From f23a4b7bb3b8a4cf533b9d69697146ebe3ef91c9 Mon Sep 17 00:00:00 2001
From: Brooklyn Nicholson <brooklyn.bb.nicholson@gmail.com>
Date: Sat, 13 Jun 2026 00:23:51 -0500
Subject: [PATCH] fix(desktop): keep queued drains quiet on transient "session
 busy"

A queued drain firing on the settle edge can race a not-yet-wound-down
turn and get a transient 4009 "session busy". Previously that appended a
red "session busy" error bubble (and toast) per attempt. For fromQueue
submits, swallow the busy error: release busy, keep the entry queued, and
let the composer's bounded auto-drain retry on the next idle.
---
 .../session/hooks/use-prompt-actions.test.tsx | 39 +++++++++++++++++++
 .../app/session/hooks/use-prompt-actions.ts   | 10 ++++-
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/apps/desktop/src/app/session/hooks/use-prompt-actions.test.tsx b/apps/desktop/src/app/session/hooks/use-prompt-actions.test.tsx
index 545bff0d45f..5966ea24679 100644
--- a/apps/desktop/src/app/session/hooks/use-prompt-actions.test.tsx
+++ b/apps/desktop/src/app/session/hooks/use-prompt-actions.test.tsx
@@ -364,6 +364,45 @@ describe('usePromptActions submit / queue drain semantics', () => {
     })
   })
 
+  it('a fromQueue drain that hits "session busy" stays quiet (no error bubble) and a retry sends it', async () => {
+    // The drain can fire on the settle edge before the gateway has fully wound
+    // the turn down → transient 4009. It must not append a red "session busy"
+    // bubble; the entry stays queued and the next idle retry succeeds.
+    let attempt = 0
+    const seeds: Record<string, unknown>[] = []
+    const requestGateway = vi.fn(async (method: string) => {
+      if (method === 'prompt.submit') {
+        attempt += 1
+
+        if (attempt === 1) {
+          throw new Error('4009: session busy')
+        }
+      }
+
+      return {} as never
+    })
+
+    let handle: HarnessHandle | null = null
+    render(
+      <Harness
+        onReady={h => (handle = h)}
+        onSeedState={s => seeds.push(s)}
+        refreshSessions={async () => undefined}
+        requestGateway={requestGateway}
+      />
+    )
+
+    const first = await handle!.submitText('queued during a turn', { fromQueue: true })
+    expect(first).toBe(false)
+    // No assistant-error message was appended for the transient busy.
+    expect(seeds.some(s => Array.isArray(s.messages) && (s.messages as { error?: string }[]).some(m => m.error))).toBe(
+      false
+    )
+
+    const second = await handle!.submitText('queued during a turn', { fromQueue: true })
+    expect(second).toBe(true)
+  })
+
   it('a normal (non-queue) submit still respects the busyRef guard', async () => {
     const busyRef = { current: true }
     const requestGateway = vi.fn(async () => ({}) as never)
diff --git a/apps/desktop/src/app/session/hooks/use-prompt-actions.ts b/apps/desktop/src/app/session/hooks/use-prompt-actions.ts
index a481728362d..5c7df471a8b 100644
--- a/apps/desktop/src/app/session/hooks/use-prompt-actions.ts
+++ b/apps/desktop/src/app/session/hooks/use-prompt-actions.ts
@@ -714,9 +714,17 @@ export function usePromptActions({
 
         return true
       } catch (err) {
+        releaseBusy()
+
+        // A queued drain that raced a not-yet-settled turn gets a transient
+        // "session busy" (4009). Don't surface an error bubble/toast — the entry
+        // stays queued and the composer's bounded auto-drain retries when idle.
+        if (options?.fromQueue && isSessionBusyError(err)) {
+          return false
+        }
+
         const message = inlineErrorMessage(err, copy.promptFailed)
 
-        releaseBusy()
         updateSessionState(sessionId, state => ({
           ...state,
           messages: [