feat: add replace arg to use_external_* wrappers

[ColinFay]

Closes #819.

Summary

• Add a replace = FALSE argument to use_external_js_file(),
  use_external_css_file(), use_external_html_template(),
  use_external_file() and use_bundled_html(). When TRUE, an
  existing file at the target location is overwritten instead of
  aborting.
• For use_bundled_html(), the extracted bundle directory (and any
  stale file at the same path) is also removed before re-extraction
  when replace = TRUE — unzip() does not clean it on its own.
• check_file_exists() gains a replace short-circuit and the abort
  message now mentions the option.
• Bump dev version to 0.6.0.9000.

NEWS.md

New features

Test plan

• devtools::test() — 625 PASS, 0 FAIL.
• New test covers the default-abort and replace = TRUE paths for
  the 4 use_external_* functions.
• New test covers check_file_exists(replace = TRUE).

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR adds a replace = FALSE option across the use_external_* file helpers (and use_bundled_html()) to allow overwriting existing target files/directories, and updates shared tooling + tests/docs accordingly.

Changes:

• Add replace parameter to use_external_js_file(), use_external_css_file(), use_external_html_template(), use_external_file(), and use_bundled_html(), and plumb it through download/check helpers.
• Update check_file_exists() to short-circuit when replace = TRUE and enhance the “already exists” message.
• Add tests for replace behavior in the external wrappers and check_file_exists(), plus update NEWS + dev version.

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
R/use_files_external.R	Adds replace arg to exported external helpers; implements bundle cleanup when replacing.
R/use_files_external_tools.R	Threads replace through the shared “checks + download” helper.
R/use_files_shared_tools.R	Extends check_file_exists() with replace support and updated abort message.
tests/testthat/test-use_files.R	Adds coverage for default-abort vs replace = TRUE across use_external_* wrappers.
tests/testthat/test-use_files_shared_tools.R	Adds coverage for check_file_exists(replace = TRUE) no-op behavior.
man/use_files.Rd	Documents the new replace parameter in the public API docs.
NEWS.md	Adds a development NEWS entry describing the new replace option.
DESCRIPTION	Bumps package version to 0.6.0.9000.

Files not reviewed (1)

• man/use_files.Rd: Language not supported

Comments suppressed due to low confidence (1)

R/use_files_shared_tools.R:66

• check_file_exists() is used by multiple helpers (e.g., internal file copy/add flows) that don’t expose a replace argument, but the abort text now tells users to “call this function again with replace = TRUE”. That makes the error message misleading in those contexts. Consider moving the replace hint to the specific public functions that support it, or wording it conditionally (e.g., “if supported by the calling function”).

		cli_abort(
			sprintf(
				"%s already exists.\n\nYou can delete it with:\nunlink('%s', recursive = TRUE).\n\nAlternatively, call this function again with `replace = TRUE`.",
				where,
				where
			)
		)

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