diff --git a/ui-tui/src/__tests__/details.test.ts b/ui-tui/src/__tests__/details.test.ts
index b6c28329b..a2babd15d 100644
--- a/ui-tui/src/__tests__/details.test.ts
+++ b/ui-tui/src/__tests__/details.test.ts
@@ -72,13 +72,22 @@ describe('resolveSections', () => {
 })
 
 describe('sectionMode', () => {
-  it('falls back to the global mode when no override is set', () => {
+  it('falls back to the global mode for sections without a built-in default', () => {
     expect(sectionMode('tools', 'collapsed', {})).toBe('collapsed')
     expect(sectionMode('tools', 'expanded', undefined)).toBe('expanded')
+    expect(sectionMode('thinking', 'collapsed', {})).toBe('collapsed')
+    expect(sectionMode('subagents', 'expanded', {})).toBe('expanded')
   })
 
-  it('honours per-section overrides over the global mode', () => {
-    expect(sectionMode('activity', 'expanded', { activity: 'hidden' })).toBe('hidden')
+  it('hides the activity panel by default regardless of global mode', () => {
+    expect(sectionMode('activity', 'collapsed', {})).toBe('hidden')
+    expect(sectionMode('activity', 'expanded', undefined)).toBe('hidden')
+    expect(sectionMode('activity', 'hidden', {})).toBe('hidden')
+  })
+
+  it('honours per-section overrides over both the section default and global mode', () => {
+    expect(sectionMode('activity', 'collapsed', { activity: 'expanded' })).toBe('expanded')
+    expect(sectionMode('activity', 'expanded', { activity: 'collapsed' })).toBe('collapsed')
     expect(sectionMode('tools', 'collapsed', { tools: 'expanded' })).toBe('expanded')
   })
 })
diff --git a/ui-tui/src/domain/details.ts b/ui-tui/src/domain/details.ts
index 4ac2e6f80..059dcdabf 100644
--- a/ui-tui/src/domain/details.ts
+++ b/ui-tui/src/domain/details.ts
@@ -49,13 +49,26 @@ export const resolveSections = (raw: unknown): SectionVisibility => {
   return out
 }
 
+// Built-in per-section defaults applied when the user has no explicit
+// override.  The activity panel (gateway hints, terminal-parity nudges,
+// background-process notifications) is hidden out of the box — it's noise
+// for the typical day-to-day user, who only cares about thinking + tools +
+// streamed content.  Tool failures still surface inline on the failing tool
+// row; this default only suppresses the ambient meta feed.
+//
+// Opt back in with `display.sections.activity: collapsed` (under chevron)
+// or `expanded` (always open) in `~/.hermes/config.yaml`, or live with
+// `/details activity collapsed`.
+const SECTION_DEFAULTS: SectionVisibility = { activity: 'hidden' }
+
 // Resolve the effective mode for one section: explicit override wins,
-// otherwise the global details_mode.  Single source of truth — every render
-// site that needs to know "is this section open by default" calls this.
+// then the SECTION_DEFAULTS fallback, then the global details_mode.
+// Single source of truth — every render site that needs to know "is this
+// section open by default" calls this.
 export const sectionMode = (
   name: SectionName,
   global: DetailsMode,
   sections?: SectionVisibility
-): DetailsMode => sections?.[name] ?? global
+): DetailsMode => sections?.[name] ?? SECTION_DEFAULTS[name] ?? global
 
 export const nextDetailsMode = (m: DetailsMode): DetailsMode => MODES[(MODES.indexOf(m) + 1) % MODES.length]!
diff --git a/website/docs/user-guide/tui.md b/website/docs/user-guide/tui.md
index fe032cf51..7e76653c5 100644
--- a/website/docs/user-guide/tui.md
+++ b/website/docs/user-guide/tui.md
@@ -120,7 +120,7 @@ display:
   sections:                  # optional: per-section overrides (any subset)
     thinking: expanded       # always open
     tools: expanded          # always open
-    activity: hidden         # never show errors/warnings/info panel
+    activity: collapsed      # opt back IN to the activity panel (hidden by default)
   mouse_tracking: true       # disable if your terminal conflicts with mouse reporting
 ```
 
@@ -130,10 +130,26 @@ Runtime toggles:
 - `/details <section> [hidden|collapsed|expanded|reset]` — override one section
   (sections: `thinking`, `tools`, `subagents`, `activity`)
 
-Per-section overrides take precedence over the global `details_mode`. With
-`activity: hidden`, errors/warnings are suppressed entirely (the floating-alert
-fallback that normally surfaces under `details_mode: hidden` is also silenced
-when activity is explicitly hidden).
+**Default visibility**
+
+- `thinking`, `tools`, `subagents` — fall through to the global `details_mode`
+  (collapsed under chevron by default, click to expand).
+- `activity` — **hidden by default**. The activity panel surfaces ambient
+  meta (gateway hints, terminal-parity nudges, background notifications) and
+  is noise for most day-to-day use. Tool failures still render inline on the
+  failing tool row, so this default suppresses the noise feed without losing
+  the signal.
+
+Per-section overrides take precedence over both the section default and the
+global `details_mode`. To opt the activity panel back in:
+
+- `display.sections.activity: collapsed` — under a chevron
+- `display.sections.activity: expanded` — always open
+- `/details activity collapsed` at runtime
+
+With `activity: hidden` (the default), errors/warnings are suppressed entirely
+— the floating-alert fallback that surfaces under `details_mode: hidden` is
+silenced as well.
 
 ## Sessions