Rewriting paths with undertow-handlers.conf doesn't work as expected - jboss7.x

Question

Background
JBoss 7.1.5 EAP back-end with an Angular 7 UI.
I need to make JBoss aware of the UI's routes, but rewrite them all to the UI's index page for routing by Angular.
The project is structured thus:
webapp/
WEB-INF/
undertow-handlers.conf
web.xml
...etc
login/
background.jpg
login.jsp
index.jsp
assets/*
...html
...js
...css
index.jsp simply response.sendRedirect("index.html")s, where index.html is part of the assets produced by the Angular CLI. JavaScript and HTML is served from webapp/, images from webapp/assets/.
Configuration
From standalone-full.xml
<subsystem xmlns="urn:jboss:domain:undertow:4.0">
<buffer-cache name="default"/>
<server name="default-server">
<http-listener name="http" socket-binding="http" redirect-socket="https"/>
<host name="default-host" alias="localhost,workstation">
<location name="/" handler="welcome-content"/>
<filter-ref name="request-dumper"/>
</host>
</server>
<servlet-container name="default">
<jsp-config x-powered-by="false"/>
<websockets/>
</servlet-container>
<handlers>
<file name="welcome-content" path="${jboss.home.dir}/welcome-content"/>
</handlers>
<filters>
<filter name="request-dumper" module="io.undertow.core" class-name="io.undertow.server.handlers.RequestDumpingHandler"/>
</filters>
</subsystem>
and
<subsystem xmlns="urn:jboss:domain:web:2.2" default-virtual-server="default-host" native="false">
<connector name="http" protocol="HTTP/1.1" scheme="http" socket-binding="http"/>
<virtual-server name="default-host">
<alias name="localhost"/>
<alias name="workstation"/>
</virtual-server>
</subsystem>
With the above configuration, I see the expected server log:
[org.wildfly.extension.undertow] (ServerService Thread Pool -- 84) WFLYUT0021: Registered web context: '/' for server 'default-server'
And I can access the site's login page, and the URI / serves the main angular index page and assets as expected.
Problem
What I need is for paths in this context (like /base or /shop/60) to be handled by Angular, so redirected to index.
As a simple test based on this answer, I have tried this single rule in WEB-INF/undertow-handlers.conf:
exists(%{RELATIVE_PATH}) -> done
path-prefix('/') -> rewrite('/');
but it seems to do nothing at all as I get a 404.
I've tried -> rewrite('/index.html') and -> rewrite('/index.jsp') to no avail.
The file is clearly being read, though, because if I put garbage into the file it throws an exception in the server log.
UT000045: Error parsing predicated handler string Invalid expression:
# path('/base') -> rewrite('/')
What have I missed?
I'm quite a neophyte to JBoss and the whole Undertow ecosystem; please let me know what other details I should add to this question.
Curiosity
With request dumper activated, I see a single initial request to / made by JBoss (User-Agent=Java/1.8.0_181) immediately after booting, but when I navigate to / from a browser, I don't see that request in the dump. But I do see the failed request for /base. Why is that?

Answer 1

I'm serving an Angular 8 SPA from /gui (like you my API is in another servlet). All I had to do with Undertow 2.0.15 (EAP 7.2) was add a WEB-INF/undertow-handlers.conf with:
path-prefix['gui'] and not file(%U) -> rewrite('/gui/index.html')
I would guess that if your SPA is served at / you could just:
not file(%U) -> rewrite('/index.html')

Answer 2

I had two problems:
I was missing rules, and I has misunderstood the function of path-prefix (which matches on complete and non-terminal path segments, rather than acting like a regex ^(group)).
My final, working undertow-handlers.conf looks like this:
regex('/login(.*)') -> done;
path-prefix('/assets') -> done;
regex('(.*).js') -> done;
regex('(.*).map') -> done;
regex('(.*).svg') -> done;
regex('(.*).png') -> done;
regex('(.*).eot') -> done;
regex('(.*).woff2') -> done;
regex('(.*).html') -> done;
path('/') -> rewrite('/index.html');
path('/base') -> rewrite('index.html');
path-prefix('/shop') -> rewrite('index.html');
...and all my other angular routes
Note that /base is a terminal path segment, and matches with path, whereas /shop/60 takes an additional path parameter, so requires path-prefex.
For whatever reason, the solution proposed in the linked question above, simply capturing it all with path-prefix('/') didn't work in my case.
Possibly-heplful side-note: we have a REST server that serves from /RestService/ in another servlet context, so no rules were needed to allow that to continue to work.
Additionally, I was using webpack's development proxy server through ng hmr, and needed to add byPassProxy rules equivalent to the undertow rules, as well.
I'm happy for improvements on this: please don't hesitate to comment or add another answer.