[DBA-136] Highlight new build in chat

src/databao_cli/commands/build.py

@@ -1,6 +1,6 @@
 from databao_context_engine import BuildDatasourceResult, DatabaoContextDomainManager
 
-from databao_cli.project.layout import ProjectLayout
+from databao_cli.project.layout import ProjectLayout, write_build_sentinel
 
 
 def build_impl(project_layout: ProjectLayout, domain: str, should_index: bool) -> list[BuildDatasourceResult]:
@@ -9,4 +9,5 @@ def build_impl(project_layout: ProjectLayout, domain: str, should_index: bool) -
         datasource_ids=None, should_index=should_index
     )
 
+    write_build_sentinel(dce_project_dir)
     return results

src/databao_cli/project/layout.py

@@ -1,8 +1,12 @@
+import logging
 import os
 from dataclasses import dataclass
 from pathlib import Path
 
+logger = logging.getLogger(__name__)
+
 ROOT_DOMAIN = "root"
+BUILD_SENTINEL = ".build_complete"
 
 
 def get_databao_project_dir(project_dir: Path) -> Path:
@@ -49,6 +53,13 @@ def get_domain_names(self) -> list[str]:
         return [domain for domain in os.listdir(domains_dir) if (domains_dir / domain).is_dir()]
 
 
+def write_build_sentinel(domain_dir: Path) -> None:
+    """Write a sentinel file to signal that a build has completed."""
+    sentinel = domain_dir / BUILD_SENTINEL
+    sentinel.write_text("")
+    logger.debug("Wrote build sentinel: %s", sentinel)
+
+
 def find_project(initial_dir: Path) -> ProjectLayout | None:
     dirs_to_check = [initial_dir, *list(initial_dir.parents)]
     for project_dir_candidate in dirs_to_check:

src/databao_cli/ui/app.py

@@ -18,7 +18,12 @@
 from databao_cli.ui.components.status import AppStatus, set_status, status_context
 from databao_cli.ui.models.chat_session import ChatSession
 from databao_cli.ui.models.settings import LLMSettings
-from databao_cli.ui.project_utils import DatabaoProjectStatus, databao_project_status, has_build_output
+from databao_cli.ui.project_utils import (
+    DatabaoProjectStatus,
+    databao_project_status,
+    get_build_fingerprint,
+    has_build_output,
+)
 from databao_cli.ui.services.storage import get_cache_dir
 
 logger = logging.getLogger(__name__)
@@ -128,6 +133,8 @@ def _initialize_agent(project: ProjectLayout) -> Agent | None:
         _agent = create_agent(**kwargs)  # type: ignore[arg-type]
 
         st.session_state.agent = _agent
+        st.session_state.build_fingerprint = get_build_fingerprint(project)
+        st.session_state.new_build_available = False
 
         return _agent
 
@@ -311,6 +318,11 @@ def init_session_state() -> None:
     if "title_futures" not in st.session_state:
         st.session_state.title_futures = {}
 
+    if "build_fingerprint" not in st.session_state:
+        st.session_state.build_fingerprint = 0.0
+    if "new_build_available" not in st.session_state:
+        st.session_state.new_build_available = False
+
     if "build_status" not in st.session_state:
         st.session_state.build_status = "not_started"
     if "build_future" not in st.session_state:

src/databao_cli/ui/components/chat.py

@@ -7,6 +7,7 @@
 
 from databao_cli.ui.components.results import render_execution_result
 from databao_cli.ui.models.chat_session import ChatMessage
+from databao_cli.ui.project_utils import get_build_fingerprint
 from databao_cli.ui.services import (
     check_query_completion,
     get_query_phase,
@@ -510,6 +511,57 @@ def _process_pending_overwrite(chat: "ChatSession") -> None:
     start_background_query(chat, pending)
 
 
+@st.fragment(run_every=5.0)
+def _new_build_notification_fragment() -> None:
+    """Poll for build changes and show an inline banner when detected.
+
+    Runs every 5 seconds.  When the on-disk build fingerprint is newer than
+    the one captured at agent init, it shows a toast (once) and renders an
+    warning banner with a Reload button.  The banner and polling live
+    in the same fragment, so no full-page ``st.rerun()`` is needed for the
+    banner to appear.
+    """
+    project = st.session_state.get("databao_project")
+    if project is None:
+        return
+
+    stored = st.session_state.get("build_fingerprint", 0.0)
+
+    # Detect change
+    if not st.session_state.get("new_build_available"):
+        current = get_build_fingerprint(project)
+        if stored == 0.0:
+            # No build existed at init. Silently adopt the first build
+            # so subsequent builds are detected.
+            if current > 0.0:
+                st.session_state.build_fingerprint = current
+            return
+        if current > stored:
+            st.session_state.new_build_available = True
+            st.toast(
+                "A new build is available. Reload to use the latest context.",
+                icon="\u26a0\ufe0f",
+            )
+
+    # Render banner
+    if not st.session_state.get("new_build_available"):
+        return
+
+    from databao_cli.ui.app import invalidate_agent
+    from databao_cli.ui.suggestions import reset_suggestions_state
+
+    col1, col2 = st.columns([10, 2], vertical_alignment="center")
+    with col1:
+        st.warning("A new build is available. Reload to use the latest context.")
+    with col2:
+        if st.button("Reload", key="new_build_reload_btn", type="primary", use_container_width=True):
+            st.session_state.new_build_available = False
+            st.session_state.build_fingerprint = 0.0
+            invalidate_agent("Reloading project...")
+            reset_suggestions_state()
+            st.rerun()
+
+
 def render_chat_interface(chat: "ChatSession") -> None:
     """Render the complete chat interface.
 
@@ -554,6 +606,7 @@ def render_chat_interface(chat: "ChatSession") -> None:
             _query_polling_fragment()
 
     st.markdown("<div style='height: 2em'></div>", unsafe_allow_html=True)
+    _new_build_notification_fragment()
     _render_chat_input_bar(chat, query_running)
 
     if "pending_plot_message_index" in st.session_state:

src/databao_cli/ui/project_utils.py

@@ -3,7 +3,7 @@
 
 from databao.agent.integrations.dce import DatabaoContextApi
 
-from databao_cli.project.layout import ProjectLayout
+from databao_cli.project.layout import BUILD_SENTINEL, ProjectLayout
 
 logger = logging.getLogger(__name__)
 
@@ -37,6 +37,22 @@ def databao_project_status(project: ProjectLayout) -> DatabaoProjectStatus:
     return DatabaoProjectStatus.VALID
 
 
+def get_build_fingerprint(project: ProjectLayout) -> float:
+    """Return a fingerprint representing the last completed build.
+
+    Reads the modification time of the ``.build_complete`` sentinel file
+    written by the build command after a successful build.  This avoids
+    false positives from files being written *during* a build.
+
+    Returns 0.0 if the sentinel does not exist.
+    """
+    sentinel = project.root_domain_dir / BUILD_SENTINEL
+    try:
+        return sentinel.stat().st_mtime
+    except OSError:
+        return 0.0
+
+
 def has_build_output(project: ProjectLayout) -> bool:
     """Check whether the project has any build output (introspected datasources).
 

src/databao_cli/ui/services/dce_operations.py

@@ -24,7 +24,7 @@
 from databao_context_engine.pluginlib.plugin_utils import check_connection_for_datasource
 
 from databao_cli.commands.init import init_impl
-from databao_cli.project.layout import ProjectLayout
+from databao_cli.project.layout import ProjectLayout, write_build_sentinel
 
 logger = logging.getLogger(__name__)
 
@@ -165,7 +165,9 @@ def verify_datasource_config(ds_type_str: str, ds_name: str, config: dict[str, A
 def build_context(project_dir: Path) -> list[BuildDatasourceResult]:
     """Build context for all datasources in the DCE project. This is a long-running operation."""
     manager = DatabaoContextDomainManager(domain_dir=project_dir)
-    return manager.build_context()
+    results = manager.build_context()
+    write_build_sentinel(project_dir)
+    return results
 
 
 def get_status_info(project_dir: Path) -> str:

tests/test_build_fingerprint.py

@@ -0,0 +1,62 @@
+"""Tests for build fingerprint detection and new-build notification logic."""
+
+import os
+from pathlib import Path
+
+import pytest
+
+from databao_cli.project.layout import BUILD_SENTINEL, ProjectLayout
+from databao_cli.ui.project_utils import get_build_fingerprint
+
+
+@pytest.fixture
+def project_with_sentinel(tmp_path: Path) -> ProjectLayout:
+    """Create a minimal project layout with a build sentinel file."""
+    domain_dir = tmp_path / "databao" / "domains" / "root"
+    domain_dir.mkdir(parents=True)
+    (domain_dir / BUILD_SENTINEL).write_text("")
+    return ProjectLayout(tmp_path)
+
+
+def test_fingerprint_returns_zero_without_sentinel(tmp_path: Path) -> None:
+    """Fingerprint is 0.0 when the sentinel file does not exist."""
+    domain_dir = tmp_path / "databao" / "domains" / "root"
+    domain_dir.mkdir(parents=True)
+    project = ProjectLayout(tmp_path)
+    assert get_build_fingerprint(project) == 0.0
+
+
+def test_fingerprint_returns_zero_for_missing_domain(tmp_path: Path) -> None:
+    """Fingerprint is 0.0 when the domain directory does not exist."""
+    project = ProjectLayout(tmp_path)
+    assert get_build_fingerprint(project) == 0.0
+
+
+def test_fingerprint_returns_nonzero_with_sentinel(
+    project_with_sentinel: ProjectLayout,
+) -> None:
+    """Fingerprint is positive when sentinel file exists."""
+    fp = get_build_fingerprint(project_with_sentinel)
+    assert fp > 0.0
+
+
+def test_fingerprint_changes_after_new_build(
+    project_with_sentinel: ProjectLayout,
+) -> None:
+    """Fingerprint changes when sentinel is rewritten (simulating a new build)."""
+    fp_before = get_build_fingerprint(project_with_sentinel)
+
+    sentinel = project_with_sentinel.root_domain_dir / BUILD_SENTINEL
+    os.utime(sentinel, (fp_before + 10, fp_before + 10))
+
+    fp_after = get_build_fingerprint(project_with_sentinel)
+    assert fp_after > fp_before
+
+
+def test_fingerprint_stable_without_changes(
+    project_with_sentinel: ProjectLayout,
+) -> None:
+    """Fingerprint is stable when sentinel is not rewritten."""
+    fp1 = get_build_fingerprint(project_with_sentinel)
+    fp2 = get_build_fingerprint(project_with_sentinel)
+    assert fp1 == fp2