fix: deduplicate tool_use IDs and enable sanitization for Anthropic

Anthropic API rejects requests with duplicate tool_use IDs across messages.
This can happen when:
1. Session transcripts have multiple assistant messages with the same tool_use ID
2. IDs contain special characters that weren't being sanitized for Anthropic

Changes:
- Add deduplication logic in repairToolUseResultPairing() to detect and rename
  duplicate tool_use IDs in assistant messages (e.g., call_1 -> call_1_2)
- Update corresponding toolResult IDs to match the remapped tool_use IDs
- Enable sanitizeToolCallIds for Anthropic provider (was only Google/Mistral)
- Add tests for deduplication scenarios

Fixes error: "messages.X.content.Y: tool_use ids must be unique"

src/agents/session-transcript-repair.test.ts

@@ -109,4 +109,97 @@ describe("sanitizeToolUseResultPairing", () => {
     expect(out.some((m) => m.role === "toolResult")).toBe(false);
     expect(out.map((m) => m.role)).toEqual(["user", "assistant"]);
   });
+
+  it("deduplicates tool_use IDs across assistant messages", () => {
+    // This test ensures that duplicate tool_use IDs in different assistant messages
+    // are remapped to unique IDs (Anthropic requires unique tool_use IDs)
+    const input = [
+      {
+        role: "assistant",
+        content: [{ type: "toolCall", id: "call_1", name: "read", arguments: {} }],
+      },
+      {
+        role: "toolResult",
+        toolCallId: "call_1",
+        toolName: "read",
+        content: [{ type: "text", text: "first result" }],
+        isError: false,
+      },
+      { role: "user", content: "do it again" },
+      {
+        role: "assistant",
+        content: [{ type: "toolCall", id: "call_1", name: "read", arguments: {} }], // Duplicate ID
+      },
+      {
+        role: "toolResult",
+        toolCallId: "call_1",
+        toolName: "read",
+        content: [{ type: "text", text: "second result" }],
+        isError: false,
+      },
+    ] satisfies AgentMessage[];
+
+    const out = sanitizeToolUseResultPairing(input);
+
+    // Both tool calls should exist but with unique IDs
+    const assistants = out.filter((m) => m.role === "assistant") as Array<{
+      content?: Array<{ type?: string; id?: string }>;
+    }>;
+    expect(assistants).toHaveLength(2);
+
+    const firstToolCallId = assistants[0]?.content?.[0]?.id;
+    const secondToolCallId = assistants[1]?.content?.[0]?.id;
+
+    // First ID should remain unchanged
+    expect(firstToolCallId).toBe("call_1");
+    // Second ID should be remapped to be unique
+    expect(secondToolCallId).not.toBe("call_1");
+    expect(secondToolCallId).toBe("call_1_2");
+
+    // Tool results should have matching IDs
+    const results = out.filter((m) => m.role === "toolResult") as Array<{
+      toolCallId?: string;
+    }>;
+    expect(results).toHaveLength(2);
+    expect(results[0]?.toolCallId).toBe(firstToolCallId);
+    expect(results[1]?.toolCallId).toBe(secondToolCallId);
+  });
+
+  it("handles toolUse type blocks with duplicate IDs", () => {
+    const input = [
+      {
+        role: "assistant",
+        content: [{ type: "toolUse", id: "toolu_1", name: "exec", input: {} }],
+      },
+      {
+        role: "toolResult",
+        toolCallId: "toolu_1",
+        toolName: "exec",
+        content: [{ type: "text", text: "ok" }],
+        isError: false,
+      },
+      { role: "user", content: "again" },
+      {
+        role: "assistant",
+        content: [{ type: "toolUse", id: "toolu_1", name: "exec", input: {} }], // Duplicate
+      },
+      {
+        role: "toolResult",
+        toolCallId: "toolu_1",
+        toolName: "exec",
+        content: [{ type: "text", text: "ok again" }],
+        isError: false,
+      },
+    ] satisfies AgentMessage[];
+
+    const out = sanitizeToolUseResultPairing(input);
+
+    const assistants = out.filter((m) => m.role === "assistant") as Array<{
+      content?: Array<{ type?: string; id?: string }>;
+    }>;
+    const ids = assistants.map((a) => a.content?.[0]?.id);
+
+    // All IDs should be unique
+    expect(new Set(ids).size).toBe(ids.length);
+  });
 });

src/agents/session-transcript-repair.ts

@@ -75,9 +75,11 @@ export function repairToolUseResultPairing(messages: AgentMessage[]): ToolUseRep
   // - moving matching toolResult messages directly after their assistant toolCall turn
   // - inserting synthetic error toolResults for missing ids
   // - dropping duplicate toolResults for the same id (anywhere in the transcript)
+  // - deduplicating tool_use IDs in assistant messages (Anthropic requires unique IDs)
   const out: AgentMessage[] = [];
   const added: Array<Extract<AgentMessage, { role: "toolResult" }>> = [];
   const seenToolResultIds = new Set<string>();
+  const seenToolUseIds = new Set<string>();
   let droppedDuplicateCount = 0;
   let droppedOrphanCount = 0;
   let moved = false;
@@ -94,6 +96,23 @@ export function repairToolUseResultPairing(messages: AgentMessage[]): ToolUseRep
     out.push(msg);
   };
 
+  // Deduplicate tool_use IDs in assistant messages by generating unique IDs for collisions
+  const deduplicateToolUseId = (id: string): string => {
+    if (!seenToolUseIds.has(id)) {
+      seenToolUseIds.add(id);
+      return id;
+    }
+    // Generate a unique ID by appending a counter
+    let counter = 2;
+    let newId = `${id}_${counter}`;
+    while (seenToolUseIds.has(newId)) {
+      counter += 1;
+      newId = `${id}_${counter}`;
+    }
+    seenToolUseIds.add(newId);
+    return newId;
+  };
+
   for (let i = 0; i < messages.length; i += 1) {
     const msg = messages[i] as AgentMessage;
     if (!msg || typeof msg !== "object") {
@@ -122,7 +141,43 @@ export function repairToolUseResultPairing(messages: AgentMessage[]): ToolUseRep
       continue;
     }
 
-    const toolCallIds = new Set(toolCalls.map((t) => t.id));
+    // Check for duplicate tool_use IDs and remap them if necessary
+    const idRemapping = new Map<string, string>();
+    let assistantNeedsRewrite = false;
+    for (const call of toolCalls) {
+      const newId = deduplicateToolUseId(call.id);
+      if (newId !== call.id) {
+        idRemapping.set(call.id, newId);
+        assistantNeedsRewrite = true;
+        changed = true;
+      }
+    }
+
+    // Rewrite assistant message if any tool_use IDs were deduplicated
+    let processedAssistant = assistant;
+    if (assistantNeedsRewrite && Array.isArray(assistant.content)) {
+      const newContent = assistant.content.map((block) => {
+        if (!block || typeof block !== "object") return block;
+        const rec = block as { type?: unknown; id?: unknown };
+        if (
+          (rec.type === "toolCall" || rec.type === "toolUse" || rec.type === "functionCall") &&
+          typeof rec.id === "string" &&
+          idRemapping.has(rec.id)
+        ) {
+          return { ...(block as unknown as Record<string, unknown>), id: idRemapping.get(rec.id) };
+        }
+        return block;
+      });
+      processedAssistant = { ...assistant, content: newContent as typeof assistant.content };
+    }
+
+    // Update toolCalls with remapped IDs for matching
+    const effectiveToolCalls = toolCalls.map((call) => ({
+      ...call,
+      id: idRemapping.get(call.id) ?? call.id,
+      originalId: call.id,
+    }));
+    const toolCallIds = new Set(effectiveToolCalls.map((t) => t.originalId));
 
     const spanResultsById = new Map<string, Extract<AgentMessage, { role: "toolResult" }>>();
     const remainder: AgentMessage[] = [];
@@ -163,17 +218,27 @@ export function repairToolUseResultPairing(messages: AgentMessage[]): ToolUseRep
       }
     }
 
-    out.push(msg);
+    out.push(processedAssistant);
 
     if (spanResultsById.size > 0 && remainder.length > 0) {
       moved = true;
       changed = true;
     }
 
-    for (const call of toolCalls) {
+    for (const call of effectiveToolCalls) {
-      const existing = spanResultsById.get(call.id);
+      const existing = spanResultsById.get(call.originalId);
       if (existing) {
-        pushToolResult(existing);
+        // Remap toolResult ID if the tool_use ID was deduplicated
+        const remappedId = idRemapping.get(call.originalId);
+        if (remappedId) {
+          const remappedResult = {
+            ...existing,
+            toolCallId: remappedId,
+          } as Extract<AgentMessage, { role: "toolResult" }>;
+          pushToolResult(remappedResult);
+        } else {
+          pushToolResult(existing);
+        }
       } else {
         const missing = makeMissingToolResult({
           toolCallId: call.id,

src/agents/transcript-policy.ts

@@ -85,7 +85,7 @@ export function resolveTranscriptPolicy(params: {
 
   const needsNonImageSanitize = isGoogle || isAnthropic || isMistral || isOpenRouterGemini;
 
-  const sanitizeToolCallIds = isGoogle || isMistral;
+  const sanitizeToolCallIds = isGoogle || isMistral || isAnthropic;
   const toolCallIdMode: ToolCallIdMode | undefined = isMistral
     ? "strict9"
     : sanitizeToolCallIds