refactor: extract shared error hierarchy + Session into idatui/errors.py

The IDAError/IDAConnectionError/IDAToolError/... exceptions and the Session
dataclass were defined in client.py (the ida-pro-mcp HTTP client), but the idalib
worker path (worker_client/domain/app) needs them without the HTTP transport.
Move them to a transport-agnostic errors.py; client.py re-exports them so the
deprecated mcp tooling and stress tests are unchanged (verified:
errors.IDAToolError IS client.IDAToolError, so cross-module `except` still works).

worker_client, domain (TYPE_CHECKING-guarded IDAClient hint), app, and __init__
now import the shared types from errors.py. This decouples the worker path from
client.py at runtime -- the prerequisite for deleting the mcp transport.

6 files changed, 99 insertions, 69 deletions

diff --git a/idatui/__init__.py b/idatui/__init__.py
index a52ba8b..92d8b5d 100644
--- a/idatui/__init__.py
+++ b/idatui/__init__.py
@@ -1,7 +1,6 @@
 """idatui — a minimal keyboard-first TUI for IDA Pro over ida-pro-mcp (idalib)."""
 
-from .client import (
-    IDAClient,
+from .errors import (
     IDAError,
     IDAConnectionError,
     IDATimeoutError,
@@ -10,8 +9,8 @@ from .client import (
     IDAToolError,
     IDASessionError,
     Session,
-    KeepAlive,
 )
+from .client import IDAClient, KeepAlive  # deprecated mcp transport
 from .domain import (
     Program,
     FunctionIndex,
diff --git a/idatui/app.py b/idatui/app.py
index 1936153..712b4de 100644
--- a/idatui/app.py
+++ b/idatui/app.py
@@ -42,7 +42,8 @@ from textual.widgets.option_list import Option
 
 from .highlight import highlight_c
 
-from .client import IDAClient, IDAToolError, IDAConnectionError
+from .errors import IDAToolError, IDAConnectionError
+from .client import IDAClient  # deprecated mcp transport (worker path uses WorkerClient)
 from .domain import DisasmModel, Func, Head, ListingModel, Program, Struct
 
 # Styles for the disassembly listing.
diff --git a/idatui/client.py b/idatui/client.py
index f39a10d..2f74cbe 100644
--- a/idatui/client.py
+++ b/idatui/client.py
@@ -66,68 +66,19 @@ SESSION_AGNOSTIC_TOOLS = frozenset({"idb_list", "idb_open", "int_convert"})
 _STALE_SESSION_MARKERS = ("session not found", "database is required")
 
 
-# --------------------------------------------------------------------------- #
-# Exceptions
-# --------------------------------------------------------------------------- #
-class IDAError(Exception):
-    """Base class for all client errors."""
-
-
-class IDAConnectionError(IDAError):
-    """The transport could not be established or was lost."""
-
-
-class IDATimeoutError(IDAError):
-    """A request exceeded its deadline."""
-
-
-class IDAProtocolError(IDAError):
-    """Malformed or unexpected HTTP / JSON-RPC framing."""
-
-
-class IDARPCError(IDAError):
-    """The JSON-RPC envelope carried an ``error`` object."""
-
-    def __init__(self, code: int, message: str, data: Any = None):
-        super().__init__(f"JSON-RPC error {code}: {message}")
-        self.code = code
-        self.message = message
-        self.data = data
-
-
-class IDAToolError(IDAError):
-    """A tool call returned ``result.isError == true`` (a hard failure)."""
-
-    def __init__(self, tool: str, message: str):
-        super().__init__(f"tool {tool!r} failed: {message}")
-        self.tool = tool
-        self.message = message
-
-
-class IDASessionError(IDAError):
-    """No IDB session is open, or several are and none was pinned."""
-
-
-# --------------------------------------------------------------------------- #
-# Session model
-# --------------------------------------------------------------------------- #
-@dataclass(frozen=True)
-class Session:
-    session_id: str
-    filename: str
-    input_path: str
-    is_active: bool = False
-    is_analyzing: bool = False
-
-    @classmethod
-    def from_dict(cls, d: dict) -> "Session":
-        return cls(
-            session_id=d.get("session_id", ""),
-            filename=d.get("filename", ""),
-            input_path=d.get("input_path", ""),
-            is_active=bool(d.get("is_active", False)),
-            is_analyzing=bool(d.get("is_analyzing", False)),
-        )
+# The error hierarchy and Session model now live in errors.py (transport-
+# agnostic, shared with the idalib worker path); re-exported here so the
+# deprecated mcp tooling and the stress tests keep importing them from client.
+from .errors import (  # noqa: E402,F401
+    IDAError,
+    IDAConnectionError,
+    IDATimeoutError,
+    IDAProtocolError,
+    IDARPCError,
+    IDAToolError,
+    IDASessionError,
+    Session,
+)
 
 
 # --------------------------------------------------------------------------- #
diff --git a/idatui/domain.py b/idatui/domain.py
index 2a3fc2b..4f72f5b 100644
--- a/idatui/domain.py
+++ b/idatui/domain.py
@@ -28,9 +28,12 @@ import threading
 import urllib.request
 from concurrent.futures import ThreadPoolExecutor
 from dataclasses import dataclass, field, replace
-from typing import Callable
+from typing import Callable, TYPE_CHECKING
 
-from .client import IDAClient, IDAToolError
+from .errors import IDAToolError
+
+if TYPE_CHECKING:  # type hint only; the runtime client is mcp IDAClient or worker
+    from .client import IDAClient  # noqa: F401
 
 # Clamps derived from measured caps (list ~700, disasm ~500). Margin included.
 LIST_PAGE = 500
diff --git a/idatui/errors.py b/idatui/errors.py
new file mode 100644
index 0000000..29b09ae
--- /dev/null
+++ b/idatui/errors.py
@@ -0,0 +1,76 @@
+"""Transport-agnostic error hierarchy and the Session model.
+
+These were originally defined in client.py (the ida-pro-mcp HTTP client), but the
+idalib worker path (worker_client / domain / app) needs the same exception types
+and Session dataclass without dragging in the HTTP transport. They live here so
+both backends share one definition; client.py re-exports them for backwards
+compatibility with the (deprecated) mcp tooling and the stress tests.
+"""
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Any
+
+
+# --------------------------------------------------------------------------- #
+# Exceptions
+# --------------------------------------------------------------------------- #
+class IDAError(Exception):
+    """Base class for all client errors."""
+
+
+class IDAConnectionError(IDAError):
+    """The transport could not be established or was lost."""
+
+
+class IDATimeoutError(IDAError):
+    """A request exceeded its deadline."""
+
+
+class IDAProtocolError(IDAError):
+    """Malformed or unexpected HTTP / JSON-RPC framing."""
+
+
+class IDARPCError(IDAError):
+    """The JSON-RPC envelope carried an ``error`` object."""
+
+    def __init__(self, code: int, message: str, data: Any = None):
+        super().__init__(f"JSON-RPC error {code}: {message}")
+        self.code = code
+        self.message = message
+        self.data = data
+
+
+class IDAToolError(IDAError):
+    """A tool call returned ``result.isError == true`` (a hard failure)."""
+
+    def __init__(self, tool: str, message: str):
+        super().__init__(f"tool {tool!r} failed: {message}")
+        self.tool = tool
+        self.message = message
+
+
+class IDASessionError(IDAError):
+    """No IDB session is open, or several are and none was pinned."""
+
+
+# --------------------------------------------------------------------------- #
+# Session model
+# --------------------------------------------------------------------------- #
+@dataclass(frozen=True)
+class Session:
+    session_id: str
+    filename: str
+    input_path: str
+    is_active: bool = False
+    is_analyzing: bool = False
+
+    @classmethod
+    def from_dict(cls, d: dict) -> "Session":
+        return cls(
+            session_id=d.get("session_id", ""),
+            filename=d.get("filename", ""),
+            input_path=d.get("input_path", ""),
+            is_active=bool(d.get("is_active", False)),
+            is_analyzing=bool(d.get("is_analyzing", False)),
+        )
diff --git a/idatui/worker_client.py b/idatui/worker_client.py
index 8dd8491..27fa660 100644
--- a/idatui/worker_client.py
+++ b/idatui/worker_client.py
@@ -23,7 +23,7 @@ import time
 import uuid
 from typing import Any
 
-from .client import IDAToolError, IDAConnectionError, Session
+from .errors import IDAToolError, IDAConnectionError, Session
 from .worker import recv as _recv
 from .worker import send as _send