diff --git a/apps/web/src/session-logic.test.ts b/apps/web/src/session-logic.test.ts
index 4a113adeb..61758e962 100644
--- a/apps/web/src/session-logic.test.ts
+++ b/apps/web/src/session-logic.test.ts
@@ -10,6 +10,7 @@ import { describe, expect, it } from "vitest";
 import {
   deriveActiveWorkStartedAt,
   deriveActivePlanState,
+  derivePhase,
   PROVIDER_OPTIONS,
   derivePendingApprovals,
   derivePendingUserInputs,
@@ -21,6 +22,7 @@ import {
   hasToolActivityForTurn,
   isLatestTurnSettled,
 } from "./session-logic";
+import type { ThreadSession } from "./types";
 
 function makeActivity(overrides: {
   id?: string;
@@ -174,6 +176,21 @@ describe("derivePendingApprovals", () => {
   });
 });
 
+describe("derivePhase", () => {
+  it("treats errored sessions as disconnected instead of ready", () => {
+    const session: ThreadSession = {
+      provider: "codex",
+      status: "error",
+      orchestrationStatus: "error",
+      createdAt: "2026-02-23T00:00:00.000Z",
+      updatedAt: "2026-02-23T00:00:01.000Z",
+      lastError: "Provider crashed",
+    };
+
+    expect(derivePhase(session)).toBe("disconnected");
+  });
+});
+
 describe("derivePendingUserInputs", () => {
   it("tracks open structured prompts and removes resolved ones", () => {
     const activities: OrchestrationThreadActivity[] = [
diff --git a/apps/web/src/session-logic.ts b/apps/web/src/session-logic.ts
index 7c3ea96e6..e1d9c5f18 100644
--- a/apps/web/src/session-logic.ts
+++ b/apps/web/src/session-logic.ts
@@ -865,7 +865,9 @@ export function inferCheckpointTurnCountByTurnId(
 }
 
 export function derivePhase(session: ThreadSession | null): SessionPhase {
-  if (!session || session.status === "closed") return "disconnected";
+  if (!session || session.status === "closed" || session.status === "error") {
+    return "disconnected";
+  }
   if (session.status === "connecting") return "connecting";
   if (session.status === "running") return "running";
   return "ready";