macOS says Line CLI can't be opened or is from an unidentified developer

The official installer removes macOS's quarantine attribute from ~/.line/bin/line, so this normally doesn't happen. If you see a warning, the file probably came another way (for example copied from another Mac or downloaded in a browser).

Fix#

Reinstall with the official script:

curl -fsSL https://install.clatterlabs.xyz/line | sh

Or, if you trust the file and know where it came from, remove the quarantine flag:

xattr -d com.apple.quarantine ~/.line/bin/line

Only run binaries from install.clatterlabs.xyz. The installer verifies the checksum of every download and refuses to install one that doesn't match.