When `git remote get-url origin` was piped directly into sed/tr, pipefail
caused the entire pipeline to fail silently (via `|| true`), producing an
empty RAW_SLUG. The basename fallback then generated a different slug,
making per-project data (checkpoints, learnings, reviews) invisible.
Two fixes:
1. Separate git command from pipeline so failures are handled explicitly
2. Cache computed slugs in ~/.gstack/slug-cache/ so subsequent sessions
always resolve to the same slug regardless of transient git state
Co-authored-by: Jared Friedman <jared@ycombinator.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>