refactor(memory): switch consolidation to token-based context windows

Move consolidation policy into MemoryConsolidator, keep backward compatibility for legacy config, and compress history by token budget instead of message count.

tests/test_config_migration.py

@@ -0,0 +1,88 @@
+import json
+
+from typer.testing import CliRunner
+
+from nanobot.cli.commands import app
+from nanobot.config.loader import load_config, save_config
+
+runner = CliRunner()
+
+
+def test_load_config_keeps_max_tokens_and_warns_on_legacy_memory_window(tmp_path) -> None:
+    config_path = tmp_path / "config.json"
+    config_path.write_text(
+        json.dumps(
+            {
+                "agents": {
+                    "defaults": {
+                        "maxTokens": 1234,
+                        "memoryWindow": 42,
+                    }
+                }
+            }
+        ),
+        encoding="utf-8",
+    )
+
+    config = load_config(config_path)
+
+    assert config.agents.defaults.max_tokens == 1234
+    assert config.agents.defaults.context_window_tokens == 65_536
+    assert config.agents.defaults.should_warn_deprecated_memory_window is True
+
+
+def test_save_config_writes_context_window_tokens_but_not_memory_window(tmp_path) -> None:
+    config_path = tmp_path / "config.json"
+    config_path.write_text(
+        json.dumps(
+            {
+                "agents": {
+                    "defaults": {
+                        "maxTokens": 2222,
+                        "memoryWindow": 30,
+                    }
+                }
+            }
+        ),
+        encoding="utf-8",
+    )
+
+    config = load_config(config_path)
+    save_config(config, config_path)
+    saved = json.loads(config_path.read_text(encoding="utf-8"))
+    defaults = saved["agents"]["defaults"]
+
+    assert defaults["maxTokens"] == 2222
+    assert defaults["contextWindowTokens"] == 65_536
+    assert "memoryWindow" not in defaults
+
+
+def test_onboard_refresh_rewrites_legacy_config_template(tmp_path, monkeypatch) -> None:
+    config_path = tmp_path / "config.json"
+    workspace = tmp_path / "workspace"
+    config_path.write_text(
+        json.dumps(
+            {
+                "agents": {
+                    "defaults": {
+                        "maxTokens": 3333,
+                        "memoryWindow": 50,
+                    }
+                }
+            }
+        ),
+        encoding="utf-8",
+    )
+
+    monkeypatch.setattr("nanobot.config.loader.get_config_path", lambda: config_path)
+    monkeypatch.setattr("nanobot.cli.commands.get_workspace_path", lambda: workspace)
+
+    result = runner.invoke(app, ["onboard"], input="n\n")
+
+    assert result.exit_code == 0
+    assert "contextWindowTokens" in result.stdout
+    saved = json.loads(config_path.read_text(encoding="utf-8"))
+    defaults = saved["agents"]["defaults"]
+    assert defaults["maxTokens"] == 3333
+    assert defaults["contextWindowTokens"] == 65_536
+    assert "memoryWindow" not in defaults