Upstream implemented the feature itself in r-lib#493's sibling
r-lib#492, so the conflict resolves to removing this patch.

This branch vectorized `cpp_source()`'s `file` argument:
`all(file.exists(file))` instead of `file.exists(file)`,
`vapply(file, generate_cpp_name, ...)` instead of one name,
and a shared-library name derived from the first file
rather than the last.

r-lib#492 teaches `cpp_source()` to source multiple files
outright, and covers each of those points:
it checks `all(file.exists(file))` and reports the first missing path,
maps `generate_cpp_name()` over `file` with `vcapply()`,
and derives the library name from `generate_package_name()`,
which sidesteps the naming problem this patch worked around.
It also adds fixtures and a test, which this patch never had.

Davis Vaughan closed the upstream pull request carrying this patch,
r-lib#337, with "Closed via r-lib#492 for a similar debugging use case".

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K8MneV8KqHYUuC8fWV3X5Q

Three files conflicted,
and only one of them belongs to this branch.

`R/source.R` and `inst/include/cpp11/protect.hpp` conflicted because
this branch was cut from an older integration branch
and carries five squash commits belonging to other patches.
Those are resolved to upstream's version:
they are not this patch's to carry,
and both of the patches behind them are themselves superseded
(r-lib#492 and r-lib#493).

`R/vendor.R` is the real conflict.
Upstream reformatted `cpp_vendor()` with Air,
so the `date` and `overwrite` arguments are re-applied
on top of that new shape rather than reverting it.

`man/cpp_vendor.Rd` and the roxygen block gain the two `@param`
entries the original patch never wrote.
Without them `R CMD check` reports undocumented arguments,
so the branch could not have passed a check as it stood.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K8MneV8KqHYUuC8fWV3X5Q