missing requirement osgi.contract=JavaServlet

[to...@quarendon.net]

I'm trying to use the Karaf maven plugin to build a custom Karaf distribution (so "karaf-assembly" packaging type)

I'm stuck on the following error though:

Failed to execute goal org.apache.karaf.tooling:karaf-maven-plugin:4.1.1:assembly (default-assembly) on project karaf-distro: Unable to build assembly: Unable to resolve root: missing requirement [root] osgi.identity; osgi.identity=core-features; type=karaf.feature; version=1.0.0.SNAPSHOT; filter:="(&(osgi.identity=core-features)(type=karaf.feature)(version>=1.0.0.SNAPSHOT))" [caused by: Unable to resolve core-features/1.0.0.SNAPSHOT: missing requirement [core-features/1.0.0.SNAPSHOT] osgi.identity; osgi.identity=mybundle; type=osgi.bundle; version="[1.0.0.201706120848,1.0.0.201706120848]"; resolution:=mandatory [caused by: Unable to resolve mybundle/1.0.0.201706120848: missing requirement [mybundle/1.0.0.201706120848] osgi.contract; osgi.contract=JavaServlet; filter:="(&(osgi.contract=JavaServlet)(version=3.1.0))"]]



I have the org.apache.karaf.features:enterprise feature as a dependency (along with framework, standard, spring), so I believe that it should have the 3.1.0 servlet API, so I don't think it's an issue of requiring 3.1.0 when something earlier is installed.

In development we use felix HTTP (we use bndtools, and that's just what it uses), and the requirement is satisfied by the Apache Felix Servlet API bundle. But Karaf uses pax-web instead, and nothing seems to provide that capability as far as I can tell (looking at output of bundle:headers in the console).

Naively adding a maven dependency on org.apache.felix.http.servlet-api give me a different, earlier, error 

    Unable to build assembly: [wrap/0.0.0]

My bundle is built using bndtools, I'm afraid I don't know at the moment how that manifest requirement comes about, haven't managed to follow the whole chain through yet.

So my question is, within Karaf, where do I get this dependency satisfied? 
Can I easily just substitute felix HTTP in place of pax-web on the basis that that's what we use in production? If so how? Naively adding felix HTTP as dependencies in my pom.xml just gives this "wrap/0.0.0" error, which means nothing to me.

Thanks.