onboarding: remove gstack, point members at agent-skills

[alongd]

Follow-up to #57. Two commits: the Copilot fixes that missed that merge, then the gstack removal.

Why

main's onboarding told every new member to run:

git clone --single-branch --depth 1 https://github.com/garrytan/gstack.git ~/.claude/skills/gstack && ./setup

That suite was removed in August 2026 (agent-skills#49). CLAUDE.global.md then handed them a # gstack section listing 35 skills and mandating /browse for all web browsing. A member following the runbook today builds a setup we don't run and inherits global rules pointing at ~30 commands that don't exist.

Commit 1 — carry forward the fixes that missed #57

#57 merged at 160bc64 while a second Copilot round was in flight. Six fixes were pushed to the branch as e807c30 but never merged: the hard-coded --backend google comment, a ```bash fence wrapping an AGY tool call, the !echo shell-escape in the smoke test, the Slack token path rationale, and two files still describing the `~/.claude/agents/` symlink that step 7 replaced with `define_subagent`.

Commit 2 — remove gstack

• Step 5 — the "natively ported to Antigravity" claim was not true; no port existed. Replaced with the real install: clone agent-skills, symlink ~/.claude/skills at it.
• New: Already installed gstack? — the migration path for members who followed the old runbook. State copy first, gated on diff -r, because ~/.gstack/projects/ holds accumulated per-project learnings the skills still read from a new path.
• CLAUDE.global.md — the # gstack heading, the /browse mandate, and the 35-skill list are gone. Skills are self-describing, so the list bought nothing and rotted.
• MAINTAINING.md — gstack row becomes a Skills row; the settings.json row loses its gstack clause. (This also closes the MAINTAINING.md:48 contradiction Copilot raised on Adapt onboarding to Antigravity (AGY) #57, which I deferred to this PR rather than aligning it to a claim that was itself false.)
• Smoke test — /browse and /ship no longer exist.

Verification

Every command in the new sections was executed in a sandbox before shipping:

• ln -s onto a pre-existing real directory nests the link inside it instead of replacing it — the naive one-liner would have silently produced ~/.claude/skills/agent-skills. The shipped version moves it aside first, verified.
• Re-running the symlink step is idempotent.
• The migration's copy + diff -r gate passes with learnings intact.

I also checked the skills named in the smoke test actually exist. My first draft named /careful, which doesn't — caught by ls, not by review. That's the same failure mode this PR exists to fix.

[Copilot]

Pull request overview

Updates the onboarding documentation to remove the deprecated gstack dependency and instead direct new members to the group-owned agent-skills repo, while also carrying forward a set of onboarding fixes that missed the prior merge (#57).

Changes:

• Replace the “agent-skills & gstack skills” onboarding step with a clone + ~/.claude/skills symlink flow, and add an explicit migration path for existing gstack installs/state.
• Remove the stale # gstack//browse mandates and skill list from CLAUDE.global.md, replacing it with a self-describing-skills explanation.
• Update MAINTAINING.md to reflect agent-skills as the member-facing skills mechanism and to resolve the prior gstack contradiction.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
onboarding/ONBOARDING.md	Replaces gstack install guidance with agent-skills symlink install + adds gstack migration + updates smoke-test and AGY scheduling guidance.
onboarding/MAINTAINING.md	Updates the artifact map and decisions/rationale to remove gstack and standardize on agent-skills.
onboarding/CLAUDE.global.md	Removes the gstack skill list and /browse mandate, replacing it with a minimal “skills are self-describing” policy.

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[alongd]

Both Copilot findings addressed, squashed into their owning commits — head is now f4c343d.

C1 (ONBOARDING.md:55) was real, and worse than it reads. I confirmed it by execution rather than inspection:

--- precondition: both skills/ and skills.bak/ exist ---
--- run the SHIPPED lines verbatim ---
skills.bak now contains: older skills
VERDICT: NESTED -> ~/.claude/skills.bak/skills

The irony is the point: that block existed specifically to guard against ln -s nesting into an existing directory, and its own mv reproduced the identical bug one line up. A member who had ever backed up before would have their skills buried inside the old backup, at which point the symlink is created over a path whose contents just moved somewhere the runbook doesn't mention.

Fixed with a timestamped backup name, which cannot collide. Re-tested:

--- case: a stale skills.bak/ ALREADY exists (what broke before) ---
old .bak intact:   older
contents saved:    mine
PASS: no nesting
--- case: re-run when skills is already the symlink ---
backup dirs:       1 (must still be 1)

C2 (ONBOARDING.md:244) also real. The paragraph claimed you'd type /schedule while showing only the call:default_api:schedule{…} form, so the one thing a reader could copy was the one thing they must not paste. Now both forms appear, labelled: what you type versus what the agent emits internally.

Fix placement was checked, not assumed — git blame put the schedule paragraph in commit 1 and the symlink block in commit 2, and each fix squashed into its own commit with no leakage between them.