feat: Add the /btw command

packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx

@@ -41,6 +41,7 @@ export type PromptProps = {
   visible?: boolean
   disabled?: boolean
   onSubmit?: () => void
+  onBeforeSubmit?: (text: string) => boolean
   ref?: (ref: PromptRef) => void
   hint?: JSX.Element
   showPlaceholder?: boolean
@@ -587,6 +588,17 @@ export function Prompt(props: PromptProps) {
     const currentMode = store.mode
     const variant = local.model.variant.current()
 
+    // Allow external interception (e.g., /btw mode)
+    if (props.onBeforeSubmit?.(inputText)) {
+      history.append({ ...store.prompt, mode: currentMode })
+      input.extmarks.clear()
+      setStore("prompt", { input: "", parts: [] })
+      setStore("extmarkToPartIndex", new Map())
+      input.clear()
+      props.onSubmit?.()
+      return
+    }
+
     if (store.mode === "shell") {
       sdk.client.session.shell({
         sessionID,

packages/opencode/src/cli/cmd/tui/routes/session/index.tsx

@@ -52,7 +52,7 @@ import { useCommandDialog } from "@tui/component/dialog-command"
 import type { DialogContext } from "@tui/ui/dialog"
 import { useKeybind } from "@tui/context/keybind"
 import { Header } from "./header"
-import { parsePatch } from "diff"
+import { diffLines, parsePatch } from "diff"
 import { useDialog } from "../../ui/dialog"
 import { TodoItem } from "../../component/todo-item"
 import { DialogMessage } from "./dialog-message"
@@ -81,9 +81,15 @@ import { DialogExportOptions } from "../../ui/dialog-export-options"
 import { formatTranscript } from "../../util/transcript"
 import { UI } from "@/cli/ui.ts"
 import { useTuiConfig } from "../../context/tui-config"
+import { Identifier } from "@/id/id"
 
 addDefaultParsers(parsers.parsers)
 
+type BtwState =
+  | { type: "waiting" }
+  | { type: "loading"; question: string; userMessageID: string }
+  | { type: "response"; question: string; responseMessageID: string }
+
 class CustomSpeedScroll implements ScrollAcceleration {
   constructor(private speed: number) {}
 
@@ -128,7 +134,8 @@ export function Session() {
       .filter((x) => x.parentID === parentID || x.id === parentID)
       .toSorted((a, b) => (a.id < b.id ? -1 : a.id > b.id ? 1 : 0))
   })
-  const messages = createMemo(() => sync.data.message[route.sessionID] ?? [])
+  const messages = createMemo(() => (sync.data.message[route.sessionID] ?? []).filter((m) => !m.btw))
+  const [btwState, setBtwState] = createSignal<BtwState | null>(null)
   const permissions = createMemo(() => {
     if (session()?.parentID) return []
     return children().flatMap((x) => sync.data.permission[x.id] ?? [])
@@ -259,6 +266,39 @@ export function Session() {
     )
   })
 
+  // Watch for btw response arriving via sync events
+  createEffect(() => {
+    const state = btwState()
+    if (!state || state.type !== "loading") return
+    const msgs = sync.data.message[route.sessionID] ?? []
+    const response = msgs.find(
+      (m): m is AssistantMessage =>
+        m.role === "assistant" &&
+        (m as AssistantMessage).parentID === state.userMessageID &&
+        m.btw === true &&
+        !!(m as AssistantMessage).finish &&
+        !["tool-calls", "unknown"].includes((m as AssistantMessage).finish!),
+    )
+    if (response) {
+      setBtwState({ type: "response", question: state.question, responseMessageID: response.id })
+    }
+  })
+
+  // Dismiss btw with esc (any state) or enter (response state)
+  useKeyboard((evt) => {
+    const state = btwState()
+    if (!state) return
+    if (evt.name === "escape") {
+      setBtwState(null)
+      evt.preventDefault()
+      evt.stopPropagation()
+    } else if (state.type === "response" && evt.name === "return") {
+      setBtwState(null)
+      evt.preventDefault()
+      evt.stopPropagation()
+    }
+  })
+
   useKeyboard((evt) => {
     if (!session()?.parentID) return
     if (keybind.match("app_exit", evt)) {
@@ -319,6 +359,33 @@ export function Session() {
     }, 50)
   }
 
+  const btwBeforeSubmit = (text: string): boolean => {
+    const state = btwState()
+    if (!state || state.type !== "waiting") return false
+    const sessionID = session()?.id
+    if (!sessionID) {
+      setBtwState(null)
+      return false
+    }
+    const userMessageID = Identifier.ascending("message")
+    setBtwState({ type: "loading", question: text, userMessageID })
+    sdk.client.session
+      .promptAsync({
+        sessionID,
+        btw: true,
+        messageID: userMessageID,
+        parts: [{ type: "text", text }],
+      })
+      .catch((error) => {
+        toast.show({
+          message: error instanceof Error ? error.message : "Failed",
+          variant: "error",
+        })
+        setBtwState(null)
+      })
+    return true
+  }
+
   const local = useLocal()
 
   function moveFirstChild() {
@@ -616,6 +683,20 @@ export function Session() {
         dialog.clear()
       },
     },
+    {
+      title: "Ask a quick question",
+      description: "Ask a quick question about your current work without adding to the conversation history.",
+      value: "session.btw",
+      keybind: "btw",
+      category: "Session",
+      slash: {
+        name: "btw",
+      },
+      onSelect: (dialog) => {
+        setBtwState({ type: "waiting" })
+        dialog.clear()
+      },
+    },
     {
       title: showDetails() ? "Hide tool details" : "Show tool details",
       value: "session.toggle.actions",
@@ -1164,6 +1245,7 @@ export function Session() {
                   </Switch>
                 )}
               </For>
+              <BtwSection state={btwState()} sync={sync} sessionID={route.sessionID} />
             </scrollbox>
             <box flexShrink={0}>
               <Show when={permissions().length > 0}>
@@ -1183,6 +1265,7 @@ export function Session() {
                   }
                 }}
                 disabled={permissions().length > 0 || questions().length > 0}
+                onBeforeSubmit={btwBeforeSubmit}
                 onSubmit={() => {
                   toBottom()
                 }}
@@ -2279,3 +2362,72 @@ function filetype(input?: string) {
   if (["typescriptreact", "javascriptreact", "javascript"].includes(language)) return "typescript"
   return language
 }
+
+function BtwSection(props: { state: BtwState | null; sync: ReturnType<typeof useSync>; sessionID: string }) {
+  const { theme, syntax } = useTheme()
+
+  const responseText = createMemo(() => {
+    const state = props.state
+    if (!state || state.type !== "response") return null
+    const msgs = props.sync.data.message[props.sessionID] ?? []
+    const msg = msgs.find((m) => m.id === state.responseMessageID)
+    if (!msg) return null
+    const parts = props.sync.data.part[msg.id] ?? []
+    return parts
+      .filter((p): p is TextPart => p.type === "text" && !(p as TextPart).synthetic)
+      .map((p) => p.text)
+      .join("")
+  })
+
+  return (
+    <Show when={props.state}>
+      <box
+        marginTop={1}
+        border={["left"]}
+        customBorderChars={SplitBorder.customBorderChars}
+        borderColor={theme.primary}
+        paddingLeft={2}
+        paddingTop={1}
+        paddingBottom={1}
+        flexShrink={0}
+        backgroundColor={theme.backgroundPanel}
+      >
+        <box flexDirection="row" gap={1}>
+          <text attributes={TextAttributes.BOLD} fg={theme.primary}>
+            /btw
+          </text>
+          <Show when={props.state!.type !== "waiting"}>
+            <text fg={theme.textMuted}>{(props.state as { type: "loading" | "response"; question: string }).question}</text>
+          </Show>
+          <Show when={props.state!.type === "waiting"}>
+            <text fg={theme.textMuted}>Type your question and press enter...</text>
+          </Show>
+        </box>
+        <Switch>
+          <Match when={props.state!.type === "loading"}>
+            <box flexDirection="row" gap={1} marginTop={1}>
+              <Spinner />
+              <text fg={theme.textMuted}>Thinking...</text>
+            </box>
+          </Match>
+          <Match when={props.state!.type === "response" && responseText()}>
+            <box marginTop={1}>
+              <code
+                filetype="markdown"
+                drawUnstyledText={false}
+                streaming={false}
+                syntaxStyle={syntax()}
+                content={responseText()!.trim()}
+                conceal={false}
+                fg={theme.text}
+              />
+            </box>
+            <text fg={theme.textMuted} marginTop={1}>
+              enter/esc to close
+            </text>
+          </Match>
+        </Switch>
+      </box>
+    </Show>
+  )
+}

packages/opencode/src/session/message-v2.ts

@@ -369,6 +369,7 @@ export namespace MessageV2 {
     system: z.string().optional(),
     tools: z.record(z.string(), z.boolean()).optional(),
     variant: z.string().optional(),
+    btw: z.boolean().optional(),
   }).meta({
     ref: "UserMessage",
   })
@@ -438,6 +439,7 @@ export namespace MessageV2 {
     structured: z.any().optional(),
     variant: z.string().optional(),
     finish: z.string().optional(),
+    btw: z.boolean().optional(),
   }).meta({
     ref: "AssistantMessage",
   })
@@ -555,8 +557,20 @@ export namespace MessageV2 {
       return { type: "json", value: output as never }
     }
 
+    // Pre-compute which btw user messages already have a response, so we can
+    // skip completed btw exchanges while still including any pending btw question
+    const answeredBtwUserIDs = new Set<string>()
+    for (const msg of input) {
+      if (msg.info.role === "assistant" && msg.info.btw) {
+        answeredBtwUserIDs.add((msg.info as Assistant).parentID)
+      }
+    }
+
     for (const msg of input) {
       if (msg.parts.length === 0) continue
+      // Skip completed btw pairs; pending btw question passes through so the model can answer it
+      if (msg.info.btw && msg.info.role === "assistant") continue
+      if (msg.info.btw && msg.info.role === "user" && answeredBtwUserIDs.has(msg.info.id)) continue
 
       if (msg.info.role === "user") {
         const userMessage: UIMessage = {