[ump45nose]

Summary

DSH reads global instructions from $DSH_HOME/AGENTS.md, or ~/.dsh/AGENTS.md by default. The user-instructions sync currently targets ~/.deepseek/AGENTS.md, so it skips an existing DSH home and writes to the wrong location when opening a session.

Resolve the native DSH home, and record its path in new backup manifests. Restore legacy backups at the former path before syncing the correct target; if DSH_HOME changes, restore the previous target before managing the new one.

This PR is based on the branch for BytePioneer-AI/codex-host#741.

Validation

• Focused harness-user-instructions.test.ts: 7 tests passed, including temporary cases for the default and custom DSH homes, legacy backup migration, and changing DSH_HOME; temporary regression cases were removed before commit per local instructions.
• ESLint and Prettier on changed files; git diff --check.
• macOS only; Windows path and filesystem behavior were not locally verified.

[ump45nose]

This change already landed on the default branch: 78a40ff fix: sync dsh user instructions to the correct home is an ancestor of vincent/release (it arrived through the integration branch, not through this PR). Merging this PR would be a no-op, and its base (feat/external-cli-codex-user-instructions) is still an open upstream branch in BytePioneer-AI#741.

Closing as completed so the stacked PR does not sit open against a base that is no longer the delivery path. (AI-assisted triage.)