diff --git a/src/lib/wrapper.hpp b/src/lib/wrapper.hpp
index 2d111dc9f..7ee0ef197 100644
--- a/src/lib/wrapper.hpp
+++ b/src/lib/wrapper.hpp
@@ -235,6 +235,15 @@ namespace wrapper {
           return *this;
         }
       
+      /** implant a default-initialised instance of the payload type */
+      ItemWrapper&
+      defaultInit()
+        {
+          discard();
+          build (TY());
+          return *this;
+        }
+      
       operator bool()  const
         {
           return isValid();
@@ -306,6 +315,12 @@ namespace wrapper {
           return *this;
         }
       
+      ItemWrapper&
+      defaultInit()  ///< @note just reset for this specialisation
+        {
+          reset();
+          return *this;
+        }
       
       
       /* == value access == */
@@ -335,7 +350,7 @@ namespace wrapper {
   /**
    * Fallback-specialisation for `ItemWrapper<void>`.
    * @remark This can be relevant when ItemWrapper is used to capture function results,
-   *         yet the given function has return type `void` and used for its side-effects.
+   *         yet the given function has return type `void` and is used for side-effects.
    */
   template<>
   class ItemWrapper<void>
@@ -352,6 +367,12 @@ namespace wrapper {
       
       /** @warning does nothing */
       void operator*() const { /* NOP */ }
+      
+      ItemWrapper&
+      defaultInit()  ///< no effect for this specialisation
+        {
+          return *this;
+        }
     };
   
   
diff --git a/src/vault/gear/activity.hpp b/src/vault/gear/activity.hpp
index d6cdeac78..af8a3a25e 100644
--- a/src/vault/gear/activity.hpp
+++ b/src/vault/gear/activity.hpp
@@ -186,7 +186,7 @@ namespace gear {
     {
 #define ASSERT_MEMBER_FUNCTOR(_EXPR_, _SIG_) \
         static_assert (lib::meta::has_Sig<decltype(_EXPR_), _SIG_>(), \
-                       "Execution-Context: " STRINGIFY(_FUN_) " expect function with signature: " STRINGIFY(_SIG_));
+                       "Execution-Context: " STRINGIFY(_EXPR_) " expect function with signature: " STRINGIFY(_SIG_));
       
       
        ASSERT_MEMBER_FUNCTOR (EXE::post, Proc(Time, Activity&, EXE&));
diff --git a/tests/vault/gear/activity-detector-test.cpp b/tests/vault/gear/activity-detector-test.cpp
index 1fa115651..153605942 100644
--- a/tests/vault/gear/activity-detector-test.cpp
+++ b/tests/vault/gear/activity-detector-test.cpp
@@ -71,6 +71,7 @@ namespace test {
           simpleUsage();
           
           verifyMockInvocation();
+          verifyFakeInvocation();
           verifyMockJobFunctor();
           verifyFakeExeContext();
           watch_activation();
@@ -149,6 +150,33 @@ namespace test {
       
       
       
+      /** @test verify a variation of the instrumented functor
+       *        to call into a custom provided _fake implementation._
+       */
+      void
+      verifyFakeInvocation()
+        {
+          ActivityDetector detector;
+          auto fun = detector.buildDiagnosticFun<int(uint)> ("fakeFun");
+          uint rnd = rand() % 10000;
+          
+          CHECK (0 == fun (rnd));
+          
+          fun.returning(42);
+          detector.incrementSeq();
+          CHECK (42 == fun (rnd));
+
+          fun.implementedAs ([](uint i){ return -i; });
+          detector.incrementSeq();
+          CHECK (-int(rnd) == fun (rnd));
+          
+          CHECK (detector.verifyInvocation("fakeFun").seq(0)
+                         .beforeInvocation("fakeFun").seq(1)
+                         .beforeInvocation("fakeFun").seq(2));
+        }
+      
+      
+      
       /** @test diagnostic setup to detect a JobFunctor activation
        *        - the ActivityDetector provides specifically rigged JobFunctor instances
        *        - these capture all invocations, based on generic invocation logging
@@ -389,7 +417,7 @@ namespace test {
           
           CHECK (detector.verifyInvocation("tap-GATE").seq(0).timeArg(tt)
                          .beforeSeqIncrement(1)
-                         .beforeInvocation("afterGATE").seq(1).timeArg(tt)
+                         .beforeInvocation("after-GATE").seq(1).timeArg(tt)
                          .beforeInvocation("CTX-tick").seq(1).timeArg(tt));
         }
     };
diff --git a/tests/vault/gear/activity-detector.hpp b/tests/vault/gear/activity-detector.hpp
index c4d9cc939..90c060887 100644
--- a/tests/vault/gear/activity-detector.hpp
+++ b/tests/vault/gear/activity-detector.hpp
@@ -268,10 +268,12 @@ namespace test {
       class DiagnosticFun
         {
           using RetVal   = lib::wrapper::ItemWrapper<RET>;
+          using ImplFun  = std::function<RET(ARGS...)>;
           
           string id_;
           EventLog* log_;
           uint const* seqNr_;
+          ImplFun implFun_;
           RetVal retVal_;
           
         public:
@@ -279,8 +281,11 @@ namespace test {
             : id_{id}
             , log_{&masterLog}
             , seqNr_{&invocationSeqNr}
+            , implFun_{}
             , retVal_{}
-            { }
+            {
+              retVal_.defaultInit();
+            }
           
           /** prepare a response value to return from the mock invocation */
           template<typename VAL>
@@ -291,6 +296,15 @@ namespace test {
               return std::move (*this);
             }
           
+          /** use the given λ to provide (optional) implementation logic */
+          template<class FUN>
+          DiagnosticFun&&
+          implementedAs (FUN&& customImpl)
+            {
+              implFun_ = std::forward<FUN> (customImpl);
+              return std::move (*this);
+            }
+          
           // default copyable
           
           /** mock function call operator: logs all invocations */
@@ -299,7 +313,8 @@ namespace test {
             {
               log_->call (log_->getID(), id_, args...)
                    .addAttrib (MARK_SEQ, util::toString(*seqNr_));
-              return *retVal_;
+              return implFun_? implFun_(std::forward<ARGS>(args)...)
+                             : *retVal_;
             }
           
           operator string()  const
diff --git a/wiki/thinkPad.ichthyo.mm b/wiki/thinkPad.ichthyo.mm
index 39c171189..e7fe317a3 100644
--- a/wiki/thinkPad.ichthyo.mm
+++ b/wiki/thinkPad.ichthyo.mm
@@ -80185,6 +80185,42 @@ Date:&#160;&#160;&#160;Thu Apr 20 18:53:17 2023 +0200<br/>
 <icon BUILTIN="flag-yellow"/>
 </node>
 </node>
+<node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1693603368706" ID="ID_1497162884" MODIFIED="1693603379725" TEXT="komplette Aufrufkette verifizieren">
+<icon BUILTIN="flag-yellow"/>
+<node BACKGROUND_COLOR="#e0ceaa" COLOR="#690f14" CREATED="1693603380721" ID="ID_1170059404" MODIFIED="1693603902911" TEXT="geht so nicht, wegen FakeExecutionCtx">
+<richcontent TYPE="NOTE"><html>
+  <head>
+    
+  </head>
+  <body>
+    <p>
+      Im ActivityDetector sind normalerweise die ctx-&#955; als reine Logging-Funktionen implementiert; aber die nun konstruierte Ausf&#252;hrungs-Logik setzt fest darauf, da&#223; ein Aufruf von ctx.post() sofort in einen ActivityLang::dispatchChain() umgesetzt wird <i><font size="2" color="#562275">(allerdings nicht wirklich immer, sondern nur in dem Fall, da&#223; wir das GroomingToken halten und die im post() gegebene Zeit die aktuelle Zeit ist)</font></i>
+    </p>
+  </body>
+</html>
+</richcontent>
+<arrowlink COLOR="#8f4550" DESTINATION="ID_1373519941" ENDARROW="Default" ENDINCLINATION="-166;-6;" ID="Arrow_ID_1164574930" STARTARROW="None" STARTINCLINATION="191;13;"/>
+<icon BUILTIN="messagebox_warning"/>
+</node>
+<node CREATED="1693603571349" ID="ID_1256896805" MODIFIED="1693603880201" TEXT="im vorliegenden Testfall k&#xf6;nnte man eigentlich diesen Aufruf durchreichen...">
+<icon BUILTIN="idea"/>
+<node BACKGROUND_COLOR="#e0ceaa" COLOR="#690f14" CREATED="1693603663534" ID="ID_1373519941" MODIFIED="1693603891817" TEXT="dem steht aber der feste Datentyp entgegen">
+<richcontent TYPE="NOTE"><html>
+  <head>
+    
+  </head>
+  <body>
+    <p>
+      <font color="#7b4438" face="Monospaced">FakeExecutionCtx</font>&#160;bzw. die dort verwendete <font color="#7b4438" face="Monospaced">DiagnosticFun</font>, auf die man ja tats&#228;chlich zugreifen k&#246;nnen sollte (um den R&#252;ckgabewert zu manipulieren) &#8212; und das w&#228;re bei einer <font face="Monospaced" color="#2f1687">std::function</font>&#160; nicht mehr m&#246;glich...
+    </p>
+  </body>
+</html>
+</richcontent>
+<linktarget COLOR="#8f4550" DESTINATION="ID_1373519941" ENDARROW="Default" ENDINCLINATION="-166;-6;" ID="Arrow_ID_1164574930" SOURCE="ID_1170059404" STARTARROW="None" STARTINCLINATION="191;13;"/>
+<icon BUILTIN="broken-line"/>
+</node>
+</node>
+</node>
 </node>
 <node BACKGROUND_COLOR="#eee5c3" COLOR="#990000" CREATED="1689200553782" ID="ID_1346681233" MODIFIED="1689200586861" TEXT="scenario_IOJob">
 <icon BUILTIN="flag-yellow"/>