Cover the per-carriage pressure advance and temperature emissions

In a parallel mode no tool changes occur, so two loops address each active
carriage explicitly: pressure advance before the print, and the second-layer
drop off the initial-layer temperature. Neither had coverage, and both fail
silently -- a carriage missing from one emits nothing at all, so it holds the
initial-layer temperature for the whole job, or runs on whatever pressure
advance the firmware was last given. The new case pins that the carriages
addressed are exactly the ones the mode declares active, each with the values of
the slot physical_extruder_map routes its head to.

The test needs filament_self_index, set here on imex_7x4_printer() so the whole
file has it. Production authors that key 1..n; its all-1s default collapses
every per-filament vector to filament 1's value through get_config_index_base(),
which leaves a per-slot assertion comparing a value against itself.

Also bounds the second-layer loop on filament_diameter alone. The bound belongs
in slot space, and filament_diameter is the one per-filament vector never
expanded per variant; the previous min() against nozzle_temperature mixed the
two index spaces without changing the result. The pressure advance loop already
bounds this way, so the two now read alike.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/libslic3r/GCode.cpp

@@ -4026,10 +4026,10 @@ void GCode::_do_export(Print& print, GCodeOutputStream &file, ThumbnailsGenerato
                  (int) initial_extruder_id < (int) m_config.physical_extruder_map.values.size())
                     ? m_config.physical_extruder_map.values[(int) initial_extruder_id]
                     : -1;
-            // enable_pressure_advance and pressure_advance are variant-expanded, so their
-            // length is columns, not filament slots. Bound in slot space -- filament_diameter
-            // is one entry per slot -- exactly as the second-layer temperature loop does, then
-            // translate the slot to its column with get_filament_config_index().
+            // enable_pressure_advance and pressure_advance are indexed by COLUMN, not by
+            // filament slot. filament_diameter is one entry per slot and is never
+            // variant-expanded, so it is the slot-space bound; translate the slot to its column
+            // with get_filament_config_index(), as the second-layer temperature loop below does.
             const int num_pa_filament_slots = (int) print.config().filament_diameter.values.size();
             for (int tool_idx : get_imex_active_tools(print)) {
                 // Unlike the second-layer temperature loop, the primary is skipped here:
@@ -6065,11 +6065,11 @@ LayerResult GCode::process_layer(
             // Mutually exclusive with the `else` below, so a head skipped here gets no
             // transition at all. `tool_idx` is physical; the printing head uses this layer's
             // own filament, the parallel carriages resolve through the head map.
-            // nozzle_temperature is variant-expanded, so its length is columns, not slots:
-            // bound in slot space, or an out-of-slot logical reaches get_filament_config_index
-            // and comes back as filament 0.
-            const int num_filament_columns = std::min((int) print.config().nozzle_temperature.values.size(),
-                                                      (int) print.config().filament_diameter.values.size());
+            // nozzle_temperature is indexed by column: bound in slot space, or an out-of-slot
+            // logical reaches get_filament_config_index and comes back as filament 0.
+            // filament_diameter is the slot-space yardstick -- one entry per filament slot,
+            // never variant-expanded -- and is the bound the pressure advance loop uses too.
+            const int num_filament_slots = (int) print.config().filament_diameter.values.size();
             // Bounds-checked, not get_at() -- see IMEXHelpers.hpp. A clamp would hand the
             // "initial" branch below to whichever secondary sits on pem[0], giving it the wrong
             // filament's transition temperature and never its own.
@@ -6083,7 +6083,7 @@ LayerResult GCode::process_layer(
                     ? (int)first_extruder_id
                     : resolve_filament_for_head(
                           m_imex_head_filament_map, m_config.physical_extruder_map, tool_idx);
-                if (logical < 0 || logical >= num_filament_columns) continue;
+                if (logical < 0 || logical >= num_filament_slots) continue;
                 // Variant-expanded printers column each filament; index as the `else` does.
                 int temperature = print.config().nozzle_temperature.get_at(get_filament_config_index(logical));
                 if (temperature > 0)