Priya is a business analyst in VS Code reviewing a checkout bug. She wants Copilot Chat to explain pricing logic in src/pricing.js in the context of Issue #412, without pasting long code or losing link traceability. Which @ mention technique should Priya use to attach content including tools, files, and issues?

Correct technique works because @-mentions attach explicit, linked context for files and GitHub issues, so Copilot Chat receives src/pricing.js content plus Issue #412 metadata with clickable traceability without consuming the prompt with pasted text, preserving provenance for the checkout review. The @workspace summary approach fails on precision because it is ideal for repository-wide reasoning but provides heuristic broad context rather than pinned references to the required file and issue, losing exact linkage. The @github-only approach fails on file grounding because it correctly links Issue #412 yet leaves pricing logic to a manual description, reintroducing verbosity and drift without source links. The open-file #selection approach fails on issue coverage because it elegantly grounds the prompt to visible code with line references while avoiding pasting, yet it omits business context from Issue #412 entirely. For exams, distinguish @ for attachable participants like files and issues from # for editor variables like selection and from / for commands, since without pasting plus link traceability signals @-mentions. As a practical check, type @ in Chat, verify file and issue resolvers and chips appear, then ask for the explanation and click links to confirm navigation.