remove --global leaves dependent projects' core symlink dangling (detect in list/doctor)

[isingh]

Problem

truecast remove <name> --global deletes the global cache + current pointer. Any project that had the persona attached has a .truecast/agents/<name>/core symlink → ~/.truecast/personas/<name>/current/core, which now points at a deleted target. We warn ("tracking projects will break next session") but cannot enumerate dependents from the global side, so those projects silently break on the next Claude Code session (the @agent can't read its corpus).

Options

• (a) Project-side detection (preferred). truecast list --project and/or truecast doctor should flag a dangling project core symlink with a clear next step — truecast remove <name> to detach, or re-install to restore.
• (b) Sharpen the global-removal warning (cheap, partial).
• (c) Record back-references at attach time so global removal can warn precisely (heavier; revisit if (a) isn't enough).

Notes

• The global side genuinely can't enumerate dependents — that's a documented limit. The realistic fix is project-side: detect the broken symlink where the project is.
• doctor already inspects the global home; this extends the same idea to a project's .truecast/agents/*/core.

Acceptance

• A project whose attached persona was removed globally is flagged (broken/dangling) by list --project and/or doctor, with a concrete remediation.