fix(com1DFA): handle dtSave updates correctly for initial timestep export

- Store original `dtSave` to ensure accurate initial timestep decisions.
- Update `dtSave` only after initial timestep export to avoid unintended modifications.
- Improve readability of conditions by explicitly referencing `dtSaveOriginal`.

 Root Cause:
  The code uses dtSave for two decisions but modifies it between them:
  1. Line 2107: Checks if dtSave contains t=0 → decides to export initial timestep
  2. Line 2114: Calls updateSavingTimeStep() which modifies dtSave (changes [0] to [2*tEnd])
  3. Line 2142: Checks dtSave again → decides whether to add t=0 to Tsave array

  The Problem:
  When tSteps = "0":
  - Line 2107 check passes → exports t=0
  - Line 2114 modifies dtSave from [0] to [2*tEnd]
  - Line 2142 check fails → Tsave remains empty
  - Result: t=0 was exported but not tracked in Tsave (inconsistency)

  Proposed Fix: ✓ CORRECT
  The fix saves the original dtSave before modifications and uses it for both decisions. This ensures
   consistency between the export and Tsave array decisions.

Author: fso42

avaframe/com1DFA/com1DFA.py

@@ -2103,15 +2103,21 @@ def DFAIterate(cfg, particles, fields, dem, inputSimLines, outDir, cuSimName, si
         outDirData = outDir / "particles"
         fU.makeADir(outDirData)
 
-    # export initial time step only if t=0 is explicitly in dtSave
-    if cfg["EXPORTS"].getboolean("exportData") and (dtSave.size > 0 and np.any(dtSave <= 1.0e-8)):
+    # Save original dtSave for initial timestep decisions
+    dtSaveOriginal = dtSave.copy()
+
+    # export initial time step only if t=0 is explicitly in dtSaveOriginal
+    if cfg["EXPORTS"].getboolean("exportData") and (
+        dtSaveOriginal.size > 0 and np.any(dtSaveOriginal <= 1.0e-8)
+    ):
         exportFields(cfg, t, fields, dem, outDir, cuSimName, TSave="initial")
 
         if "particles" in resTypes:
             savePartToPickle(particles, outDirData, cuSimName)
 
         # Update dtSave to remove the initial timestep we just saved
-        dtSave = updateSavingTimeStep(dtSave, cfgGen, t)
+        dtSave = updateSavingTimeStep(dtSaveOriginal, cfgGen, t)
+
 
     # export particles properties for visulation
     if cfg["VISUALISATION"].getboolean("writePartToCSV"):
@@ -2139,10 +2145,11 @@ def DFAIterate(cfg, particles, fields, dem, inputSimLines, outDir, cuSimName, si
         cfgRangeTime["GENERAL"]["simHash"] = simHash
 
     # add initial time step to Tsave array only if it was exported
-    if dtSave.size > 0 and np.any(dtSave <= 1.0e-8):
+    if dtSaveOriginal.size > 0 and np.any(dtSaveOriginal <= 1.0e-8):
         Tsave = [0]
     else:
         Tsave = []
+
     # derive time step for first iteration
     if cfgGen.getboolean("sphKernelRadiusTimeStepping"):
         dtSPHKR = tD.getSphKernelRadiusTimeStep(dem, cfgGen)