refactor: unify agent history and harden runtime diagnostics

Preserve user guidance through history compression, stabilize Flash index targets, and retire withdrawn checks without applying stale verdicts.

Improve runtime diagnostics, tool responses, and history rendering. Simplify documentation and comments.

Validation: 2076 tests passed in the full suite; 381 affected tests and 26 frontend tests passed after cleanup. Ruff and the quality ratchet passed.

tests/unit/tools/test_read_note_tool.py

@@ -68,7 +68,7 @@ async def test_read_note_direct_execution_success(mock_ctx, tmp_path):
     save_note_content(tmp_path, "sample", "line 1\nline 2\nline 3\nline 4\nline 5")
 
     result = await read_note.execute(ctx=mock_ctx, key="sample")
-    assert "Successfully read note 'sample'." in result
+    assert "Note 'sample' (" in result
     assert "line 1\nline 2\nline 3\nline 4\nline 5" in result
 
 
@@ -83,7 +83,7 @@ async def test_read_note_slice(mock_ctx, tmp_path):
         start_line=2,
         end_line=4,
     )
-    assert "Successfully read note 'sample' (lines 2 to 4)." in result
+    assert "Note 'sample' (lines 2 to 4):" in result
     assert "line 1" not in result
     assert "line 2\nline 3\nline 4" in result
     assert "line 5" not in result
@@ -95,7 +95,7 @@ async def test_read_note_callable_execution(mock_ctx, tmp_path):
     save_note_content(tmp_path, "callable_sample", "hello from callable")
 
     result = await read_note(ctx=mock_ctx, key="callable_sample")
-    assert "Successfully read note 'callable_sample'." in result
+    assert "Note 'callable_sample' (" in result
     assert "hello from callable" in result
 
 
@@ -115,7 +115,7 @@ async def test_read_note_with_state_tool_message(mock_ctx, tmp_path):
 
     assert isinstance(result, ToolMessage)
     assert result.tool_call_id == "call_read_999"
-    assert "Successfully read note 'state_sample'." in result.content
+    assert "Note 'state_sample' (" in result.content
     assert "state note content" in result.content
     assert result.status == "success"
 
@@ -147,7 +147,7 @@ async def test_get_read_note_tool_langchain_ainvoke(mock_ctx, tmp_path):
     assert lc_tool.name == "read_note"
 
     result = await lc_tool.ainvoke({"key": "lc_sample"})
-    assert "Successfully read note 'lc_sample'." in result
+    assert "Note 'lc_sample' (" in result
     assert "langchain content" in result
 
 
@@ -160,5 +160,5 @@ async def test_get_read_note_tool_pure(mock_ctx, tmp_path):
     assert pure_tool.name == "read_note"
 
     result = await pure_tool.ainvoke({"key": "pure_sample"})
-    assert "Successfully read note 'pure_sample'." in result
+    assert "Note 'pure_sample' (" in result
     assert "pure content" in result