diff --git a/ui-tui/packages/hermes-ink/src/ink/ink.tsx b/ui-tui/packages/hermes-ink/src/ink/ink.tsx
index d05b743a09..ff6570f8cf 100644
--- a/ui-tui/packages/hermes-ink/src/ink/ink.tsx
+++ b/ui-tui/packages/hermes-ink/src/ink/ink.tsx
@@ -62,10 +62,10 @@ import {
   getSelectedText,
   hasSelection,
   moveFocus,
+  selectionBounds,
   type SelectionState,
   selectLineAt,
   selectWordAt,
-  selectionBounds,
   shiftAnchor,
   shiftSelection,
   shiftSelectionForFollow,
diff --git a/ui-tui/src/__tests__/createSlashHandler.test.ts b/ui-tui/src/__tests__/createSlashHandler.test.ts
index 32c92c00ab..a51c89c5b8 100644
--- a/ui-tui/src/__tests__/createSlashHandler.test.ts
+++ b/ui-tui/src/__tests__/createSlashHandler.test.ts
@@ -119,6 +119,7 @@ describe('createSlashHandler', () => {
     expect(getUiState().detailsMode).toBe('collapsed')
     expect(createSlashHandler(ctx)('/details toggle')).toBe(true)
     expect(getUiState().detailsMode).toBe('expanded')
+    expect(getUiState().detailsModeCommandOverride).toBe(true)
     expect(ctx.gateway.rpc).toHaveBeenCalledWith('config.set', {
       key: 'details_mode',
       value: 'expanded'
diff --git a/ui-tui/src/__tests__/details.test.ts b/ui-tui/src/__tests__/details.test.ts
index 0f567b2f72..04a1fca90e 100644
--- a/ui-tui/src/__tests__/details.test.ts
+++ b/ui-tui/src/__tests__/details.test.ts
@@ -78,19 +78,25 @@ describe('sectionMode', () => {
     expect(sectionMode('subagents', 'hidden', {})).toBe('hidden')
   })
 
-  it('streams thinking + tools expanded by default regardless of global mode', () => {
+  it('streams thinking + tools expanded by default for persisted config values', () => {
     expect(sectionMode('thinking', 'collapsed', {})).toBe('expanded')
     expect(sectionMode('thinking', 'hidden', undefined)).toBe('expanded')
     expect(sectionMode('tools', 'collapsed', {})).toBe('expanded')
     expect(sectionMode('tools', 'hidden', undefined)).toBe('expanded')
   })
 
-  it('hides the activity panel by default regardless of global mode', () => {
+  it('hides the activity panel by default for persisted config values', () => {
     expect(sectionMode('activity', 'collapsed', {})).toBe('hidden')
     expect(sectionMode('activity', 'expanded', undefined)).toBe('hidden')
     expect(sectionMode('activity', 'hidden', {})).toBe('hidden')
   })
 
+  it('applies in-session /details mode globally over built-in defaults', () => {
+    expect(sectionMode('thinking', 'collapsed', {}, true)).toBe('collapsed')
+    expect(sectionMode('tools', 'hidden', {}, true)).toBe('hidden')
+    expect(sectionMode('activity', 'expanded', undefined, true)).toBe('expanded')
+  })
+
   it('honours per-section overrides over both the section default and global mode', () => {
     expect(sectionMode('thinking', 'collapsed', { thinking: 'collapsed' })).toBe('collapsed')
     expect(sectionMode('tools', 'collapsed', { tools: 'hidden' })).toBe('hidden')
diff --git a/ui-tui/src/app/interfaces.ts b/ui-tui/src/app/interfaces.ts
index 032eee87ab..34919aca02 100644
--- a/ui-tui/src/app/interfaces.ts
+++ b/ui-tui/src/app/interfaces.ts
@@ -90,6 +90,7 @@ export interface UiState {
   busy: boolean
   compact: boolean
   detailsMode: DetailsMode
+  detailsModeCommandOverride: boolean
   info: null | SessionInfo
   inlineDiffs: boolean
   mouseTracking: boolean
diff --git a/ui-tui/src/app/slash/commands/core.ts b/ui-tui/src/app/slash/commands/core.ts
index 6d927fedcc..70804a1f5b 100644
--- a/ui-tui/src/app/slash/commands/core.ts
+++ b/ui-tui/src/app/slash/commands/core.ts
@@ -184,7 +184,7 @@ export const coreCommands: SlashCommand[] = [
             }
 
             const mode = parseDetailsMode(r?.value) ?? ui.detailsMode
-            patchUiState({ detailsMode: mode })
+            patchUiState({ detailsMode: mode, detailsModeCommandOverride: false })
 
             const overrides = SECTION_NAMES.filter(s => ui.sections[s])
               .map(s => `${s}=${ui.sections[s]}`)
@@ -224,7 +224,7 @@ export const coreCommands: SlashCommand[] = [
         return transcript.sys(DETAILS_USAGE)
       }
 
-      patchUiState({ detailsMode: next })
+      patchUiState({ detailsMode: next, detailsModeCommandOverride: true })
       gateway.rpc<ConfigSetResponse>('config.set', { key: 'details_mode', value: next }).catch(() => {})
       transcript.sys(`details: ${next}`)
     }
diff --git a/ui-tui/src/app/uiStore.ts b/ui-tui/src/app/uiStore.ts
index fc17a6948f..1b3a841e18 100644
--- a/ui-tui/src/app/uiStore.ts
+++ b/ui-tui/src/app/uiStore.ts
@@ -11,6 +11,7 @@ const buildUiState = (): UiState => ({
   busy: false,
   compact: false,
   detailsMode: 'collapsed',
+  detailsModeCommandOverride: false,
   info: null,
   inlineDiffs: true,
   mouseTracking: MOUSE_TRACKING,
diff --git a/ui-tui/src/app/useConfigSync.ts b/ui-tui/src/app/useConfigSync.ts
index 3ceb8c635a..26d02d6204 100644
--- a/ui-tui/src/app/useConfigSync.ts
+++ b/ui-tui/src/app/useConfigSync.ts
@@ -45,6 +45,7 @@ export const applyDisplay = (cfg: ConfigFullResponse | null, setBell: (v: boolea
   patchUiState({
     compact: !!d.tui_compact,
     detailsMode: resolveDetailsMode(d),
+    detailsModeCommandOverride: false,
     inlineDiffs: d.inline_diffs !== false,
     mouseTracking: d.tui_mouse !== false,
     sections: resolveSections(d.sections),
diff --git a/ui-tui/src/app/useMainApp.ts b/ui-tui/src/app/useMainApp.ts
index d46744a032..6e07f8f8c1 100644
--- a/ui-tui/src/app/useMainApp.ts
+++ b/ui-tui/src/app/useMainApp.ts
@@ -26,6 +26,7 @@ import { createGatewayEventHandler } from './createGatewayEventHandler.js'
 import { createSlashHandler } from './createSlashHandler.js'
 import { type GatewayRpc, type TranscriptRow } from './interfaces.js'
 import { $overlayState, patchOverlayState } from './overlayStore.js'
+import { scrollWithSelectionBy } from './scroll.js'
 import { turnController } from './turnController.js'
 import { $turnState, patchTurnState } from './turnStore.js'
 import { $uiState, getUiState, patchUiState } from './uiStore.js'
@@ -33,7 +34,6 @@ import { useComposerState } from './useComposerState.js'
 import { useConfigSync } from './useConfigSync.js'
 import { useInputHandlers } from './useInputHandlers.js'
 import { useLongRunToolCharms } from './useLongRunToolCharms.js'
-import { scrollWithSelectionBy } from './scroll.js'
 import { useSessionLifecycle } from './useSessionLifecycle.js'
 import { useSubmission } from './useSubmission.js'
 
@@ -593,7 +593,9 @@ export function useMainApp(gw: GatewayClient) {
   // resolved to hidden, the only thing ToolTrail will surface is the
   // floating-alert backstop (errors/warnings).  Mirror that so we don't
   // render an empty wrapper Box above the streaming area in quiet mode.
-  const anyPanelVisible = SECTION_NAMES.some(s => sectionMode(s, ui.detailsMode, ui.sections) !== 'hidden')
+  const anyPanelVisible = SECTION_NAMES.some(
+    s => sectionMode(s, ui.detailsMode, ui.sections, ui.detailsModeCommandOverride) !== 'hidden'
+  )
 
   const showProgressArea = anyPanelVisible
     ? Boolean(
diff --git a/ui-tui/src/components/appLayout.tsx b/ui-tui/src/components/appLayout.tsx
index 170d0649ac..b302fed66f 100644
--- a/ui-tui/src/components/appLayout.tsx
+++ b/ui-tui/src/components/appLayout.tsx
@@ -25,6 +25,7 @@ const StreamingAssistant = memo(function StreamingAssistant({
   cols,
   compact,
   detailsMode,
+  detailsModeCommandOverride,
   progress,
   sections,
   t
@@ -40,6 +41,7 @@ const StreamingAssistant = memo(function StreamingAssistant({
           cols={cols}
           compact={compact}
           detailsMode={detailsMode}
+          detailsModeCommandOverride={detailsModeCommandOverride}
           key={`seg:${i}`}
           msg={msg}
           sections={sections}
@@ -52,6 +54,7 @@ const StreamingAssistant = memo(function StreamingAssistant({
           <ToolTrail
             activity={progress.activity}
             busy={busy}
+            commandOverride={detailsModeCommandOverride}
             detailsMode={detailsMode}
             outcome={progress.outcome}
             reasoning={progress.reasoning}
@@ -73,6 +76,7 @@ const StreamingAssistant = memo(function StreamingAssistant({
           cols={cols}
           compact={compact}
           detailsMode={detailsMode}
+          detailsModeCommandOverride={detailsModeCommandOverride}
           isStreaming
           msg={{
             role: 'assistant',
@@ -89,6 +93,7 @@ const StreamingAssistant = memo(function StreamingAssistant({
           cols={cols}
           compact={compact}
           detailsMode={detailsMode}
+          detailsModeCommandOverride={detailsModeCommandOverride}
           msg={{ kind: 'trail', role: 'system', text: '', tools: progress.streamPendingTools }}
           sections={sections}
           t={t}
@@ -127,6 +132,7 @@ const TranscriptPane = memo(function TranscriptPane({
                   cols={composer.cols}
                   compact={ui.compact}
                   detailsMode={ui.detailsMode}
+                  detailsModeCommandOverride={ui.detailsModeCommandOverride}
                   msg={row.msg}
                   sections={ui.sections}
                   t={ui.theme}
@@ -142,6 +148,7 @@ const TranscriptPane = memo(function TranscriptPane({
             cols={composer.cols}
             compact={ui.compact}
             detailsMode={ui.detailsMode}
+            detailsModeCommandOverride={ui.detailsModeCommandOverride}
             progress={progress}
             sections={ui.sections}
             t={ui.theme}
@@ -353,6 +360,7 @@ interface StreamingAssistantProps {
   cols: number
   compact?: boolean
   detailsMode: DetailsMode
+  detailsModeCommandOverride: boolean
   progress: AppLayoutProgressProps
   sections?: SectionVisibility
   t: Theme
diff --git a/ui-tui/src/components/messageLine.tsx b/ui-tui/src/components/messageLine.tsx
index 9807b1bbfd..bb6f811a94 100644
--- a/ui-tui/src/components/messageLine.tsx
+++ b/ui-tui/src/components/messageLine.tsx
@@ -16,6 +16,7 @@ export const MessageLine = memo(function MessageLine({
   cols,
   compact,
   detailsMode = 'collapsed',
+  detailsModeCommandOverride = false,
   isStreaming = false,
   msg,
   sections,
@@ -28,15 +29,16 @@ export const MessageLine = memo(function MessageLine({
   // feeds Thinking + Tool calls.  Gating on every section would let
   // `thinking` (expanded by default) keep an empty wrapper alive when only
   // `tools` is hidden — exactly the empty-Box bug Copilot caught.
-  const thinkingMode = sectionMode('thinking', detailsMode, sections)
-  const toolsMode = sectionMode('tools', detailsMode, sections)
-  const activityMode = sectionMode('activity', detailsMode, sections)
+  const thinkingMode = sectionMode('thinking', detailsMode, sections, detailsModeCommandOverride)
+  const toolsMode = sectionMode('tools', detailsMode, sections, detailsModeCommandOverride)
+  const activityMode = sectionMode('activity', detailsMode, sections, detailsModeCommandOverride)
   const thinking = msg.thinking?.trim() ?? ''
 
   if (msg.kind === 'trail' && (msg.tools?.length || thinking)) {
     return thinkingMode !== 'hidden' || toolsMode !== 'hidden' || activityMode !== 'hidden' ? (
       <Box flexDirection="column">
         <ToolTrail
+          commandOverride={detailsModeCommandOverride}
           detailsMode={detailsMode}
           reasoning={thinking}
           reasoningTokens={msg.thinkingTokens}
@@ -118,6 +120,7 @@ export const MessageLine = memo(function MessageLine({
       {showDetails && (
         <Box flexDirection="column" marginBottom={1}>
           <ToolTrail
+            commandOverride={detailsModeCommandOverride}
             detailsMode={detailsMode}
             reasoning={thinking}
             reasoningTokens={msg.thinkingTokens}
@@ -146,6 +149,7 @@ interface MessageLineProps {
   cols: number
   compact?: boolean
   detailsMode?: DetailsMode
+  detailsModeCommandOverride?: boolean
   isStreaming?: boolean
   msg: Msg
   sections?: SectionVisibility
diff --git a/ui-tui/src/components/thinking.tsx b/ui-tui/src/components/thinking.tsx
index 2d52102b51..dcddd4a914 100644
--- a/ui-tui/src/components/thinking.tsx
+++ b/ui-tui/src/components/thinking.tsx
@@ -681,6 +681,7 @@ interface Group {
 
 export const ToolTrail = memo(function ToolTrail({
   busy = false,
+  commandOverride = false,
   detailsMode = 'collapsed',
   outcome = '',
   reasoningActive = false,
@@ -696,6 +697,7 @@ export const ToolTrail = memo(function ToolTrail({
   activity = []
 }: {
   busy?: boolean
+  commandOverride?: boolean
   detailsMode?: DetailsMode
   outcome?: string
   reasoningActive?: boolean
@@ -712,12 +714,12 @@ export const ToolTrail = memo(function ToolTrail({
 }) {
   const visible = useMemo(
     () => ({
-      thinking: sectionMode('thinking', detailsMode, sections),
-      tools: sectionMode('tools', detailsMode, sections),
-      subagents: sectionMode('subagents', detailsMode, sections),
-      activity: sectionMode('activity', detailsMode, sections)
+      thinking: sectionMode('thinking', detailsMode, sections, commandOverride),
+      tools: sectionMode('tools', detailsMode, sections, commandOverride),
+      subagents: sectionMode('subagents', detailsMode, sections, commandOverride),
+      activity: sectionMode('activity', detailsMode, sections, commandOverride)
     }),
-    [detailsMode, sections]
+    [commandOverride, detailsMode, sections]
   )
 
   const [now, setNow] = useState(() => Date.now())
diff --git a/ui-tui/src/domain/details.ts b/ui-tui/src/domain/details.ts
index 079b08ea71..b0f5bf79a1 100644
--- a/ui-tui/src/domain/details.ts
+++ b/ui-tui/src/domain/details.ts
@@ -57,9 +57,20 @@ export const resolveSections = (raw: unknown): SectionVisibility =>
       ) as SectionVisibility)
     : {}
 
-// Effective mode for one section: explicit override → SECTION_DEFAULTS → global.
-// Single source of truth for "is this section open by default / rendered at all".
-export const sectionMode = (name: SectionName, global: DetailsMode, sections?: SectionVisibility): DetailsMode =>
-  sections?.[name] ?? SECTION_DEFAULTS[name] ?? global
+// Effective mode for one section: explicit override → global command mode →
+// built-in live-stream defaults → global config mode.
+//
+// The `commandOverride` flag is set for in-session `/details <mode>` changes.
+// That command should immediately apply to every section, including sections
+// with built-in defaults like thinking/tools=expanded and activity=hidden. On
+// startup/config sync we keep those defaults layered above the persisted global
+// config so the TUI still opens live reasoning/tools by default unless the user
+// pins explicit per-section overrides.
+export const sectionMode = (
+  name: SectionName,
+  global: DetailsMode,
+  sections?: SectionVisibility,
+  commandOverride = false
+): DetailsMode => sections?.[name] ?? (commandOverride ? global : (SECTION_DEFAULTS[name] ?? global))
 
 export const nextDetailsMode = (m: DetailsMode): DetailsMode => MODES[(MODES.indexOf(m) + 1) % MODES.length]!