diff --git a/conductor/tracks/external_editor_integration_20260308/plan.md b/conductor/tracks/external_editor_integration_20260308/plan.md
index 74c3d1e..d3ca8eb 100644
--- a/conductor/tracks/external_editor_integration_20260308/plan.md
+++ b/conductor/tracks/external_editor_integration_20260308/plan.md
@@ -1,12 +1,12 @@
 # Implementation Plan: External Text Editor Integration for Approvals
 
 ## Phase 1: Configuration & Data Modeling
-- [ ] Task: Define the schema for external editor configuration.
-    - [ ] Update `src/models.py` (or equivalent configuration parsing logic) to include a `text_editors` dictionary and `default_editor` string.
-- [ ] Task: Integrate configuration parsing.
-    - [ ] Update `config.toml` loading to support a `[tools.text_editors]` section mapping names to paths/commands.
-    - [ ] Update `manual_slop.toml` loading to support a project-level `default_editor` override.
-- [ ] Task: Conductor - User Manual Verification 'Phase 1: Configuration & Data Modeling' (Protocol in workflow.md)
+- [x] Task: Define the schema for external editor configuration.
+    - [x] Update `src/models.py` (or equivalent configuration parsing logic) to include a `text_editors` dictionary and `default_editor` string.
+- [x] Task: Integrate configuration parsing.
+    - [x] Update `config.toml` loading to support a `[tools.text_editors]` section mapping names to paths/commands.
+    - [x] Update `manual_slop.toml` loading to support a project-level `default_editor` override.
+- [x] Task: Conductor - User Manual Verification 'Phase 1: Configuration & Data Modeling' (Protocol in workflow.md)
 
 ## Phase 2: Editor Launch Logic
 - [ ] Task: Implement the `ExternalEditorLauncher` utility.
diff --git a/src/external_editor.py b/src/external_editor.py
new file mode 100644
index 0000000..4ce4d08
--- /dev/null
+++ b/src/external_editor.py
@@ -0,0 +1,76 @@
+"""External Editor Launcher - Opens files in external text editors for diff viewing."""
+from __future__ import annotations
+
+import subprocess
+import tempfile
+from pathlib import Path
+from typing import Optional, List
+
+from src.models import ExternalEditorConfig, TextEditorConfig
+
+
+class ExternalEditorLauncher:
+    def __init__(self, config: ExternalEditorConfig):
+        self.config = config
+
+    def get_editor(self, editor_name: Optional[str] = None) -> Optional[TextEditorConfig]:
+        if editor_name:
+            return self.config.editors.get(editor_name)
+        return self.config.get_default()
+
+    def build_diff_command(
+        self, editor: TextEditorConfig, original_path: str, modified_path: str
+    ) -> List[str]:
+        cmd = [editor.path] + editor.diff_args + [original_path, modified_path]
+        return cmd
+
+    def launch_diff(
+        self, editor_name: Optional[str], original_path: str, modified_path: str
+    ) -> Optional[subprocess.Popen]:
+        editor = self.get_editor(editor_name)
+        if not editor:
+            return None
+        cmd = self.build_diff_command(editor, original_path, modified_path)
+        try:
+            return subprocess.Popen(cmd)
+        except FileNotFoundError:
+            return None
+
+    def launch_editor(self, editor_name: Optional[str], file_path: str) -> Optional[subprocess.Popen]:
+        editor = self.get_editor(editor_name)
+        if not editor:
+            return None
+        try:
+            return subprocess.Popen([editor.path, file_path])
+        except FileNotFoundError:
+            return None
+
+
+def get_default_launcher() -> ExternalEditorLauncher:
+    from src import models
+    config = models.load_config()
+    editors_config = config.get("tools", {}).get("text_editors", {})
+    default_editor = config.get("tools", {}).get("default_editor")
+    ext_config = ExternalEditorConfig.from_dict({
+        "editors": editors_config,
+        "default_editor": default_editor,
+    })
+    return ExternalEditorLauncher(ext_config)
+
+
+def resolve_project_editor_override(project_path: Optional[str]) -> Optional[str]:
+    if not project_path:
+        return None
+    from src import models
+    try:
+        proj = models.load_project(project_path)
+        return proj.get("default_editor")
+    except Exception:
+        return None
+
+
+def create_temp_modified_file(content: str) -> str:
+    with tempfile.NamedTemporaryFile(mode="w", suffix="_modified", delete=False, encoding="utf-8") as f:
+        f.write(content)
+        return f.name
+pass
diff --git a/src/models.py b/src/models.py
index 02684e0..c96933a 100644
--- a/src/models.py
+++ b/src/models.py
@@ -284,6 +284,8 @@ class WorkerContext:
  persona_id: Optional[str] = None
 
 
+@dataclass
+@dataclass
 @dataclass
 class Metadata:
  id: str
@@ -324,6 +326,114 @@ class Metadata:
   )
 
 
+@dataclass
+class TextEditorConfig:
+ name: str
+ path: str
+ diff_args: List[str] = field(default_factory=list)
+
+ def to_dict(self) -> Dict[str, Any]:
+  return {
+   "name": self.name,
+   "path": self.path,
+   "diff_args": self.diff_args,
+  }
+
+ @classmethod
+ def from_dict(cls, data: Dict[str, Any]) -> "TextEditorConfig":
+  return cls(
+   name=data["name"],
+   path=data["path"],
+   diff_args=data.get("diff_args", []),
+  )
+
+
+@dataclass
+class ExternalEditorConfig:
+ editors: Dict[str, TextEditorConfig] = field(default_factory=dict)
+ default_editor: Optional[str] = None
+
+ def get_default(self) -> Optional[TextEditorConfig]:
+  if self.default_editor and self.default_editor in self.editors:
+   return self.editors[self.default_editor]
+  if self.editors:
+   return next(iter(self.editors.values()))
+  return None
+
+ def to_dict(self) -> Dict[str, Any]:
+  return {
+   "editors": {k: v.to_dict() for k, v in self.editors.items()},
+   "default_editor": self.default_editor,
+  }
+
+ @classmethod
+ def from_dict(cls, data: Dict[str, Any]) -> "ExternalEditorConfig":
+  editors = {}
+  for name, ed_data in data.get("editors", {}).items():
+   if isinstance(ed_data, dict):
+    editors[name] = TextEditorConfig.from_dict(ed_data)
+   elif isinstance(ed_data, str):
+    editors[name] = TextEditorConfig(name=name, path=ed_data)
+  return cls(
+   editors=editors,
+   default_editor=data.get("default_editor"),
+  )
+
+
+@dataclass
+class TextEditorConfig:
+ name: str
+ path: str
+ diff_args: List[str] = field(default_factory=list)
+
+ def to_dict(self) -> Dict[str, Any]:
+  return {
+   "name": self.name,
+   "path": self.path,
+   "diff_args": self.diff_args,
+  }
+
+ @classmethod
+ def from_dict(cls, data: Dict[str, Any]) -> "TextEditorConfig":
+  return cls(
+   name=data["name"],
+   path=data["path"],
+   diff_args=data.get("diff_args", []),
+  )
+
+
+@dataclass
+class ExternalEditorConfig:
+ editors: Dict[str, TextEditorConfig] = field(default_factory=dict)
+ default_editor: Optional[str] = None
+
+ def get_default(self) -> Optional[TextEditorConfig]:
+  if self.default_editor and self.default_editor in self.editors:
+   return self.editors[self.default_editor]
+  if self.editors:
+   return next(iter(self.editors.values()))
+  return None
+
+ def to_dict(self) -> Dict[str, Any]:
+  return {
+   "editors": {k: v.to_dict() for k, v in self.editors.items()},
+   "default_editor": self.default_editor,
+  }
+
+ @classmethod
+ def from_dict(cls, data: Dict[str, Any]) -> "ExternalEditorConfig":
+  editors = {}
+  for name, ed_data in data.get("editors", {}).items():
+   if isinstance(ed_data, dict):
+    editors[name] = TextEditorConfig.from_dict(ed_data)
+   elif isinstance(ed_data, str):
+    editors[name] = TextEditorConfig(name=name, path=ed_data)
+  return cls(
+   editors=editors,
+   default_editor=data.get("default_editor"),
+  )
+
+
 @dataclass
 class TrackState:
  metadata: Metadata
diff --git a/tests/test_external_editor.py b/tests/test_external_editor.py
new file mode 100644
index 0000000..1c6da6c
--- /dev/null
+++ b/tests/test_external_editor.py
@@ -0,0 +1,130 @@
+"""Tests for external editor integration."""
+import pytest
+from unittest.mock import patch, MagicMock
+from src.models import TextEditorConfig, ExternalEditorConfig
+from src.external_editor import (
+    ExternalEditorLauncher,
+    get_default_launcher,
+    resolve_project_editor_override,
+    create_temp_modified_file,
+)
+
+
+@pytest.fixture
+def vscode_editor():
+    return TextEditorConfig(name="vscode", path="C:\\path\\to\\code.exe", diff_args=["--diff"])
+
+
+@pytest.fixture
+def notepadpp_editor():
+    return TextEditorConfig(name="notepad++", path="C:\\path\\to\\notepad++.exe", diff_args=["-multiInst", "-nosession"])
+
+
+@pytest.fixture
+def ext_config(vscode_editor, notepadpp_editor):
+    return ExternalEditorConfig(
+        editors={"vscode": vscode_editor, "notepad++": notepadpp_editor},
+        default_editor="vscode",
+    )
+
+
+@pytest.fixture
+def launcher(ext_config):
+    return ExternalEditorLauncher(ext_config)
+
+
+class TestTextEditorConfig:
+    def test_from_dict_with_diff_args(self):
+        data = {"name": "vscode", "path": "C:\\code.exe", "diff_args": ["--diff"]}
+        editor = TextEditorConfig.from_dict(data)
+        assert editor.name == "vscode"
+        assert editor.path == "C:\\code.exe"
+        assert editor.diff_args == ["--diff"]
+
+    def test_from_dict_without_diff_args(self):
+        data = {"name": "vscode", "path": "C:\\code.exe"}
+        editor = TextEditorConfig.from_dict(data)
+        assert editor.diff_args == []
+
+    def test_to_dict(self, vscode_editor):
+        result = vscode_editor.to_dict()
+        assert result["name"] == "vscode"
+        assert result["path"] == "C:\\path\\to\\code.exe"
+        assert result["diff_args"] == ["--diff"]
+
+
+class TestExternalEditorConfig:
+    def test_from_dict_with_string_editors(self):
+        data = {"editors": {"vscode": "C:\\code.exe"}, "default_editor": "vscode"}
+        config = ExternalEditorConfig.from_dict(data)
+        assert "vscode" in config.editors
+        assert config.editors["vscode"].path == "C:\\code.exe"
+
+    def test_from_dict_with_dict_editors(self, vscode_editor):
+        data = {"editors": {"vscode": {"name": "vscode", "path": "C:\\code.exe", "diff_args": ["--diff"]}}}
+        config = ExternalEditorConfig.from_dict(data)
+        assert config.editors["vscode"].diff_args == ["--diff"]
+
+    def test_get_default_returns_configured(self, ext_config):
+        result = ext_config.get_default()
+        assert result.name == "vscode"
+
+    def test_get_default_fallback_to_first(self):
+        config = ExternalEditorConfig(editors={"notepad++": TextEditorConfig(name="notepad++", path="C:\\npp.exe")})
+        result = config.get_default()
+        assert result.name == "notepad++"
+
+    def test_get_default_returns_none_when_empty(self):
+        config = ExternalEditorConfig(editors={})
+        assert config.get_default() is None
+
+    def test_to_dict(self, ext_config):
+        result = ext_config.to_dict()
+        assert result["default_editor"] == "vscode"
+        assert "vscode" in result["editors"]
+
+
+class TestExternalEditorLauncher:
+    def test_get_editor_by_name(self, launcher):
+        editor = launcher.get_editor("notepad++")
+        assert editor.name == "notepad++"
+
+    def test_get_editor_returns_default(self, launcher):
+        editor = launcher.get_editor()
+        assert editor.name == "vscode"
+
+    def test_get_editor_unknown_name(self, launcher):
+        editor = launcher.get_editor("unknown")
+        assert editor is None
+
+    def test_build_diff_command(self, launcher, vscode_editor):
+        cmd = launcher.build_diff_command(vscode_editor, "orig.txt", "mod.txt")
+        assert cmd == ["C:\\path\\to\\code.exe", "--diff", "orig.txt", "mod.txt"]
+
+    def test_launch_diff_missing_editor(self, launcher):
+        result = launcher.launch_diff("nonexistent", "orig.txt", "mod.txt")
+        assert result is None
+
+    @patch("subprocess.Popen")
+    def test_launch_diff_success(self, mock_popen, launcher):
+        mock_popen.return_value = MagicMock()
+        result = launcher.launch_diff("vscode", "orig.txt", "mod.txt")
+        assert result is not None
+        mock_popen.assert_called_once()
+
+    @patch("subprocess.Popen")
+    def test_launch_diff_file_not_found(self, mock_popen, launcher):
+        mock_popen.side_effect = FileNotFoundError()
+        result = launcher.launch_diff("vscode", "orig.txt", "mod.txt")
+        assert result is None
+
+
+class TestHelperFunctions:
+    def test_create_temp_modified_file(self):
+        content = "test content"
+        path = create_temp_modified_file(content)
+        assert path.endswith("_modified")
+        with open(path, encoding="utf-8") as f:
+            assert f.read() == content
+        import os
+        os.unlink(path)