feat: temporal trends CLI script + Dash tab (Task D.1)

D.1a: cli/compute_trends.py — standalone CLI that imports existing pipeline
functions to replay pathway computation for ~10 historical 6-month endpoints.
Creates pathway_trends table via CREATE TABLE IF NOT EXISTS.

D.1b: Trends tab (10th PP tab) with metric toggle (patients/cost/cost_pp_pa).
Query gracefully returns empty when table doesn't exist, figure shows
instruction message to run compute_trends.

dash_app/callbacks/chart.py

@@ -417,6 +417,25 @@ def _render_doses(app_state, title):
     return create_dosing_distribution_figure(data, title)
 
 
+def _render_trends(app_state, title, metric="patients"):
+    """Build the temporal trends line chart."""
+    from dash_app.data.queries import get_trend_data
+    from visualization.plotly_generator import create_trend_figure
+
+    selected_dirs = (app_state or {}).get("selected_directorates") or []
+    selected_drugs = (app_state or {}).get("selected_drugs") or []
+    directory = selected_dirs[0] if len(selected_dirs) == 1 else None
+    drug = selected_drugs[0] if len(selected_drugs) == 1 else None
+
+    try:
+        data = get_trend_data(metric=metric, directory=directory, drug=drug)
+    except Exception:
+        log.exception("Failed to load trend data")
+        return _empty_figure("Failed to load trend data.")
+
+    return create_trend_figure(data, title, metric=metric)
+
+
 def register_chart_callbacks(app):
     """Register tab switching, pathway data loading, and chart rendering callbacks."""
 
@@ -496,18 +515,21 @@ def register_chart_callbacks(app):
         Output("pathway-chart", "figure"),
         Output("chart-subtitle", "children"),
         Output("heatmap-metric-wrapper", "style"),
+        Output("trends-metric-wrapper", "style"),
         Input("chart-data", "data"),
         Input("active-tab", "data"),
         Input("app-state", "data"),
         Input("heatmap-metric-toggle", "value"),
+        Input("trends-metric-toggle", "value"),
     )
-    def update_chart(chart_data, active_tab, app_state, heatmap_metric):
+    def update_chart(chart_data, active_tab, app_state, heatmap_metric, trends_metric):
         """Render the active tab's chart from chart-data nodes."""
         active_tab = active_tab or "icicle"
         chart_type = (app_state or {}).get("chart_type", "directory")
 
-        # Show/hide heatmap metric toggle based on active tab
-        toggle_style = {} if active_tab == "heatmap" else {"display": "none"}
+        # Show/hide metric toggles based on active tab
+        heatmap_toggle_style = {} if active_tab == "heatmap" else {"display": "none"}
+        trends_toggle_style = {} if active_tab == "trends" else {"display": "none"}
 
         if chart_type == "indication":
             subtitle = "Trust \u2192 Indication \u2192 Drug \u2192 Patient Pathway"
@@ -515,17 +537,24 @@ def register_chart_callbacks(app):
             subtitle = "Trust \u2192 Directorate \u2192 Drug \u2192 Patient Pathway"
 
         if not chart_data:
-            return no_update, no_update, toggle_style
+            return no_update, no_update, heatmap_toggle_style, trends_toggle_style
 
         error_msg = chart_data.get("error")
         if error_msg:
-            return _empty_figure(error_msg), subtitle, toggle_style
+            return _empty_figure(error_msg), subtitle, heatmap_toggle_style, trends_toggle_style
+
+        # Trends tab doesn't depend on chart-data nodes
+        if active_tab == "trends":
+            title = _generate_chart_title(app_state) if app_state else ""
+            metric = trends_metric or "patients"
+            fig = _render_trends(app_state, title, metric=metric)
+            return fig, subtitle, heatmap_toggle_style, trends_toggle_style
 
         if not chart_data.get("nodes"):
             return _empty_figure(
                 "No matching pathways found.\n"
                 "Try adjusting your filters."
-            ), subtitle, toggle_style
+            ), subtitle, heatmap_toggle_style, trends_toggle_style
 
         # Lazy rendering — only compute the active tab's chart
         title = _generate_chart_title(app_state) if app_state else ""
@@ -580,4 +609,4 @@ def register_chart_callbacks(app):
             tab_label = dict(TAB_DEFINITIONS).get(active_tab, active_tab)
             fig = _empty_figure(f"{tab_label} chart — coming soon")
 
-        return fig, subtitle, toggle_style
+        return fig, subtitle, heatmap_toggle_style, trends_toggle_style

dash_app/components/chart_card.py

@@ -14,6 +14,7 @@ TAB_DEFINITIONS = [
     ("network", "Network"),
     ("timeline", "Timeline"),
     ("doses", "Doses"),
+    ("trends", "Trends"),
 ]
 
 # Full set retained for Trust Comparison dashboard (Phase 10.8)
@@ -94,6 +95,23 @@ def make_chart_card():
                             ),
                         ],
                     ),
+                    # Trends metric toggle — visible only when trends tab active
+                    html.Div(
+                        id="trends-metric-wrapper",
+                        style={"display": "none"},
+                        children=[
+                            dmc.SegmentedControl(
+                                id="trends-metric-toggle",
+                                data=[
+                                    {"value": "patients", "label": "Patients"},
+                                    {"value": "total_cost", "label": "Cost"},
+                                    {"value": "cost_pp_pa", "label": "Cost p.a."},
+                                ],
+                                value="patients",
+                                size="xs",
+                            ),
+                        ],
+                    ),
                 ],
             ),
             # Chart area with loading spinner

dash_app/data/queries.py

@@ -30,6 +30,7 @@ from data_processing.pathway_queries import (
     get_drug_network as _get_drug_network,
     get_drug_timeline as _get_drug_timeline,
     get_dosing_distribution as _get_dosing_distribution,
+    get_trend_data as _get_trend_data,
 )
 
 DB_PATH = Path(__file__).resolve().parents[2] / "data" / "pathways.db"
@@ -249,3 +250,12 @@ def get_dosing_distribution(
 ) -> list[dict]:
     """Average administered dose counts per drug."""
     return _get_dosing_distribution(DB_PATH, date_filter_id, chart_type, directory, trust)
+
+
+def get_trend_data(
+    metric: str = "patients",
+    directory: Optional[str] = None,
+    drug: Optional[str] = None,
+) -> list[dict]:
+    """Time-series trend data from pathway_trends table."""
+    return _get_trend_data(DB_PATH, metric, directory, drug)