diff --git a/base/mp_init.sas b/base/mp_init.sas
index ee2231b..68b4e19 100644
--- a/base/mp_init.sas
+++ b/base/mp_init.sas
@@ -41,8 +41,9 @@
   &prefix._INIT_NUM  /* initialisation time as numeric                        */
   &prefix._INIT_DTTM /* initialisation time in E8601DT26.6 format             */
   &prefix.WORK       /* avoid typing %sysfunc(pathname(work)) every time      */
+  &prefix.PROCESSMODE
+  &prefix._STPSRV_HEADER_LOC
 ;
-
 %let sasjs_prefix=&prefix;
 
 data _null_;
diff --git a/tests/viyaonly/mv_castabsave.test.sas b/tests/viyaonly/mv_castabsave.test.sas
new file mode 100644
index 0000000..20bb0f6
--- /dev/null
+++ b/tests/viyaonly/mv_castabsave.test.sas
@@ -0,0 +1,158 @@
+/**
+  @file
+  @brief Testing mv_castabsave macro
+
+  <h4> SAS Macros </h4>
+  @li mf_uid.sas
+  @li mp_assert.sas
+  @li mp_assertscope.sas
+  @li mv_castabsave.sas
+
+**/
+
+options mprint;
+
+/* -------------------------------------------------------------------- */
+/* Setup: start a CAS session and load a table that has a tracked       */
+/*        source file so mv_castabsave can discover it via the REST API */
+/* -------------------------------------------------------------------- */
+cas mysess;
+caslib _all_ assign;
+
+%let testcaslib=Public;
+
+proc cas;
+  table.caslibInfo result=r / ;
+  found=0;
+  do row over r.CASLibInfo;
+    if upcase(row.Name)=upcase("&testcaslib") then found=1;
+  end;
+  if found=0 then do;
+    print "ERROR: caslib &testcaslib not available";
+    exit;
+  end;
+quit;
+%put NOTE: Using testcaslib=&testcaslib;
+
+%let tab1=T%mf_uid();
+
+/* Load sashelp.class into CAS, save as sashdat, reload from that file
+    so the table has a tracked source path (needed for REST discovery) */
+proc casutil;
+  load data=sashelp.class
+    outcaslib="&testcaslib" casout="&tab1" replace;
+  save casdata="&tab1" incaslib="&testcaslib"
+    casout="&tab1..sashdat" outcaslib="&testcaslib" replace;
+  /* Drop any existing global-scope version before promoting */
+  /* runs twice (with quiet) as first would drop local scope if exists */
+  droptable casdata="&tab1" incaslib="&testcaslib" quiet;
+  droptable casdata="&tab1" incaslib="&testcaslib" quiet;
+
+  load casdata="&tab1..sashdat" incaslib="&testcaslib"
+    casout="&tab1" outcaslib="&testcaslib" promote;
+quit;
+
+libname mylib cas caslib="&testcaslib";
+
+
+/* -------------------------------------------------------------------- */
+%put TEST 1 - save in-memory table back to disk + no scope leakage;
+/* -------------------------------------------------------------------- */
+
+/* Source file is removed so that the reload proves mv_castabsave
+    created the file from scratch, not that a prior version existed   */
+proc casutil;
+  deletesource casdata="&tab1..sashdat"
+    incaslib="&testcaslib" quiet;
+quit;
+
+/* Insert a sentinel row - it must survive the full save/drop/reload   */
+data work.appendme;
+  set mylib.&tab1;
+  name='TESTROW';
+  output;
+  stop;
+proc casutil;
+  load data=work.appendme casout="&tab1" outcaslib="&testcaslib" append;
+quit;
+
+%mp_assertscope(SNAPSHOT)
+
+%mv_castabsave(lib=mylib, table=&tab1, mdebug=1)
+
+%mp_assertscope(COMPARE,
+  desc=Check mv_castabsave does not leak macro variables into GLOBAL scope,
+  ignorelist=MC0_JADP1LEN MC0_JADP2LEN MC0_JADP3LEN MC0_JADPNUM MC0_JADVLEN
+)
+
+proc casutil;
+  droptable casdata="&tab1" incaslib="&testcaslib" quiet;
+  droptable casdata="&tab1" incaslib="&testcaslib" quiet;
+  load casdata="&tab1..sashdat" incaslib="&testcaslib"
+    casout="&tab1" outcaslib="&testcaslib" promote;
+quit;
+
+%let _rowcount=0;
+proc sql noprint;
+  select count(*) into :_rowcount
+  from mylib.&tab1
+  where name='TESTROW';
+quit;
+
+%mp_assert(
+  iftrue=(&_rowcount=1),
+  desc=Check inserted row survives mv_castabsave round-trip to disk
+)
+
+
+/* -------------------------------------------------------------------- */
+%put TEST 2 - save overwrites an existing source file;
+/* -------------------------------------------------------------------- */
+
+/* Source file already exists from the TEST 1 save - append a new row  */
+data work.appendme;
+  set mylib.&tab1;
+  name='TESTROW2';
+  output;
+  stop;
+proc casutil;
+  load data=work.appendme casout="&tab1"
+    outcaslib="&testcaslib" append;
+quit;
+
+%mv_castabsave(lib=mylib, table=&tab1, mdebug=1)
+
+proc casutil;
+  droptable casdata="&tab1" incaslib="&testcaslib" quiet;
+  droptable casdata="&tab1" incaslib="&testcaslib" quiet;
+  load casdata="&tab1..sashdat" incaslib="&testcaslib"
+    casout="&tab1" outcaslib="&testcaslib" promote;
+quit;
+
+%let _rowcount=0;
+proc sql noprint;
+  select count(*) into :_rowcount
+  from mylib.&tab1
+  where name='TESTROW2';
+quit;
+
+%mp_assert(
+  iftrue=(&_rowcount=1),
+  desc=Check inserted row survives save over an existing source file
+)
+
+
+/* -------------------------------------------------------------------- */
+/* Teardown                                                              */
+/* -------------------------------------------------------------------- */
+libname mylib clear;
+
+proc casutil;
+  droptable casdata="&tab1" incaslib="&testcaslib" quiet;
+  deletesource casdata="&tab1..sashdat"
+    incaslib="&testcaslib" quiet;
+quit;
+
+cas mysess terminate;
+
+%let syscc=0;
diff --git a/viya/mv_castabsave.sas b/viya/mv_castabsave.sas
new file mode 100644
index 0000000..87d6aa1
--- /dev/null
+++ b/viya/mv_castabsave.sas
@@ -0,0 +1,192 @@
+/**
+  @file mv_castabsave.sas
+  @brief Saves an in-memory CAS table back to persistent storage
+  @details Runs in SPRE against an active CAS session.  Accepts a
+    SAS libref, derives the CAS caslib and session UUID from
+    sashelp.vlibnam, locates the owning CAS server via the
+    casManagement REST API, then queries the table endpoint to
+    discover the original source file and saves back to that path.
+    CASUTIL infers the file type from the output file extension.
+
+    A CAS session must already be established by the caller, eg:
+
+        cas mysess;
+        libname mylib cas caslib=Public;
+        %mv_castabsave(lib=mylib, table=BASEBALL)
+
+  @param [in] lib=    SAS libref for the CAS caslib
+  @param [in] table=  Name of the in-memory CAS table to save
+  @param [in] mdebug= (0) Set to 1 to enable verbose logging:
+                        - echoes resolved parameters
+                        - prints HTTP response body
+                        - enables mprint/notes during PROC calls
+
+  <h4> SAS Macros </h4>
+  @li mf_getplatform.sas
+  @li mf_getuniquefileref.sas
+  @li mf_getuniquelibref.sas
+  @li mp_abort.sas
+
+**/
+
+%macro mv_castabsave(
+    lib=
+    ,table=
+    ,mdebug=0
+);
+
+%local _sysopts base_uri caslib uuid server
+      srcfile srccaslib fname1 libref1 ftmp i _svcount;
+%let _sysopts=%sysfunc(getoption(mprint)) %sysfunc(getoption(notes));
+
+/* ---- input validation -------------------------------------------------- */
+%mp_abort(
+  iftrue=("&lib"="" or "&table"=""),
+  msg=%str(lib= and table= are required)
+)
+
+%if &mdebug=1 %then %do;
+  %put &=lib;
+  %put &=table;
+  options mprint notes;
+%end;
+
+/* ---- derive caslib and session UUID from sashelp.vlibnam --------------- */
+data _null_;
+  set sashelp.vlibnam(
+    where=(libname="%upcase(&lib)"
+      and sysname in ("Caslib","Session UUID"))
+  );
+  if sysname="Caslib" then call symputx('caslib',sysvalue,'L');
+  else call symputx('uuid',sysvalue,'L');
+run;
+
+%mp_abort(
+  iftrue=("&caslib"=""),
+  msg=%str(&lib is not an assigned CAS libref)
+)
+
+%mp_abort(
+  iftrue=("&uuid"=""),
+  msg=%str(No session UUID found for libref &lib)
+)
+
+%if &mdebug=1 %then %do;
+  %put &=caslib;
+  %put &=uuid;
+%end;
+
+%let base_uri=%mf_getplatform(VIYARESTAPI);
+
+/* ---- get list of CAS servers ------------------------------------------- */
+%let fname1=%mf_getuniquefileref();
+%let libref1=%mf_getuniquelibref();
+
+proc http method='GET' out=&fname1 oauth_bearer=sas_services
+    url="&base_uri/casManagement/servers";
+run;
+
+%mp_abort(
+  iftrue=(&SYS_PROCHTTP_STATUS_CODE ne 200),
+  msg=%str(&SYS_PROCHTTP_STATUS_CODE &SYS_PROCHTTP_STATUS_PHRASE)
+)
+
+libname &libref1 JSON fileref=&fname1;
+
+data _null_;
+  set &libref1..items;
+  call symputx(cats('_sv_', _n_), name, 'L');
+  call symputx('_svcount', _n_, 'L');
+run;
+
+libname &libref1 clear;
+filename &fname1 clear;
+
+/* ---- find which server owns this session ------------------------------- */
+%do i=1 %to &_svcount;
+  %if "&server"="" %then %do;
+    %if &mdebug=1 %then %put checking server: &&_sv_&i;
+    %let ftmp=%mf_getuniquefileref();
+    proc http method='GET' out=&ftmp oauth_bearer=sas_services
+        url="&base_uri/casManagement/servers/&&_sv_&i/sessions/&uuid";
+    run;
+    %if &SYS_PROCHTTP_STATUS_CODE=200
+      %then %let server=&&_sv_&i;
+    filename &ftmp clear;
+  %end;
+%end;
+
+%mp_abort(
+  iftrue=("&server"=""),
+  msg=%str(Could not find owning server for CAS session &uuid)
+)
+
+%if &mdebug=1 %then %put &=server;
+
+/* ---- discover srcfile from REST endpoint ------------------------------- */
+%let fname1=%mf_getuniquefileref();
+%let libref1=%mf_getuniquelibref();
+
+proc http method='GET' out=&fname1 oauth_bearer=sas_services
+    url="&base_uri/casManagement/servers/&server/caslibs/&caslib/tables/&table";
+run;
+
+%if &mdebug=1 %then %do;
+  %put &=SYS_PROCHTTP_STATUS_CODE &=SYS_PROCHTTP_STATUS_PHRASE;
+  data _null_;
+    infile &fname1;
+    input;
+    putlog _infile_;
+  run;
+%end;
+
+%mp_abort(
+  iftrue=(&SYS_PROCHTTP_STATUS_CODE=404),
+  msg=%str(&caslib..&table not found - is it loaded in memory?)
+)
+%mp_abort(
+  iftrue=(&SYS_PROCHTTP_STATUS_CODE ne 200),
+  msg=%str(&SYS_PROCHTTP_STATUS_CODE &SYS_PROCHTTP_STATUS_PHRASE)
+)
+
+libname &libref1 JSON fileref=&fname1;
+
+data _null_;
+  set &libref1..tablereference;
+  call symputx('srcfile', sourceTableName, 'L');
+  call symputx('srccaslib', sourceCaslibName, 'L');
+  stop;
+run;
+
+libname &libref1 clear;
+filename &fname1 clear;
+
+%mp_abort(
+  iftrue=("&srcfile"="" or "&srccaslib"=""),
+  msg=%str(No sourceTableName/sourceCaslibName for &caslib..&table)
+)
+
+%if &mdebug=1 %then %put &=srcfile;
+
+/* ---- save to disk ------------------------------------------------------- */
+proc casutil;
+  save casdata="&table"
+      incaslib="&caslib"
+      casout="&srcfile"
+      outcaslib="&srccaslib"
+      replace;
+quit;
+
+%mp_abort(
+  iftrue=(&syscc ne 0),
+  msg=%str(Save failed for &caslib..&table)
+)
+
+%put NOTE: Table &caslib..&table saved to &srcfile;
+
+/* ---- restore options --------------------------------------------------- */
+%if &mdebug=1 %then %do;
+  options &_sysopts;
+%end;
+
+%mend mv_castabsave;