diff --git a/libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_file_search.py b/libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_file_search.py
index 40aeedd71bd..bb3340d9818 100644
--- a/libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_file_search.py
+++ b/libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_file_search.py
@@ -7,6 +7,9 @@ import pytest
 
 from langchain.agents.middleware.file_search import (
     FilesystemFileSearchMiddleware,
+    _expand_include_patterns,
+    _is_valid_include_pattern,
+    _match_include_pattern,
 )
 
 
@@ -259,3 +262,105 @@ class TestPathTraversalSecurity:
 
         assert result == "No matches found"
         assert "secret" not in result
+
+
+class TestExpandIncludePatterns:
+    """Tests for _expand_include_patterns helper function."""
+
+    def test_expand_patterns_basic_brace_expansion(self) -> None:
+        """Test basic brace expansion with multiple options."""
+        result = _expand_include_patterns("*.{py,txt}")
+        assert result == ["*.py", "*.txt"]
+
+    def test_expand_patterns_nested_braces(self) -> None:
+        """Test nested brace expansion."""
+        result = _expand_include_patterns("test.{a,b}.{c,d}")
+        assert result is not None
+        assert len(result) == 4
+        assert "test.a.c" in result
+        assert "test.b.d" in result
+
+    @pytest.mark.parametrize(
+        "pattern",
+        [
+            "*.py}",  # closing brace without opening
+            "*.{}",  # empty braces
+            "*.{py",  # unclosed brace
+        ],
+    )
+    def test_expand_patterns_invalid_braces(self, pattern: str) -> None:
+        """Test patterns with invalid brace syntax return None."""
+        result = _expand_include_patterns(pattern)
+        assert result is None
+
+
+class TestValidateIncludePattern:
+    """Tests for _is_valid_include_pattern helper function."""
+
+    @pytest.mark.parametrize(
+        "pattern",
+        [
+            "",  # empty pattern
+            "*.py\x00",  # null byte
+            "*.py\n",  # newline
+        ],
+    )
+    def test_validate_invalid_patterns(self, pattern: str) -> None:
+        """Test that invalid patterns are rejected."""
+        assert not _is_valid_include_pattern(pattern)
+
+
+class TestMatchIncludePattern:
+    """Tests for _match_include_pattern helper function."""
+
+    def test_match_pattern_with_braces(self) -> None:
+        """Test matching with brace expansion."""
+        assert _match_include_pattern("test.py", "*.{py,txt}")
+        assert _match_include_pattern("test.txt", "*.{py,txt}")
+        assert not _match_include_pattern("test.md", "*.{py,txt}")
+
+    def test_match_pattern_invalid_expansion(self) -> None:
+        """Test matching with pattern that cannot be expanded returns False."""
+        assert not _match_include_pattern("test.py", "*.{}")
+
+
+class TestGrepEdgeCases:
+    """Tests for edge cases in grep search."""
+
+    def test_grep_with_special_chars_in_pattern(self, tmp_path: Path) -> None:
+        """Test grep with special characters in pattern."""
+        (tmp_path / "test.py").write_text("def test():\n    pass\n", encoding="utf-8")
+
+        middleware = FilesystemFileSearchMiddleware(root_path=str(tmp_path), use_ripgrep=False)
+
+        result = middleware.grep_search.func(pattern="def.*:")
+
+        assert "/test.py" in result
+
+    def test_grep_case_insensitive(self, tmp_path: Path) -> None:
+        """Test grep with case-insensitive search."""
+        (tmp_path / "test.py").write_text("HELLO world\n", encoding="utf-8")
+
+        middleware = FilesystemFileSearchMiddleware(root_path=str(tmp_path), use_ripgrep=False)
+
+        result = middleware.grep_search.func(pattern="(?i)hello")
+
+        assert "/test.py" in result
+
+    def test_grep_with_large_file_skipping(self, tmp_path: Path) -> None:
+        """Test that grep skips files larger than max_file_size_mb."""
+        # Create a file larger than 1MB
+        large_content = "x" * (2 * 1024 * 1024)  # 2MB
+        (tmp_path / "large.txt").write_text(large_content, encoding="utf-8")
+        (tmp_path / "small.txt").write_text("x", encoding="utf-8")
+
+        middleware = FilesystemFileSearchMiddleware(
+            root_path=str(tmp_path),
+            use_ripgrep=False,
+            max_file_size_mb=1,  # 1MB limit
+        )
+
+        result = middleware.grep_search.func(pattern="x")
+
+        # Large file should be skipped
+        assert "/small.txt" in result
diff --git a/libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_shell_tool.py b/libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_shell_tool.py
index 37891df9412..e534d837a79 100644
--- a/libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_shell_tool.py
+++ b/libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_shell_tool.py
@@ -1,17 +1,21 @@
 from __future__ import annotations
 
-import time
+import asyncio
 import gc
 import tempfile
+import time
 from pathlib import Path
 
 import pytest
+from langchain_core.messages import AIMessage, ToolMessage
+from langchain_core.tools.base import ToolException
 
 from langchain.agents.middleware.shell_tool import (
     HostExecutionPolicy,
+    RedactionRule,
     ShellToolMiddleware,
     _SessionResources,
-    RedactionRule,
+    _ShellToolInput,
 )
 from langchain.agents.middleware.types import AgentState
 
@@ -173,3 +177,294 @@ def test_session_resources_finalizer_cleans_up(tmp_path: Path) -> None:
     assert not finalizer.alive
     assert session.stopped
     assert not tempdir_path.exists()
+
+
+def test_shell_tool_input_validation() -> None:
+    """Test _ShellToolInput validation rules."""
+    # Both command and restart not allowed
+    with pytest.raises(ValueError, match="only one"):
+        _ShellToolInput(command="ls", restart=True)
+
+    # Neither command nor restart provided
+    with pytest.raises(ValueError, match="requires either"):
+        _ShellToolInput()
+
+    # Valid: command only
+    valid_cmd = _ShellToolInput(command="ls")
+    assert valid_cmd.command == "ls"
+    assert not valid_cmd.restart
+
+    # Valid: restart only
+    valid_restart = _ShellToolInput(restart=True)
+    assert valid_restart.restart is True
+    assert valid_restart.command is None
+
+
+def test_normalize_shell_command_empty() -> None:
+    """Test that empty shell command raises an error."""
+    with pytest.raises(ValueError, match="at least one argument"):
+        ShellToolMiddleware(shell_command=[])
+
+
+def test_normalize_env_non_string_keys() -> None:
+    """Test that non-string environment keys raise an error."""
+    with pytest.raises(TypeError, match="must be strings"):
+        ShellToolMiddleware(env={123: "value"})  # type: ignore[dict-item]
+
+
+def test_normalize_env_coercion(tmp_path: Path) -> None:
+    """Test that environment values are coerced to strings."""
+    middleware = ShellToolMiddleware(
+        workspace_root=tmp_path / "workspace", env={"NUM": 42, "BOOL": True}
+    )
+    try:
+        state: AgentState = _empty_state()
+        updates = middleware.before_agent(state, None)
+        if updates:
+            state.update(updates)
+        resources = middleware._ensure_resources(state)  # type: ignore[attr-defined]
+        result = middleware._run_shell_tool(
+            resources, {"command": "echo $NUM $BOOL"}, tool_call_id=None
+        )
+        assert "42" in result
+        assert "True" in result
+    finally:
+        updates = middleware.after_agent(state, None)
+        if updates:
+            state.update(updates)
+
+
+def test_shell_tool_missing_command_string(tmp_path: Path) -> None:
+    """Test that shell tool raises an error when command is not a string."""
+    middleware = ShellToolMiddleware(workspace_root=tmp_path / "workspace")
+    try:
+        state: AgentState = _empty_state()
+        updates = middleware.before_agent(state, None)
+        if updates:
+            state.update(updates)
+        resources = middleware._ensure_resources(state)  # type: ignore[attr-defined]
+
+        with pytest.raises(ToolException, match="expects a 'command' string"):
+            middleware._run_shell_tool(resources, {"command": None}, tool_call_id=None)
+
+        with pytest.raises(ToolException, match="expects a 'command' string"):
+            middleware._run_shell_tool(
+                resources,
+                {"command": 123},  # type: ignore[dict-item]
+                tool_call_id=None,
+            )
+    finally:
+        updates = middleware.after_agent(state, None)
+        if updates:
+            state.update(updates)
+
+
+def test_tool_message_formatting_with_id(tmp_path: Path) -> None:
+    """Test that tool messages are properly formatted with tool_call_id."""
+    middleware = ShellToolMiddleware(workspace_root=tmp_path / "workspace")
+    try:
+        state: AgentState = _empty_state()
+        updates = middleware.before_agent(state, None)
+        if updates:
+            state.update(updates)
+        resources = middleware._ensure_resources(state)  # type: ignore[attr-defined]
+
+        result = middleware._run_shell_tool(
+            resources, {"command": "echo test"}, tool_call_id="test-id-123"
+        )
+
+        assert isinstance(result, ToolMessage)
+        assert result.tool_call_id == "test-id-123"
+        assert result.name == "shell"
+        assert result.status == "success"
+        assert "test" in result.content
+    finally:
+        updates = middleware.after_agent(state, None)
+        if updates:
+            state.update(updates)
+
+
+def test_nonzero_exit_code_returns_error(tmp_path: Path) -> None:
+    """Test that non-zero exit codes are marked as errors."""
+    middleware = ShellToolMiddleware(workspace_root=tmp_path / "workspace")
+    try:
+        state: AgentState = _empty_state()
+        updates = middleware.before_agent(state, None)
+        if updates:
+            state.update(updates)
+        resources = middleware._ensure_resources(state)  # type: ignore[attr-defined]
+
+        result = middleware._run_shell_tool(
+            resources,
+            {"command": "false"},  # Command that exits with 1 but doesn't kill shell
+            tool_call_id="test-id",
+        )
+
+        assert isinstance(result, ToolMessage)
+        assert result.status == "error"
+        assert "Exit code: 1" in result.content
+        assert result.artifact["exit_code"] == 1  # type: ignore[index]
+    finally:
+        updates = middleware.after_agent(state, None)
+        if updates:
+            state.update(updates)
+
+
+def test_truncation_by_bytes(tmp_path: Path) -> None:
+    """Test that output is truncated by bytes when max_output_bytes is exceeded."""
+    policy = HostExecutionPolicy(max_output_bytes=50, command_timeout=5.0)
+    middleware = ShellToolMiddleware(workspace_root=tmp_path / "workspace", execution_policy=policy)
+    try:
+        state: AgentState = _empty_state()
+        updates = middleware.before_agent(state, None)
+        if updates:
+            state.update(updates)
+        resources = middleware._ensure_resources(state)  # type: ignore[attr-defined]
+
+        result = middleware._run_shell_tool(
+            resources, {"command": "python3 -c 'print(\"x\" * 100)'"}, tool_call_id=None
+        )
+
+        assert "truncated at 50 bytes" in result.lower()
+    finally:
+        updates = middleware.after_agent(state, None)
+        if updates:
+            state.update(updates)
+
+
+def test_startup_command_failure(tmp_path: Path) -> None:
+    """Test that startup command failure raises an error."""
+    policy = HostExecutionPolicy(startup_timeout=1.0)
+    middleware = ShellToolMiddleware(
+        workspace_root=tmp_path / "workspace", startup_commands=("exit 1",), execution_policy=policy
+    )
+    state: AgentState = _empty_state()
+    with pytest.raises(RuntimeError, match="Startup command.*failed"):
+        middleware.before_agent(state, None)
+
+
+def test_shutdown_command_failure_logged(tmp_path: Path) -> None:
+    """Test that shutdown command failures are logged but don't raise."""
+    policy = HostExecutionPolicy(command_timeout=1.0)
+    middleware = ShellToolMiddleware(
+        workspace_root=tmp_path / "workspace",
+        shutdown_commands=("exit 1",),
+        execution_policy=policy,
+    )
+    try:
+        state: AgentState = _empty_state()
+        updates = middleware.before_agent(state, None)
+        if updates:
+            state.update(updates)
+    finally:
+        # Should not raise despite shutdown command failing
+        middleware.after_agent(state, None)
+
+
+def test_shutdown_command_timeout_logged(tmp_path: Path) -> None:
+    """Test that shutdown command timeouts are logged but don't raise."""
+    policy = HostExecutionPolicy(command_timeout=0.1)
+    middleware = ShellToolMiddleware(
+        workspace_root=tmp_path / "workspace",
+        execution_policy=policy,
+        shutdown_commands=("sleep 2",),
+    )
+    try:
+        state: AgentState = _empty_state()
+        updates = middleware.before_agent(state, None)
+        if updates:
+            state.update(updates)
+    finally:
+        # Should not raise despite shutdown command timing out
+        middleware.after_agent(state, None)
+
+
+def test_ensure_resources_missing_state(tmp_path: Path) -> None:
+    """Test that _ensure_resources raises when resources are missing."""
+    middleware = ShellToolMiddleware(workspace_root=tmp_path / "workspace")
+    state: AgentState = _empty_state()
+
+    with pytest.raises(ToolException, match="Shell session resources are unavailable"):
+        middleware._ensure_resources(state)  # type: ignore[attr-defined]
+
+
+def test_empty_output_replaced_with_no_output(tmp_path: Path) -> None:
+    """Test that empty command output is replaced with '<no output>'."""
+    middleware = ShellToolMiddleware(workspace_root=tmp_path / "workspace")
+    try:
+        state: AgentState = _empty_state()
+        updates = middleware.before_agent(state, None)
+        if updates:
+            state.update(updates)
+        resources = middleware._ensure_resources(state)  # type: ignore[attr-defined]
+
+        result = middleware._run_shell_tool(
+            resources,
+            {"command": "true"},  # Command that produces no output
+            tool_call_id=None,
+        )
+
+        assert "<no output>" in result
+    finally:
+        updates = middleware.after_agent(state, None)
+        if updates:
+            state.update(updates)
+
+
+def test_stderr_output_labeling(tmp_path: Path) -> None:
+    """Test that stderr output is properly labeled."""
+    middleware = ShellToolMiddleware(workspace_root=tmp_path / "workspace")
+    try:
+        state: AgentState = _empty_state()
+        updates = middleware.before_agent(state, None)
+        if updates:
+            state.update(updates)
+        resources = middleware._ensure_resources(state)  # type: ignore[attr-defined]
+
+        result = middleware._run_shell_tool(
+            resources, {"command": "echo error >&2"}, tool_call_id=None
+        )
+
+        assert "[stderr] error" in result
+    finally:
+        updates = middleware.after_agent(state, None)
+        if updates:
+            state.update(updates)
+
+
+@pytest.mark.parametrize(
+    ("startup_commands", "expected"),
+    [
+        ("echo test", ("echo test",)),  # String
+        (["echo test", "pwd"], ("echo test", "pwd")),  # List
+        (("echo test",), ("echo test",)),  # Tuple
+        (None, ()),  # None
+    ],
+)
+def test_normalize_commands_string_tuple_list(
+    tmp_path: Path,
+    startup_commands: str | list[str] | tuple[str, ...] | None,
+    expected: tuple[str, ...],
+) -> None:
+    """Test various command normalization formats."""
+    middleware = ShellToolMiddleware(
+        workspace_root=tmp_path / "workspace", startup_commands=startup_commands
+    )
+    assert middleware._startup_commands == expected  # type: ignore[attr-defined]
+
+
+def test_async_methods_delegate_to_sync(tmp_path: Path) -> None:
+    """Test that async methods properly delegate to sync methods."""
+    middleware = ShellToolMiddleware(workspace_root=tmp_path / "workspace")
+    try:
+        state: AgentState = _empty_state()
+
+        # Test abefore_agent
+        updates = asyncio.run(middleware.abefore_agent(state, None))
+        if updates:
+            state.update(updates)
+
+        # Test aafter_agent
+        asyncio.run(middleware.aafter_agent(state, None))
+    finally:
+        pass
diff --git a/libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_summarization.py b/libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_summarization.py
index b7a3943f2e7..84c67b0402c 100644
--- a/libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_summarization.py
+++ b/libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_summarization.py
@@ -1,11 +1,11 @@
 from typing import TYPE_CHECKING
+from unittest.mock import patch
 
 import pytest
 from langchain_core.language_models.chat_models import BaseChatModel
 from langchain_core.messages import AIMessage, AnyMessage, HumanMessage, RemoveMessage, ToolMessage
 from langchain_core.outputs import ChatGeneration, ChatResult
 from langgraph.graph.message import REMOVE_ALL_MESSAGES
-from unittest.mock import patch
 
 from langchain.agents.middleware.summarization import SummarizationMiddleware
 
@@ -15,6 +15,35 @@ if TYPE_CHECKING:
     from langchain_model_profiles import ModelProfile
 
 
+class MockChatModel(BaseChatModel):
+    """Mock chat model for testing."""
+
+    def invoke(self, prompt):  # type: ignore[no-untyped-def]
+        return AIMessage(content="Generated summary")
+
+    def _generate(self, messages, **kwargs):  # type: ignore[no-untyped-def]
+        return ChatResult(generations=[ChatGeneration(message=AIMessage(content="Summary"))])
+
+    @property
+    def _llm_type(self) -> str:
+        return "mock"
+
+
+class ProfileChatModel(BaseChatModel):
+    """Mock chat model with profile for testing."""
+
+    def _generate(self, messages, **kwargs):  # type: ignore[no-untyped-def]
+        return ChatResult(generations=[ChatGeneration(message=AIMessage(content="Summary"))])
+
+    @property
+    def _llm_type(self) -> str:
+        return "mock"
+
+    @property
+    def profile(self) -> "ModelProfile":
+        return {"max_input_tokens": 1000}
+
+
 def test_summarization_middleware_initialization() -> None:
     """Test SummarizationMiddleware initialization."""
     model = FakeToolCallingModel()
@@ -139,19 +168,7 @@ def test_summarization_middleware_tool_call_safety() -> None:
 
 def test_summarization_middleware_summary_creation() -> None:
     """Test SummarizationMiddleware summary creation."""
-
-    class MockModel(BaseChatModel):
-        def invoke(self, prompt):
-            return AIMessage(content="Generated summary")
-
-        def _generate(self, messages, **kwargs):
-            return ChatResult(generations=[ChatGeneration(message=AIMessage(content="Summary"))])
-
-        @property
-        def _llm_type(self):
-            return "mock"
-
-    middleware = SummarizationMiddleware(model=MockModel(), trigger=("tokens", 1000))
+    middleware = SummarizationMiddleware(model=MockChatModel(), trigger=("tokens", 1000))
 
     # Test normal summary creation
     messages = [HumanMessage(content="Hello"), AIMessage(content="Hi")]
@@ -180,25 +197,16 @@ def test_summarization_middleware_summary_creation() -> None:
 
     # Test we raise warning if max_tokens_before_summary or messages_to_keep is specified
     with pytest.warns(DeprecationWarning, match="max_tokens_before_summary is deprecated"):
-        SummarizationMiddleware(model=MockModel(), max_tokens_before_summary=500)
+        SummarizationMiddleware(model=MockChatModel(), max_tokens_before_summary=500)
     with pytest.warns(DeprecationWarning, match="messages_to_keep is deprecated"):
-        SummarizationMiddleware(model=MockModel(), messages_to_keep=5)
+        SummarizationMiddleware(model=MockChatModel(), messages_to_keep=5)
 
 
 def test_summarization_middleware_trim_limit_none_keeps_all_messages() -> None:
     """Verify disabling trim limit preserves full message sequence."""
-
-    class MockModel(BaseChatModel):
-        def _generate(self, messages, **kwargs):
-            return ChatResult(generations=[ChatGeneration(message=AIMessage(content="Summary"))])
-
-        @property
-        def _llm_type(self):
-            return "mock"
-
     messages = [HumanMessage(content=str(i)) for i in range(10)]
     middleware = SummarizationMiddleware(
-        model=MockModel(),
+        model=MockChatModel(),
         trim_tokens_to_summarize=None,
     )
     middleware.token_counter = lambda msgs: len(msgs)
@@ -209,23 +217,10 @@ def test_summarization_middleware_trim_limit_none_keeps_all_messages() -> None:
 
 def test_summarization_middleware_profile_inference_triggers_summary() -> None:
     """Ensure automatic profile inference triggers summarization when limits are exceeded."""
-
-    class ProfileModel(BaseChatModel):
-        def _generate(self, messages, **kwargs):
-            return ChatResult(generations=[ChatGeneration(message=AIMessage(content="Summary"))])
-
-        @property
-        def _llm_type(self) -> str:
-            return "mock"
-
-        @property
-        def profile(self) -> "ModelProfile":
-            return {"max_input_tokens": 1000}
-
     token_counter = lambda messages: len(messages) * 200
 
     middleware = SummarizationMiddleware(
-        model=ProfileModel(),
+        model=ProfileChatModel(),
         trigger=("fraction", 0.81),
         keep=("fraction", 0.5),
         token_counter=token_counter,
@@ -250,7 +245,7 @@ def test_summarization_middleware_profile_inference_triggers_summary() -> None:
     # Engage summarization
     # 0.80 * 1000 == 800 <= 800
     middleware = SummarizationMiddleware(
-        model=ProfileModel(),
+        model=ProfileChatModel(),
         trigger=("fraction", 0.80),
         keep=("fraction", 0.5),
         token_counter=token_counter,
@@ -270,7 +265,7 @@ def test_summarization_middleware_profile_inference_triggers_summary() -> None:
     # With keep=("fraction", 0.6) the target token allowance becomes 600,
     # so the cutoff shifts to keep the last three messages instead of two.
     middleware = SummarizationMiddleware(
-        model=ProfileModel(),
+        model=ProfileChatModel(),
         trigger=("fraction", 0.80),
         keep=("fraction", 0.6),
         token_counter=token_counter,
@@ -287,7 +282,7 @@ def test_summarization_middleware_profile_inference_triggers_summary() -> None:
     # context (target tokens = 800), so token-based retention keeps everything
     # and summarization is skipped entirely.
     middleware = SummarizationMiddleware(
-        model=ProfileModel(),
+        model=ProfileChatModel(),
         trigger=("fraction", 0.80),
         keep=("fraction", 0.8),
         token_counter=token_counter,
@@ -296,7 +291,7 @@ def test_summarization_middleware_profile_inference_triggers_summary() -> None:
 
     # Test with tokens_to_keep as absolute int value
     middleware_int = SummarizationMiddleware(
-        model=ProfileModel(),
+        model=ProfileChatModel(),
         trigger=("fraction", 0.80),
         keep=("tokens", 400),  # Keep exactly 400 tokens (2 messages)
         token_counter=token_counter,
@@ -310,7 +305,7 @@ def test_summarization_middleware_profile_inference_triggers_summary() -> None:
 
     # Test with tokens_to_keep as larger int value
     middleware_int_large = SummarizationMiddleware(
-        model=ProfileModel(),
+        model=ProfileChatModel(),
         trigger=("fraction", 0.80),
         keep=("tokens", 600),  # Keep 600 tokens (3 messages)
         token_counter=token_counter,
@@ -327,23 +322,11 @@ def test_summarization_middleware_profile_inference_triggers_summary() -> None:
 def test_summarization_middleware_token_retention_pct_respects_tool_pairs() -> None:
     """Ensure token retention keeps pairs together even if exceeding target tokens."""
 
-    class ProfileModel(BaseChatModel):
-        def _generate(self, messages, **kwargs):
-            return ChatResult(generations=[ChatGeneration(message=AIMessage(content="Summary"))])
-
-        @property
-        def _llm_type(self) -> str:
-            return "mock"
-
-        @property
-        def profile(self) -> "ModelProfile":
-            return {"max_input_tokens": 1000}
-
-    def token_counter(messages):
+    def token_counter(messages: list[AnyMessage]) -> int:
         return sum(len(getattr(message, "content", "")) for message in messages)
 
     middleware = SummarizationMiddleware(
-        model=ProfileModel(),
+        model=ProfileChatModel(),
         trigger=("fraction", 0.1),
         keep=("fraction", 0.5),
     )
@@ -400,22 +383,10 @@ def test_summarization_middleware_missing_profile() -> None:
 
 def test_summarization_middleware_full_workflow() -> None:
     """Test SummarizationMiddleware complete summarization workflow."""
-
-    class MockModel(BaseChatModel):
-        def invoke(self, prompt):
-            return AIMessage(content="Generated summary")
-
-        def _generate(self, messages, **kwargs):
-            return ChatResult(generations=[ChatGeneration(message=AIMessage(content="Summary"))])
-
-        @property
-        def _llm_type(self):
-            return "mock"
-
     with pytest.warns(DeprecationWarning):
         # keep test for functionality
         middleware = SummarizationMiddleware(
-            model=MockModel(), max_tokens_before_summary=1000, messages_to_keep=2
+            model=MockChatModel(), max_tokens_before_summary=1000, messages_to_keep=2
         )
 
     # Mock high token count to trigger summarization
@@ -504,21 +475,9 @@ async def test_summarization_middleware_full_workflow_async() -> None:
 
 def test_summarization_middleware_keep_messages() -> None:
     """Test SummarizationMiddleware with keep parameter specifying messages."""
-
-    class MockModel(BaseChatModel):
-        def invoke(self, prompt):
-            return AIMessage(content="Generated summary")
-
-        def _generate(self, messages, **kwargs):
-            return ChatResult(generations=[ChatGeneration(message=AIMessage(content="Summary"))])
-
-        @property
-        def _llm_type(self):
-            return "mock"
-
     # Test that summarization is triggered when message count reaches threshold
     middleware = SummarizationMiddleware(
-        model=MockModel(), trigger=("messages", 5), keep=("messages", 2)
+        model=MockChatModel(), trigger=("messages", 5), keep=("messages", 2)
     )
 
     # Below threshold - no summarization
@@ -561,6 +520,379 @@ def test_summarization_middleware_keep_messages() -> None:
     assert [message.content for message in result["messages"][2:]] == ["5", "6"]
 
     # Test with both parameters disabled
-    middleware_disabled = SummarizationMiddleware(model=MockModel(), trigger=None)
+    middleware_disabled = SummarizationMiddleware(model=MockChatModel(), trigger=None)
     result = middleware_disabled.before_model(state_above, None)
     assert result is None
+
+
+@pytest.mark.parametrize(
+    ("param_name", "param_value", "expected_error"),
+    [
+        ("trigger", ("fraction", 0.0), "Fractional trigger values must be between 0 and 1"),
+        ("trigger", ("fraction", 1.5), "Fractional trigger values must be between 0 and 1"),
+        ("keep", ("fraction", -0.1), "Fractional keep values must be between 0 and 1"),
+        ("trigger", ("tokens", 0), "trigger thresholds must be greater than 0"),
+        ("trigger", ("messages", -5), "trigger thresholds must be greater than 0"),
+        ("keep", ("tokens", 0), "keep thresholds must be greater than 0"),
+        ("trigger", ("invalid", 100), "Unsupported context size type"),
+        ("keep", ("invalid", 100), "Unsupported context size type"),
+    ],
+)
+def test_summarization_middleware_validation_edge_cases(
+    param_name: str, param_value: tuple[str, float | int], expected_error: str
+) -> None:
+    """Test validation of context size parameters with edge cases."""
+    model = FakeToolCallingModel()
+    with pytest.raises(ValueError, match=expected_error):
+        SummarizationMiddleware(model=model, **{param_name: param_value})
+
+
+def test_summarization_middleware_multiple_triggers() -> None:
+    """Test middleware with multiple trigger conditions."""
+    # Test with multiple triggers - should activate when ANY condition is met
+    middleware = SummarizationMiddleware(
+        model=MockChatModel(),
+        trigger=[("messages", 10), ("tokens", 500)],
+        keep=("messages", 2),
+    )
+
+    # Mock token counter to return low count
+    def mock_low_tokens(messages):
+        return 100
+
+    middleware.token_counter = mock_low_tokens
+
+    # Should not trigger - neither condition met
+    messages = [HumanMessage(content=str(i)) for i in range(5)]
+    state = {"messages": messages}
+    result = middleware.before_model(state, None)
+    assert result is None
+
+    # Should trigger - message count threshold met
+    messages = [HumanMessage(content=str(i)) for i in range(10)]
+    state = {"messages": messages}
+    result = middleware.before_model(state, None)
+    assert result is not None
+
+    # Test token trigger
+    def mock_high_tokens(messages):
+        return 600
+
+    middleware.token_counter = mock_high_tokens
+    messages = [HumanMessage(content=str(i)) for i in range(5)]
+    state = {"messages": messages}
+    result = middleware.before_model(state, None)
+    assert result is not None
+
+
+def test_summarization_middleware_profile_edge_cases() -> None:
+    """Test profile retrieval with various edge cases."""
+
+    class NoProfileModel(BaseChatModel):
+        def _generate(self, messages, **kwargs):
+            return ChatResult(generations=[ChatGeneration(message=AIMessage(content="Summary"))])
+
+        @property
+        def _llm_type(self):
+            return "mock"
+
+    # Model without profile attribute
+    middleware = SummarizationMiddleware(model=NoProfileModel(), trigger=("messages", 5))
+    assert middleware._get_profile_limits() is None
+
+    class InvalidProfileModel(BaseChatModel):
+        def _generate(self, messages, **kwargs):
+            return ChatResult(generations=[ChatGeneration(message=AIMessage(content="Summary"))])
+
+        @property
+        def _llm_type(self):
+            return "mock"
+
+        @property
+        def profile(self):
+            return "invalid_profile_type"
+
+    # Model with non-dict profile
+    middleware = SummarizationMiddleware(model=InvalidProfileModel(), trigger=("messages", 5))
+    assert middleware._get_profile_limits() is None
+
+    class MissingTokensModel(BaseChatModel):
+        def _generate(self, messages, **kwargs):
+            return ChatResult(generations=[ChatGeneration(message=AIMessage(content="Summary"))])
+
+        @property
+        def _llm_type(self):
+            return "mock"
+
+        @property
+        def profile(self):
+            return {"other_field": 100}
+
+    # Model with profile but no max_input_tokens
+    middleware = SummarizationMiddleware(model=MissingTokensModel(), trigger=("messages", 5))
+    assert middleware._get_profile_limits() is None
+
+    class InvalidTokenTypeModel(BaseChatModel):
+        def _generate(self, messages, **kwargs):
+            return ChatResult(generations=[ChatGeneration(message=AIMessage(content="Summary"))])
+
+        @property
+        def _llm_type(self):
+            return "mock"
+
+        @property
+        def profile(self):
+            return {"max_input_tokens": "not_an_int"}
+
+    # Model with non-int max_input_tokens
+    middleware = SummarizationMiddleware(model=InvalidTokenTypeModel(), trigger=("messages", 5))
+    assert middleware._get_profile_limits() is None
+
+
+def test_summarization_middleware_trim_messages_error_fallback() -> None:
+    """Test that trim_messages_for_summary falls back gracefully on errors."""
+    middleware = SummarizationMiddleware(model=MockChatModel(), trigger=("messages", 5))
+
+    # Create a mock token counter that raises an exception
+    def failing_token_counter(messages):
+        raise Exception("Token counting failed")
+
+    middleware.token_counter = failing_token_counter
+
+    # Should fall back to last 15 messages
+    messages = [HumanMessage(content=str(i)) for i in range(20)]
+    trimmed = middleware._trim_messages_for_summary(messages)
+    assert len(trimmed) == 15
+    assert trimmed == messages[-15:]
+
+
+def test_summarization_middleware_binary_search_edge_cases() -> None:
+    """Test binary search in _find_token_based_cutoff with edge cases."""
+    middleware = SummarizationMiddleware(
+        model=MockChatModel(), trigger=("messages", 5), keep=("tokens", 100)
+    )
+
+    # Test with single message that's too large
+    def token_counter_single_large(messages):
+        return len(messages) * 200
+
+    middleware.token_counter = token_counter_single_large
+
+    single_message = [HumanMessage(content="x" * 200)]
+    cutoff = middleware._find_token_based_cutoff(single_message)
+    assert cutoff == 0
+
+    # Test with empty messages
+    cutoff = middleware._find_token_based_cutoff([])
+    assert cutoff == 0
+
+    # Test when all messages fit within token budget
+    def token_counter_small(messages):
+        return len(messages) * 10
+
+    middleware.token_counter = token_counter_small
+    messages = [HumanMessage(content=str(i)) for i in range(5)]
+    cutoff = middleware._find_token_based_cutoff(messages)
+    assert cutoff == 0
+
+
+def test_summarization_middleware_tool_call_extraction_edge_cases() -> None:
+    """Test tool call ID extraction with various message formats."""
+    model = FakeToolCallingModel()
+    middleware = SummarizationMiddleware(model=model, trigger=("messages", 5))
+
+    # Test with dict-style tool calls
+    ai_message_dict = AIMessage(
+        content="test", tool_calls=[{"name": "tool1", "args": {}, "id": "id1"}]
+    )
+    ids = middleware._extract_tool_call_ids(ai_message_dict)
+    assert ids == {"id1"}
+
+    # Test with multiple tool calls
+    ai_message_multiple = AIMessage(
+        content="test",
+        tool_calls=[
+            {"name": "tool1", "args": {}, "id": "id1"},
+            {"name": "tool2", "args": {}, "id": "id2"},
+        ],
+    )
+    ids = middleware._extract_tool_call_ids(ai_message_multiple)
+    assert ids == {"id1", "id2"}
+
+    # Test with empty tool calls list
+    ai_message_empty = AIMessage(content="test", tool_calls=[])
+    ids = middleware._extract_tool_call_ids(ai_message_empty)
+    assert len(ids) == 0
+
+
+def test_summarization_middleware_complex_tool_pair_scenarios() -> None:
+    """Test complex tool call pairing scenarios."""
+    model = FakeToolCallingModel()
+    middleware = SummarizationMiddleware(model=model, trigger=("messages", 5), keep=("messages", 3))
+
+    # Test with multiple AI messages with tool calls
+    messages = [
+        HumanMessage(content="msg1"),
+        AIMessage(content="ai1", tool_calls=[{"name": "tool1", "args": {}, "id": "call1"}]),
+        ToolMessage(content="result1", tool_call_id="call1"),
+        HumanMessage(content="msg2"),
+        AIMessage(content="ai2", tool_calls=[{"name": "tool2", "args": {}, "id": "call2"}]),
+        ToolMessage(content="result2", tool_call_id="call2"),
+        HumanMessage(content="msg3"),
+    ]
+
+    # Test cutoff at index 1 - unsafe (separates first AI/Tool pair)
+    assert not middleware._is_safe_cutoff_point(messages, 2)
+
+    # Test cutoff at index 3 - safe (keeps first pair together)
+    assert middleware._is_safe_cutoff_point(messages, 3)
+
+    # Test cutoff at index 5 - unsafe (separates second AI/Tool pair)
+    assert not middleware._is_safe_cutoff_point(messages, 5)
+
+    # Test _cutoff_separates_tool_pair directly
+    assert middleware._cutoff_separates_tool_pair(messages, 1, 2, {"call1"})
+    assert not middleware._cutoff_separates_tool_pair(messages, 1, 0, {"call1"})
+    assert not middleware._cutoff_separates_tool_pair(messages, 1, 3, {"call1"})
+
+
+def test_summarization_middleware_tool_call_in_search_range() -> None:
+    """Test tool call safety with messages at edge of search range."""
+    model = FakeToolCallingModel()
+    middleware = SummarizationMiddleware(
+        model=model, trigger=("messages", 10), keep=("messages", 2)
+    )
+
+    # Create messages with tool pair separated by some distance
+    # Search range is 5, so messages within 5 positions of cutoff are checked
+    messages = [
+        HumanMessage(content="msg1"),
+        HumanMessage(content="msg2"),
+        AIMessage(content="ai", tool_calls=[{"name": "tool", "args": {}, "id": "call1"}]),
+        HumanMessage(content="msg3"),
+        HumanMessage(content="msg4"),
+        ToolMessage(content="result", tool_call_id="call1"),
+        HumanMessage(content="msg6"),
+    ]
+
+    # Cutoff at index 3 would separate: [0,1,2] from [3,4,5,6]
+    # AI at index 2 is before cutoff, Tool at index 5 is after cutoff - unsafe
+    assert not middleware._is_safe_cutoff_point(messages, 3)
+
+    # Cutoff at index 6 keeps AI and Tool both in summarized section
+    assert middleware._is_safe_cutoff_point(messages, 6)
+
+    # Cutoff at index 0 or 1 also safe - both AI and Tool in preserved section
+    assert middleware._is_safe_cutoff_point(messages, 0)
+    assert middleware._is_safe_cutoff_point(messages, 1)
+
+
+def test_summarization_middleware_zero_and_negative_target_tokens() -> None:
+    """Test handling of edge cases with target token calculations."""
+    # Test with very small fraction that rounds to zero
+    middleware = SummarizationMiddleware(
+        model=ProfileChatModel(), trigger=("fraction", 0.0001), keep=("fraction", 0.0001)
+    )
+
+    # Should set threshold to 1 when calculated value is <= 0
+    messages = [HumanMessage(content="test")]
+    state = {"messages": messages}
+
+    # The trigger fraction calculation: int(1000 * 0.0001) = 0, but should be set to 1
+    # Token count of 1 message should exceed threshold of 1
+    def token_counter(msgs):
+        return 2
+
+    middleware.token_counter = token_counter
+    assert middleware._should_summarize(messages, 2)
+
+
+async def test_summarization_middleware_async_error_handling() -> None:
+    """Test async summary creation with errors."""
+
+    class ErrorAsyncModel(BaseChatModel):
+        def _generate(self, messages, **kwargs):
+            return ChatResult(generations=[ChatGeneration(message=AIMessage(content="Summary"))])
+
+        async def _agenerate(self, messages, **kwargs):
+            raise Exception("Async model error")
+
+        @property
+        def _llm_type(self):
+            return "mock"
+
+    middleware = SummarizationMiddleware(model=ErrorAsyncModel(), trigger=("messages", 5))
+    messages = [HumanMessage(content="test")]
+    summary = await middleware._acreate_summary(messages)
+    assert "Error generating summary: Async model error" in summary
+
+
+def test_summarization_middleware_cutoff_at_boundary() -> None:
+    """Test cutoff index determination at exact message boundaries."""
+    middleware = SummarizationMiddleware(
+        model=MockChatModel(), trigger=("messages", 5), keep=("messages", 5)
+    )
+
+    # When we want to keep exactly as many messages as we have
+    messages = [HumanMessage(content=str(i)) for i in range(5)]
+    cutoff = middleware._find_safe_cutoff(messages, 5)
+    assert cutoff == 0  # Should not cut anything
+
+    # When we want to keep more messages than we have
+    cutoff = middleware._find_safe_cutoff(messages, 10)
+    assert cutoff == 0
+
+
+def test_summarization_middleware_deprecated_parameters_with_defaults() -> None:
+    """Test that deprecated parameters work correctly with default values."""
+    # Test that deprecated max_tokens_before_summary is ignored when trigger is set
+    with pytest.warns(DeprecationWarning):
+        middleware = SummarizationMiddleware(
+            model=MockChatModel(), trigger=("tokens", 2000), max_tokens_before_summary=1000
+        )
+    assert middleware.trigger == ("tokens", 2000)
+
+    # Test that messages_to_keep is ignored when keep is not default
+    with pytest.warns(DeprecationWarning):
+        middleware = SummarizationMiddleware(
+            model=MockChatModel(), keep=("messages", 5), messages_to_keep=10
+        )
+    assert middleware.keep == ("messages", 5)
+
+
+def test_summarization_middleware_fraction_trigger_with_no_profile() -> None:
+    """Test fractional trigger condition when profile data becomes unavailable."""
+    middleware = SummarizationMiddleware(
+        model=ProfileChatModel(),
+        trigger=[("fraction", 0.5), ("messages", 100)],
+        keep=("messages", 5),
+    )
+
+    # Test that when fractional condition can't be evaluated, other triggers still work
+    messages = [HumanMessage(content=str(i)) for i in range(100)]
+
+    # Mock _get_profile_limits to return None
+    original_method = middleware._get_profile_limits
+    middleware._get_profile_limits = lambda: None
+
+    # Should still trigger based on message count
+    state = {"messages": messages}
+    result = middleware.before_model(state, None)
+    assert result is not None
+
+    # Restore original method
+    middleware._get_profile_limits = original_method
+
+
+def test_summarization_middleware_is_safe_cutoff_at_end() -> None:
+    """Test _is_safe_cutoff_point when cutoff is at or past the end."""
+    model = FakeToolCallingModel()
+    middleware = SummarizationMiddleware(model=model, trigger=("messages", 5))
+
+    messages = [HumanMessage(content=str(i)) for i in range(5)]
+
+    # Cutoff at exactly the length should be safe
+    assert middleware._is_safe_cutoff_point(messages, len(messages))
+
+    # Cutoff past the length should also be safe
+    assert middleware._is_safe_cutoff_point(messages, len(messages) + 5)
diff --git a/libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_tool_selection.py b/libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_tool_selection.py
index 031bb60fe2d..1a8c6422453 100644
--- a/libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_tool_selection.py
+++ b/libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_tool_selection.py
@@ -1,22 +1,22 @@
 """Unit tests for LLM tool selection middleware."""
 
 import typing
-from typing import Union, Any, Literal
-
 from itertools import cycle
+from typing import Any, Literal, Union
+
+import pytest
 from pydantic import BaseModel
 
 from langchain.agents import create_agent
-from langchain.agents.middleware import AgentState, ModelRequest, wrap_model_call
-from langchain.agents.middleware import LLMToolSelectorMiddleware
+from langchain.agents.middleware import LLMToolSelectorMiddleware, ModelRequest, wrap_model_call
+from langchain.agents.middleware.tool_selection import _create_tool_selection_response
+from langchain.agents.middleware.types import AgentState
 from langchain.messages import AIMessage
 from langchain_core.language_models import LanguageModelInput
 from langchain_core.language_models.fake_chat_models import GenericFakeChatModel
-from langchain_core.messages import BaseMessage
-from langchain_core.messages import HumanMessage
+from langchain_core.messages import BaseMessage, HumanMessage
 from langchain_core.runnables import Runnable
-from langchain_core.tools import BaseTool
-from langchain_core.tools import tool
+from langchain_core.tools import BaseTool, tool
 
 
 @tool
@@ -596,3 +596,12 @@ class TestDuplicateAndInvalidTools:
             assert len(tool_names) == 2
             assert "get_weather" in tool_names
             assert "search_web" in tool_names
+
+
+class TestEdgeCases:
+    """Test edge cases and error handling."""
+
+    def test_empty_tools_list_raises_error(self) -> None:
+        """Test that empty tools list raises an error in schema creation."""
+        with pytest.raises(AssertionError, match="tools must be non-empty"):
+            _create_tool_selection_response([])