fix(recovery): keep thinking blocks on resume for reasoning-echo providers (#957)

src/utils/conversationRecovery.test.ts

@@ -171,3 +171,64 @@ test('deserializeMessages preserves thinking blocks for GitHub native Claude tra
   }>
   expect(content.some(block => block.type === 'thinking')).toBe(true)
 })
+
+test('deserializeMessages preserves thinking blocks for DeepSeek 3P provider (#957)', async () => {
+  // Regression: DeepSeek requires `reasoning_content` echoed back on assistant
+  // messages in thinking mode. The shim reads the thinking block to populate
+  // that field — stripping it on resume left the shim with no source and the
+  // provider 400'd ("reasoning_content in the thinking mode must be passed
+  // back"). preserveReasoningContent: true (from runtimeMetadata's DeepSeek
+  // shim config inference) must opt the provider out of the 3P thinking strip.
+  clearProviderEnv()
+  process.env.CLAUDE_CODE_USE_OPENAI = '1'
+  process.env.OPENAI_BASE_URL = 'https://api.deepseek.com/v1'
+  process.env.OPENAI_MODEL = 'deepseek-v4-flash'
+  const { deserializeMessages } = await importFreshConversationRecovery()
+
+  const deserialized = deserializeMessages([
+    {
+      type: 'assistant',
+      message: {
+        role: 'assistant',
+        content: [
+          { type: 'thinking', thinking: 'chain of thought' },
+          { type: 'text', text: 'answer' },
+        ],
+      },
+    } as any,
+  ])
+
+  const content = (deserialized[0] as any)?.message?.content as Array<{
+    type: string
+  }>
+  expect(content.some(block => block.type === 'thinking')).toBe(true)
+})
+
+test('deserializeMessages still strips thinking blocks for generic OpenAI 3P (no preserveReasoningContent)', async () => {
+  // Counter-test: providers that don't set preserveReasoningContent keep the
+  // original strip behaviour from #248 — thinking blocks were causing 400s
+  // there, and the fix for #957 must not regress that path.
+  clearProviderEnv()
+  process.env.CLAUDE_CODE_USE_OPENAI = '1'
+  process.env.OPENAI_BASE_URL = 'https://api.openai.com/v1'
+  process.env.OPENAI_MODEL = 'gpt-5-mini'
+  const { deserializeMessages } = await importFreshConversationRecovery()
+
+  const deserialized = deserializeMessages([
+    {
+      type: 'assistant',
+      message: {
+        role: 'assistant',
+        content: [
+          { type: 'thinking', thinking: 'noise' },
+          { type: 'text', text: 'answer' },
+        ],
+      },
+    } as any,
+  ])
+
+  const content = (deserialized[0] as any)?.message?.content as Array<{
+    type: string
+  }>
+  expect(content.some(block => block.type === 'thinking')).toBe(false)
+})

src/utils/conversationRecovery.ts

@@ -25,7 +25,10 @@ import {
 } from './fileHistory.js'
 import { logError } from './log.js'
 import { getAPIProvider } from './model/providers.js'
-import { usesAnthropicNativeMessageFormat } from '../integrations/runtimeMetadata.js'
+import {
+  resolveOpenAIShimRuntimeContext,
+  usesAnthropicNativeMessageFormat,
+} from '../integrations/runtimeMetadata.js'
 import {
   createAssistantMessage,
   createUserMessage,
@@ -198,9 +201,25 @@ function stripThinkingBlocks(messages: NormalizedMessage[]): NormalizedMessage[]
   }, [])
 }
 
+// Some 3P providers require `reasoning_content` echoed back on assistant
+// messages (DeepSeek thinking mode, Moonshot/Kimi, Z.AI GLM, MiMo, etc.). The
+// openai-shim re-shapes those messages and reads the source-of-truth from the
+// `thinking` block on the Anthropic side. Stripping the block leaves the shim
+// with no reasoning text and the provider 400s with
+// "reasoning_content in the thinking mode must be passed back" (issue #957).
+//
+// Vendors declare this need via `openaiShim.preserveReasoningContent: true`
+// in their descriptor, so derive the answer from the resolved shim config
+// instead of hardcoding model name prefixes — that automatically covers any
+// future vendor that opts in without code changes here.
 function shouldPreserveThinkingBlocksForProviderReplay(): boolean {
-  const model = process.env.OPENAI_MODEL?.trim().toLowerCase() ?? ''
-  return model.startsWith('mimo-v2')
+  return (
+    resolveOpenAIShimRuntimeContext({
+      processEnv: process.env,
+      baseUrl: process.env.OPENAI_BASE_URL,
+      model: process.env.OPENAI_MODEL,
+    }).openaiShimConfig.preserveReasoningContent === true
+  )
 }
 
 /**
@@ -256,6 +275,13 @@ export function deserializeMessagesWithInterruptDetection(
     // 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).
+    //
+    // Exception: providers that require `reasoning_content` echoed back on
+    // assistant messages (DeepSeek thinking mode, Moonshot/Kimi, Z.AI GLM, etc.)
+    // read the source-of-truth from the `thinking` block when re-shaping the
+    // outgoing OpenAI-format message. Stripping the block leaves the shim with
+    // no reasoning text to attach, and the provider 400s with
+    // "reasoning_content in the thinking mode must be passed back" (issue #957).
     const provider = getAPIProvider()
     const isAnthropicNativeTransport = usesAnthropicNativeMessageFormat({
       processEnv: process.env,
@@ -264,10 +290,10 @@ export function deserializeMessagesWithInterruptDetection(
     })
     const isThirdPartyProvider =
       provider !== 'foundry' && !isAnthropicNativeTransport
-    const thinkingStripped = isThirdPartyProvider
-      && !shouldPreserveThinkingBlocksForProviderReplay()
-      ? stripThinkingBlocks(filteredThinking)
-      : filteredThinking
+    const thinkingStripped =
+      isThirdPartyProvider && !shouldPreserveThinkingBlocksForProviderReplay()
+        ? 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.