diff --git a/nanobot/agent/runner.py b/nanobot/agent/runner.py
index aff921c0..d8f5434b 100644
--- a/nanobot/agent/runner.py
+++ b/nanobot/agent/runner.py
@@ -5,6 +5,7 @@ from __future__ import annotations
 import asyncio
 import inspect
 import os
+from collections import deque
 from contextlib import suppress
 from copy import deepcopy
 from dataclasses import dataclass, field
@@ -1361,18 +1362,29 @@ class AgentRunner:
     def _dedupe_tool_calls(
         messages: list[dict[str, Any]],
     ) -> list[dict[str, Any]]:
-        """Remove duplicate tool_call / tool_result ids from the history.
+        """Make duplicate tool_call ids unique while keeping matching results paired.
 
         Anthropic rejects any request where two tool_use blocks share an id
         ("tool_use ids must be unique"). An accidental duplicate (e.g. from a
-        mis-assembled stream) otherwise poisons the session permanently, since
-        the bad message is re-sent on every turn. Keep the first occurrence of
-        each id across all assistant tool_calls, and likewise keep only the
-        first tool result per id so pairing stays 1:1.
+        mis-assembled stream) otherwise poisons the session permanently. Some
+        Anthropic-compatible providers also reuse ids for distinct parallel
+        calls, so preserve every call and rewrite later duplicates instead of
+        silently dropping work. Tool results are remapped in call order.
         """
         seen_call_ids: set[str] = set()
-        seen_result_ids: set[str] = set()
+        duplicate_counts: dict[str, int] = {}
+        pending_result_ids: dict[str, deque[str]] = {}
         updated: list[dict[str, Any]] | None = None
+
+        def _unique_id(raw_id: str) -> str:
+            duplicate_counts[raw_id] = duplicate_counts.get(raw_id, 1) + 1
+            suffix = duplicate_counts[raw_id]
+            while True:
+                candidate = f"{raw_id}__dedupe_{suffix}"
+                if candidate not in seen_call_ids:
+                    return candidate
+                suffix += 1
+
         for idx, msg in enumerate(messages):
             role = msg.get("role")
             replacement: dict[str, Any] | None = None
@@ -1383,11 +1395,20 @@ class AgentRunner:
                 changed = False
                 for tc in msg.get("tool_calls") or []:
                     tid = tc.get("id") if isinstance(tc, dict) else None
-                    if tid and str(tid) in seen_call_ids:
-                        changed = True
+                    if not tid:
+                        kept.append(tc)
                         continue
-                    if tid:
-                        seen_call_ids.add(str(tid))
+                    raw_id = str(tid)
+                    mapped_id = raw_id
+                    if raw_id in seen_call_ids:
+                        mapped_id = _unique_id(raw_id)
+                        changed = True
+                    seen_call_ids.add(mapped_id)
+                    pending_result_ids.setdefault(raw_id, deque()).append(mapped_id)
+                    if mapped_id != tid:
+                        tc = dict(tc)
+                        tc["id"] = mapped_id
+                        changed = True
                     kept.append(tc)
                 if changed:
                     replacement = dict(msg)
@@ -1395,10 +1416,17 @@ class AgentRunner:
             elif role == "tool":
                 tid = msg.get("tool_call_id")
                 if tid:
-                    if str(tid) in seen_result_ids:
+                    raw_id = str(tid)
+                    queue = pending_result_ids.get(raw_id)
+                    if not queue:
                         drop = True
                     else:
-                        seen_result_ids.add(str(tid))
+                        mapped_id = queue.popleft()
+                        if not queue:
+                            pending_result_ids.pop(raw_id, None)
+                        if mapped_id != tid:
+                            replacement = dict(msg)
+                            replacement["tool_call_id"] = mapped_id
 
             if (replacement is not None or drop) and updated is None:
                 updated = [dict(m) for m in messages[:idx]]
diff --git a/nanobot/providers/anthropic_provider.py b/nanobot/providers/anthropic_provider.py
index 3d0c5322..97335afd 100644
--- a/nanobot/providers/anthropic_provider.py
+++ b/nanobot/providers/anthropic_provider.py
@@ -530,15 +530,19 @@ class AnthropicProvider(LLMProvider):
             if block.type == "text":
                 content_parts.append(block.text)
             elif block.type == "tool_use":
-                # Anthropic requires every tool_use id to be unique. A mis-assembled
-                # stream can occasionally surface the same block twice; keep the first
-                # and drop the duplicate so it never poisons the persisted history.
-                if block.id in seen_tool_ids:
-                    logger.warning("dropping duplicate tool_use id from response: {}", block.id)
-                    continue
-                seen_tool_ids.add(block.id)
+                tool_id = str(block.id or _gen_tool_id())
+                if tool_id in seen_tool_ids:
+                    original_id = tool_id
+                    while tool_id in seen_tool_ids:
+                        tool_id = _gen_tool_id()
+                    logger.warning(
+                        "remapping duplicate tool_use id from response: {} -> {}",
+                        original_id,
+                        tool_id,
+                    )
+                seen_tool_ids.add(tool_id)
                 tool_calls.append(ToolCallRequest(
-                    id=block.id,
+                    id=tool_id,
                     name=block.name,
                     arguments=block.input,
                 ))
diff --git a/tests/agent/test_runner_governance.py b/tests/agent/test_runner_governance.py
index 1bcb6e87..5e8fc784 100644
--- a/tests/agent/test_runner_governance.py
+++ b/tests/agent/test_runner_governance.py
@@ -7,7 +7,7 @@ from unittest.mock import AsyncMock, MagicMock, patch
 import pytest
 
 from nanobot.config.schema import AgentDefaults
-from nanobot.providers.base import LLMResponse, ToolCallRequest
+from nanobot.providers.base import LLMResponse
 
 _MAX_TOOL_RESULT_CHARS = AgentDefaults().max_tool_result_chars
 
@@ -184,7 +184,7 @@ async def test_backfill_missing_tool_results_inserts_error():
     assert backfilled[0]["name"] == "read_file"
 
 
-def test_dedupe_tool_calls_removes_duplicate_ids():
+def test_dedupe_tool_calls_remaps_duplicate_ids():
     from nanobot.agent.runner import AgentRunner
 
     messages = [
@@ -194,15 +194,14 @@ def test_dedupe_tool_calls_removes_duplicate_ids():
             "content": "",
             "tool_calls": [
                 {"id": "a", "type": "function", "function": {"name": "x", "arguments": "{}"}},
-                {"id": "b", "type": "function", "function": {"name": "y", "arguments": "{}"}},
-                # Duplicate of "b" — would trigger "tool_use ids must be unique".
-                {"id": "b", "type": "function", "function": {"name": "y", "arguments": "{}"}},
+                {"id": "b", "type": "function", "function": {"name": "y", "arguments": '{"path":"a.txt"}'}},
+                # Duplicate id with different arguments should be preserved, not dropped.
+                {"id": "b", "type": "function", "function": {"name": "y", "arguments": '{"path":"b.txt"}'}},
             ],
         },
         {"role": "tool", "tool_call_id": "a", "name": "x", "content": "ra"},
         {"role": "tool", "tool_call_id": "b", "name": "y", "content": "rb"},
-        # Duplicate result for "b".
-        {"role": "tool", "tool_call_id": "b", "name": "y", "content": "rb-dup"},
+        {"role": "tool", "tool_call_id": "b", "name": "y", "content": "rb-remapped"},
     ]
 
     cleaned = AgentRunner._dedupe_tool_calls(messages)
@@ -214,11 +213,13 @@ def test_dedupe_tool_calls_removes_duplicate_ids():
             "content": "",
             "tool_calls": [
                 {"id": "a", "type": "function", "function": {"name": "x", "arguments": "{}"}},
-                {"id": "b", "type": "function", "function": {"name": "y", "arguments": "{}"}},
+                {"id": "b", "type": "function", "function": {"name": "y", "arguments": '{"path":"a.txt"}'}},
+                {"id": "b__dedupe_2", "type": "function", "function": {"name": "y", "arguments": '{"path":"b.txt"}'}},
             ],
         },
         {"role": "tool", "tool_call_id": "a", "name": "x", "content": "ra"},
         {"role": "tool", "tool_call_id": "b", "name": "y", "content": "rb"},
+        {"role": "tool", "tool_call_id": "b__dedupe_2", "name": "y", "content": "rb-remapped"},
     ]
 
 
diff --git a/tests/providers/test_anthropic_tool_result.py b/tests/providers/test_anthropic_tool_result.py
index 0ae89723..eb284074 100644
--- a/tests/providers/test_anthropic_tool_result.py
+++ b/tests/providers/test_anthropic_tool_result.py
@@ -10,6 +10,8 @@ Also tests that bare dicts without a "type" field are coerced to text
 blocks, fixing Anthropic "content.0.type: Field required" rejections (#3993).
 """
 
+from types import SimpleNamespace
+
 from nanobot.providers.anthropic_provider import AnthropicProvider
 
 
@@ -132,3 +134,33 @@ def test_anthropic_sanitized_tool_ids_avoid_simple_collisions():
     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)
+
+
+def test_anthropic_parse_response_remaps_duplicate_tool_use_ids():
+    response = SimpleNamespace(
+        content=[
+            SimpleNamespace(
+                type="tool_use",
+                id="toolu_same",
+                name="read_file",
+                input={"path": "a.txt"},
+            ),
+            SimpleNamespace(
+                type="tool_use",
+                id="toolu_same",
+                name="read_file",
+                input={"path": "b.txt"},
+            ),
+        ],
+        stop_reason="tool_use",
+        usage=None,
+    )
+
+    result = AnthropicProvider._parse_response(response)
+
+    assert len(result.tool_calls) == 2
+    assert result.tool_calls[0].id == "toolu_same"
+    assert result.tool_calls[0].arguments == {"path": "a.txt"}
+    assert result.tool_calls[1].id != "toolu_same"
+    assert result.tool_calls[1].id.startswith("toolu_")
+    assert result.tool_calls[1].arguments == {"path": "b.txt"}