fix: sanitize Read tool args to prevent retry loops from non-Anthropic models (#1144)

* fix: sanitize Read tool args to prevent retry loops from non-Anthropic models

* fix: sanitize invalid Read pages from tool args

Non-Anthropic models sometimes emit optional Read args like pages: "" for
non-PDF files, which Claude Code rejects before the tool runs. Drop invalid
pages values, keep valid PDF page ranges, and coerce numeric string bounds
before clamping limit/offset.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

open-sse/translator/response/openai-to-claude.js

@@ -4,21 +4,40 @@ import { FORMATS } from "../formats.js";
 // Prefix for Claude OAuth tool names (must match request translator)
 const CLAUDE_OAUTH_TOOL_PREFIX = "proxy_";
 
-// Strip optional empty-string tool arguments that some providers emit.
+// Sanitize tool call arguments to fix bad params from non-Anthropic models
-// Claude Code's Read tool rejects pages: "" but accepts pages being absent.
+function sanitizeToolArgs(toolName, argsJson) {
-function sanitizeToolArguments(toolName, argsJson) {
   try {
     const args = JSON.parse(argsJson);
-    if (typeof args === "object" && args !== null) {
+    const name = toolName.startsWith(CLAUDE_OAUTH_TOOL_PREFIX)
-      if (toolName === "Read" && args.pages === "") {
+      ? toolName.slice(CLAUDE_OAUTH_TOOL_PREFIX.length)
+      : toolName;
+    if (name === "Read") sanitizeReadArgs(args);
+    return JSON.stringify(args);
+  } catch {
+    return argsJson;
+  }
+}
+
+function sanitizeReadArgs(args) {
+  if (typeof args.limit === "string" && /^\d+$/.test(args.limit)) args.limit = Number(args.limit);
+  if (typeof args.offset === "string" && /^-?\d+$/.test(args.offset)) args.offset = Number(args.offset);
+
+  if (typeof args.limit === "number") {
+    if (args.limit > 2000) args.limit = 2000;
+    if (args.limit < 1) delete args.limit;
+  }
+  if (typeof args.offset === "number" && args.offset < 0) args.offset = 0;
+
+  if ("pages" in args && !isValidPdfPagesArg(args.file_path, args.pages)) {
     delete args.pages;
   }
-      return JSON.stringify(args);
+}
-    }
+
-  } catch {
+function isValidPdfPagesArg(filePath, pages) {
-    // Not valid JSON yet (streaming chunk) — return as-is
+  return typeof filePath === "string" &&
-  }
+    filePath.toLowerCase().endsWith(".pdf") &&
-  return argsJson;
+    typeof pages === "string" &&
+    /^\d+(?:-\d+)?$/.test(pages);
 }
 
 // Helper: stop thinking block if started
@@ -187,12 +206,9 @@ export function openaiToClaudeResponse(chunk, state) {
       if (tc.function?.arguments) {
         const toolInfo = state.toolCalls.get(idx);
         if (toolInfo) {
-          const sanitized = sanitizeToolArguments(toolInfo.name, tc.function.arguments);
+          // Buffer args instead of streaming — sanitize at finish to fix bad params
-          results.push({
+          if (!state.toolArgBuffers) state.toolArgBuffers = new Map();
-            type: "content_block_delta",
+          state.toolArgBuffers.set(idx, (state.toolArgBuffers.get(idx) || "") + tc.function.arguments);
-            index: toolInfo.blockIndex,
-            delta: { type: "input_json_delta", partial_json: sanitized }
-          });
         }
       }
     }
@@ -203,7 +219,17 @@ export function openaiToClaudeResponse(chunk, state) {
     stopThinkingBlock(state, results);
     stopTextBlock(state, results);
 
-    for (const [, toolInfo] of state.toolCalls) {
+    for (const [idx, toolInfo] of state.toolCalls) {
+      // Emit buffered + sanitized args as single delta before stop
+      const buffered = state.toolArgBuffers?.get(idx);
+      if (buffered) {
+        const sanitized = sanitizeToolArgs(toolInfo.name, buffered);
+        results.push({
+          type: "content_block_delta",
+          index: toolInfo.blockIndex,
+          delta: { type: "input_json_delta", partial_json: sanitized }
+        });
+      }
       results.push({
         type: "content_block_stop",
         index: toolInfo.blockIndex
@@ -238,4 +264,3 @@ function convertFinishReason(reason) {
 
 // Register
 register(FORMATS.OPENAI, FORMATS.CLAUDE, null, openaiToClaudeResponse);
-

tests/unit/openai-to-claude-response-tools.test.js

@@ -0,0 +1,61 @@
+import { describe, expect, it } from "vitest";
+import { openaiToClaudeResponse } from "../../open-sse/translator/response/openai-to-claude.js";
+
+function createState() {
+  return { toolCalls: new Map(), nextBlockIndex: 0 };
+}
+
+function getInputJsonDelta(events) {
+  return events.find((event) => event.type === "content_block_delta" && event.delta?.type === "input_json_delta")?.delta.partial_json;
+}
+
+describe("openaiToClaudeResponse tool argument sanitization", () => {
+  it("drops invalid Read pages and clamps numeric bounds", () => {
+    const state = createState();
+
+    openaiToClaudeResponse({
+      id: "chatcmpl-test-read",
+      model: "test-model",
+      choices: [{ delta: { tool_calls: [{ index: 0, id: "toolu_read", function: { name: "Read" } }] } }],
+    }, state);
+
+    const events = openaiToClaudeResponse({
+      id: "chatcmpl-test-read",
+      model: "test-model",
+      choices: [{
+        delta: { tool_calls: [{ index: 0, function: { arguments: JSON.stringify({ file_path: "F:/repo/file.js", offset: -5, limit: 999999999, pages: "" }) } }] },
+        finish_reason: "tool_calls",
+      }],
+    }, state);
+
+    expect(JSON.parse(getInputJsonDelta(events))).toEqual({
+      file_path: "F:/repo/file.js",
+      offset: 0,
+      limit: 2000,
+    });
+  });
+
+  it("keeps valid PDF pages", () => {
+    const state = createState();
+
+    openaiToClaudeResponse({
+      id: "chatcmpl-test-pdf",
+      model: "test-model",
+      choices: [{ delta: { tool_calls: [{ index: 0, id: "toolu_pdf", function: { name: "proxy_Read" } }] } }],
+    }, state);
+
+    const events = openaiToClaudeResponse({
+      id: "chatcmpl-test-pdf",
+      model: "test-model",
+      choices: [{
+        delta: { tool_calls: [{ index: 0, function: { arguments: JSON.stringify({ file_path: "F:/repo/doc.pdf", pages: "1-3" }) } }] },
+        finish_reason: "tool_calls",
+      }],
+    }, state);
+
+    expect(JSON.parse(getInputJsonDelta(events))).toEqual({
+      file_path: "F:/repo/doc.pdf",
+      pages: "1-3",
+    });
+  });
+});