diff --git a/agent/anthropic_adapter.py b/agent/anthropic_adapter.py
index bf2b8a62c..d8d181cc1 100644
--- a/agent/anthropic_adapter.py
+++ b/agent/anthropic_adapter.py
@@ -1525,3 +1525,42 @@ def normalize_anthropic_response(
         ),
         finish_reason,
     )
+
+
+def normalize_anthropic_response_v2(
+    response,
+    strip_tool_prefix: bool = False,
+) -> "NormalizedResponse":
+    """Normalize Anthropic response to NormalizedResponse.
+
+    Wraps the existing normalize_anthropic_response() and maps its output
+    to the shared transport types.  This allows incremental migration —
+    one call site at a time — without changing the original function.
+    """
+    from agent.transports.types import NormalizedResponse, build_tool_call
+
+    assistant_msg, finish_reason = normalize_anthropic_response(response, strip_tool_prefix)
+
+    tool_calls = None
+    if assistant_msg.tool_calls:
+        tool_calls = [
+            build_tool_call(
+                id=tc.id,
+                name=tc.function.name,
+                arguments=tc.function.arguments,
+            )
+            for tc in assistant_msg.tool_calls
+        ]
+
+    provider_data = {}
+    if getattr(assistant_msg, "reasoning_details", None):
+        provider_data["reasoning_details"] = assistant_msg.reasoning_details
+
+    return NormalizedResponse(
+        content=assistant_msg.content,
+        tool_calls=tool_calls,
+        finish_reason=finish_reason,
+        reasoning=getattr(assistant_msg, "reasoning", None),
+        usage=None,  # Anthropic usage is on the raw response, not the normaliser
+        provider_data=provider_data or None,
+    )
diff --git a/agent/transports/__init__.py b/agent/transports/__init__.py
new file mode 100644
index 000000000..6ee1c5117
--- /dev/null
+++ b/agent/transports/__init__.py
@@ -0,0 +1 @@
+"""Transport layer types for provider response normalization."""
diff --git a/agent/transports/types.py b/agent/transports/types.py
new file mode 100644
index 000000000..2b048fcaa
--- /dev/null
+++ b/agent/transports/types.py
@@ -0,0 +1,100 @@
+"""Shared types for normalized provider responses.
+
+These dataclasses define the canonical shape that all provider adapters
+normalize responses to.  The shared surface is intentionally minimal —
+only fields that every downstream consumer reads are top-level.
+Protocol-specific state goes in ``provider_data`` dicts (response-level
+and per-tool-call) so that protocol-aware code paths can access it
+without polluting the shared type.
+"""
+
+from __future__ import annotations
+
+import json
+from dataclasses import dataclass, field
+from typing import Any, Dict, List, Optional
+
+
+@dataclass
+class ToolCall:
+    """A normalized tool call from any provider.
+
+    ``id`` is the protocol's canonical identifier — what gets used in
+    ``tool_call_id`` / ``tool_use_id`` when constructing tool result
+    messages.  May be ``None`` when the provider omits it; the agent
+    fills it via ``_deterministic_call_id()`` before storing in history.
+
+    ``provider_data`` carries per-tool-call protocol metadata that only
+    protocol-aware code reads:
+
+    * Codex: ``{"call_id": "call_XXX", "response_item_id": "fc_XXX"}``
+    * Gemini: ``{"extra_content": {"google": {"thought_signature": "..."}}}``
+    * Others: ``None``
+    """
+
+    id: Optional[str]
+    name: str
+    arguments: str  # JSON string
+    provider_data: Optional[Dict[str, Any]] = field(default=None, repr=False)
+
+
+@dataclass
+class Usage:
+    """Token usage from an API response."""
+
+    prompt_tokens: int = 0
+    completion_tokens: int = 0
+    total_tokens: int = 0
+    cached_tokens: int = 0
+
+
+@dataclass
+class NormalizedResponse:
+    """Normalized API response from any provider.
+
+    Shared fields are truly cross-provider — every caller can rely on
+    them without branching on api_mode.  Protocol-specific state goes in
+    ``provider_data`` so that only protocol-aware code paths read it.
+
+    Response-level ``provider_data`` examples:
+
+    * Anthropic: ``{"reasoning_details": [...]}``
+    * Codex: ``{"codex_reasoning_items": [...]}``
+    * Others: ``None``
+    """
+
+    content: Optional[str]
+    tool_calls: Optional[List[ToolCall]]
+    finish_reason: str  # "stop", "tool_calls", "length", "content_filter"
+    reasoning: Optional[str] = None
+    usage: Optional[Usage] = None
+    provider_data: Optional[Dict[str, Any]] = field(default=None, repr=False)
+
+
+# ---------------------------------------------------------------------------
+# Factory helpers
+# ---------------------------------------------------------------------------
+
+def build_tool_call(
+    id: Optional[str],
+    name: str,
+    arguments: Any,
+    **provider_fields: Any,
+) -> ToolCall:
+    """Build a ``ToolCall``, auto-serialising *arguments* if it's a dict.
+
+    Any extra keyword arguments are collected into ``provider_data``.
+    """
+    args_str = json.dumps(arguments) if isinstance(arguments, dict) else str(arguments)
+    pd = dict(provider_fields) if provider_fields else None
+    return ToolCall(id=id, name=name, arguments=args_str, provider_data=pd)
+
+
+def map_finish_reason(reason: Optional[str], mapping: Dict[str, str]) -> str:
+    """Translate a provider-specific stop reason to the normalised set.
+
+    Falls back to ``"stop"`` for unknown or ``None`` reasons.
+    """
+    if reason is None:
+        return "stop"
+    return mapping.get(reason, "stop")
diff --git a/run_agent.py b/run_agent.py
index 49240d70f..e69d30ff2 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -10778,10 +10778,33 @@ class AIAgent:
                 if self.api_mode == "codex_responses":
                     assistant_message, finish_reason = self._normalize_codex_response(response)
                 elif self.api_mode == "anthropic_messages":
-                    from agent.anthropic_adapter import normalize_anthropic_response
-                    assistant_message, finish_reason = normalize_anthropic_response(
+                    from agent.anthropic_adapter import normalize_anthropic_response_v2
+                    _nr = normalize_anthropic_response_v2(
                         response, strip_tool_prefix=self._is_anthropic_oauth
                     )
+                    # Back-compat shim: downstream code expects SimpleNamespace with
+                    # .content, .tool_calls, .reasoning, .reasoning_content,
+                    # .reasoning_details attributes.  This shim makes the cost of the
+                    # old interface visible — it vanishes when the full transport
+                    # wiring lands (PR 3+).
+                    assistant_message = SimpleNamespace(
+                        content=_nr.content,
+                        tool_calls=[
+                            SimpleNamespace(
+                                id=tc.id,
+                                type="function",
+                                function=SimpleNamespace(name=tc.name, arguments=tc.arguments),
+                            )
+                            for tc in (_nr.tool_calls or [])
+                        ] or None,
+                        reasoning=_nr.reasoning,
+                        reasoning_content=None,
+                        reasoning_details=(
+                            _nr.provider_data.get("reasoning_details")
+                            if _nr.provider_data else None
+                        ),
+                    )
+                    finish_reason = _nr.finish_reason
                 else:
                     assistant_message = response.choices[0].message
                 
diff --git a/tests/agent/test_anthropic_normalize_v2.py b/tests/agent/test_anthropic_normalize_v2.py
new file mode 100644
index 000000000..9d5c16139
--- /dev/null
+++ b/tests/agent/test_anthropic_normalize_v2.py
@@ -0,0 +1,238 @@
+"""Regression tests: normalize_anthropic_response_v2 vs v1.
+
+Constructs mock Anthropic responses and asserts that the v2 function
+(returning NormalizedResponse) produces identical field values to the
+original v1 function (returning SimpleNamespace + finish_reason).
+"""
+
+import json
+import pytest
+from types import SimpleNamespace
+
+from agent.anthropic_adapter import (
+    normalize_anthropic_response,
+    normalize_anthropic_response_v2,
+)
+from agent.transports.types import NormalizedResponse, ToolCall
+
+
+# ---------------------------------------------------------------------------
+# Helpers to build mock Anthropic SDK responses
+# ---------------------------------------------------------------------------
+
+def _text_block(text: str):
+    return SimpleNamespace(type="text", text=text)
+
+
+def _thinking_block(thinking: str, signature: str = "sig_abc"):
+    return SimpleNamespace(type="thinking", thinking=thinking, signature=signature)
+
+
+def _tool_use_block(id: str, name: str, input: dict):
+    return SimpleNamespace(type="tool_use", id=id, name=name, input=input)
+
+
+def _response(content_blocks, stop_reason="end_turn"):
+    return SimpleNamespace(
+        content=content_blocks,
+        stop_reason=stop_reason,
+        usage=SimpleNamespace(
+            input_tokens=10,
+            output_tokens=5,
+        ),
+    )
+
+
+# ---------------------------------------------------------------------------
+# Tests
+# ---------------------------------------------------------------------------
+
+class TestTextOnly:
+    """Text-only response — no tools, no thinking."""
+
+    def setup_method(self):
+        self.resp = _response([_text_block("Hello world")])
+        self.v1_msg, self.v1_finish = normalize_anthropic_response(self.resp)
+        self.v2 = normalize_anthropic_response_v2(self.resp)
+
+    def test_type(self):
+        assert isinstance(self.v2, NormalizedResponse)
+
+    def test_content_matches(self):
+        assert self.v2.content == self.v1_msg.content
+
+    def test_finish_reason_matches(self):
+        assert self.v2.finish_reason == self.v1_finish
+
+    def test_no_tool_calls(self):
+        assert self.v2.tool_calls is None
+        assert self.v1_msg.tool_calls is None
+
+    def test_no_reasoning(self):
+        assert self.v2.reasoning is None
+        assert self.v1_msg.reasoning is None
+
+
+class TestWithToolCalls:
+    """Response with tool calls."""
+
+    def setup_method(self):
+        self.resp = _response(
+            [
+                _text_block("I'll check that"),
+                _tool_use_block("toolu_abc", "terminal", {"command": "ls"}),
+                _tool_use_block("toolu_def", "read_file", {"path": "/tmp"}),
+            ],
+            stop_reason="tool_use",
+        )
+        self.v1_msg, self.v1_finish = normalize_anthropic_response(self.resp)
+        self.v2 = normalize_anthropic_response_v2(self.resp)
+
+    def test_finish_reason(self):
+        assert self.v2.finish_reason == "tool_calls"
+        assert self.v1_finish == "tool_calls"
+
+    def test_tool_call_count(self):
+        assert len(self.v2.tool_calls) == 2
+        assert len(self.v1_msg.tool_calls) == 2
+
+    def test_tool_call_ids_match(self):
+        for i in range(2):
+            assert self.v2.tool_calls[i].id == self.v1_msg.tool_calls[i].id
+
+    def test_tool_call_names_match(self):
+        assert self.v2.tool_calls[0].name == "terminal"
+        assert self.v2.tool_calls[1].name == "read_file"
+        for i in range(2):
+            assert self.v2.tool_calls[i].name == self.v1_msg.tool_calls[i].function.name
+
+    def test_tool_call_arguments_match(self):
+        for i in range(2):
+            assert self.v2.tool_calls[i].arguments == self.v1_msg.tool_calls[i].function.arguments
+
+    def test_content_preserved(self):
+        assert self.v2.content == self.v1_msg.content
+        assert "check that" in self.v2.content
+
+
+class TestWithThinking:
+    """Response with thinking blocks (Claude 3.5+ extended thinking)."""
+
+    def setup_method(self):
+        self.resp = _response([
+            _thinking_block("Let me think about this carefully..."),
+            _text_block("The answer is 42."),
+        ])
+        self.v1_msg, self.v1_finish = normalize_anthropic_response(self.resp)
+        self.v2 = normalize_anthropic_response_v2(self.resp)
+
+    def test_reasoning_matches(self):
+        assert self.v2.reasoning == self.v1_msg.reasoning
+        assert "think about this" in self.v2.reasoning
+
+    def test_reasoning_details_in_provider_data(self):
+        v1_details = self.v1_msg.reasoning_details
+        v2_details = self.v2.provider_data.get("reasoning_details") if self.v2.provider_data else None
+        assert v1_details is not None
+        assert v2_details is not None
+        assert len(v2_details) == len(v1_details)
+
+    def test_content_excludes_thinking(self):
+        assert self.v2.content == "The answer is 42."
+
+
+class TestMixed:
+    """Response with thinking + text + tool calls."""
+
+    def setup_method(self):
+        self.resp = _response(
+            [
+                _thinking_block("Planning my approach..."),
+                _text_block("I'll run the command"),
+                _tool_use_block("toolu_xyz", "terminal", {"command": "pwd"}),
+            ],
+            stop_reason="tool_use",
+        )
+        self.v1_msg, self.v1_finish = normalize_anthropic_response(self.resp)
+        self.v2 = normalize_anthropic_response_v2(self.resp)
+
+    def test_all_fields_present(self):
+        assert self.v2.content is not None
+        assert self.v2.tool_calls is not None
+        assert self.v2.reasoning is not None
+        assert self.v2.finish_reason == "tool_calls"
+
+    def test_content_matches(self):
+        assert self.v2.content == self.v1_msg.content
+
+    def test_reasoning_matches(self):
+        assert self.v2.reasoning == self.v1_msg.reasoning
+
+    def test_tool_call_matches(self):
+        assert self.v2.tool_calls[0].id == self.v1_msg.tool_calls[0].id
+        assert self.v2.tool_calls[0].name == self.v1_msg.tool_calls[0].function.name
+
+
+class TestStopReasons:
+    """Verify finish_reason mapping matches between v1 and v2."""
+
+    @pytest.mark.parametrize("stop_reason,expected", [
+        ("end_turn", "stop"),
+        ("tool_use", "tool_calls"),
+        ("max_tokens", "length"),
+        ("stop_sequence", "stop"),
+        ("refusal", "content_filter"),
+        ("model_context_window_exceeded", "length"),
+        ("unknown_future_reason", "stop"),
+    ])
+    def test_stop_reason_mapping(self, stop_reason, expected):
+        resp = _response([_text_block("x")], stop_reason=stop_reason)
+        v1_msg, v1_finish = normalize_anthropic_response(resp)
+        v2 = normalize_anthropic_response_v2(resp)
+        assert v2.finish_reason == v1_finish == expected
+
+
+class TestStripToolPrefix:
+    """Verify mcp_ prefix stripping works identically."""
+
+    def test_prefix_stripped(self):
+        resp = _response(
+            [_tool_use_block("toolu_1", "mcp_terminal", {"cmd": "ls"})],
+            stop_reason="tool_use",
+        )
+        v1_msg, _ = normalize_anthropic_response(resp, strip_tool_prefix=True)
+        v2 = normalize_anthropic_response_v2(resp, strip_tool_prefix=True)
+        assert v1_msg.tool_calls[0].function.name == "terminal"
+        assert v2.tool_calls[0].name == "terminal"
+
+    def test_prefix_kept(self):
+        resp = _response(
+            [_tool_use_block("toolu_1", "mcp_terminal", {"cmd": "ls"})],
+            stop_reason="tool_use",
+        )
+        v1_msg, _ = normalize_anthropic_response(resp, strip_tool_prefix=False)
+        v2 = normalize_anthropic_response_v2(resp, strip_tool_prefix=False)
+        assert v1_msg.tool_calls[0].function.name == "mcp_terminal"
+        assert v2.tool_calls[0].name == "mcp_terminal"
+
+
+class TestEdgeCases:
+    """Edge cases: empty content, no blocks, etc."""
+
+    def test_empty_content_blocks(self):
+        resp = _response([])
+        v1_msg, v1_finish = normalize_anthropic_response(resp)
+        v2 = normalize_anthropic_response_v2(resp)
+        assert v2.content == v1_msg.content
+        assert v2.content is None
+
+    def test_no_reasoning_details_means_none_provider_data(self):
+        resp = _response([_text_block("hi")])
+        v2 = normalize_anthropic_response_v2(resp)
+        assert v2.provider_data is None
+
+    def test_v2_returns_dataclass_not_namespace(self):
+        resp = _response([_text_block("hi")])
+        v2 = normalize_anthropic_response_v2(resp)
+        assert isinstance(v2, NormalizedResponse)
+        assert not isinstance(v2, SimpleNamespace)
diff --git a/tests/agent/transports/__init__.py b/tests/agent/transports/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/tests/agent/transports/test_types.py b/tests/agent/transports/test_types.py
new file mode 100644
index 000000000..0be18c688
--- /dev/null
+++ b/tests/agent/transports/test_types.py
@@ -0,0 +1,151 @@
+"""Tests for agent/transports/types.py — dataclass construction + helpers."""
+
+import json
+import pytest
+
+from agent.transports.types import (
+    NormalizedResponse,
+    ToolCall,
+    Usage,
+    build_tool_call,
+    map_finish_reason,
+)
+
+
+# ---------------------------------------------------------------------------
+# ToolCall
+# ---------------------------------------------------------------------------
+
+class TestToolCall:
+    def test_basic_construction(self):
+        tc = ToolCall(id="call_abc", name="terminal", arguments='{"cmd": "ls"}')
+        assert tc.id == "call_abc"
+        assert tc.name == "terminal"
+        assert tc.arguments == '{"cmd": "ls"}'
+        assert tc.provider_data is None
+
+    def test_none_id(self):
+        tc = ToolCall(id=None, name="read_file", arguments="{}")
+        assert tc.id is None
+
+    def test_provider_data(self):
+        tc = ToolCall(
+            id="call_x",
+            name="t",
+            arguments="{}",
+            provider_data={"call_id": "call_x", "response_item_id": "fc_x"},
+        )
+        assert tc.provider_data["call_id"] == "call_x"
+        assert tc.provider_data["response_item_id"] == "fc_x"
+
+
+# ---------------------------------------------------------------------------
+# Usage
+# ---------------------------------------------------------------------------
+
+class TestUsage:
+    def test_defaults(self):
+        u = Usage()
+        assert u.prompt_tokens == 0
+        assert u.completion_tokens == 0
+        assert u.total_tokens == 0
+        assert u.cached_tokens == 0
+
+    def test_explicit(self):
+        u = Usage(prompt_tokens=100, completion_tokens=50, total_tokens=150, cached_tokens=80)
+        assert u.total_tokens == 150
+
+
+# ---------------------------------------------------------------------------
+# NormalizedResponse
+# ---------------------------------------------------------------------------
+
+class TestNormalizedResponse:
+    def test_text_only(self):
+        r = NormalizedResponse(content="hello", tool_calls=None, finish_reason="stop")
+        assert r.content == "hello"
+        assert r.tool_calls is None
+        assert r.finish_reason == "stop"
+        assert r.reasoning is None
+        assert r.usage is None
+        assert r.provider_data is None
+
+    def test_with_tool_calls(self):
+        tcs = [ToolCall(id="call_1", name="terminal", arguments='{"cmd":"pwd"}')]
+        r = NormalizedResponse(content=None, tool_calls=tcs, finish_reason="tool_calls")
+        assert r.finish_reason == "tool_calls"
+        assert len(r.tool_calls) == 1
+        assert r.tool_calls[0].name == "terminal"
+
+    def test_with_reasoning(self):
+        r = NormalizedResponse(
+            content="answer",
+            tool_calls=None,
+            finish_reason="stop",
+            reasoning="I thought about it",
+        )
+        assert r.reasoning == "I thought about it"
+
+    def test_with_provider_data(self):
+        r = NormalizedResponse(
+            content=None,
+            tool_calls=None,
+            finish_reason="stop",
+            provider_data={"reasoning_details": [{"type": "thinking", "thinking": "hmm"}]},
+        )
+        assert r.provider_data["reasoning_details"][0]["type"] == "thinking"
+
+
+# ---------------------------------------------------------------------------
+# build_tool_call
+# ---------------------------------------------------------------------------
+
+class TestBuildToolCall:
+    def test_dict_arguments_serialized(self):
+        tc = build_tool_call(id="call_1", name="terminal", arguments={"cmd": "ls"})
+        assert tc.arguments == json.dumps({"cmd": "ls"})
+        assert tc.provider_data is None
+
+    def test_string_arguments_passthrough(self):
+        tc = build_tool_call(id="call_2", name="read_file", arguments='{"path": "/tmp"}')
+        assert tc.arguments == '{"path": "/tmp"}'
+
+    def test_provider_fields(self):
+        tc = build_tool_call(
+            id="call_3",
+            name="terminal",
+            arguments="{}",
+            call_id="call_3",
+            response_item_id="fc_3",
+        )
+        assert tc.provider_data == {"call_id": "call_3", "response_item_id": "fc_3"}
+
+    def test_none_id(self):
+        tc = build_tool_call(id=None, name="t", arguments="{}")
+        assert tc.id is None
+
+
+# ---------------------------------------------------------------------------
+# map_finish_reason
+# ---------------------------------------------------------------------------
+
+class TestMapFinishReason:
+    ANTHROPIC_MAP = {
+        "end_turn": "stop",
+        "tool_use": "tool_calls",
+        "max_tokens": "length",
+        "stop_sequence": "stop",
+        "refusal": "content_filter",
+    }
+
+    def test_known_reason(self):
+        assert map_finish_reason("end_turn", self.ANTHROPIC_MAP) == "stop"
+        assert map_finish_reason("tool_use", self.ANTHROPIC_MAP) == "tool_calls"
+        assert map_finish_reason("max_tokens", self.ANTHROPIC_MAP) == "length"
+        assert map_finish_reason("refusal", self.ANTHROPIC_MAP) == "content_filter"
+
+    def test_unknown_reason_defaults_to_stop(self):
+        assert map_finish_reason("something_new", self.ANTHROPIC_MAP) == "stop"
+
+    def test_none_reason(self):
+        assert map_finish_reason(None, self.ANTHROPIC_MAP) == "stop"