diff --git a/apps/web/components/task/chat/chat-input-area.tsx b/apps/web/components/task/chat/chat-input-area.tsx
index 55dad36d95..cdb0576901 100644
--- a/apps/web/components/task/chat/chat-input-area.tsx
+++ b/apps/web/components/task/chat/chat-input-area.tsx
@@ -413,6 +413,7 @@ export function ChatInputArea({
         onPlanModeChange={handlePlanModeChange}
         isAgentBusy={isAgentBusy}
         isStarting={panelState.isStarting}
+        isPreparingEnvironment={panelState.isPreparingEnvironment}
         isMoving={isMoving}
         isSending={isSending}
         onCancel={handleCancelTurn}
diff --git a/apps/web/components/task/chat/chat-input-container.tsx b/apps/web/components/task/chat/chat-input-container.tsx
index e62974f6bc..306a3a5385 100644
--- a/apps/web/components/task/chat/chat-input-container.tsx
+++ b/apps/web/components/task/chat/chat-input-container.tsx
@@ -57,6 +57,11 @@ type ChatInputContainerProps = {
   onPlanModeChange: (enabled: boolean) => void;
   isAgentBusy: boolean;
   isStarting: boolean;
+  /** True only while a containerized executor is bootstrapping (Docker
+   * prepare, Sprites sandbox spin-up). Distinct from the brief STARTING
+   * state every session — including local quick-chat — passes through;
+   * see useSessionState. */
+  isPreparingEnvironment?: boolean;
   isMoving?: boolean;
   isSending: boolean;
   onCancel: () => void;
@@ -292,6 +297,7 @@ export const ChatInputContainer = forwardRef<ChatInputContainerHandle, ChatInput
       sessionId,
       isSending,
       isStarting,
+      isPreparingEnvironment: props.isPreparingEnvironment ?? false,
       isMoving,
       isFailed: p.isFailed,
       needsRecovery: props.needsRecovery ?? false,
diff --git a/apps/web/components/task/chat/use-chat-input-container.test.ts b/apps/web/components/task/chat/use-chat-input-container.test.ts
index 4d6b74f840..3e160f47f3 100644
--- a/apps/web/components/task/chat/use-chat-input-container.test.ts
+++ b/apps/web/components/task/chat/use-chat-input-container.test.ts
@@ -11,6 +11,7 @@ function renderInputState(overrides: Partial<Parameters<typeof useChatInputConta
       sessionId: "session-1",
       isSending: false,
       isStarting: false,
+      isPreparingEnvironment: false,
       isMoving: false,
       isFailed: false,
       needsRecovery: false,
diff --git a/apps/web/components/task/chat/use-chat-input-container.ts b/apps/web/components/task/chat/use-chat-input-container.ts
index 05ec53b80a..598d0f8bff 100644
--- a/apps/web/components/task/chat/use-chat-input-container.ts
+++ b/apps/web/components/task/chat/use-chat-input-container.ts
@@ -16,6 +16,11 @@ type UseChatInputContainerParams = {
   sessionId: string | null;
   isSending: boolean;
   isStarting: boolean;
+  /** True only during a real Docker/Sprites prepare phase. Different from
+   * `isStarting`, which fires for every session that's transitioning
+   * through STARTING (including local quick-chat). Submit gating uses
+   * this narrower flag so quick-chat sessions aren't blocked. */
+  isPreparingEnvironment: boolean;
   isMoving: boolean;
   isFailed: boolean;
   needsRecovery: boolean;
@@ -82,6 +87,7 @@ function getInputPlaceholder(
 
 function computeDerivedState(params: {
   isStarting: boolean;
+  isPreparingEnvironment: boolean;
   isMoving: boolean;
   isSending: boolean;
   isFailed: boolean;
@@ -102,8 +108,15 @@ function computeDerivedState(params: {
     params.isFailed ||
     params.needsRecovery ||
     params.executorUnavailable;
-  const submitDisabled = params.isStarting || isDisabled;
-  const submitDisabledReason = params.isStarting ? "The agent is still being set up." : undefined;
+  // Only an active container/sandbox prepare blocks the submit and surfaces
+  // the "agent still being set up" tooltip. The brief STARTING transition
+  // every session passes through (including local quick-chat) intentionally
+  // does NOT block — the e2e suite presses Cmd+Enter as soon as the editor
+  // becomes editable, and a STARTING-only block silently dropped messages.
+  const submitDisabled = params.isPreparingEnvironment || isDisabled;
+  const submitDisabledReason = params.isPreparingEnvironment
+    ? "The agent is still being set up."
+    : undefined;
   const hasClarification = !!(params.pendingClarification && params.onClarificationResolved);
   const hasPendingComments = !!(
     params.pendingCommentsByFile && Object.keys(params.pendingCommentsByFile).length > 0
@@ -129,26 +142,11 @@ function computeDerivedState(params: {
 }
 
 export function useChatInputContainer(params: UseChatInputContainerParams) {
-  const {
-    ref,
-    sessionId,
-    isSending,
-    isStarting,
-    isMoving,
-    isFailed,
-    needsRecovery,
-    executorUnavailable,
-    isAgentBusy,
-    hasAgentCommands,
-    placeholder,
-    contextItems,
-    pendingClarification,
-    onClarificationResolved,
-    pendingCommentsByFile,
-    showRequestChangesTooltip,
-    onRequestChangesTooltipDismiss,
-    onSubmit,
-  } = params;
+  const { ref, sessionId, isSending, isStarting, isPreparingEnvironment, isMoving } = params;
+  const { isFailed, needsRecovery, executorUnavailable, isAgentBusy, hasAgentCommands } = params;
+  const { placeholder, contextItems, pendingClarification, onClarificationResolved } = params;
+  const { pendingCommentsByFile, showRequestChangesTooltip } = params;
+  const { onRequestChangesTooltipDismiss, onSubmit } = params;
 
   const [isInputFocused, setIsInputFocused] = useState(false);
   const [showNewSessionDialog, setShowNewSessionDialog] = useState(false);
@@ -202,6 +200,7 @@ export function useChatInputContainer(params: UseChatInputContainerParams) {
 
   const derived = computeDerivedState({
     isStarting,
+    isPreparingEnvironment,
     isMoving,
     isSending,
     isFailed,
diff --git a/apps/web/hooks/domains/session/use-session-state.ts b/apps/web/hooks/domains/session/use-session-state.ts
index bc4bb48d5a..458764f33f 100644
--- a/apps/web/hooks/domains/session/use-session-state.ts
+++ b/apps/web/hooks/domains/session/use-session-state.ts
@@ -48,5 +48,11 @@ export function useSessionState(sessionId: string | null) {
     ...flags,
     isStarting: flags.isStarting || isPreparingEnvironment,
     isWorking: flags.isWorking || isPreparingEnvironment,
+    // Exposed separately so consumers that gate on "is the executor still
+    // bootstrapping" (e.g. the chat input "agent is still being set up"
+    // tooltip) can distinguish a brief STARTING transition — which every
+    // session passes through, including local quick-chat — from an active
+    // Docker / Sprites prepare-environment phase.
+    isPreparingEnvironment,
   };
 }