From d09c994b9138638379306c2e312e4460b58e2a22 Mon Sep 17 00:00:00 2001
From: Sisyphus <sisyphus@mengmota.com>
Date: Sat, 3 Jan 2026 09:46:45 +0900
Subject: [PATCH] fix(session-recovery): detect 'final block cannot be
 thinking' error pattern (#420)

---
 src/hooks/session-recovery/index.test.ts | 203 +++++++++++++++++++++++
 src/hooks/session-recovery/index.ts      |   4 +-
 2 files changed, 206 insertions(+), 1 deletion(-)
 create mode 100644 src/hooks/session-recovery/index.test.ts

diff --git a/src/hooks/session-recovery/index.test.ts b/src/hooks/session-recovery/index.test.ts
new file mode 100644
index 0000000..15b9e17
--- /dev/null
+++ b/src/hooks/session-recovery/index.test.ts
@@ -0,0 +1,203 @@
+import { describe, expect, it } from "bun:test"
+import { detectErrorType } from "./index"
+
+describe("detectErrorType", () => {
+  describe("thinking_block_order errors", () => {
+    it("should detect 'first block' error pattern", () => {
+      // #given an error about thinking being the first block
+      const error = {
+        message: "messages.0: thinking block must not be the first block",
+      }
+
+      // #when detectErrorType is called
+      const result = detectErrorType(error)
+
+      // #then should return thinking_block_order
+      expect(result).toBe("thinking_block_order")
+    })
+
+    it("should detect 'must start with' error pattern", () => {
+      // #given an error about message must start with something
+      const error = {
+        message: "messages.5: thinking must start with text or tool_use",
+      }
+
+      // #when detectErrorType is called
+      const result = detectErrorType(error)
+
+      // #then should return thinking_block_order
+      expect(result).toBe("thinking_block_order")
+    })
+
+    it("should detect 'preceeding' error pattern", () => {
+      // #given an error about preceeding block
+      const error = {
+        message: "messages.10: thinking requires preceeding text block",
+      }
+
+      // #when detectErrorType is called
+      const result = detectErrorType(error)
+
+      // #then should return thinking_block_order
+      expect(result).toBe("thinking_block_order")
+    })
+
+    it("should detect 'expected/found' error pattern", () => {
+      // #given an error about expected vs found
+      const error = {
+        message: "messages.3: thinking block expected text but found tool_use",
+      }
+
+      // #when detectErrorType is called
+      const result = detectErrorType(error)
+
+      // #then should return thinking_block_order
+      expect(result).toBe("thinking_block_order")
+    })
+
+    it("should detect 'final block cannot be thinking' error pattern", () => {
+      // #given an error about final block cannot be thinking
+      const error = {
+        message:
+          "messages.125: The final block in an assistant message cannot be thinking.",
+      }
+
+      // #when detectErrorType is called
+      const result = detectErrorType(error)
+
+      // #then should return thinking_block_order
+      expect(result).toBe("thinking_block_order")
+    })
+
+    it("should detect 'final block' variant error pattern", () => {
+      // #given an error mentioning final block with thinking
+      const error = {
+        message:
+          "messages.17: thinking in the final block is not allowed in assistant messages",
+      }
+
+      // #when detectErrorType is called
+      const result = detectErrorType(error)
+
+      // #then should return thinking_block_order
+      expect(result).toBe("thinking_block_order")
+    })
+
+    it("should detect 'cannot be thinking' error pattern", () => {
+      // #given an error using 'cannot be thinking' phrasing
+      const error = {
+        message:
+          "messages.219: The last block in an assistant message cannot be thinking content",
+      }
+
+      // #when detectErrorType is called
+      const result = detectErrorType(error)
+
+      // #then should return thinking_block_order
+      expect(result).toBe("thinking_block_order")
+    })
+  })
+
+  describe("tool_result_missing errors", () => {
+    it("should detect tool_use/tool_result mismatch", () => {
+      // #given an error about tool_use without tool_result
+      const error = {
+        message: "tool_use block requires corresponding tool_result",
+      }
+
+      // #when detectErrorType is called
+      const result = detectErrorType(error)
+
+      // #then should return tool_result_missing
+      expect(result).toBe("tool_result_missing")
+    })
+  })
+
+  describe("thinking_disabled_violation errors", () => {
+    it("should detect thinking disabled violation", () => {
+      // #given an error about thinking being disabled
+      const error = {
+        message:
+          "thinking is disabled for this model and cannot contain thinking blocks",
+      }
+
+      // #when detectErrorType is called
+      const result = detectErrorType(error)
+
+      // #then should return thinking_disabled_violation
+      expect(result).toBe("thinking_disabled_violation")
+    })
+  })
+
+  describe("unrecognized errors", () => {
+    it("should return null for unrecognized error patterns", () => {
+      // #given an unrelated error
+      const error = {
+        message: "Rate limit exceeded",
+      }
+
+      // #when detectErrorType is called
+      const result = detectErrorType(error)
+
+      // #then should return null
+      expect(result).toBeNull()
+    })
+
+    it("should return null for empty error", () => {
+      // #given an empty error
+      const error = {}
+
+      // #when detectErrorType is called
+      const result = detectErrorType(error)
+
+      // #then should return null
+      expect(result).toBeNull()
+    })
+
+    it("should return null for null error", () => {
+      // #given a null error
+      const error = null
+
+      // #when detectErrorType is called
+      const result = detectErrorType(error)
+
+      // #then should return null
+      expect(result).toBeNull()
+    })
+  })
+
+  describe("nested error objects", () => {
+    it("should detect error in data.error.message path", () => {
+      // #given an error with nested structure
+      const error = {
+        data: {
+          error: {
+            message:
+              "messages.163: The final block in an assistant message cannot be thinking.",
+          },
+        },
+      }
+
+      // #when detectErrorType is called
+      const result = detectErrorType(error)
+
+      // #then should return thinking_block_order
+      expect(result).toBe("thinking_block_order")
+    })
+
+    it("should detect error in error.message path", () => {
+      // #given an error with error.message structure
+      const error = {
+        error: {
+          message: "messages.169: final block cannot be thinking",
+        },
+      }
+
+      // #when detectErrorType is called
+      const result = detectErrorType(error)
+
+      // #then should return thinking_block_order
+      expect(result).toBe("thinking_block_order")
+    })
+  })
+})
diff --git a/src/hooks/session-recovery/index.ts b/src/hooks/session-recovery/index.ts
index 89fb460..68ddb3f 100644
--- a/src/hooks/session-recovery/index.ts
+++ b/src/hooks/session-recovery/index.ts
@@ -122,7 +122,7 @@ function extractMessageIndex(error: unknown): number | null {
   return match ? parseInt(match[1], 10) : null
 }
 
-function detectErrorType(error: unknown): RecoveryErrorType {
+export function detectErrorType(error: unknown): RecoveryErrorType {
   const message = getErrorMessage(error)
 
   if (message.includes("tool_use") && message.includes("tool_result")) {
@@ -134,6 +134,8 @@ function detectErrorType(error: unknown): RecoveryErrorType {
     (message.includes("first block") ||
       message.includes("must start with") ||
       message.includes("preceeding") ||
+      message.includes("final block") ||
+      message.includes("cannot be thinking") ||
       (message.includes("expected") && message.includes("found")))
   ) {
     return "thinking_block_order"