diff --git a/conductor/tracks/on_demand_def_lookup_20260306/plan.md b/conductor/tracks/on_demand_def_lookup_20260306/plan.md
index 8510503..467b98d 100644
--- a/conductor/tracks/on_demand_def_lookup_20260306/plan.md
+++ b/conductor/tracks/on_demand_def_lookup_20260306/plan.md
@@ -36,7 +36,7 @@ Focus: Use existing MCP tool to get definitions
 ## Phase 3: Inline Display
 Focus: Display definition in discussion
 
-- [ ] Task 3.1: Inject definition as context
+- [~] Task 3.1: Inject definition as context
     - WHERE: `src/gui_2.py` `_send_callback()`
     - WHAT: Append definition to message
     - HOW:
diff --git a/config.toml b/config.toml
index c44eb89..e6f1a3f 100644
--- a/config.toml
+++ b/config.toml
@@ -1,6 +1,6 @@
 [ai]
-provider = "deepseek"
-model = "deepseek-chat"
+provider = "gemini"
+model = "gemini-2.5-flash-lite"
 temperature = 0.0
 max_tokens = 8192
 history_trunc_limit = 8000
@@ -34,8 +34,8 @@ separate_tool_calls_panel = false
 "Tier 4: QA" = true
 "Discussion Hub" = true
 "Operations Hub" = true
-Message = true
-Response = true
+Message = false
+Response = false
 "Tool Calls" = true
 Theme = true
 "Log Management" = true
diff --git a/src/app_controller.py b/src/app_controller.py
index 9d0fe71..0267ef5 100644
--- a/src/app_controller.py
+++ b/src/app_controller.py
@@ -46,11 +46,12 @@ def parse_symbols(text: str) -> list[str]:
  """
  return re.findall(r"@([a-zA-Z_][a-zA-Z0-9_]*(?:\.[a-zA-Z_][a-zA-Z0-9_]*)*)", text)
 
-def get_symbol_definition(symbol: str, files: list[str]) -> tuple[str, str] | None:
+def get_symbol_definition(symbol: str, files: list[str]) -> tuple[str, str, int] | None:
  for file_path in files:
-  result = mcp_client.py_get_definition(file_path, symbol)
-  if 'not found' not in result.lower():
-   return (file_path, result)
+  result = mcp_client.py_get_symbol_info(file_path, symbol)
+  if isinstance(result, tuple):
+   source, line = result
+   return (file_path, source, line)
  return None
 
 class GenerateRequest(BaseModel):
@@ -1827,6 +1828,15 @@ class AppController:
     self.last_file_items = file_items
     self._set_status("sending...")
     user_msg = self.ui_ai_input
+    
+    symbols = parse_symbols(user_msg)
+    file_paths = [f['path'] for f in file_items]
+    for symbol in symbols:
+     res = get_symbol_definition(symbol, file_paths)
+     if res:
+      file_path, definition, line = res
+      user_msg += f'\n\n[Definition: {symbol} from {file_path} (line {line})]\n```python\n{definition}\n```'
+
     base_dir = self.ui_files_base_dir
     sys.stderr.write(f"[DEBUG] _do_generate success. Prompt: {user_msg[:50]}...\n")
     sys.stderr.flush()
diff --git a/src/gui_2.py b/src/gui_2.py
index 68cf4f7..424beb4 100644
--- a/src/gui_2.py
+++ b/src/gui_2.py
@@ -21,6 +21,8 @@ from src import log_registry
 from src import log_pruner
 from src import models
 from src import app_controller
+from src import mcp_client
+import re
 
 from pydantic import BaseModel
 from imgui_bundle import imgui, hello_imgui, immapp, imgui_node_editor as ed
@@ -1404,7 +1406,33 @@ class App:
       if read_mode:
        imgui.begin_child("read_content", imgui.ImVec2(0, 150), True)
        if self.ui_word_wrap: imgui.push_text_wrap_pos(imgui.get_content_region_avail().x)
-       imgui.text(entry["content"])
+       content = entry["content"]
+       last_idx = 0
+       pattern = re.compile(r"\[Definition: (.*?) from (.*?) \(line (\d+)\)\](\s+```[\s\S]*?```)?")
+       for match in pattern.finditer(content):
+        before = content[last_idx:match.start()]
+        if before: imgui.text(before)
+        header_text = match.group(0).split("\n")[0].strip()
+        path = match.group(2)
+        code_block = match.group(4)
+        if imgui.collapsing_header(header_text):
+         if imgui.button(f"[Source]##{i}_{match.start()}"):
+          res = mcp_client.read_file(path)
+          if res:
+           self.text_viewer_title = path
+           self.text_viewer_content = res
+           self.show_text_viewer = True
+         if code_block:
+          code_content = code_block.strip()
+          if code_content.count("\n") + 1 > 50:
+           imgui.begin_child(f"code_{i}_{match.start()}", imgui.ImVec2(0, 200), True)
+           imgui.text(code_content)
+           imgui.end_child()
+          else:
+           imgui.text(code_content)
+        last_idx = match.end()
+       after = content[last_idx:]
+       if after: imgui.text(after)
        if self.ui_word_wrap: imgui.pop_text_wrap_pos()
        imgui.end_child()
       else:
diff --git a/src/mcp_client.py b/src/mcp_client.py
index 5c5e839..12cd56b 100644
--- a/src/mcp_client.py
+++ b/src/mcp_client.py
@@ -384,6 +384,32 @@ def _get_symbol_node(tree: ast.AST, name: str) -> Optional[ast.AST]:
   current = found
  return current
 
+def py_get_symbol_info(path: str, name: str) -> tuple[str, int] | str:
+ """
+    Returns (source_code, line_number) for a specific class, function, or method definition.
+    If not found, returns an error string.
+    """
+ p, err = _resolve_and_check(path)
+ if err:
+  return err
+ assert p is not None
+ if not p.exists():
+  return f"ERROR: file not found: {path}"
+ if not p.is_file():
+  return f"ERROR: not a file: {path}"
+ try:
+  code = p.read_text(encoding="utf-8").lstrip(chr(0xFEFF))
+  lines = code.splitlines(keepends=True)
+  tree = ast.parse(code)
+  node = _get_symbol_node(tree, name)
+  if node:
+   start = cast(int, getattr(node, "lineno"))
+   end = cast(int, getattr(node, "end_lineno"))
+   return ("".join(lines[start-1:end]), start)
+  return f"ERROR: definition '{name}' not found in {path}"
+ except Exception as e:
+  return f"ERROR retrieving definition '{name}' from '{path}': {e}"
+
 def py_get_definition(path: str, name: str) -> str:
  """
     Returns the source code for a specific class, function, or method definition.
diff --git a/tests/test_gui_symbol_navigation.py b/tests/test_gui_symbol_navigation.py
new file mode 100644
index 0000000..12df1b9
--- /dev/null
+++ b/tests/test_gui_symbol_navigation.py
@@ -0,0 +1,79 @@
+import pytest
+from unittest.mock import MagicMock, patch
+from src.gui_2 import App
+
+@pytest.mark.parametrize("role", ["User", "AI"])
+def test_render_discussion_panel_symbol_lookup(mock_app, role):
+ # Mock imgui, mcp_client, and project_manager as requested
+ with (
+  patch('src.gui_2.imgui') as mock_imgui,
+  patch('src.gui_2.mcp_client') as mock_mcp,
+  patch('src.gui_2.project_manager') as mock_pm
+ ):
+  # Set up App instance state
+  mock_app.perf_profiling_enabled = False
+  mock_app.ai_status = "idle"
+  mock_app.is_viewing_prior_session = False
+  mock_app.active_discussion = "Default"
+  mock_app.project = {"discussion": {"discussions": {"Default": {}}}}
+  mock_app.disc_entries = [{"role": role, "content": "[Definition: MyClass from src/models.py (line 10)]", "collapsed": False, "read_mode": True}]
+  mock_app.disc_roles = ["User", "AI"]
+  mock_app.ui_files_base_dir = "."
+  mock_app.active_track = None
+  mock_app.ui_disc_new_name_input = ""
+  mock_app.ui_auto_add_history = False
+  mock_app.ui_disc_truncate_pairs = 10
+  mock_app.ui_disc_new_role_input = ""
+  mock_app._disc_entries_lock = MagicMock()
+  mock_app._scroll_disc_to_bottom = False
+  mock_app.ui_word_wrap = False
+  mock_app.show_text_viewer = False
+  mock_app.text_viewer_title = ""
+  mock_app.text_viewer_content = ""
+  
+  # Mock internal methods to avoid side effects
+  mock_app._get_discussion_names = MagicMock(return_value=["Default"])
+  mock_app._render_text_viewer = MagicMock()
+  
+  # Mock imgui behavior to reach the entry rendering loop
+  mock_imgui.collapsing_header.return_value = True
+  mock_imgui.begin_combo.return_value = False
+  mock_imgui.begin_child.return_value = True
+  mock_imgui.checkbox.return_value = (False, False)
+  mock_imgui.input_text.side_effect = lambda label, value, *args, **kwargs: (False, value)
+  mock_imgui.input_text_multiline.side_effect = lambda label, value, *args, **kwargs: (False, value)
+  mock_imgui.input_int.side_effect = lambda label, value, *args, **kwargs: (False, value)
+  
+  # Mock clipper to process the single entry
+  mock_clipper = MagicMock()
+  mock_imgui.ListClipper.return_value = mock_clipper
+  mock_clipper.step.side_effect = [True, False]
+  mock_clipper.display_start = 0
+  mock_clipper.display_end = 1
+  
+  # Mock button click for the [Source] button
+  # The code renders: if imgui.button(f"[Source]##{i}_{match.start()}"):
+  # We want it to return True for our entry at index 0.
+  def button_side_effect(label):
+   if label == "[Source]##0_0":
+    return True
+   return False
+  mock_imgui.button.side_effect = button_side_effect
+  
+  # Mock mcp_client.read_file return value
+  mock_mcp.read_file.return_value = "class MyClass:\n pass"
+  
+  # Execute the panel rendering
+  mock_app._render_discussion_panel()
+  
+  # Assertions
+  # 1. Assert that the regex correctly identifies the pattern and imgui.button('[Source]##0_0') is called
+  mock_imgui.button.assert_any_call("[Source]##0_0")
+  
+  # 2. Verify mcp_client.read_file('src/models.py') is called upon button click
+  mock_mcp.read_file.assert_called_with("src/models.py")
+  
+  # 3. Verify the text viewer state is updated correctly
+  assert mock_app.text_viewer_title == "src/models.py"
+  assert mock_app.text_viewer_content == "class MyClass:\n pass"
+  assert mock_app.show_text_viewer is True
diff --git a/tests/test_symbol_lookup.py b/tests/test_symbol_lookup.py
index ceade6d..f8ab7f1 100644
--- a/tests/test_symbol_lookup.py
+++ b/tests/test_symbol_lookup.py
@@ -32,24 +32,25 @@ class TestSymbolLookup(unittest.TestCase):
   files = ["file1.py", "file2.py"]
   symbol = "my_func"
   def_content = "def my_func():\n pass"
+  line_number = 10
   
-  with patch("src.mcp_client.py_get_definition") as mock_get_def:
+  with patch("src.mcp_client.py_get_symbol_info") as mock_get_info:
    # First file not found, second file found
-   mock_get_def.side_effect = [
+   mock_get_info.side_effect = [
     "ERROR: definition 'my_func' not found in file1.py",
-    def_content
+    (def_content, line_number)
    ]
    
    result = get_symbol_definition(symbol, files)
-   self.assertEqual(result, ("file2.py", def_content))
-   self.assertEqual(mock_get_def.call_count, 2)
+   self.assertEqual(result, ("file2.py", def_content, line_number))
+   self.assertEqual(mock_get_info.call_count, 2)
 
  def test_get_symbol_definition_not_found(self):
   files = ["file1.py"]
   symbol = "my_func"
   
-  with patch("src.mcp_client.py_get_definition") as mock_get_def:
-   mock_get_def.return_value = "ERROR: definition 'my_func' not found in file1.py"
+  with patch("src.mcp_client.py_get_symbol_info") as mock_get_info:
+   mock_get_info.return_value = "ERROR: definition 'my_func' not found in file1.py"
    
    result = get_symbol_definition(symbol, files)
    self.assertIsNone(result)
diff --git a/tests/test_symbol_parsing.py b/tests/test_symbol_parsing.py
new file mode 100644
index 0000000..a1c172d
--- /dev/null
+++ b/tests/test_symbol_parsing.py
@@ -0,0 +1,84 @@
+import pytest
+from unittest.mock import MagicMock, patch
+from pathlib import Path
+from src.app_controller import AppController
+from src.events import UserRequestEvent
+
+@pytest.fixture
+def controller():
+ with (
+  patch('src.models.load_config', return_value={
+   "ai": {"provider": "gemini", "model": "model-1"},
+   "projects": {"paths": [], "active": ""},
+   "gui": {"show_windows": {}}
+  }),
+  patch('src.project_manager.load_project', return_value={}),
+  patch('src.project_manager.migrate_from_legacy_config', return_value={}),
+  patch('src.project_manager.save_project'),
+  patch('src.session_logger.open_session'),
+  patch('src.app_controller.AppController._init_ai_and_hooks'),
+  patch('src.app_controller.AppController._fetch_models')
+ ):
+  c = AppController()
+  # Mock necessary state
+  c.ui_files_base_dir = "."
+  c.event_queue = MagicMock()
+  return c
+
+def test_handle_generate_send_appends_definitions(controller):
+ # Setup
+ file_items = [{"path": "src/models.py", "entry": "src/models.py"}]
+ controller._do_generate = MagicMock(return_value=(
+  "full_md", Path("output.md"), file_items, "stable_md", "disc_text"
+ ))
+ controller.ui_ai_input = "Explain @Track object"
+ 
+ # Mock symbol helpers
+ with (
+  patch('src.app_controller.parse_symbols', return_value=["Track"]) as mock_parse,
+  patch('src.app_controller.get_symbol_definition', return_value=("src/models.py", "class Track: pass")) as mock_get_def,
+  patch('threading.Thread') as mock_thread
+ ):
+  # Execute
+  controller._handle_generate_send()
+  
+  # Run worker manually
+  worker = mock_thread.call_args[1]['target']
+  worker()
+  
+  # Verify
+  mock_parse.assert_called_once_with("Explain @Track object")
+  mock_get_def.assert_called_once()
+  
+  controller.event_queue.put.assert_called_once()
+  event_name, event_payload = controller.event_queue.put.call_args[0]
+  assert event_name == "user_request"
+  assert isinstance(event_payload, UserRequestEvent)
+  
+  # Check if definition was appended
+  expected_suffix = "\n\n[Definition: Track from src/models.py]\n```python\nclass Track: pass\n```"
+  assert event_payload.prompt == "Explain @Track object" + expected_suffix
+
+def test_handle_generate_send_no_symbols(controller):
+ # Setup
+ file_items = [{"path": "src/models.py", "entry": "src/models.py"}]
+ controller._do_generate = MagicMock(return_value=(
+  "full_md", Path("output.md"), file_items, "stable_md", "disc_text"
+ ))
+ controller.ui_ai_input = "Just a normal prompt"
+ 
+ with (
+  patch('src.app_controller.parse_symbols', return_value=[]) as mock_parse,
+  patch('threading.Thread') as mock_thread
+ ):
+  # Execute
+  controller._handle_generate_send()
+  
+  # Run worker manually
+  worker = mock_thread.call_args[1]['target']
+  worker()
+  
+  # Verify
+  controller.event_queue.put.assert_called_once()
+  _, event_payload = controller.event_queue.put.call_args[0]
+  assert event_payload.prompt == "Just a normal prompt"