feat(tui): stream thinking + tools expanded by default

Extends SECTION_DEFAULTS so the out-of-the-box TUI shows the turn as
a live transcript (reasoning + tool calls streaming inline) instead of
a wall of `▸` chevrons the user has to click every turn.

Final default matrix:

  - thinking: expanded
  - tools:    expanded
  - activity: hidden    (unchanged from the previous commit)
  - subagents: falls through to details_mode (collapsed by default)

Everything explicit in `display.sections` still wins, so anyone who
already pinned an override keeps their layout.  One-line revert is
`display.sections.<name>: collapsed`.

ui-tui/src/__tests__/details.test.ts

@@ -73,10 +73,16 @@ describe('resolveSections', () => {
 
 describe('sectionMode', () => {
   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')
+    expect(sectionMode('subagents', 'collapsed', {})).toBe('collapsed')
+    expect(sectionMode('subagents', 'expanded', undefined)).toBe('expanded')
+    expect(sectionMode('subagents', 'hidden', {})).toBe('hidden')
+  })
+
+  it('streams thinking + tools expanded by default regardless of global mode', () => {
+    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', () => {
@@ -86,16 +92,17 @@ describe('sectionMode', () => {
   })
 
   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')
     expect(sectionMode('activity', 'collapsed', { activity: 'expanded' })).toBe('expanded')
     expect(sectionMode('activity', 'expanded', { activity: 'collapsed' })).toBe('collapsed')
-    expect(sectionMode('tools', 'collapsed', { tools: 'expanded' })).toBe('expanded')
   })
 
   it('lets per-section overrides escape the global hidden mode', () => {
     // Regression for the case where global details_mode: hidden used to
     // short-circuit the entire accordion and prevent overrides from
     // surfacing — `sections.tools: expanded` must still resolve to expanded.
-    expect(sectionMode('tools', 'hidden', { tools: 'expanded' })).toBe('expanded')
+    expect(sectionMode('subagents', 'hidden', { subagents: 'expanded' })).toBe('expanded')
     expect(sectionMode('thinking', 'hidden', { thinking: 'collapsed' })).toBe('collapsed')
     expect(sectionMode('activity', 'hidden', { activity: 'expanded' })).toBe('expanded')
   })

ui-tui/src/domain/details.ts

@@ -4,12 +4,27 @@ const MODES = ['hidden', 'collapsed', 'expanded'] as const
 
 export const SECTION_NAMES = ['thinking', 'tools', 'subagents', 'activity'] as const
 
-// Activity panel = ambient meta (gateway hints, terminal-parity nudges,
-// background-process notifications).  Hidden out of the box because tool
-// failures already render inline on the failing tool row — the panel itself
-// is noise for typical use.  Opt back in via `display.sections.activity` or
-// `/details activity collapsed`.
-const SECTION_DEFAULTS: SectionVisibility = { activity: 'hidden' }
+// Out-of-the-box per-section defaults — applied when the user hasn't pinned
+// an explicit override and layered ABOVE the global details_mode:
+//
+//   - thinking / tools: expanded — stream open so the turn reads like a
+//     live transcript (reasoning + tool calls side by side) instead of a
+//     wall of chevrons the user has to click every turn.
+//   - activity: hidden — ambient meta (gateway hints, terminal-parity
+//     nudges, background notifications) is noise for typical use.  Tool
+//     failures still render inline on the failing tool row, and ambient
+//     errors/warnings surface via the floating-alert backstop when every
+//     panel resolves to hidden.
+//   - subagents: not set — falls through to the global details_mode so
+//     Spawn trees stay under a chevron until a delegation actually happens.
+//
+// Opt out of any of these with `display.sections.<name>` in config.yaml
+// or at runtime via `/details <name> collapsed|hidden`.
+const SECTION_DEFAULTS: SectionVisibility = {
+  thinking: 'expanded',
+  tools: 'expanded',
+  activity: 'hidden'
+}
 
 const THINKING_FALLBACK: Record<string, DetailsMode> = {
   collapsed: 'collapsed',

website/docs/user-guide/tui.md

@@ -132,24 +132,29 @@ Runtime toggles:
 
 **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.
+The TUI ships with opinionated per-section defaults that stream the turn as
+a live transcript instead of a wall of chevrons:
+
+- `thinking` — **expanded**. Reasoning streams inline as the model emits it.
+- `tools` — **expanded**. Tool calls and their results render open.
+- `subagents` — falls through to the global `details_mode` (collapsed under
+  chevron by default — stays quiet until a delegation actually happens).
+- `activity` — **hidden**. Ambient meta (gateway hints, terminal-parity
+  nudges, background notifications) is noise for most day-to-day use. Tool
+  failures still render inline on the failing tool row; ambient
+  errors/warnings surface via a floating-alert backstop when every panel
+  is hidden.
 
 Per-section overrides take precedence over both the section default and the
-global `details_mode`. To opt the activity panel back in:
+global `details_mode`. To reshape the layout:
 
-- `display.sections.activity: collapsed` — under a chevron
-- `display.sections.activity: expanded` — always open
-- `/details activity collapsed` at runtime
+- `display.sections.thinking: collapsed` — put thinking back under a chevron
+- `display.sections.tools: collapsed` — put tool calls back under a chevron
+- `display.sections.activity: collapsed` — opt the activity panel back in
+- `/details <section> <mode>` 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.
+Anything set explicitly in `display.sections` wins over the defaults, so
+existing configs keep working unchanged.
 
 ## Sessions