From 9c66c3de51a4e27402ccf6026f91361af591115c Mon Sep 17 00:00:00 2001
From: Ashvin Nihalani <ashvin.nihalani@gmail.com>
Date: Thu, 26 Mar 2026 00:30:50 -0700
Subject: [PATCH] Bind session reuse to active provider session

- Require an active provider session before treating thread.session as reusable
- Add regression coverage for starting a fresh session when only projected state exists
---
 .../Layers/ProviderCommandReactor.test.ts     | 55 +++++++++++++++++++
 .../Layers/ProviderCommandReactor.ts          |  4 +-
 2 files changed, 57 insertions(+), 2 deletions(-)

diff --git a/apps/server/src/orchestration/Layers/ProviderCommandReactor.test.ts b/apps/server/src/orchestration/Layers/ProviderCommandReactor.test.ts
index ded64fb9e6..fb4d13f071 100644
--- a/apps/server/src/orchestration/Layers/ProviderCommandReactor.test.ts
+++ b/apps/server/src/orchestration/Layers/ProviderCommandReactor.test.ts
@@ -1241,6 +1241,61 @@ describe("ProviderCommandReactor", () => {
     });
   });
 
+  it("starts a fresh session when only projected session state exists", async () => {
+    const harness = await createHarness();
+    const now = new Date().toISOString();
+
+    await Effect.runPromise(
+      harness.engine.dispatch({
+        type: "thread.session.set",
+        commandId: CommandId.make("cmd-session-set-stale"),
+        threadId: ThreadId.make("thread-1"),
+        session: {
+          threadId: ThreadId.make("thread-1"),
+          status: "ready",
+          providerName: "codex",
+          runtimeMode: "approval-required",
+          activeTurnId: null,
+          lastError: null,
+          updatedAt: now,
+        },
+        createdAt: now,
+      }),
+    );
+
+    await Effect.runPromise(
+      harness.engine.dispatch({
+        type: "thread.turn.start",
+        commandId: CommandId.make("cmd-turn-start-stale"),
+        threadId: ThreadId.make("thread-1"),
+        message: {
+          messageId: asMessageId("user-message-stale"),
+          role: "user",
+          text: "resume codex",
+          attachments: [],
+        },
+        interactionMode: DEFAULT_PROVIDER_INTERACTION_MODE,
+        runtimeMode: "approval-required",
+        createdAt: now,
+      }),
+    );
+
+    await waitFor(() => harness.startSession.mock.calls.length === 1);
+    await waitFor(() => harness.sendTurn.mock.calls.length === 1);
+
+    expect(harness.startSession.mock.calls[0]?.[1]).toMatchObject({
+      threadId: ThreadId.make("thread-1"),
+      modelSelection: {
+        provider: "codex",
+        model: "gpt-5-codex",
+      },
+      runtimeMode: "approval-required",
+    });
+    expect(harness.sendTurn.mock.calls[0]?.[0]).toMatchObject({
+      threadId: ThreadId.make("thread-1"),
+    });
+  });
+
   it("reacts to thread.approval.respond by forwarding provider approval response", async () => {
     const harness = await createHarness();
     const now = new Date().toISOString();
diff --git a/apps/server/src/orchestration/Layers/ProviderCommandReactor.ts b/apps/server/src/orchestration/Layers/ProviderCommandReactor.ts
index a1a69f0efa..a728129fa8 100644
--- a/apps/server/src/orchestration/Layers/ProviderCommandReactor.ts
+++ b/apps/server/src/orchestration/Layers/ProviderCommandReactor.ts
@@ -290,14 +290,14 @@ const make = Effect.gen(function* () {
         createdAt,
       });
 
+    const activeSession = yield* resolveActiveSession(threadId);
     const existingSessionThreadId =
-      thread.session && thread.session.status !== "stopped" ? thread.id : null;
+      thread.session && thread.session.status !== "stopped" && activeSession ? thread.id : null;
     if (existingSessionThreadId) {
       const runtimeModeChanged = thread.runtimeMode !== thread.session?.runtimeMode;
       const providerChanged =
         requestedModelSelection !== undefined &&
         requestedModelSelection.provider !== currentProvider;
-      const activeSession = yield* resolveActiveSession(existingSessionThreadId);
       const sessionModelSwitch =
         currentProvider === undefined
           ? "in-session"