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/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