Feature request: first-class support for a non-git "umbrella" dir over multiple git subprojects

[sartori00]

Context

Common monorepo-ish layout: a parent directory that is not a git repo, containing N independent git subprojects — e.g.:

MyProduct/            # not a git repo
├── backend/          # git repo
├── frontend/         # git repo
└── CLAUDE.md         # documents both

What already works well

Running /gstack-spec, /gstack-plan-eng-review, and /gstack-plan-design-review from the umbrella dir is great: the agent gets unified cross-project context, which is exactly what you want for a feature that spans backend + frontend. This is the natural place to plan.

The gap

Project-scoped infra keys on a git remote/slug:

• cross-session decision memory (~/.gstack/projects/<slug>/decisions.jsonl)
• the learnings store

Run from a non-git umbrella there's no remote → it falls back to a local/degraded identity. So the high-value decisions captured during planning (CEO/eng/spec reviews) aren't tied to a stable project identity, and they don't carry over to the per-subproject sessions where implementation and /ship actually happen. The plan is made under one identity (umbrella) and built under another (subproject), and decision memory doesn't bridge them.

Proposed directions

1. Detect child git repos under a non-git parent and allow an explicit umbrella project slug (e.g. a .gstack marker file at the umbrella root, or ~/.gstack/config.yaml) so project-scoped infra works there.
2. Optionally let subprojects "link" to an umbrella project, so decision memory + learnings are shared across the umbrella and its children — planning in the umbrella, building in a child, with continuous memory.