bcp Issue: `--namespace` renames the namespace but NOT the library target name

Start with bcp's library-prefix renaming logic and the generated libs/regex/build/Jamfile.v2 from the reproduction. Check how the modular lib boost_regex target is handled when using --namespace=myboost. Done means the target becomes lib myboost_regex and the build produces the expected libmyboost_regex.* artifacts.

Boost version: 1.90.0 (BOOST_VERSION 109000)
Tool: bcp (from dist/bin/bcp)
Platform: Linux x86_64, gcc-14, b2

Summary

bcp --namespace=myboost is documented to rename both the C++ boost
namespace and the binary library prefix. The namespace rename works, but the
Boost.Build library target name in libs/regex/build/Jamfile.v2 is left
unchanged (lib boost_regex). Consequently the built artifact is
libboost_regex.* instead of the expected libmyboost_regex.*.

Reproduction

ROOT=/path/to/boost
"$ROOT/dist/bin/bcp" \
  --boost="$ROOT" \
  --namespace=myboost --namespace-alias --unix-lines \
  regex config build assert concept_check preprocessor static_assert \
  type_traits core throw_exception predef \
  "$ROOT/.build"

cd "$ROOT/.build" && ./bootstrap.sh && ./b2 --with-regex -j4

Observed

Namespace rename — WORKS

Headers and sources are rewritten to namespace myboost, with a boost alias
inserted (from --namespace-alias):

// boost/assert.hpp
namespace myboost {} namespace boost = myboost; namespace myboost { ... }

Library target name — NOT renamed

.build/libs/regex/build/Jamfile.v2 still declares:

lib boost_regex : ../src/$(SOURCES) icu_options ...

(identical to the original — the boost_regex target name was not rewritten to
myboost_regex.)

Produced artifacts — wrong prefix

stage/lib/libboost_regex.so.1.90.0
stage/lib/libboost_regex.so
stage/lib/libboost_regex.a

Expected: libmyboost_regex.so.1.90.0, libmyboost_regex.so, libmyboost_regex.a.

Expected behaviour

Per bcp docs ("Also renames Boost binaries to use newname rather than boost
as a prefix"), the lib boost_regex target in the modular
libs/regex/build/Jamfile.v2 should be renamed to lib myboost_regex, so the
built library is libmyboost_regex.*.

Likely cause

In the modular (1.90) layout the library target is declared in
libs/regex/build/Jamfile.v2. bcp's library-prefix renaming logic does not
appear to rewrite the lib <name> target declaration in these modular build
Jamfiles.