diff --git a/packages/tui/src/routes/session/message-parts.tsx b/packages/tui/src/routes/session/message-parts.tsx
index 5a7af359311f..c61c2058b450 100644
--- a/packages/tui/src/routes/session/message-parts.tsx
+++ b/packages/tui/src/routes/session/message-parts.tsx
@@ -1,4 +1,4 @@
-import { createMemo, createSignal, Match, Show, Switch } from "solid-js"
+import { createEffect, createMemo, createSignal, Match, on, Show, Switch } from "solid-js"
 import { RGBA, TextAttributes, type MouseEvent } from "@opentui/core"
 import { useRenderer, type JSX } from "@opentui/solid"
 import type {
@@ -52,15 +52,20 @@ export function ReasoningPart(props: {
     generateThinkingSyntax(syntax(), theme.text.muted, renderer.nativeScene),
   )
   const ctx = use()
-  // Collapsed by default in hide mode: a single line throughout, so the
-  // layout never shifts. Click to open the full markdown block, click to close.
-  const [expanded, setExpanded] = createSignal(false)
+  // Open by default when thinking is shown, collapsed to one line when hidden.
+  // Clicking the header overrides that default either way, so a block can be
+  // folded without hiding every block in the session.
+  const [override, setOverride] = createSignal<boolean>()
 
   const content = createMemo(() => reasoningContent(props.part))
   const isDone = createMemo(
     () => props.part.time?.completed !== undefined || props.message.time.completed !== undefined,
   )
   const inMinimal = createMemo(() => ctx.thinkingMode() === "hide")
+  // A new session default applies to every block; drop per-block overrides so
+  // switching between show and hide cannot leave a stale folded state behind.
+  createEffect(on(inMinimal, () => setOverride(undefined), { defer: true }))
+  const open = () => override() ?? !inMinimal()
   const duration = createMemo(() => {
     const end = props.part.time?.completed ?? props.message.time.completed
     const start = props.part.time?.created ?? props.message.time.created
@@ -68,30 +73,30 @@ export function ReasoningPart(props: {
   })
   const summary = createMemo(() => reasoningSummary(content()))
   const toggle = () => {
-    if (!inMinimal()) return
-    setExpanded((prev) => !prev)
+    // Selecting the header text for a copy must not fold the block.
+    if (renderer.getSelection()?.getSelectedText()) return
+    setOverride(!open())
   }
 
   return (
     <Show when={content()}>
       <box paddingLeft={3} flexDirection="column" flexShrink={0}>
         <box
-          border={!inMinimal() || expanded() ? ["left"] : undefined}
+          border={open() ? ["left"] : undefined}
           customBorderChars={SplitBorder.customBorderChars}
           borderColor={theme.decrease(theme.background.base)}
-          paddingLeft={!inMinimal() || expanded() ? 1 : 0}
+          paddingLeft={open() ? 1 : 0}
         >
           <box onMouseUp={toggle}>
             <ReasoningHeader
-              toggleable={inMinimal()}
-              open={!inMinimal() || expanded()}
+              open={open()}
               done={isDone()}
-              title={inMinimal() && !expanded() ? summary().title : null}
+              title={open() ? null : summary().title}
               duration={isDone() ? Locale.duration(duration()) : undefined}
             />
           </box>
         </box>
-        <Show when={!inMinimal() || expanded()}>
+        <Show when={open()}>
           <box marginTop={1}>
             <box
               border={["left"]}
@@ -121,13 +126,7 @@ export function reasoningContent(part: SessionMessageAssistantReasoning) {
   return part.text.replace("[REDACTED]", "").trim()
 }
 
-function ReasoningHeader(props: {
-  toggleable: boolean
-  open: boolean
-  done: boolean
-  title: string | null
-  duration?: string
-}) {
+function ReasoningHeader(props: { open: boolean; done: boolean; title: string | null; duration?: string }) {
   const theme = useTheme()
   const fg = () =>
     props.open
@@ -148,9 +147,7 @@ function ReasoningHeader(props: {
       </Match>
       <Match when={true}>
         <text fg={fg()} wrapMode="none">
-          <Show when={props.toggleable}>
-            <span>{props.open ? "- " : "+ "}</span>
-          </Show>
+          <span>{props.open ? "- " : "+ "}</span>
           <span>Thought</span>
           <Show when={props.title || props.duration}>
             <span>: </span>
diff --git a/packages/tui/test/cli/tui/reasoning-disclosure.test.tsx b/packages/tui/test/cli/tui/reasoning-disclosure.test.tsx
new file mode 100644
index 000000000000..19264463cbd7
--- /dev/null
+++ b/packages/tui/test/cli/tui/reasoning-disclosure.test.tsx
@@ -0,0 +1,109 @@
+import { expect, test } from "bun:test"
+import { testRender } from "@opentui/solid"
+import { addDefaultParsers } from "@opentui/core"
+import { createSignal } from "solid-js"
+import type { SessionMessageAssistant, SessionMessageAssistantReasoning } from "@opencode/client"
+import parsers from "../../../src/parsers-config"
+import { ConfigProvider } from "../../../src/config"
+import { ThemeProvider } from "../../../src/context/theme"
+import { createTimelineAnchors } from "../../../src/routes/session/anchors"
+import { ReasoningPart } from "../../../src/routes/session/message-parts"
+import { context } from "../../../src/routes/session/render-context"
+import { emptyThemeSource } from "../../fixture/fixture"
+import { TestTuiContexts } from "../../fixture/tui-environment"
+import { createTuiResolvedConfig } from "../../fixture/tui-runtime"
+
+test("toggles a reasoning block in show and hide modes", async () => {
+  addDefaultParsers(parsers.parsers)
+  const [mode, setMode] = createSignal<"show" | "hide">("show")
+  const part: SessionMessageAssistantReasoning = {
+    type: "reasoning",
+    text: "**Inspecting stability**\n\nThe body of the thought.",
+    time: { created: 0, completed: 2000 },
+  }
+  const message: SessionMessageAssistant = {
+    id: "msg_reasoning",
+    type: "assistant",
+    agent: "build",
+    model: { providerID: "fixture", id: "fixture" },
+    time: { created: 0, completed: 2000 },
+    content: [part],
+  }
+  const config = createTuiResolvedConfig({ animations: false })
+  const app = await testRender(
+    () => (
+      <TestTuiContexts>
+        <ConfigProvider config={config}>
+          <ThemeProvider mode="dark" source={emptyThemeSource}>
+            <context.Provider
+              value={{
+                width: 60,
+                terminal: { width: 60, height: 20 },
+                sessionID: "fixture",
+                anchors: createTimelineAnchors(),
+                groupExpanded: () => false,
+                setGroupExpanded: () => {},
+                thinkingMode: mode,
+                markdownMode: () => "rendered",
+                groupExploration: () => false,
+                legacyTurns: () => false,
+                diffWrapMode: () => "word",
+                models: () => [],
+                messageIndex: () => undefined,
+                config,
+                mutatePending: async () => true,
+                pendingDelivery: () => undefined,
+              }}
+            >
+              <box paddingTop={2}>
+                <ReasoningPart last part={part} message={message} />
+              </box>
+            </context.Provider>
+          </ThemeProvider>
+        </ConfigProvider>
+      </TestTuiContexts>
+    ),
+    { width: 60, height: 20 },
+  )
+  const frame = () => app.captureCharFrame()
+  const headerRow = () =>
+    frame()
+      .split("\n")
+      .findIndex((line) => line.includes("Thought"))
+  const click = async () => {
+    // A double click turns into a word selection, and a selected header is
+    // intentionally not a disclosure toggle.
+    app.renderer.clearSelection()
+    const row = headerRow()
+    expect(row).toBeGreaterThan(0)
+    await app.mockMouse.click(6, row)
+    await app.renderOnce()
+  }
+  try {
+    app.renderer.start()
+    await app.waitForFrame((value) => value.includes("The body of the thought."))
+    expect(frame()).toContain("- Thought")
+    expect(frame()).toContain("Inspecting stability")
+
+    await click()
+    await app.waitForVisualIdle({ quietFrames: 3 })
+    expect(frame()).not.toContain("The body of the thought.")
+    expect(frame()).toContain("+ Thought: Inspecting stability")
+
+    await click()
+    await app.waitForFrame((value) => value.includes("The body of the thought."))
+
+    setMode("hide")
+    await app.waitForVisualIdle({ quietFrames: 3 })
+    expect(frame()).not.toContain("The body of the thought.")
+    expect(frame()).toContain("+ Thought: Inspecting stability")
+
+    await click()
+    await app.waitForFrame((value) => value.includes("The body of the thought."))
+
+    setMode("show")
+    await app.waitForFrame((value) => value.includes("The body of the thought."))
+  } finally {
+    app.renderer.destroy()
+  }
+})