diff --git a/src/integrations/runtimeMetadata.test.ts b/src/integrations/runtimeMetadata.test.ts
new file mode 100644
index 0000000000..8527a5ebd2
--- /dev/null
+++ b/src/integrations/runtimeMetadata.test.ts
@@ -0,0 +1,90 @@
+import { describe, it, expect } from 'bun:test'
+import { resolveOpenAIShimRuntimeContext } from '../integrations/runtimeMetadata'
+
+describe('resolveOpenAIShimRuntimeContext - segment-boundary heuristic', () => {
+  describe('DeepSeek models', () => {
+    it('should NOT infer preserveReasoningContent for custom aliases (false-positive case)', () => {
+      // my-deepseek-rag is a custom alias, NOT a provider path
+      // Should NOT trigger the DeepSeek detection
+      const result = resolveOpenAIShimRuntimeContext({
+        model: 'my-deepseek-rag',
+      })
+      // Custom aliases should NOT get preserveReasoningContent
+      expect(result.openaiShimConfig.preserveReasoningContent).toBeUndefined()
+    })
+
+    it('should infer preserveReasoningContent for openrouter/deepseek/... paths (true-positive case)', () => {
+      // openrouter/deepseek/deepseek-chat is a provider path with segments
+      // Should trigger the DeepSeek detection
+      const result = resolveOpenAIShimRuntimeContext({
+        model: 'openrouter/deepseek/deepseek-chat',
+      })
+      expect(result.openaiShimConfig.preserveReasoningContent).toBe(true)
+      expect(result.openaiShimConfig.reasoningContentFallback).toBe('')
+    })
+
+    it('should infer preserveReasoningContent for accounts/fireworks/... paths (true-positive case)', () => {
+      // accounts/fireworks/models/deepseek-v3 is a provider path with multiple segments
+      // Should trigger the DeepSeek detection
+      const result = resolveOpenAIShimRuntimeContext({
+        model: 'accounts/fireworks/models/deepseek-v3',
+      })
+      expect(result.openaiShimConfig.preserveReasoningContent).toBe(true)
+      expect(result.openaiShimConfig.reasoningContentFallback).toBe('')
+    })
+
+    it('should infer preserveReasoningContent for deepseek-chat directly (standard case)', () => {
+      const result = resolveOpenAIShimRuntimeContext({
+        model: 'deepseek-chat',
+      })
+      expect(result.openaiShimConfig.preserveReasoningContent).toBe(true)
+    })
+
+    it('should infer preserveReasoningContent for deepseek-coder (model name)', () => {
+      const result = resolveOpenAIShimRuntimeContext({
+        model: 'deepseek-coder',
+      })
+      expect(result.openaiShimConfig.preserveReasoningContent).toBe(true)
+    })
+  })
+
+  describe('Kimi/Moonshot models', () => {
+    it('should NOT infer preserveReasoningContent for custom kimi aliases', () => {
+      // Custom alias should not trigger
+      const result = resolveOpenAIShimRuntimeContext({
+        model: 'my-kimi-assistant',
+      })
+      expect(result.openaiShimConfig.preserveReasoningContent).toBeUndefined()
+    })
+
+    it('should infer preserveReasoningContent for moonshot AI paths', () => {
+      const result = resolveOpenAIShimRuntimeContext({
+        model: 'moonshot/moonshot-v1',
+      })
+      expect(result.openaiShimConfig.preserveReasoningContent).toBe(true)
+    })
+
+    it('should infer preserveReasoningContent for kimi on moonshot paths', () => {
+      const result = resolveOpenAIShimRuntimeContext({
+        model: 'moonshot/kimi-kpro',
+      })
+      expect(result.openaiShimConfig.preserveReasoningContent).toBe(true)
+    })
+  })
+
+  describe('Non-matching models', () => {
+    it('should return undefined for gpt-4o (negative case)', () => {
+      const result = resolveOpenAIShimRuntimeContext({
+        model: 'gpt-4o',
+      })
+      expect(result.openaiShimConfig.preserveReasoningContent).toBeUndefined()
+    })
+
+    it('should return undefined for claude models (negative case)', () => {
+      const result = resolveOpenAIShimRuntimeContext({
+        model: 'claude-sonnet-4-20250514',
+      })
+      expect(result.openaiShimConfig.preserveReasoningContent).toBeUndefined()
+    })
+  })
+})
\ No newline at end of file
diff --git a/src/integrations/runtimeMetadata.ts b/src/integrations/runtimeMetadata.ts
index a3ab3c3971..b70ac29e8d 100644
--- a/src/integrations/runtimeMetadata.ts
+++ b/src/integrations/runtimeMetadata.ts
@@ -151,7 +151,11 @@ function inferRemoteModelOpenAIShimConfig(
     }
   }
 
-  if (normalizedModel.includes('deepseek')) {
+  // Segment-boundary-aware matcher: avoids false-positives like "my-deepseek-rag"
+  // while still catching aggregator paths e.g. "openrouter/deepseek/deepseek-chat".
+  const segments = normalizedModel.split('/')
+  const hasDeepseek = segments.some(s => s.startsWith('deepseek'))
+  if (hasDeepseek) {
     return {
       preserveReasoningContent: true,
       requireReasoningContentOnAssistantMessages: true,
@@ -162,7 +166,10 @@ function inferRemoteModelOpenAIShimConfig(
     }
   }
 
-  if (normalizedModel.includes('kimi') || normalizedModel.includes('moonshot')) {
+   const hasKimiMoonshot = segments.some(
+     s => s.startsWith('kimi') || s.startsWith('moonshot'),
+   )
+   if (hasKimiMoonshot) {
     return {
       preserveReasoningContent: true,
       requireReasoningContentOnAssistantMessages: true,