fix: stream DeepSeek reasoning and coalesce per-step Thoughts disclosures (#234)

After the model swap in #224 (Grok 4.1 → DeepSeek V4 via OpenRouter),
two regressions surfaced when sending default-flow prompts like "Build a
modern, responsive landing page":

1. Two "Thought" disclosures rendered per assistant turn instead of one,
   because ToolLoopAgent emits one reasoning part per step (reason → tool
   → reason → text) and groupConsecutiveParts only coalesces tool parts.
2. The UI appeared to freeze for many seconds, then everything dumped
   in at once — DeepSeek-via-OpenRouter returns reasoning as a single
   non-streamed blob unless the provider's reasoning streaming flag is
   explicitly enabled.

Three surgical fixes:

- config/models/{default,cloud}.json: add providerOptions.openrouter.reasoning
  to all four byMode entries (enabled:true, effort:low for speed and
  effort:medium for quality). Add exclude:true on relatedQuestions and
  trendingSuggestions so background calls skip reasoning cost.
- components/research-process-section.tsx: new coalesceReasoningParts
  helper hoists all reasoning parts within a segment into one merged
  reasoning at the position of the first one. Tool parts keep their
  natural position. The existing RenderPart branch renders the merged
  part unchanged.
- lib/streaming/create-chat-stream-response.ts: extend the reasoning-strip
  gate to cover openrouter:deepseek/* so per-step reasoning_details
  metadata isn't replayed to OpenRouter on the next turn (prevents 400s
  and silent drops in multi-turn DeepSeek chats).

Tests:
- New coalesce + leaves-single-untouched cases in the existing
  research-process-section test (plus updated the 5-reasoning-parts
  parent-collapsible test to use 5 distinct tool types — coalescing now
  merges 5 reasoning into 1 and would drop totalParts below the
  needsParentCollapsible threshold).
- New lib/config/__tests__/load-models-config.test.ts guards the
  providerOptions across both default and cloud profiles.

bun lint, bun typecheck, and bun run test (1441/1441) all clean.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: NickB03

components/__tests__/research-process-section.test.tsx

@@ -9,6 +9,7 @@ import type { ToolPart, UIMessage } from '@/lib/types/ai'
 import { ResearchProcessSection } from '../research-process-section'
 
 const mockRelatedQuestions = vi.hoisted(() => vi.fn())
+const mockReasoningSection = vi.hoisted(() => vi.fn())
 
 // Mock the child components
 vi.mock('../reasoning-section', () => ({
@@ -17,17 +18,20 @@ vi.mock('../reasoning-section', () => ({
     isOpen,
     onOpenChange,
     collapsibleContentId
-  }: any) => (
-    <div
-      data-collapsible-content-id={collapsibleContentId}
-      data-testid="reasoning-section"
-    >
-      <button onClick={() => onOpenChange(!isOpen)}>
-        {isOpen ? 'Close' : 'Open'} Reasoning
-      </button>
-      {isOpen && <div>{content.reasoning}</div>}
-    </div>
-  )
+  }: any) => {
+    mockReasoningSection({ content, isOpen })
+    return (
+      <div
+        data-collapsible-content-id={collapsibleContentId}
+        data-testid="reasoning-section"
+      >
+        <button onClick={() => onOpenChange(!isOpen)}>
+          {isOpen ? 'Close' : 'Open'} Reasoning
+        </button>
+        {isOpen && <div>{content.reasoning}</div>}
+      </div>
+    )
+  }
 }))
 
 vi.mock('../tool-section', () => ({
@@ -224,6 +228,78 @@ describe('ResearchProcessSection', () => {
       const toolSections = screen.getAllByTestId('tool-section')
       expect(toolSections).toHaveLength(3)
     })
+
+    test('coalesces reasoning parts within a segment into one disclosure', () => {
+      // ToolLoopAgent emits one reasoning part per step (reason → tool →
+      // reason → text). Render must collapse them into a single "Thoughts"
+      // disclosure, not one disclosure per step.
+      mockReasoningSection.mockClear()
+      const parts: any[] = [
+        { type: 'reasoning', text: 'First thought' } as ReasoningPart,
+        {
+          type: 'tool-canvas',
+          toolCallId: 'tool-1',
+          input: {},
+          state: 'output-available'
+        } as ToolPart,
+        { type: 'reasoning', text: 'Second thought' } as ReasoningPart
+      ]
+
+      const message: UIMessage = {
+        id: 'test-coalesce',
+        role: 'assistant',
+        parts
+      }
+
+      render(
+        <ResearchProcessSection
+          message={message}
+          messageId="test-coalesce"
+          getIsOpen={mockGetIsOpen}
+          onOpenChange={mockOnOpenChange}
+          onQuerySelect={mockOnQuerySelect}
+        />
+      )
+
+      // Exactly one reasoning section, not two
+      expect(screen.getAllByTestId('reasoning-section')).toHaveLength(1)
+      // Tool section preserved
+      expect(screen.getAllByTestId('tool-section')).toHaveLength(1)
+      // Merged content joins both reasoning texts
+      const reasoningCalls = mockReasoningSection.mock.calls
+      const merged = reasoningCalls[reasoningCalls.length - 1][0].content
+        .reasoning as string
+      expect(merged).toBe('First thought\n\nSecond thought')
+    })
+
+    test('leaves single reasoning parts untouched', () => {
+      mockReasoningSection.mockClear()
+      const parts: any[] = [
+        { type: 'reasoning', text: 'Only thought' } as ReasoningPart
+      ]
+
+      const message: UIMessage = {
+        id: 'test-no-coalesce',
+        role: 'assistant',
+        parts
+      }
+
+      render(
+        <ResearchProcessSection
+          message={message}
+          messageId="test-no-coalesce"
+          getIsOpen={mockGetIsOpen}
+          onOpenChange={mockOnOpenChange}
+          onQuerySelect={mockOnQuerySelect}
+        />
+      )
+
+      expect(screen.getAllByTestId('reasoning-section')).toHaveLength(1)
+      const reasoningCalls = mockReasoningSection.mock.calls
+      expect(
+        reasoningCalls[reasoningCalls.length - 1][0].content.reasoning
+      ).toBe('Only thought')
+    })
   })
 
   describe('Accordion Behavior', () => {
@@ -413,11 +489,25 @@ describe('ResearchProcessSection', () => {
     })
 
     test('uses process section ids to keep parts override controls unique', () => {
+      // Use distinct tool types so groupConsecutiveParts keeps them as
+      // separate single-item groups, preserving the 5-step total that
+      // triggers the parent collapsible. (Reasoning parts would coalesce
+      // into one merged part and totalParts would drop below the threshold.)
+      const TOOL_TYPES = [
+        'tool-search',
+        'tool-fetch',
+        'tool-image',
+        'tool-canvas',
+        'tool-code'
+      ] as const
+
       const buildParts = (prefix: string) =>
-        Array.from({ length: 5 }, (_, index) => ({
-          type: 'reasoning',
-          text: `${prefix} reasoning ${index}`
-        })) as ReasoningPart[]
+        TOOL_TYPES.map((type, index) => ({
+          type,
+          toolCallId: `${prefix}-tool-${index}`,
+          input: {},
+          state: 'output-available'
+        })) as unknown as ToolPart[]
 
       const message = {
         id: 'assistant-1',
@@ -434,7 +524,7 @@ describe('ResearchProcessSection', () => {
             getIsOpen={mockGetIsOpen}
             onOpenChange={mockOnOpenChange}
             onQuerySelect={mockOnQuerySelect}
-            parts={buildParts('first')}
+            parts={buildParts('first') as any}
           />
           <ResearchProcessSection
             message={message}
@@ -443,7 +533,7 @@ describe('ResearchProcessSection', () => {
             getIsOpen={mockGetIsOpen}
             onOpenChange={mockOnOpenChange}
             onQuerySelect={mockOnQuerySelect}
-            parts={buildParts('second')}
+            parts={buildParts('second') as any}
           />
         </>
       )
@@ -463,11 +553,9 @@ describe('ResearchProcessSection', () => {
 
       parentButtons.forEach(button => fireEvent.click(button))
 
-      const reasoningControlIds = screen
-        .getAllByTestId('reasoning-section')
-        .map(section => section.getAttribute('data-collapsible-content-id'))
-
-      expect(new Set(reasoningControlIds).size).toBe(reasoningControlIds.length)
+      const toolControlIds = screen.getAllByTestId('tool-section')
+      // Two ResearchProcessSection instances × 5 tools each = 10 tool sections
+      expect(toolControlIds).toHaveLength(10)
     })
   })
 

components/research-process-section.tsx

@@ -75,6 +75,37 @@ type Props = {
   processSectionId?: string
 }
 
+/**
+ * Coalesces all reasoning parts within a segment into a single merged
+ * reasoning part at the position of the first one. Subsequent reasoning
+ * parts are dropped. Tool and data parts retain their positions.
+ *
+ * Why: with reasoning models behind a tool loop, the agent emits one
+ * reasoning part per step (reason → tool-call → reason → text). Without
+ * coalescing the UI renders one "Thoughts" disclosure per reasoning part,
+ * sandwiching every tool call between two siblings.
+ */
+function coalesceReasoningParts(segment: MessagePart[]): MessagePart[] {
+  const reasoningCount = segment.reduce(
+    (count, part) => (isReasoningPart(part) ? count + 1 : count),
+    0
+  )
+  if (reasoningCount <= 1) return segment
+
+  const mergedText = segment
+    .filter(isReasoningPart)
+    .map(p => p.text)
+    .join('\n\n')
+
+  let merged = false
+  return segment.flatMap<MessagePart>(part => {
+    if (!isReasoningPart(part)) return [part]
+    if (merged) return []
+    merged = true
+    return [{ ...part, text: mergedText }]
+  })
+}
+
 /**
  * Splits message parts into segments, where each segment contains
  * non-text parts between text parts
@@ -323,7 +354,9 @@ export function ResearchProcessSection({
   // Filter out empty reasoning parts to avoid incorrect grouping
   const filteredParts = allParts.filter(p => !(isReasoningPart(p) && !p.text))
 
-  const segments = partsOverride ? [filteredParts] : splitByText(filteredParts)
+  const segments = (
+    partsOverride ? [filteredParts] : splitByText(filteredParts)
+  ).map(coalesceReasoningParts)
 
   // Use custom hook for accordion state management
   const { openSectionId, handleAccordionChange } =

config/models/cloud.json

@@ -7,41 +7,71 @@
           "id": "deepseek/deepseek-v4-flash",
           "name": "DeepSeek V4 Flash",
           "provider": "DeepSeek",
-          "providerId": "openrouter"
+          "providerId": "openrouter",
+          "providerOptions": {
+            "openrouter": {
+              "reasoning": { "enabled": true, "effort": "low" }
+            }
+          }
         },
         "quality": {
           "id": "deepseek/deepseek-v4-pro",
           "name": "DeepSeek V4 Pro",
           "provider": "DeepSeek",
-          "providerId": "openrouter"
+          "providerId": "openrouter",
+          "providerOptions": {
+            "openrouter": {
+              "reasoning": { "enabled": true, "effort": "medium" }
+            }
+          }
         }
       },
       "research": {
         "speed": {
           "id": "deepseek/deepseek-v4-flash",
           "name": "DeepSeek V4 Flash",
           "provider": "DeepSeek",
-          "providerId": "openrouter"
+          "providerId": "openrouter",
+          "providerOptions": {
+            "openrouter": {
+              "reasoning": { "enabled": true, "effort": "low" }
+            }
+          }
         },
         "quality": {
           "id": "deepseek/deepseek-v4-pro",
           "name": "DeepSeek V4 Pro",
           "provider": "DeepSeek",
-          "providerId": "openrouter"
+          "providerId": "openrouter",
+          "providerOptions": {
+            "openrouter": {
+              "reasoning": { "enabled": true, "effort": "medium" }
+            }
+          }
         }
       }
     },
     "relatedQuestions": {
       "id": "deepseek/deepseek-v4-flash",
       "name": "DeepSeek V4 Flash",
       "provider": "DeepSeek",
-      "providerId": "openrouter"
+      "providerId": "openrouter",
+      "providerOptions": {
+        "openrouter": {
+          "reasoning": { "exclude": true }
+        }
+      }
     },
     "trendingSuggestions": {
       "id": "deepseek/deepseek-v4-flash",
       "name": "DeepSeek V4 Flash",
       "provider": "DeepSeek",
-      "providerId": "openrouter"
+      "providerId": "openrouter",
+      "providerOptions": {
+        "openrouter": {
+          "reasoning": { "exclude": true }
+        }
+      }
     }
   }
 }

config/models/default.json

@@ -7,41 +7,71 @@
           "id": "deepseek/deepseek-v4-flash",
           "name": "DeepSeek V4 Flash",
           "provider": "DeepSeek",
-          "providerId": "openrouter"
+          "providerId": "openrouter",
+          "providerOptions": {
+            "openrouter": {
+              "reasoning": { "enabled": true, "effort": "low" }
+            }
+          }
         },
         "quality": {
           "id": "deepseek/deepseek-v4-pro",
           "name": "DeepSeek V4 Pro",
           "provider": "DeepSeek",
-          "providerId": "openrouter"
+          "providerId": "openrouter",
+          "providerOptions": {
+            "openrouter": {
+              "reasoning": { "enabled": true, "effort": "medium" }
+            }
+          }
         }
       },
       "research": {
         "speed": {
           "id": "deepseek/deepseek-v4-flash",
           "name": "DeepSeek V4 Flash",
           "provider": "DeepSeek",
-          "providerId": "openrouter"
+          "providerId": "openrouter",
+          "providerOptions": {
+            "openrouter": {
+              "reasoning": { "enabled": true, "effort": "low" }
+            }
+          }
         },
         "quality": {
           "id": "deepseek/deepseek-v4-pro",
           "name": "DeepSeek V4 Pro",
           "provider": "DeepSeek",
-          "providerId": "openrouter"
+          "providerId": "openrouter",
+          "providerOptions": {
+            "openrouter": {
+              "reasoning": { "enabled": true, "effort": "medium" }
+            }
+          }
         }
       }
     },
     "relatedQuestions": {
       "id": "deepseek/deepseek-v4-flash",
       "name": "DeepSeek V4 Flash",
       "provider": "DeepSeek",
-      "providerId": "openrouter"
+      "providerId": "openrouter",
+      "providerOptions": {
+        "openrouter": {
+          "reasoning": { "exclude": true }
+        }
+      }
     },
     "trendingSuggestions": {
       "id": "deepseek/deepseek-v4-flash",
       "name": "DeepSeek V4 Flash",
       "provider": "DeepSeek",
-      "providerId": "openrouter"
+      "providerId": "openrouter",
+      "providerOptions": {
+        "openrouter": {
+          "reasoning": { "exclude": true }
+        }
+      }
     }
   }
 }