diff --git a/nanobot/providers/anthropic_provider.py b/nanobot/providers/anthropic_provider.py
index f9e97bf3..58d4265a 100644
--- a/nanobot/providers/anthropic_provider.py
+++ b/nanobot/providers/anthropic_provider.py
@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import asyncio
+import hashlib
 import re
 import secrets
 import string
@@ -37,7 +38,9 @@ def _sanitize_tool_id(tid: str) -> str:
     """
     if not tid or _VALID_TOOL_ID.match(tid):
         return tid
-    return re.sub(r"[^a-zA-Z0-9_-]", "_", tid)
+    safe_prefix = re.sub(r"[^a-zA-Z0-9_-]", "_", tid)[:48].strip("_") or "toolu"
+    digest = hashlib.sha1(tid.encode()).hexdigest()[:8]
+    return f"{safe_prefix}_{digest}"
 
 
 class AnthropicProvider(LLMProvider):
diff --git a/tests/providers/test_anthropic_tool_result.py b/tests/providers/test_anthropic_tool_result.py
index 3021ff0b..0ae89723 100644
--- a/tests/providers/test_anthropic_tool_result.py
+++ b/tests/providers/test_anthropic_tool_result.py
@@ -94,3 +94,41 @@ def test_convert_assistant_message_repairs_history_tool_arguments():
 
     assert blocks[0]["type"] == "tool_use"
     assert blocks[0]["input"] == {"path": "foo.txt"}
+
+
+def test_anthropic_sanitizes_invalid_tool_ids_consistently():
+    """Invalid restored IDs must be valid for Anthropic and keep pairs matched."""
+    blocks = AnthropicProvider._assistant_blocks({
+        "role": "assistant",
+        "content": None,
+        "tool_calls": [{
+            "id": "call_abc|rs.same",
+            "function": {"name": "read_file", "arguments": "{}"},
+        }],
+    })
+    result = AnthropicProvider._tool_result_block({
+        "role": "tool",
+        "tool_call_id": "call_abc|rs.same",
+        "content": "ok",
+    })
+
+    tool_id = blocks[0]["id"]
+    assert tool_id == result["tool_use_id"]
+    assert tool_id != "call_abc|rs.same"
+    assert all(ch.isalnum() or ch in "_-" for ch in tool_id)
+
+
+def test_anthropic_sanitized_tool_ids_avoid_simple_collisions():
+    """Replacement-only sanitizing would collapse these two ids to call_a."""
+    blocks = AnthropicProvider._assistant_blocks({
+        "role": "assistant",
+        "content": None,
+        "tool_calls": [
+            {"id": "call.a", "function": {"name": "a", "arguments": "{}"}},
+            {"id": "call|a", "function": {"name": "b", "arguments": "{}"}},
+        ],
+    })
+
+    ids = [block["id"] for block in blocks if block["type"] == "tool_use"]
+    assert len(ids) == len(set(ids)) == 2
+    assert all(all(ch.isalnum() or ch in "_-" for ch in tool_id) for tool_id in ids)