        string json,
+        string expectedMessageFragment)
+    {
+        using var file = TemporaryConfiguration.Create(json);
+        using var output = new StringWriter();
+        using var error = new StringWriter();
+
+        int exitCode = HeadlessEntryPoint.Run(
+            ["validate", "--config", file.Path],
+            output,
+            error);
+
+        Assert.Equal((int)HeadlessExitCode.ConfigurationError, exitCode);
+        Assert.Contains(
+            expectedMessageFragment,
+            error.ToString(),
+            StringComparison.OrdinalIgnoreCase);
+        Assert.Equal(string.Empty, output.ToString());
+    }
+
+    /// <summary>
+    /// Campaign LA slice LA2: a valid probe-mode session (mode "probe",
+    /// character/policy both omitted) passes `validate` — the launcher's
+    /// "refresh characters" flow only needs the process to accept the
+    /// document, not to run it.
+    /// </summary>
+    [Fact]
+    public void ValidateAcceptsProbeSessionOmittingCharacterAndPolicy()
+    {
+        using var file = TemporaryConfiguration.Create(
+            """
+            {"version":1,"sessions":[{"id":"probe","endpoint":{"host":"127.0.0.1","port":9000},"account":"account","mode":"probe","credential":{"provider":"environment","reference":"X"}}]}
+            """);
+        using var output = new StringWriter();
+        using var error = new StringWriter();
+
+        int exitCode = HeadlessEntryPoint.Run(
+            ["validate", "--config", file.Path],
+            output,
+            error);
+
+        Assert.Equal((int)HeadlessExitCode.Success, exitCode);
+        Assert.Contains("1 session(s)", output.ToString());
+        Assert.Equal(string.Empty, error.ToString());
+    }
+
     [Fact]
     public void UnknownCommandReturnsUsageError()
     {

tests/AcDream.Headless.Tests/HeadlessSessionHostTests.cs

@@ -151,6 +151,170 @@ public sealed class HeadlessSessionHostTests
         // writer is a permanent no-op with no configured path.
     }
 
+    /// <summary>
+    /// Campaign LA slice LA2: a probe-mode session's status stream reports
+    /// started/connected/characterList and then converges straight to
+    /// exited(reason:"probe", code:0) — never enteredWorld — and the
+    /// underlying operations fake proves EnterWorld was literally never
+    /// called (not merely that no wire message happened to arrive).
+    /// </summary>
+    [Fact]
+    public void ProbeSessionEmitsRosterThenExitsSuccessfullyWithoutEnteringWorld()
+    {
+        string statusPath = Path.Combine(
+            Path.GetTempPath(),
+            $"acdream-headless-probe-status-{Guid.NewGuid():N}.jsonl");
+        try
+        {
+            var operations = new FixtureSessionOperations();
+            using var diagnosticsOutput = new StringWriter();
+            using var credential = new HeadlessCredentialSecret(
+                "fixture",
+                "password");
+            using var host = new HeadlessSessionHost(
+                ProbeDescriptor(statusFile: statusPath),
+                credential,
+                new HeadlessDiagnosticWriter(diagnosticsOutput),
+                operations);
+
+            RuntimeSessionStartResult started = host.Start();
+            Assert.Equal(RuntimeSessionStartStatus.ProbeComplete, started.Status);
+            Assert.Equal(0, operations.EnterWorldCallCount);
+            Assert.False(host.Runtime.Session.IsInWorld);
+
+            host.Dispose();
+
+            Assert.Equal(0, operations.EnterWorldCallCount);
+            Assert.True(host.Runtime.CaptureOwnership().IsConverged);
+
+            string[] lines = File.ReadAllLines(statusPath);
+            string[] eventNames = lines
+                .Select(line => JsonDocument.Parse(line)
+                    .RootElement.GetProperty("e").GetString()!)
+                .ToArray();
+            Assert.DoesNotContain("enteredWorld", eventNames);
+            Assert.Contains("characterList", eventNames);
+            Assert.Contains("exited", eventNames);
+            Assert.True(
+                Array.IndexOf(eventNames, "characterList")
+                    < Array.IndexOf(eventNames, "exited"),
+                "characterList must land before the terminal exited event.");
+
+            using JsonDocument exitedDoc = JsonDocument.Parse(
+                lines[Array.IndexOf(eventNames, "exited")]);
+            Assert.Equal(0, exitedDoc.RootElement.GetProperty("code").GetInt32());
+            Assert.Equal(
+                "probe",
+                exitedDoc.RootElement.GetProperty("reason").GetString());
+
+            string contents = File.ReadAllText(statusPath);
+            Assert.DoesNotContain("password", contents, StringComparison.Ordinal);
+        }
+        finally
+        {
+            if (File.Exists(statusPath))
+                File.Delete(statusPath);
+        }
+    }
+
+    /// <summary>
+    /// Campaign LA slice LA2: <see cref="HeadlessProcessHost.RunOnUpdateThread"/>
+    /// maps a ProbeComplete start to <see cref="HeadlessExitCode.Success"/>
+    /// (0) rather than <see cref="HeadlessExitCode.ConnectionError"/> — a
+    /// single-session probe-only process must exit cleanly and promptly
+    /// without ever needing SIGINT/cancellation, because
+    /// ProbeHeadlessBotPolicy reports IsComplete immediately.
+    /// </summary>
+    [Fact]
+    public async Task ProcessHostMapsProbeCompleteStartToSuccessExitCode()
+    {
+        var configuration = new HeadlessConfiguration
+        {
+            Version = 1,
+            Sessions =
+            [
+                ProbeDescriptor(
+                    provider: HeadlessCredentialProviderKind.StandardInput,
+                    credentialReference: "probe-password"),
+            ],
+        };
+        HeadlessPathSet paths = HeadlessPathSet.Resolve(
+            new HeadlessPathOverrides());
+        using var diagnostics = new StringWriter();
+        var operations = new FixtureSessionOperations();
+        using var host = new HeadlessProcessHost(
+            configuration,
+            paths,
+            new System.IO.StringReader("probe-password" + Environment.NewLine),
+            diagnostics,
+            operations);
+        // Deliberately NOT cancelled — a probe-only process must return on
+        // its own; a hang here would mean the scheduler never recognized
+        // the probe session as already complete.
+        using var cancellation = new CancellationTokenSource(
+            TimeSpan.FromSeconds(10));
+
+        HeadlessExitCode result = await host.RunAsync(cancellation.Token);
+
+        Assert.Equal(HeadlessExitCode.Success, result);
+        Assert.Equal(0, operations.EnterWorldCallCount);
+        Assert.False(cancellation.IsCancellationRequested);
+    }
+
+    /// <summary>
+    /// Campaign LA slice LA2: a probe session completing must not tear down
+    /// a sibling play session sharing the same process — the process exit
+    /// code is 0 only once every configured session has succeeded (the
+    /// probe counts as success the instant it completes; the play session
+    /// keeps running until cancellation).
+    /// </summary>
+    [Fact]
+    public async Task ProbeSessionSharingAProcessDoesNotTearDownASiblingPlaySession()
+    {
+        var configuration = new HeadlessConfiguration
+        {
+            Version = 1,
+            Sessions =
+            [
+                ProbeDescriptor(
+                    "probe-sibling",
+                    provider: HeadlessCredentialProviderKind.StandardInput,
+                    credentialReference: "probe-password"),
+                Descriptor(
+                    HeadlessCredentialProviderKind.StandardInput,
+                    "play-password"),
+            ],
+        };
+        HeadlessPathSet paths = HeadlessPathSet.Resolve(
+            new HeadlessPathOverrides());
+        using var diagnostics = new StringWriter();
+        var operations = new FixtureSessionOperations();
+        using var host = new HeadlessProcessHost(
+            configuration,
+            paths,
+            new System.IO.StringReader(
+                "probe-password" + Environment.NewLine
+                + "play-password" + Environment.NewLine),
+            diagnostics,
+            operations);
+        using var cancellation = new CancellationTokenSource();
+        cancellation.Cancel();
+
+        HeadlessExitCode result = await host.RunAsync(cancellation.Token);
+
+        Assert.Equal(HeadlessExitCode.Success, result);
+        Assert.Equal(2, host.Sessions.Count);
+        HeadlessSessionHost probeSession = Assert.Single(
+            host.Sessions,
+            s => s.SessionId == "probe-sibling");
+        HeadlessSessionHost playSession = Assert.Single(
+            host.Sessions,
+            s => s.SessionId == "bot");
+        Assert.False(probeSession.Runtime.Session.IsInWorld);
+        Assert.True(playSession.Runtime.Session.IsInWorld);
+        Assert.False(playSession.IsFaulted);
+    }
+
     [Fact]
     public async Task ProcessHostRunsUntilCancellationAndReturnsStableExitCode()
     {
@@ -2086,6 +2250,32 @@ public sealed class HeadlessSessionHostTests
         StatusFile = statusFile,
     };
 
+    /// <summary>Campaign LA slice LA2: a probe-mode descriptor — mode
+    /// "probe", <c>Character</c>/<c>Policy</c> both omitted per the pinned
+    /// contract shape <see cref="HeadlessConfigurationLoader"/> enforces.</summary>
+    private static HeadlessSessionDescriptor ProbeDescriptor(
+        string id = "probe-bot",
+        HeadlessCredentialProviderKind provider =
+            HeadlessCredentialProviderKind.Environment,
+        string credentialReference = "PROBE_PASSWORD",
+        string? statusFile = null) => new()
+    {
+        Id = id,
+        Endpoint = new HeadlessEndpointDescriptor
+        {
+            Host = "127.0.0.1",
+            Port = 9000,
+        },
+        Account = "account",
+        Mode = HeadlessSessionMode.Probe,
+        Credential = new HeadlessCredentialReference
+        {
+            Provider = provider,
+            Reference = credentialReference,
+        },
+        StatusFile = statusFile,
+    };
+
     private static void HydrateGroundedPlayer(GameRuntime runtime)
     {
         const uint player = 0x50000002u;
@@ -2773,10 +2963,15 @@ public sealed class HeadlessSessionHostTests
                 true,
                 true);
 
+        /// <summary>Campaign LA slice LA2: lets a probe test assert the
+        /// live-session controller never reached EnterWorld.</summary>
+        public int EnterWorldCallCount { get; private set; }
+
         public void EnterWorld(
             WorldSession session,
             int activeCharacterIndex)
         {
+            EnterWorldCallCount++;
         }
 
         public void Tick(WorldSession session)

tests/AcDream.Headless.Tests/SessionConfigurationSharedFixtureTests.cs

@@ -28,8 +28,8 @@ public sealed class SessionConfigurationSharedFixtureTests
         Assert.Equal("127.0.0.1", session.Endpoint.Host);
         Assert.Equal(9000, session.Endpoint.Port);
         Assert.Equal("sharedaccount", session.Account);
-        Assert.Equal("SharedToon", session.Character.Name);
+        Assert.Equal("SharedToon", session.Character!.Name);
-        Assert.Equal("idle", session.Policy.Id);
+        Assert.Equal("idle", session.Policy!.Id);
         Assert.Equal(
             HeadlessCredentialProviderKind.Environment,
             session.Credential.Provider);

tests/AcDream.Runtime.Tests/Session/LiveSessionControllerTests.cs

@@ -389,6 +389,81 @@ public sealed class LiveSessionControllerTests
         Assert.Equal(1, operations.DisposeCounts[operations.Sessions[0]]);
     }
 
+    /// <summary>
+    /// Campaign LA slice LA2: the probe short-circuit — connect, receive
+    /// CharacterList, report the roster, then gracefully disconnect via the
+    /// SAME StopCore teardown <see cref="Start_NoAvailableCharacterTearsDownExactScope"/>
+    /// exercises, returning <see cref="LiveSessionStartStatus.ProbeComplete"/>
+    /// instead of ever reaching TrySelectCharacter/ApplySelectedCharacter/
+    /// EnterWorld. Asserted directly against the operations fake:
+    /// <see cref="TestOperations.EnterWorldCount"/> stays zero and "enter:*"/
+    /// "selected"/"activate"/"entered" never appear in the call trace.
+    /// </summary>
+    [Fact]
+    public void Start_ProbeReportsRosterThenGracefullyDisconnectsWithoutSelectionOrEnterWorld()
+    {
+        var calls = new List<string>();
+        var operations = new TestOperations(calls);
+        var host = new TestHost(calls);
+        var controller = new LiveSessionController(operations);
+
+        LiveSessionStartResult result = controller.Start(
+            LiveOptions(probe: true),
+            host);
+
+        Assert.Equal(LiveSessionStartStatus.ProbeComplete, result.Status);
+        Assert.Null(result.Selection);
+        Assert.Equal(
+            [
+                "reset", "resolve", "create", "bind", "report-connecting",
+                "connect", "report-connected", "roster", "deactivate",
+                "detach-events", "dispose-session", "detach-session", "reset",
+            ],
+            calls);
+        Assert.DoesNotContain("selected", calls);
+        Assert.DoesNotContain("activate", calls);
+        Assert.DoesNotContain("entered", calls);
+        Assert.Equal(0, operations.EnterWorldCount);
+        LiveSessionRosterReport roster = Assert.Single(host.Rosters);
+        Assert.Equal("Canonical", roster.AccountName);
+        Assert.False(controller.IsInWorld);
+        Assert.Null(controller.CurrentSession);
+        Assert.Equal(1, operations.DisposeCounts[operations.Sessions[0]]);
+
+        // The same 4-stage graceful teardown the NoCharacters path uses —
+        // the probe's scope fully converges without requiring
+        // controller.Dispose().
+        LiveSessionOwnershipSnapshot ownership = controller.CaptureOwnership();
+        Assert.Equal(RuntimeTeardownStage.Complete, ownership.LastTeardownStages);
+        Assert.False(ownership.HasActiveSession);
+        Assert.False(ownership.HasRetiredSession);
+        Assert.False(ownership.HasPendingOperation);
+    }
+
+    /// <summary>
+    /// The probe short-circuit fires even when the server never returns a
+    /// CharacterList at all (GetCharacters returns null) — a probe is a
+    /// connectivity check, not itself a character-selection operation, so it
+    /// must not fall through to the NoCharacters path.
+    /// </summary>
+    [Fact]
+    public void Start_ProbeWithoutCharacterListStillCompletesGracefully()
+    {
+        var calls = new List<string>();
+        var operations = new TestOperations(calls) { Characters = null };
+        var host = new TestHost(calls);
+        var controller = new LiveSessionController(operations);
+
+        LiveSessionStartResult result = controller.Start(
+            LiveOptions(probe: true),
+            host);
+
+        Assert.Equal(LiveSessionStartStatus.ProbeComplete, result.Status);
+        Assert.Empty(host.Rosters);
+        Assert.Equal(0, operations.EnterWorldCount);
+        Assert.False(controller.IsInWorld);
+    }
+
     [Theory]
     [InlineData("index")]
     [InlineData("id")]
@@ -1141,14 +1216,16 @@ public sealed class LiveSessionControllerTests
     private static LiveSessionConnectOptions LiveOptions(
         bool live = true,
         string? user = "user",
-        LiveSessionCharacterSelector? selector = null) =>
+        LiveSessionCharacterSelector? selector = null,
+        bool probe = false) =>
         new(
             live,
             "127.0.0.1",
             9000,
             user ?? string.Empty,
             "password",
-            selector);
+            selector,
+            probe);
 
     private static CharacterList.Parsed AvailableCharacters() => new(
         0u,