mcpp new --template imgui fails on all platforms: package 'imgui@1.92.8' has no mcpp.toml #265

Summary

mcpp new <name> --template imgui fails on all three platforms in the
post-release / scheduled ci-fresh-install workflow:

 Downloading compat.imgui v1.92.8
error: package 'imgui@1.92.8' has no mcpp.toml

The step is Template: mcpp new --template imgui (fetch path), and it fails
identically on Linux fresh install, macOS fresh install and
Windows fresh install.

Not a 0.0.102 regression

Found while verifying the 0.0.102 release, but it predates it. The error text
is byte-identical in the scheduled run that executed before the 0.0.102
batch landed:

So the regression window is between 2026-07-20 and 2026-07-21 — after
0.0.101's post-release verification passed and before the July 21 schedule.
Nothing in mcpp released in that window, which points at the package/index
side (compat.imgui 1.92.8 or the template's fetch path) rather than at the
engine.

Where to look

• compat.imgui at 1.92.8: does the payload actually carry an mcpp.toml,
  or is it expected to be synthesized from the descriptor's mcpp = { ... }
  segment? The message comes from the template/scaffold fetch path, which
  looks for a manifest inside the fetched package.
• Whether the template flow and the ordinary dependency flow disagree about
  which of those two forms is acceptable — an ordinary [dependencies] use
  of compat.imgui is not reported failing, which would make this specific
  to the scaffold path.

Secondary observation in the same runs

The same jobs print

error: index requires mcpp >= 0.0.101 but this is mcpp 0.0.100 [E0006]

That one was the workspace bootstrap pin in .xlings.json lagging the index
floor; fixed by b5dece0 (pin -> 0.0.102). It is unrelated to the template
failure, which continues after it.

Environment

ci-fresh-install on ubuntu-24.04 / macOS ARM64 / windows, mcpp installed
from the published release via install.sh.