[REFACTOR] tab2: extract refresh_active_methods from _sync_constraint_widgets so it can be called without visiting Tab 2

tabs/tab2_constraints.py

@@ -3,7 +3,7 @@ import streamlit as st
 
 from config.config import CO2_UNIT, method_groups, method_order, method_tooltips, secondary_resources, hidden_resource_names
 from utils.ui_helpers import show_bar
-from utils.data_utils import strip_unit_suffix, is_other_method, get_other_method_variants, make_variant_name, default_constraint
+from utils.data_utils import strip_unit_suffix, get_other_method_variants, make_variant_name, default_constraint
 
 
 def _make_slider_cb(m):
@@ -385,30 +385,37 @@ def build_summary_df():
 
 
 
-def _sync_constraint_widgets(cost_sliders_norm):
-    """Drive all constraint widget keys from the constraint dict before any widget is drawn.
+def refresh_active_methods(cost_sliders_norm):
+    """Auto-activate/deactivate methods based on real resource availability.
 
-    Two modes:
-    - force mode: after a file/scenario load (constraints_just_loaded flag) or for
-      freshly activated methods (just_activated_methods). All keys are set
-      unconditionally from the constraint.
-    - normal mode: setdefault only; never overrides a value the user already set.
+    A method is auto-deactivated when it's missing a required resource, and
+    auto-reactivated (only if it was previously auto-deactivated, not
+    manually turned off by the user) once that resource becomes available
+    again.
+
+    This must run on every app render — not just when Tab 2 itself draws —
+    otherwise a user who goes straight from Tab 1 to Tab 3/4/5 without
+    visiting Tab 2 first finds every method stuck at its initial
+    "active: False" state (set once at app startup), and the optimisation
+    fails with "No active methods" despite correctly configured resources.
+    Call this from app.py's shared init in addition to Tab 2's own
+    _sync_constraint_widgets (which calls it too, for its widget-key sync).
 
     Args:
-        cost_sliders_norm (dict): {method: {resource: {min, median, max}}} with unit suffixes stripped.
+        cost_sliders_norm (dict): {method: {resource: {min, median, max}}} with
+            unit suffixes stripped.
 
     Returns:
-        None
+        set[str]: method names that were just (re)activated by this call.
     """
-    just_loaded = st.session_state.pop("constraints_just_loaded", False)
-    just_activated = st.session_state.pop("just_activated_methods", set())
     auto_disabled = st.session_state.get("auto_disabled_methods", set())
+    just_activated = set()
 
     for m, c in st.session_state.constraints.items():
         if get_all_missing_required(m, cost_sliders_norm):
             st.session_state.constraints[m]["active"] = False
-            # Keep the method in auto_disabled so apply_auto_disable_logic can
-            # re-enable it (and fire just_activated) once the resource is added.
+            # Keep the method in auto_disabled so it gets re-enabled (and
+            # fires just_activated) once the resource is added.
             auto_disabled.add(m)
             st.session_state.pop(f"toggle_{m}", None)
             st.session_state.pop(f"cap_type_{m}", None)
@@ -421,6 +428,30 @@ def _sync_constraint_widgets(cost_sliders_norm):
             auto_disabled.discard(m)
             just_activated.add(m)
 
+    st.session_state["auto_disabled_methods"] = auto_disabled
+    return just_activated
+
+
+def _sync_constraint_widgets(cost_sliders_norm):
+    """Drive all constraint widget keys from the constraint dict before any widget is drawn.
+
+    Two modes:
+    - force mode: after a file/scenario load (constraints_just_loaded flag) or for
+      freshly activated methods (just_activated_methods). All keys are set
+      unconditionally from the constraint.
+    - normal mode: setdefault only; never overrides a value the user already set.
+
+    Args:
+        cost_sliders_norm (dict): {method: {resource: {min, median, max}}} with unit suffixes stripped.
+
+    Returns:
+        None
+    """
+    just_loaded = st.session_state.pop("constraints_just_loaded", False)
+    just_activated = st.session_state.pop("just_activated_methods", set())
+    just_activated |= refresh_active_methods(cost_sliders_norm)
+
+    for m, c in st.session_state.constraints.items():
         force = just_loaded or (m in just_activated)
         if c["active"]:
             cap_type = c.get("cap_type", "percent")
@@ -457,8 +488,6 @@ def _sync_constraint_widgets(cost_sliders_norm):
             st.session_state.pop(f"slider_{m}", None)
             st.session_state.pop(f"manual_{m}", None)
 
-    st.session_state["auto_disabled_methods"] = auto_disabled
-
 
 def render_constraints_summary():
     """Render the summary dataframe of active methods and their caps.