diff --git a/src/services/api/openaiShim.ts b/src/services/api/openaiShim.ts
index 015c0e2e4..fa56e6596 100644
--- a/src/services/api/openaiShim.ts
+++ b/src/services/api/openaiShim.ts
@@ -517,6 +517,20 @@ function convertMessages(
           (b: { type?: string }) => b.type !== 'tool_use' && b.type !== 'thinking',
         )
 
+        // Compute reasoning_content upfront so it is part of the object literal
+        // rather than a dynamic assignment. Some bundler/runtime paths may drop
+        // dynamically-added properties when the object flows through multiple
+        // transforms before JSON.stringify.
+        //
+        // DeepSeek requires reasoning_content on EVERY assistant message when
+        // thinking mode is active, even if the content is empty (e.g. the model
+        // produced no visible chain-of-thought for that turn).
+        const reasoningContent = preserveReasoningContent
+          ? ((thinkingBlock as { thinking?: string } | undefined)?.thinking ?? '')
+          : undefined
+        const hasThinkingBlock = thinkingBlock !== undefined
+        const shouldAttachReasoning = preserveReasoningContent
+
         const assistantMsg: OpenAIMessage = {
           role: 'assistant',
           content: (() => {
@@ -527,21 +541,9 @@ function convertMessages(
                 ? c.map((p: { text?: string }) => p.text ?? '').join('')
                 : ''
           })(),
-        }
-
-        // Providers that validate reasoning continuity (Moonshot/Kimi Code: "thinking
-        // is enabled but reasoning_content is missing in assistant tool call
-        // message at index N" 400) need the original chain-of-thought echoed
-        // back on each assistant message that carries a tool_call. We kept
-        // the thinking block on the Anthropic side; re-attach it here as the
-        // `reasoning_content` field on the outgoing OpenAI-shaped message.
-        // Gated per-provider because other endpoints either ignore the field
-        // (harmless) or strict-reject unknown fields (harmful).
-        if (preserveReasoningContent) {
-          const thinkingText = (thinkingBlock as { thinking?: string } | undefined)?.thinking
-          if (typeof thinkingText === 'string' && thinkingText.trim().length > 0) {
-            assistantMsg.reasoning_content = thinkingText
-          }
+          ...(shouldAttachReasoning && {
+            reasoning_content: reasoningContent,
+          }),
         }
 
         if (toolUses.length > 0) {
@@ -633,6 +635,9 @@ function convertMessages(
                 ? c.map((p: { text?: string }) => p.text ?? '').join('')
                 : ''
           })(),
+          ...(preserveReasoningContent && {
+            reasoning_content: '',
+          }),
         }
 
         if (assistantMsg.content) {
@@ -659,6 +664,9 @@ function convertMessages(
       coalesced.push({
         role: 'assistant',
         content: '[Tool execution interrupted by user]',
+        ...(preserveReasoningContent && {
+          reasoning_content: '',
+        }),
       })
     }
 
diff --git a/src/utils/conversationRecovery.hooks.test.ts b/src/utils/conversationRecovery.hooks.test.ts
index b19ae2559..d9284ede8 100644
--- a/src/utils/conversationRecovery.hooks.test.ts
+++ b/src/utils/conversationRecovery.hooks.test.ts
@@ -70,7 +70,7 @@ test('loadConversationForResume rejects oversized transcripts before resume hook
   expect(hookSpy).not.toHaveBeenCalled()
 })
 
-test('deserializeMessagesWithInterruptDetection strips thinking blocks only for OpenAI-compatible providers', async () => {
+test('deserializeMessagesWithInterruptDetection preserves thinking blocks for all providers (shim handles provider-specific filtering)', async () => {
   const serializedMessages = [
     user(id(10), 'hello'),
     {
@@ -120,13 +120,18 @@ test('deserializeMessagesWithInterruptDetection strips thinking blocks only for
     message => message.type === 'assistant',
   )
 
+  // The first assistant message keeps its thinking block (the OpenAI shim will
+  // convert it to reasoning_content for DeepSeek/Moonshot as needed).
+  // The second assistant message is thinking-only and orphaned, so it is removed
+  // by filterOrphanedThinkingOnlyMessages — not by provider-specific stripping.
   expect(thirdPartyAssistantMessages).toHaveLength(2)
   expect(thirdPartyAssistantMessages[0]?.message?.content).toEqual([
+    { type: 'thinking', thinking: 'secret reasoning' },
     { type: 'text', text: 'visible reply' },
   ])
   expect(
     JSON.stringify(thirdPartyAssistantMessages.map(message => message.message?.content)),
-  ).not.toContain('secret reasoning')
+  ).toContain('secret reasoning')
   expect(
     JSON.stringify(thirdPartyAssistantMessages.map(message => message.message?.content)),
   ).not.toContain('only hidden reasoning')
diff --git a/src/utils/conversationRecovery.ts b/src/utils/conversationRecovery.ts
index 3d4ad44bc..773490f1e 100644
--- a/src/utils/conversationRecovery.ts
+++ b/src/utils/conversationRecovery.ts
@@ -24,7 +24,6 @@ import {
   type FileHistorySnapshot,
 } from './fileHistory.js'
 import { logError } from './log.js'
-import { getAPIProvider } from './model/providers.js'
 import {
   createAssistantMessage,
   createUserMessage,
@@ -178,25 +177,6 @@ export type DeserializeResult = {
   turnInterruptionState: TurnInterruptionState
 }
 
-/**
- * Remove thinking/redacted_thinking content blocks from assistant messages.
- * Messages that become empty after stripping are removed entirely.
- */
-function stripThinkingBlocks(messages: NormalizedMessage[]): NormalizedMessage[] {
-  return messages.reduce<NormalizedMessage[]>((acc, msg) => {
-    if (msg.type !== 'assistant' || !Array.isArray(msg.message?.content)) {
-      acc.push(msg)
-      return acc
-    }
-    const filtered = msg.message.content.filter(
-      (block: { type?: string }) => block.type !== 'thinking' && block.type !== 'redacted_thinking',
-    )
-    if (filtered.length === 0) return acc
-    acc.push({ ...msg, message: { ...msg.message, content: filtered } })
-    return acc
-  }, [])
-}
-
 /**
  * Deserializes messages from a log file into the format expected by the REPL.
  * Filters unresolved tool uses, orphaned thinking messages, and appends a
@@ -247,19 +227,10 @@ export function deserializeMessagesWithInterruptDetection(
       filteredToolUses,
     ) as NormalizedMessage[]
 
-    // Strip thinking/redacted_thinking content blocks from assistant messages
-    // when resuming against a 3P provider. These Anthropic-specific blocks cause
-    // 400 errors or context corruption on OpenAI-compatible providers (issue #248 finding 5).
-    const provider = getAPIProvider()
-    const isThirdPartyProvider = provider !== 'firstParty' && provider !== 'bedrock' && provider !== 'vertex' && provider !== 'foundry'
-    const thinkingStripped = isThirdPartyProvider
-      ? stripThinkingBlocks(filteredThinking)
-      : filteredThinking
-
     // Filter out assistant messages with only whitespace text content.
     // This can happen when model outputs "\n\n" before thinking, user cancels mid-stream.
     const filteredMessages = filterWhitespaceOnlyAssistantMessages(
-      thinkingStripped,
+      filteredThinking,
     ) as NormalizedMessage[]
 
     const internalState = detectTurnInterruption(filteredMessages)