Add vcs_shape prep question and state dstack's line on version control

[petaltank]

Summary

Roadmap item 5 (meta/roadmap-0.4.md). Based on #6; GitHub retargets to master once #6 merges. Independent of the other feature PRs (if #8, #9 or #10 also land, the spec's principles list needs a one-line renumber — each adds an "18."; and if #8 lands, this becomes prep question 6 rather than 5).

Where the line is. dstack owns exactly three things about version control, for every project: the unit (one ticket = one commit bundling code + re-spec + status; never rewritten once pushed), the trailers (Dstack-Project / Dstack-Ticket), and the shape (below). It deliberately does not own — and reads from the host repo's CLAUDE.md — merge strategy, CI, review rules, branch protection, PR templates, release tagging. Stated once in the spec's Tooling section, echoed in the README FAQ.

The shape, new prep question vcs_shape, recommended from team_shape:

shape	branch	commit	PR
branch-per-project (solo default; today's yolo behavior)	dstack/<project>, once	one per ticket	phase boundary / close-out, with the retro suggestion
branch-per-ticket (team default)	per ticket, from main — or stacked on a dependency's branch if its PR is still open	one per ticket	one per ticket; re-spec section = PR body
trunk	none	one per ticket	none

• Stacking differs by command, per the discussion: dstack-yolo stacks on its own (it's autonomous and warm), logs "stacked on (#N)", and pauses at two unmerged PRs deep; dstack-ticket asks the human — stack or wait — because stacking is a real commitment.
• Fork A branch names are Linear's own per-issue branch name, verbatim (branchName via MCP), so Linear auto-links. Its format is a workspace setting, not dstack's — not configurable here, by design.
• /dstack-ticket gains Step 7 — Close the ticket: verify → re-spec (Fork A: Linear comment first, then description) → status + Execution log → one commit with trailers → PR per shape → hand back. Step 4 now offers it for any [~] ticket whose work landed but was never closed — the Keystone's failure mode in progress.
• dstack-yolo: Operating contract, Step 5 (branch per shape), Step 6 (PR per shape), Step 8 (new stop condition: at gate-every-ticket don't build a dependent on an unreviewed PR; at any tier don't stack three deep). dstack-retro reads PR open→merged timing as review latency.
• Reference project: vcs_shape: branch-per-project, D1.md footer names the branch. README: walkthrough step 7, Decision guide entry, FAQ fallback + "how opinionated is dstack about git?".

Verification

• ./install.sh into a scratch repo; vcs_shape present in spec, skill, all three commands.
• Read yolo Steps 5–6 end to end as branch-per-ticket and as trunk; read ticket Step 7 once — no contradictions with Step 6's confirm.

🤖 Generated with Claude Code

https://claude.ai/code/session_01NLMK6F3vQ1HzyU1Mxqt6Kr