feat(ui): collapsible thinking blocks with merged per-turn view and user toggle (#1273)

* feat: add collapsible reasoning traces with animated labels

* feat(ui): redesign reasoning blocks with merged collapsible Thought view

- Replace per-part reasoning blocks with a single merged block per turn
  (VSCode Copilot pattern), controlled by new `groupReasoningBlocks` store flag
- `ReasoningTimelineBlock` redesigned: chevron toggle, summary preview on
  collapsed header, 'Thinking'/'Justification' label when expanded, BusyDots
  while streaming, auto-scroll to bottom during live streaming
- Short texts (< 120 chars) render inline without a toggle
- Summary now strips markdown and truncates at a word boundary with ellipsis
- New `MergedReasoningPart` component merges all reasoning parts for a message
  into one block at the position of the first reasoning part
- `defaultExpanded` prop lets callers override initial expand state
- Remove `.thinking-dot` CSS animation (replaced by BusyDots component)
- Fix reasoning markdown font-size: use `--text-markdown` instead of `--text-meta`

* refactor(ui): scope working phrases inside useAssistantStatus and simplify reasoning status

- Move WORKING_PHRASES array and getRandomWorkingPhrase() inside the hook
  so they are no longer exported (were only consumed by ReasoningPart which
  no longer needs them)
- Change the 'reasoning' activity status text from a random working phrase
  to the deterministic string 'thinking' — matches the new UI label

* test(ui): expand ReasoningPart tests for new collapsible and summary behavior

- Update baseline test to use text long enough to trigger the collapsible
  path (short texts now render inline) and assert on the correct aria markup
- Add test for 'Justification' label when pre-expanded via defaultExpanded
- Add test for 'Thinking' label for the thinking variant when expanded
- Add test verifying summary is a word-boundary-truncated excerpt ending with
  an ellipsis character

* i18n: rename 'Reasoning Traces' to 'Thinking Blocks' and add thought key

- Rename settings label from 'Show Reasoning Traces' → 'Show Thinking Blocks'
  across all supported locales (en, es, ko, pl, pt-BR, uk, zh-CN)
- Add `chat.reasoningTrace.thought` key to all locales (used by merged
  reasoning block header in completed state)

* feat(ui): add collapsibleThinkingBlocks setting with full persistence wiring

- New boolean store field `collapsibleThinkingBlocks` (default true) with
  `setCollapsibleThinkingBlocks` action; persisted to localStorage
- Threaded through DesktopSettings, SettingsPayload (API types), desktop
  persistence (sanitize + apply), web appearance persistence, appearance
  auto-save watcher, and server-side settings-helpers sanitize/format
- Server defaults to true when the field is absent in formatSettingsResponse
- MessageBody reads the flag: false → render reasoning as plain AssistantTextPart;
  true → existing collapsible/merged block path

* feat(settings): expose Collapsible Reasoning Blocks toggle in visual settings

Add a checkbox under the 'Show Thinking Blocks' row (visible only when
showReasoningTraces is enabled) that toggles the collapsibleThinkingBlocks
preference. Follows the existing toggle pattern: div role=button, keyboard
handler for Enter/Space, Checkbox primitive, aria-pressed attribute.

* i18n: revert showReasoningTraces label rename and add collapsibleThinkingBlocks strings

- Revert 'Show Reasoning Traces' → 'Show Thinking Blocks' rename (the
  collapsibleThinkingBlocks toggle is now a separate control, so the parent
  label stays as 'Reasoning Traces' for clarity)
- Add `collapsibleThinkingBlocks` / `collapsibleThinkingBlocksAria` strings
  across all seven supported locales (en, es, ko, pl, pt-BR, uk, zh-CN)

* test(server): add settings-helpers coverage for collapsibleThinkingBlocks

- Verify sanitizeSettingsUpdate accepts boolean true/false and rejects
  non-boolean values (string, number)
- Verify formatSettingsResponse forwards the value correctly for both true
  and false, and defaults to true when the field is absent

* fix(ui): respect defaultExpanded prop and remove dead alwaysShowActions from ReasoningTimelineBlock

The useEffect on [isStreaming] was firing on mount and immediately calling
setIsExpanded(false) (since isStreaming is false for completed blocks),
overriding any defaultExpanded={true} passed by callers. The fix uses a
prevIsStreamingRef so the effect only collapses the block on a true→false
transition and is a no-op on initial mount.

Also removes alwaysShowActions from ReasoningTimelineBlockProps — the new
header design always shows the chevron, making the prop obsolete. The prop
was already absent from the component destructuring (a dead type entry) and
was silently ignored at runtime. Removed it from ReasoningPartProps,
MergedReasoningPartProps, and the two call-sites in MessageBody as well.

* chore: remove unused reasoningpresentation module and test

* fix(ui): polish collapsible reasoning block UI

---------

Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>

packages/web/server/lib/opencode/settings-helpers.test.js

@@ -71,4 +71,39 @@ describe('settings helpers', () => {
 
     expect(helpers.sanitizeSettingsUpdate({ mobileKeyboardMode: 'fixed-layout' })).toEqual({});
   });
+
+  it('accepts collapsibleThinkingBlocks as a persisted shared setting', () => {
+    const helpers = createTestHelpers();
+
+    expect(helpers.sanitizeSettingsUpdate({ collapsibleThinkingBlocks: true })).toEqual({
+      collapsibleThinkingBlocks: true,
+    });
+    expect(helpers.sanitizeSettingsUpdate({ collapsibleThinkingBlocks: false })).toEqual({
+      collapsibleThinkingBlocks: false,
+    });
+  });
+
+  it('rejects non-boolean collapsibleThinkingBlocks values', () => {
+    const helpers = createTestHelpers();
+
+    expect(helpers.sanitizeSettingsUpdate({ collapsibleThinkingBlocks: 'true' })).toEqual({});
+    expect(helpers.sanitizeSettingsUpdate({ collapsibleThinkingBlocks: 1 })).toEqual({});
+  });
+
+  it('includes collapsibleThinkingBlocks in formatSettingsResponse', () => {
+    const helpers = createTestHelpers();
+
+    const response = helpers.formatSettingsResponse({ collapsibleThinkingBlocks: false });
+    expect(response.collapsibleThinkingBlocks).toBe(false);
+
+    const responseTrue = helpers.formatSettingsResponse({ collapsibleThinkingBlocks: true });
+    expect(responseTrue.collapsibleThinkingBlocks).toBe(true);
+  });
+
+  it('defaults collapsibleThinkingBlocks to true in formatSettingsResponse when absent', () => {
+    const helpers = createTestHelpers();
+
+    const response = helpers.formatSettingsResponse({});
+    expect(response.collapsibleThinkingBlocks).toBe(true);
+  });
 });