fix: merge assistant activity groups

docs/issues/merged-activity-groups/plan.md

@@ -0,0 +1,32 @@
+# Plan
+
+## Current Behavior
+
+`buildAssistantRenderItems` buffers completed reasoning and tool-call blocks while grouping is
+enabled. The buffer flushes when a block is not completed activity.
+
+In affected histories, an empty `reasoning_content` block with provider metadata can sit between
+visible reasoning and tool-call blocks. Because that empty reasoning block is not visible but still
+flushes the activity buffer, one continuous assistant work span becomes several activity summaries.
+
+The compact summary details are currently hidden with `v-show`, so expansion changes the detail body
+from `display: none` to normal layout in one frame. Long merged activity histories can make the
+message list jump visibly while row measurement catches up.
+
+## Implementation
+
+- Treat empty settled reasoning blocks as invisible metadata blocks for activity grouping.
+- Keep buffering visible completed reasoning and tool calls across those ignored metadata blocks.
+- Replace the activity group detail `v-show` with an always-mounted transition shell that animates
+  grid row height and opacity.
+- Avoid leaving collapsed spacing behind by moving the body gap to the animated shell's expanded
+  margin state.
+- Mark the collapsed shell inert so mounted hidden controls cannot receive focus or pointer input.
+- Add renderer regression coverage around provider signed empty reasoning blocks.
+- Update the activity group component test to assert accessible collapsed state and mounted details
+  rather than relying on `display: none` visibility.
+
+## Validation
+
+- Run focused renderer tests for message activity grouping.
+- Run repository-required quality gates: `pnpm run format`, `pnpm run i18n`, and `pnpm run lint`.

docs/issues/merged-activity-groups/spec.md

@@ -0,0 +1,42 @@
+# Merged Activity Groups
+
+## Problem
+
+Some providers emit an empty `reasoning_content` block carrying provider metadata between visible
+reasoning and tool-call blocks. The chat view does not render that empty reasoning block, but the
+activity grouping pass currently treats it as a normal boundary. This splits one continuous assistant
+work span into several collapsed activity summaries.
+
+## User Story
+
+As a chat user reviewing an imported or previously merged session, I want reasoning and tool-call
+activity to stay attached to the correct assistant segment so expanded activity details match the
+visible answer they summarize.
+
+## Acceptance Criteria
+
+- Empty reasoning metadata blocks do not split the reasoning/tool-call activity they sit between.
+- Consecutive activity blocks within the same assistant segment collapse into one compact summary.
+- Internal tool calls remain hidden from the assistant activity list.
+- The final assistant text continues to render after its activity summaries.
+- Expanding or collapsing the compact activity summary does not hard-toggle the details with
+  `display: none`; details remain mounted and use a bounded height/opacity transition to reduce
+  scroll and layout jitter. Collapsed details are not pointer- or keyboard-interactive.
+- The compact activity summary keeps the chevron and title close enough to read as one control.
+- A regression test covers the MiniMax-style sequence: visible reasoning, empty signed reasoning,
+  tool call, next visible reasoning, empty signed reasoning, next tool call.
+- A component test covers the collapsed and expanded activity detail states after the transition
+  wrapper change.
+
+## Non-goals
+
+- Redesign activity group copy, visual hierarchy, or per-block detail components.
+- Change session storage or import schema.
+- Change the content of reasoning/tool-call blocks.
+
+## Constraints
+
+- Keep the fix scoped to renderer-side render item construction unless investigation shows the source
+  data is malformed.
+- Do not introduce new user-facing strings.
+- Follow existing message rendering and test patterns.

docs/issues/merged-activity-groups/tasks.md

@@ -0,0 +1,9 @@
+# Tasks
+
+- [x] Trace assistant block metadata and existing grouping tests.
+- [x] Add a regression test for empty signed reasoning blocks between reasoning and tool calls.
+- [x] Update activity grouping to honor segment boundaries.
+- [x] Smooth the activity group detail expand/collapse path to reduce layout jitter.
+- [x] Update component assertions for the always-mounted transition shell.
+- [x] Run focused tests and required quality gates.
+- [x] Tighten the activity summary chevron/title spacing.

src/renderer/src/components/message/MessageBlockActivityGroup.vue

@@ -1,40 +1,56 @@
 <template>
-  <div class="flex flex-col w-full gap-1.5" data-testid="activity-group">
+  <div class="flex flex-col w-full" data-testid="activity-group">
     <button
       type="button"
       data-testid="activity-group-toggle"
-      class="inline-flex max-w-full min-w-0 items-center gap-[10px] self-start text-xs leading-4 text-[rgba(37,37,37,0.5)] dark:text-white/50 select-none rounded-sm focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2 focus-visible:ring-offset-background"
+      class="inline-flex max-w-full min-w-0 items-center gap-1 self-start text-xs leading-4 text-[rgba(37,37,37,0.5)] dark:text-white/50 select-none rounded-sm focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2 focus-visible:ring-offset-background"
       :aria-expanded="isExpanded"
       :aria-label="toggleLabel"
       @click="toggleExpanded"
     >
       <Icon
-        :icon="isExpanded ? 'lucide:chevron-down' : 'lucide:chevron-right'"
-        class="w-[14px] h-[14px] shrink-0 text-[rgba(37,37,37,0.5)] dark:text-white/50"
+        icon="lucide:chevron-right"
+        class="w-[14px] h-[14px] shrink-0 text-[rgba(37,37,37,0.5)] dark:text-white/50 transition-transform duration-[var(--dc-motion-fast)] ease-[var(--dc-ease-out-soft)] motion-reduce:transition-none"
+        :class="isExpanded ? 'rotate-90' : 'rotate-0'"
       />
       <span class="min-w-0 truncate">
         {{ titleText }}
       </span>
     </button>
 
-    <div v-show="isExpanded" class="flex flex-col w-full gap-1.5" data-testid="activity-group-body">
-      <template v-for="(block, index) in blocks" :key="buildActivityBlockKey(block, index)">
-        <MessageBlockThink
-          v-if="
-            (block.type === 'reasoning_content' || block.type === 'artifact-thinking') &&
-            block.content
-          "
-          :block="block"
-          :usage="usage"
-          @toggle-collapse="handleChildCollapseToggle"
-        />
-        <MessageBlockToolCall
-          v-else-if="block.type === 'tool_call'"
-          :block="block"
-          :message-id="messageId"
-          :thread-id="threadId"
-        />
-      </template>
+    <div
+      class="grid w-full overflow-hidden transition-[grid-template-rows,opacity,margin-top] duration-[var(--dc-motion-default)] ease-[var(--dc-ease-out-express)] motion-reduce:transition-none"
+      :class="
+        isExpanded
+          ? 'mt-1.5 grid-rows-[1fr] opacity-100'
+          : 'mt-0 grid-rows-[0fr] opacity-0 pointer-events-none'
+      "
+      :aria-hidden="!isExpanded"
+      :inert="isExpanded ? undefined : true"
+      data-testid="activity-group-body-shell"
+    >
+      <div
+        class="min-h-0 flex flex-col w-full gap-1.5 overflow-hidden"
+        data-testid="activity-group-body"
+      >
+        <template v-for="(block, index) in blocks" :key="buildActivityBlockKey(block, index)">
+          <MessageBlockThink
+            v-if="
+              (block.type === 'reasoning_content' || block.type === 'artifact-thinking') &&
+              block.content
+            "
+            :block="block"
+            :usage="usage"
+            @toggle-collapse="handleChildCollapseToggle"
+          />
+          <MessageBlockToolCall
+            v-else-if="block.type === 'tool_call'"
+            :block="block"
+            :message-id="messageId"
+            :thread-id="threadId"
+          />
+        </template>
+      </div>
     </div>
   </div>
 </template>

src/renderer/src/components/message/messageActivityGroups.ts

@@ -53,6 +53,10 @@ const isReasoningActivityBlock = (block: DisplayAssistantMessageBlock): boolean
   typeof block.content === 'string' &&
   block.content.trim().length > 0
 
+const isEmptyReasoningBlock = (block: DisplayAssistantMessageBlock): boolean =>
+  (block.type === 'reasoning_content' || block.type === 'artifact-thinking') &&
+  (typeof block.content !== 'string' || block.content.trim().length === 0)
+
 export const isCompletedActivityBlock = (block: DisplayAssistantMessageBlock): boolean => {
   if (!ACTIVITY_BLOCK_TYPES.has(block.type)) {
     return false
@@ -144,6 +148,10 @@ export const buildAssistantRenderItems = ({
       return
     }
 
+    if (shouldGroup && isEmptyReasoningBlock(block)) {
+      return
+    }
+
     if (shouldGroup && isCompletedActivityBlock(block)) {
       activityBuffer.push({ block, index })
       return

test/renderer/components/message/MessageBlockActivityGroup.test.ts

@@ -123,7 +123,17 @@ describe('MessageBlockActivityGroup', () => {
     expect(wrapper.get('[data-testid="activity-group-toggle"]').attributes('aria-expanded')).toBe(
       'false'
     )
-    expect(wrapper.get('[data-testid="activity-group-body"]').isVisible()).toBe(false)
+    expect(wrapper.get('[data-testid="activity-group-body-shell"]').attributes('aria-hidden')).toBe(
+      'true'
+    )
+    expect(
+      wrapper.get('[data-testid="activity-group-body-shell"]').attributes('inert')
+    ).toBeDefined()
+    expect(wrapper.get('[data-testid="activity-group-body-shell"]').classes()).toContain(
+      'grid-rows-[0fr]'
+    )
+    expect(wrapper.find('[data-testid="think-block"]').exists()).toBe(true)
+    expect(wrapper.find('[data-testid="tool-block"]').exists()).toBe(true)
   })
 
   it('toggles expanded state and shows the original activity blocks', async () => {
@@ -134,7 +144,15 @@ describe('MessageBlockActivityGroup', () => {
     expect(wrapper.get('[data-testid="activity-group-toggle"]').attributes('aria-expanded')).toBe(
       'true'
     )
-    expect(wrapper.get('[data-testid="activity-group-body"]').isVisible()).toBe(true)
+    expect(wrapper.get('[data-testid="activity-group-body-shell"]').attributes('aria-hidden')).toBe(
+      'false'
+    )
+    expect(
+      wrapper.get('[data-testid="activity-group-body-shell"]').attributes('inert')
+    ).toBeUndefined()
+    expect(wrapper.get('[data-testid="activity-group-body-shell"]').classes()).toContain(
+      'grid-rows-[1fr]'
+    )
     expect(wrapper.find('[data-testid="think-block"]').text()).toBe('thinking')
     expect(wrapper.find('[data-testid="tool-block"]').text()).toBe('shell_command')
 
@@ -143,6 +161,12 @@ describe('MessageBlockActivityGroup', () => {
     expect(wrapper.get('[data-testid="activity-group-toggle"]').attributes('aria-expanded')).toBe(
       'false'
     )
+    expect(wrapper.get('[data-testid="activity-group-body-shell"]').attributes('aria-hidden')).toBe(
+      'true'
+    )
+    expect(
+      wrapper.get('[data-testid="activity-group-body-shell"]').attributes('inert')
+    ).toBeDefined()
   })
 
   it('does not persist expanded state across remounts', async () => {

test/renderer/components/message/messageActivityGroups.test.ts

@@ -79,6 +79,90 @@ describe('messageActivityGroups', () => {
     expect(items.map((item) => item.kind)).toEqual(['activity-group', 'block', 'activity-group'])
   })
 
+  it('ignores empty reasoning signature blocks when merging continuous activity', () => {
+    const items = buildAssistantRenderItems({
+      messageId: 'm1',
+      messageUpdatedAt: 12_000,
+      shouldGroup: true,
+      blocks: [
+        createBlock('reasoning_content', {
+          content: 'The user wants to see files.',
+          timestamp: 1_000
+        }),
+        createBlock('reasoning_content', {
+          content: '',
+          timestamp: 1_100,
+          extra: {
+            providerOptionsJson: '{"anthropic":{"signature":"sig-1"}}'
+          }
+        }),
+        createBlock('tool_call', {
+          timestamp: 2_000,
+          tool_call: {
+            id: 'tc1',
+            name: 'exec'
+          }
+        }),
+        createBlock('reasoning_content', {
+          content: 'The working directory does not exist.',
+          timestamp: 3_000
+        }),
+        createBlock('reasoning_content', {
+          content: '',
+          timestamp: 3_100,
+          extra: {
+            providerOptionsJson: '{"anthropic":{"signature":"sig-2"}}'
+          }
+        }),
+        createBlock('tool_call', {
+          timestamp: 4_000,
+          tool_call: {
+            id: 'tc2',
+            name: 'exec'
+          }
+        }),
+        createBlock('reasoning_content', {
+          content: 'I should ask the user to confirm the workspace.',
+          timestamp: 5_000
+        }),
+        createBlock('reasoning_content', {
+          content: '',
+          timestamp: 5_100,
+          extra: {
+            providerOptionsJson: '{"anthropic":{"signature":"sig-3"}}'
+          }
+        }),
+        createBlock('content', {
+          content: 'Please confirm the folder.',
+          timestamp: 6_000
+        })
+      ]
+    })
+
+    expect(items.map((item) => item.kind)).toEqual(['activity-group', 'block'])
+
+    const groups = items.filter((item) => item.kind === 'activity-group')
+    expect(groups).toHaveLength(1)
+    expect(groups.map((item) => item.blocks.map((block) => block.type))).toEqual([
+      ['reasoning_content', 'tool_call', 'reasoning_content', 'tool_call', 'reasoning_content']
+    ])
+    expect(
+      groups.map((item) => item.blocks.map((block) => block.tool_call?.id ?? block.content))
+    ).toEqual([
+      [
+        'The user wants to see files.',
+        'tc1',
+        'The working directory does not exist.',
+        'tc2',
+        'I should ask the user to confirm the workspace.'
+      ]
+    ])
+    expect(groups[0]).toMatchObject({
+      reasoningCount: 3,
+      toolCallCount: 2
+    })
+  })
+
   it('does not group when the turn is not settled', () => {
     const items = buildAssistantRenderItems({
       messageId: 'm1',