fix(server): preserve native history in busy Codex forks

apps/server/src/orchestration-v2/Adapters/CodexAdapterV2.ts

@@ -250,6 +250,7 @@ export const CodexProviderCapabilitiesV2 = {
     canRollbackThread: true,
     canForkThread: true,
     canForkFromTurn: true,
+    canForkWhileRunning: true,
     canForkFromSubagentThread: true,
     exposesNativeThreadId: true,
   },

apps/server/src/orchestration-v2/CommandPolicy.test.ts

@@ -258,6 +258,7 @@ layer("CommandPolicyV2", (it) => {
         capabilities: CursorProviderCapabilitiesV2,
         sameProvider: true,
         hasStrongNativeSource: true,
+        hasNativeTurnBoundary: false,
         sourceRunStatus: "completed",
         fromSpecificTurn: true,
         sourceBusy: false,
@@ -267,24 +268,39 @@ layer("CommandPolicyV2", (it) => {
     }),
   );
 
-  it.effect("forks a busy source through portable context", () =>
-    Effect.gen(function* () {
-      const policy = yield* CommandPolicy.CommandPolicyV2;
-      const decide = (sourceBusy: boolean) =>
-        policy.decideForkExecution({
-          commandId,
-          threadId,
-          providerInstanceId: ProviderInstanceId.make("codex"),
-          capabilities: CodexProviderCapabilitiesV2,
-          sameProvider: true,
-          hasStrongNativeSource: true,
-          sourceRunStatus: "completed",
-          fromSpecificTurn: true,
-          sourceBusy,
-        });
+  it.effect.each([
+    { canForkWhileRunning: true, hasNativeTurnBoundary: true, busyStrategy: "native_fork" },
+    { canForkWhileRunning: false, hasNativeTurnBoundary: true, busyStrategy: "portable_context" },
+    {
+      canForkWhileRunning: undefined,
+      hasNativeTurnBoundary: true,
+      busyStrategy: "portable_context",
+    },
+    { canForkWhileRunning: true, hasNativeTurnBoundary: false, busyStrategy: "portable_context" },
+  ] as const)(
+    "forks a busy source with canForkWhileRunning=$canForkWhileRunning and hasNativeTurnBoundary=$hasNativeTurnBoundary",
+    ({ canForkWhileRunning, hasNativeTurnBoundary, busyStrategy }) =>
+      Effect.gen(function* () {
+        const policy = yield* CommandPolicy.CommandPolicyV2;
+        const decide = (sourceBusy: boolean) =>
+          policy.decideForkExecution({
+            commandId,
+            threadId,
+            providerInstanceId: ProviderInstanceId.make("codex"),
+            capabilities: {
+              ...CodexProviderCapabilitiesV2,
+              threads: { ...CodexProviderCapabilitiesV2.threads, canForkWhileRunning },
+            },
+            sameProvider: true,
+            hasStrongNativeSource: true,
+            hasNativeTurnBoundary,
+            sourceRunStatus: "completed",
+            fromSpecificTurn: true,
+            sourceBusy,
+          });
 
-      assert.equal(yield* decide(false), "native_fork");
-      assert.equal(yield* decide(true), "portable_context");
-    }),
+        assert.equal(yield* decide(false), "native_fork");
+        assert.equal(yield* decide(true), busyStrategy);
+      }),
   );
 });

apps/server/src/orchestration-v2/CommandPolicy.ts

@@ -209,9 +209,10 @@ export interface CommandPolicyV2Shape {
     input: CapabilityCheckInput & {
       readonly sameProvider: boolean;
       readonly hasStrongNativeSource: boolean;
+      readonly hasNativeTurnBoundary: boolean;
       readonly sourceRunStatus: OrchestrationV2Run["status"];
       readonly fromSpecificTurn: boolean;
-      /** Later source runs are still active; providers cannot fork a thread mid-turn. */
+      /** Later source runs are still active. */
       readonly sourceBusy: boolean;
     },
   ) => Effect.Effect<ForkExecutionPolicyV2, CommandPolicyV2Error>;
@@ -376,7 +377,8 @@ const decideForkExecution: CommandPolicyV2Shape["decideForkExecution"] = (input)
     (input.sourceRunStatus === "completed" || input.sourceRunStatus === "waiting") &&
     input.sameProvider &&
     input.hasStrongNativeSource &&
-    !input.sourceBusy &&
+    (!input.sourceBusy ||
+      (input.capabilities.threads.canForkWhileRunning === true && input.hasNativeTurnBoundary)) &&
     input.capabilities.threads.canForkThread &&
     (!input.fromSpecificTurn || input.capabilities.threads.canForkFromTurn) &&
     input.capabilities.identity.nativeThreadIds === "strong";

apps/server/src/orchestration-v2/Orchestrator.ts

@@ -6775,6 +6775,9 @@ const makeOrchestrator = Effect.fn("orchestrationV2.Orchestrator.layer")(functio
               sameProvider:
                 pendingForkTransfer.sourceProviderInstanceId === modelSelection.instanceId,
               hasStrongNativeSource: sourceProviderThread?.nativeThreadRef?.strength === "strong",
+              hasNativeTurnBoundary:
+                sourceProjection?.providerTurns.find((turn) => turn.id === sourceProviderTurnId)
+                  ?.nativeTurnRef != null,
               sourceRunStatus: sourceRun.status,
               fromSpecificTurn: sourceRun !== null,
               sourceBusy: sourceRunsAfterFork.some(isActiveRun),