refactor(app): make session start terminal

Move live-session startup and its existing diagnostics into the typed Phase-9 owner. GameWindow.OnLoad now ends immediately after that phase, so no callback binding, publication, or allocation can occur after the session becomes active.

Co-authored-by: Codex <codex@openai.com>

docs/ISSUES.md

@@ -35,9 +35,10 @@ What does NOT go here:
   every late edge explicitly. I.8a now owns the focused session factory,
   command targets, and sole gameplay input subscriber before frame publication.
   I.8b now owns the complete update/render construction, exact atomic frame
-  publication, and lifecycle resource snapshot source. `GameWindow.OnUpdate`
+  publication, and lifecycle resource snapshot source. I.8c makes session
-  and `GameWindow.OnRender` are typed orchestration handoffs and the class is
+  start the terminal `OnLoad` operation. `GameWindow.OnUpdate` and
-  1,919 raw lines. I.8c–I.9 plus the remaining
+  `GameWindow.OnRender` are typed orchestration handoffs and the class is
+  1,910 raw lines. I.9 plus the remaining
   shutdown/closeout
   cleanup is active in
   [`docs/architecture/code-structure.md`](architecture/code-structure.md).

docs/architecture/code-structure.md

@@ -739,10 +739,11 @@ diagnostic command targets, and sole gameplay input subscriber into Phase 7
 before frame publication. I.8b moves the complete update/render construction
 body into `FrameRootCompositionPhase`, publishes the pair through an exact
 lease, and gives lifecycle resource sampling a focused source. `GameWindow` is
-1,919 raw lines. I.8c–L remain active, with terminal session start next. The
+1,910 raw lines after I.8c makes live-session start the terminal `OnLoad`
-App gate passes 3,429 tests / 3 intentional skips and the complete Release suite
+operation. I.9–L remain active, with the complete Checkpoint-I audit next. The
-passes 7,801 tests / 5 intentional skips. The clean solution build retains only
+App gate passes 3,430 tests / 3 intentional skips and the complete Release suite
-the 17 test-project warnings tracked by #228; the I.8b corrected-diff review is
+passes 7,802 tests / 5 intentional skips. The clean solution build retains only
+the 17 test-project warnings tracked by #228; the I.8c corrected-diff review is
 clean.
 
 ### 4.4 Exit criteria

docs/plans/2026-04-11-roadmap.md

@@ -104,11 +104,11 @@ controllers, selection/radar, landblock publishers, and portal/sky/particle
 resources have transactional phase ownership and exact-owner late bindings.
 I.7 adds the complete streaming/session/hydration/local-player/teleport phase,
 including explicit reversible ownership for every late edge. `GameWindow` is
-now 1,919 raw lines after I.8b, which also composes and atomically publishes the
+now 1,910 raw lines after I.8c, which makes session start the terminal `OnLoad`
-complete update/render pair and extracts lifecycle resource sampling. I.8c–I.9,
+operation. I.9, shutdown, canonical soak snapshots, and closeout checkpoints
-shutdown, canonical soak snapshots, and closeout checkpoints J–L remain. The
+J–L remain. The App gate passes 3,430 tests / 3 intentional skips, the complete
-App gate passes 3,429 tests / 3 intentional skips, the complete Release suite
+Release suite passes 7,802 tests / 5 skips, and the I.8c corrected-diff review
-passes 7,801 tests / 5 skips, and the I.8b corrected-diff review is clean.
+is clean.
 
 This is a behavior-preserving structural program. Severe regressions still get
 root-cause fixes in separate commits; ordinary feature work resumes with M4

docs/plans/2026-05-12-milestones.md

@@ -62,11 +62,12 @@ session, hydration, local-player, combat, and teleport startup graph, including
 named reversible late edges. I.8a adds the focused live-session runtime factory
 and attaches command/input owners before frame publication. I.8b composes and
 atomically publishes the complete frame pair and extracts lifecycle resource
-sampling. `GameWindow` is 1,919 raw lines. I.8c–I.9 and checkpoints J–L remain
+sampling. I.8c makes session start the terminal `OnLoad` operation.
-active. Issue #232 tracks
+`GameWindow` is 1,910 raw lines. I.9 and checkpoints J–L remain active. Issue
+#232 tracks
 process-residency variance in the soak without loosening its leak threshold.
-The App gate passes 3,429 tests / 3 skips, the complete Release suite passes
+The App gate passes 3,430 tests / 3 skips, the complete Release suite passes
-7,801 tests / 5 skips, and the I.8b corrected-diff review is clean.
+7,802 tests / 5 skips, and the I.8c corrected-diff review is clean.
 
 Carried:
 #153 far-teleport residual, #116 slide-response, the remaining R6 ownership cleanup plus

docs/plans/2026-07-22-gamewindow-slice-8-checkpoint-i-ordered-composition.md

@@ -297,8 +297,10 @@ ledger only after the complete pipeline is live.
   input subscriber now belong to Phase 7 and publish before any frame root.
   I.8b composes the unchanged update/render graph in a focused phase, publishes
   the pair through an exact owned slot lease, and moves lifecycle resource
-  sampling out of the window. `GameWindow.cs` is 1,919 raw lines. I.8c terminal
+  sampling out of the window. I.8c makes the exact session start and its
-  session start is the active cut.
+  existing diagnostics the terminal `OnLoad` operation. `GameWindow.cs` is
+  1,910 raw lines. I.9 corrected-diff review and documentation closeout is the
+  active cut.
   Checkpoint I remains active until I.9 closes the complete nine-phase pipeline.
 
 ## 6. Automated acceptance

docs/plans/2026-07-22-gamewindow-slice-8-checkpoint-i8-frame-roots-session-start.md

@@ -1,6 +1,6 @@
 # GameWindow Slice 8 — Checkpoint I.8 Frame Roots and Session Start
 
-**Status:** Active — I.8a–I.8b complete; I.8c terminal start next
+**Status:** Complete 2026-07-22
 
 **Parent:** `2026-07-22-gamewindow-slice-8-checkpoint-i-ordered-composition.md`
 
@@ -144,6 +144,12 @@ shutdown. Replacement is rejected atomically.
 
 ## 4. I.8c — terminal start and window cutover
 
+**Completed 2026-07-22.** `SessionStartCompositionPhase` invokes the exact
+Phase-7 host through the Phase-8 result and owns the existing missing-credential
+and failed-start diagnostics. The phase call is the final statement in
+`GameWindow.OnLoad`; no binding, publication, allocation, or diagnostics setup
+follows it.
+
 Add `SessionStartCompositionPhase` implementing
 `ISessionStartCompositionPhase<FrameRootResult>`. It invokes only
 `LiveSessionHost.Start(RuntimeOptions)` and preserves the existing diagnostics

docs/plans/2026-07-22-gamewindow-slice-8-composition-lifecycle.md

@@ -29,8 +29,8 @@ audit.
 - [x] H — give terrain atlas, sky shader, retained `UiHost`, and both frame roots
   explicit single ownership and transfer seams.
 - [ ] I — group `OnLoad` into small ordered, fakeable composition phases with
-  transactional partial-acquisition rollback. I.1–I.8b are complete; I.8c
+  transactional partial-acquisition rollback. I.1–I.8 are complete; I.9
-  terminal session start is active. Detailed plan:
+  corrected-diff review and checkpoint closeout is active. Detailed plan:
   [`2026-07-22-gamewindow-slice-8-checkpoint-i-ordered-composition.md`](2026-07-22-gamewindow-slice-8-checkpoint-i-ordered-composition.md).
 - [ ] J — move the exact retryable shutdown manifest to a focused lifetime
   owner and prove all partial-load/reentrant/retry paths.

src/AcDream.App/Composition/SessionStartComposition.cs

@@ -0,0 +1,47 @@
+using AcDream.App.Net;
+
+namespace AcDream.App.Composition;
+
+internal sealed record SessionStartDependencies(
+    RuntimeOptions Options,
+    Action<string> Log);
+
+/// <summary>
+/// Terminal startup phase. Every callback, command target, and frame root is
+/// already published when this owner asks the canonical session host to start.
+/// </summary>
+internal sealed class SessionStartCompositionPhase
+    : ISessionStartCompositionPhase<FrameRootResult>
+{
+    private readonly SessionStartDependencies _dependencies;
+
+    public SessionStartCompositionPhase(SessionStartDependencies dependencies) =>
+        _dependencies = dependencies
+            ?? throw new ArgumentNullException(nameof(dependencies));
+
+    public void Start(FrameRootResult frame)
+    {
+        ArgumentNullException.ThrowIfNull(frame);
+        LiveSessionStartResult result =
+            frame.SessionHost.Start(_dependencies.Options);
+        Report(result, _dependencies.Log);
+    }
+
+    internal static void Report(
+        LiveSessionStartResult result,
+        Action<string> log)
+    {
+        ArgumentNullException.ThrowIfNull(result);
+        ArgumentNullException.ThrowIfNull(log);
+        switch (result.Status)
+        {
+            case LiveSessionStartStatus.MissingCredentials:
+                log(
+                    "live: ACDREAM_LIVE set but TEST_USER/TEST_PASS missing; skipping");
+                break;
+            case LiveSessionStartStatus.Failed:
+                log($"live: session failed: {result.Error}");
+                break;
+        }
+    }
+}

src/AcDream.App/Rendering/GameWindow.cs

@@ -1420,18 +1420,9 @@ public sealed class GameWindow :
                 livePresentation,
                 sessionPlayer);
 
-        AcDream.App.Net.LiveSessionStartResult liveStart =
+        new SessionStartCompositionPhase(
-            frameRoots.SessionHost.Start(_options);
+            new SessionStartDependencies(_options, Console.WriteLine))
-        switch (liveStart.Status)
+            .Start(frameRoots);
-        {
-            case AcDream.App.Net.LiveSessionStartStatus.MissingCredentials:
-                Console.WriteLine(
-                    "live: ACDREAM_LIVE set but TEST_USER/TEST_PASS missing; skipping");
-                break;
-            case AcDream.App.Net.LiveSessionStartStatus.Failed:
-                Console.WriteLine($"live: session failed: {liveStart.Error}");
-                break;
-        }
     }
 
     private void OnUpdate(double dt)

tests/AcDream.App.Tests/Composition/SessionStartCompositionTests.cs

@@ -0,0 +1,38 @@
+using AcDream.App.Composition;
+using AcDream.App.Net;
+
+namespace AcDream.App.Tests.Composition;
+
+public sealed class SessionStartCompositionTests
+{
+    [Fact]
+    public void DiagnosticsPreserveMissingCredentialAndFailureMessagesOnly()
+    {
+        var messages = new List<string>();
+
+        SessionStartCompositionPhase.Report(
+            new LiveSessionStartResult(
+                LiveSessionStartStatus.MissingCredentials),
+            messages.Add);
+        SessionStartCompositionPhase.Report(
+            new LiveSessionStartResult(
+                LiveSessionStartStatus.Failed,
+                Error: new InvalidOperationException("boom")),
+            messages.Add);
+        SessionStartCompositionPhase.Report(
+            new LiveSessionStartResult(LiveSessionStartStatus.Disabled),
+            messages.Add);
+        SessionStartCompositionPhase.Report(
+            new LiveSessionStartResult(LiveSessionStartStatus.Connected),
+            messages.Add);
+
+        Assert.Equal(2, messages.Count);
+        Assert.Equal(
+            "live: ACDREAM_LIVE set but TEST_USER/TEST_PASS missing; skipping",
+            messages[0]);
+        Assert.StartsWith(
+            "live: session failed: System.InvalidOperationException: boom",
+            messages[1],
+            StringComparison.Ordinal);
+    }
+}

tests/AcDream.App.Tests/Rendering/GameWindowSlice8BoundaryTests.cs

@@ -66,7 +66,8 @@ public sealed class GameWindowSlice8BoundaryTests
             "this).Compose(",
             "new SessionPlayerCompositionPhase(",
             "FrameRootResult frameRoots = new FrameRootCompositionPhase(",
-            "frameRoots.SessionHost.Start(_options)");
+            "new SessionStartCompositionPhase(",
+            ".Start(frameRoots);");
 
         string framePhase = File.ReadAllText(Path.Combine(
             FindRepoRoot(),
@@ -97,7 +98,7 @@ public sealed class GameWindowSlice8BoundaryTests
             "_publication.PublishSessionPlayer(result);");
         Assert.Equal(1, CountOccurrences(
             body,
-            "frameRoots.SessionHost.Start(_options)"));
+            ".Start(frameRoots);"));
         string phaseOne = Slice(
             File.ReadAllText(Path.Combine(
                 FindRepoRoot(),
@@ -117,11 +118,22 @@ public sealed class GameWindowSlice8BoundaryTests
             "if (firstKeyboard is not null && firstMouse is not null)",
             phaseOne,
             StringComparison.Ordinal);
+        string startPhase = File.ReadAllText(Path.Combine(
+            FindRepoRoot(),
+            "src",
+            "AcDream.App",
+            "Composition",
+            "SessionStartComposition.cs"));
+        AssertAppearsInOrder(
+            startPhase,
+            "frame.SessionHost.Start(_dependencies.Options)",
+            "switch (result.Status)",
+            "case LiveSessionStartStatus.MissingCredentials:",
+            "case LiveSessionStartStatus.Failed:");
         int start = body.IndexOf(
-            "frameRoots.SessionHost.Start(_options)",
+            ".Start(frameRoots);",
             StringComparison.Ordinal);
-        string postStart = body[start..];
+        string postStart = body[(start + ".Start(frameRoots);".Length)..];
-        Assert.Contains("switch (liveStart.Status)", postStart, StringComparison.Ordinal);
         Assert.Empty(System.Text.RegularExpressions.Regex.Matches(
             postStart,
             @"(?m)^\s+_[A-Za-z]\w*\s*(?:\?\?=|=)"));
@@ -343,7 +355,8 @@ public sealed class GameWindowSlice8BoundaryTests
             "new WorldRenderCompositionPhase(",
             "new SessionPlayerCompositionPhase(",
             "new FrameRootCompositionPhase(",
-            "frameRoots.SessionHost.Start(_options)");
+            "new SessionStartCompositionPhase(",
+            ".Start(frameRoots);");
         string sessionPhase = File.ReadAllText(Path.Combine(
             FindRepoRoot(),
             "src",