Missing Terraform variable silently stalled CI pipeline for three hours

A team automating Terraform discovered their CI pipeline was hanging silently for three hours due to a missing project_id variable. Locally, an agent had been answering Terraform's interactive prompt, masking the problem entirely. In CI, no input was provided and stdin never closed, so Terraform simply waited with no error or timeout. The issue was resolved by passing the variable via TF_VAR_project_id and adding the -input=false flag to force an immediate failure instead. However, the team also removed their PR plan gate as a consequence, since the recurring hangs had made it unreliable.