diff --git a/src/services/api/openaiShim.test.ts b/src/services/api/openaiShim.test.ts
index 5824967b..23a7dd30 100644
--- a/src/services/api/openaiShim.test.ts
+++ b/src/services/api/openaiShim.test.ts
@@ -2856,3 +2856,91 @@ test('classifies chat-completions endpoint 404 failures with endpoint_not_found
     }),
   ).rejects.toThrow('openai_category=endpoint_not_found')
 })
+
+test('preserves valid tool_result and drops orphan tool_result', async () => {
+  let requestBody: Record<string, unknown> | undefined
+
+  globalThis.fetch = (async (_input, init) => {
+    requestBody = JSON.parse(String(init?.body))
+
+    return new Response(
+      JSON.stringify({
+        id: 'chatcmpl-1',
+        model: 'mistral-large-latest',
+        choices: [
+          {
+            message: {
+              role: 'assistant',
+              content: 'done',
+            },
+            finish_reason: 'stop',
+          },
+        ],
+        usage: {
+          prompt_tokens: 12,
+          completion_tokens: 4,
+          total_tokens: 16,
+        },
+      }),
+      {
+        headers: {
+          'Content-Type': 'application/json',
+        },
+      },
+    )
+  }) as FetchType
+
+  const client = createOpenAIShimClient({}) as OpenAIShimClient
+
+  await client.beta.messages.create({
+    model: 'mistral-large-latest',
+    system: 'test system',
+    messages: [
+      { role: 'user', content: 'Search and then I will interrupt' },
+      {
+        role: 'assistant',
+        content: [
+          {
+            type: 'tool_use',
+            id: 'valid_call_1',
+            name: 'Search',
+            input: { query: 'openclaude' },
+          },
+        ],
+      },
+      {
+        role: 'user',
+        content: [
+          {
+            type: 'tool_result',
+            tool_use_id: 'valid_call_1',
+            content: 'Found it!',
+          },
+          {
+            type: 'tool_result',
+            tool_use_id: 'orphan_call_2',
+            content: 'Interrupted result',
+          },
+          {
+            role: 'user',
+            content: 'What happened?',
+          }
+        ],
+      },
+    ],
+    max_tokens: 64,
+    stream: false,
+  })
+
+  const messages = requestBody?.messages as Array<Record<string, unknown>>
+  
+  // Should have: system, user, assistant (tool_use), tool (valid_call_1), user
+  // Should NOT have: tool (orphan_call_2)
+  
+  const toolMessages = messages.filter(m => m.role === 'tool')
+  expect(toolMessages.length).toBe(1)
+  expect(toolMessages[0].tool_call_id).toBe('valid_call_1')
+  
+  const orphanMessage = toolMessages.find(m => m.tool_call_id === 'orphan_call_2')
+  expect(orphanMessage).toBeUndefined()
+})
diff --git a/src/services/api/openaiShim.ts b/src/services/api/openaiShim.ts
index e2bb665f..c263a093 100644
--- a/src/services/api/openaiShim.ts
+++ b/src/services/api/openaiShim.ts
@@ -349,6 +349,7 @@ function convertMessages(
   system: unknown,
 ): OpenAIMessage[] {
   const result: OpenAIMessage[] = []
+  const knownToolCallIds = new Set<string>()
 
   // System message first
   const sysText = convertSystemPrompt(system)
@@ -368,13 +369,21 @@ function convertMessages(
         const toolResults = content.filter((b: { type?: string }) => b.type === 'tool_result')
         const otherContent = content.filter((b: { type?: string }) => b.type !== 'tool_result')
 
-        // Emit tool results as tool messages
+        // Emit tool results as tool messages, but ONLY if we have a matching tool_use ID.
+        // Mistral/OpenAI strictly require tool messages to follow an assistant message with tool_calls.
+        // If the user interrupted (ESC) and a synthetic tool_result was generated without a recorded tool_use,
+        // emitting it here would cause a "role must alternate" or "unexpected role" error.
         for (const tr of toolResults) {
-          result.push({
-            role: 'tool',
-            tool_call_id: tr.tool_use_id ?? 'unknown',
-            content: convertToolResultContent(tr.content, tr.is_error),
-          })
+          const id = tr.tool_use_id ?? 'unknown'
+          if (knownToolCallIds.has(id)) {
+            result.push({
+              role: 'tool',
+              tool_call_id: id,
+              content: convertToolResultContent(tr.content, tr.is_error),
+            })
+          } else {
+            logForDebugging(`Dropping orphan tool_result for ID: ${id} to prevent API error`)
+          }
         }
 
         // Emit remaining user content
@@ -415,9 +424,11 @@ function convertMessages(
               input?: unknown
               extra_content?: Record<string, unknown>
               signature?: string
-            }, index) => {
+            }) => {
+              const id = tu.id ?? `call_${crypto.randomUUID().replace(/-/g, '')}`
+              knownToolCallIds.add(id)
               const toolCall: NonNullable<OpenAIMessage['tool_calls']>[number] = {
-                id: tu.id ?? `call_${crypto.randomUUID().replace(/-/g, '')}`,
+                id,
                 type: 'function' as const,
                 function: {
                   name: tu.name ?? 'unknown',
@@ -442,7 +453,6 @@ function convertMessages(
 
                 // Merge into existing google-specific metadata if present
                 const existingGoogle = (toolCall.extra_content?.google as Record<string, unknown>) ?? {}
-
                 toolCall.extra_content = {
                   ...toolCall.extra_content,
                   google: {