set tick0_time using detector clocks services in wirecell simulation

Author: lynnt20

sbndcode/WireCell/cfg/pgrapher/experiment/sbnd/params.jsonnet

@@ -120,19 +120,14 @@ base {
         // For running in LArSoft, the simulation must be in fixed time mode. 
         fixed: true,
 
-        // The "absolute" time (ie, relative to trigger time?) that the lower edge
-        // of final readout tick #0 should correspond to.  This is a
-        // "fixed" notion.
-        local tick0_time = -205*wc.us, // updated in January 2025, front porch in data = 410 ticks
-
         // Open the ductor's gate a bit early.
         local response_time_offset = $.det.response_plane / $.lar.drift_speed,
         local response_nticks = wc.roundToInt(response_time_offset / $.daq.tick),
 
         ductor : {
             nticks: $.daq.nticks + response_nticks,
             readout_time: self.nticks * $.daq.tick,
-            start_time: tick0_time - response_time_offset,
+            start_time: $.sim.tick0_time - response_time_offset,
         },
 
         // To counter the enlarged duration of the ductor, a Reframer

sbndcode/WireCell/cfg/pgrapher/experiment/sbnd/simparams.jsonnet

@@ -76,6 +76,13 @@ base {
     continuous: false,
     fluctuate: false,
 
+    // The "absolute" time (ie, relative to trigger time?) that the lower edge
+    // of final readout tick #0 should correspond to.  This is a
+    // "fixed" notion.
+    // note: should be overriden by extVar in main jsonnet to maintain consistency
+    // with the larsoft clock service
+    local tick0_time = -200*wc.us, 
+
     //ductor : super.ductor {
     //    start_time: $.daq.start_time - $.elec.fields.drift_dt + $.trigger.time,
     //},

sbndcode/WireCell/cfg/pgrapher/experiment/sbnd/wcls-sim-drift-depoflux-nf-sp.jsonnet

@@ -28,6 +28,10 @@ local params = base {
     // Electron drift speed, assumes a certain applied E-field
     drift_speed: std.extVar('driftSpeed') * wc.mm / wc.us,
   },
+  sim: super.sim {
+    // front porch size [us]
+    tick0_time: std.extVar('tick0_time') * wc.us,
+  }
 };
 
 local tools = tools_maker(params);

sbndcode/WireCell/wcsimsp_sbnd.fcl

@@ -1,3 +1,4 @@
+#include "detectorclocks_sbnd.fcl"
 BEGIN_PROLOG
 
 sbnd_wcls: { 
@@ -68,6 +69,8 @@ sbnd_wcls_simsp.wcls_main.structs:  {
                                      lifetime: 100.0
                                      ## Electron drift speed, assumes 0.5 kV/cm and 88.4 K. Units: mm/us
                                      driftSpeed: 1.563
+                                     ## simulated front porch size [us]
+                                     tick0_time: @local::sbnd_detectorclocks.TriggerOffsetTPC
                                     }
 
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