Generated GitHub cross-repo references use `repo#123`, which does not resolve

Summary

Cross-repository references generated by the assistant use the repo#123 form (e.g. device-builder#2665), which GitHub does not auto-link. GitHub only linkifies a bare #123 inside the same repository, or a fully qualified owner/repo#123 (e.g. esphome/device-builder#2665). The repo#123 form renders as plain text, so no reference link and no cross-reference/back-link is created.

Repro

Ask the assistant to write an issue or PR body referencing issues in another repository. It emits, e.g.:

This is the reconcile step from device-builder#2665 and device-builder#2679.

resulting in unlinked plain text.

Expected

Emit fully qualified references for anything outside the current repository:

... from esphome/device-builder#2665 and esphome/device-builder#2679.

and only use a bare #123 when the target is the same repository the text is being posted in.

Suggested fix

Add a rule to the system prompt / instructions: when writing GitHub issue or PR references, always qualify cross-repository targets as owner/repo#number; never use the unqualified repo#number form, which GitHub does not resolve.

Impact

Broken back-references in generated issues/PRs/commit messages: readers cannot click through, and GitHub does not create the cross-reference timeline entries.