Trunk

Trunk is the long-lived branch every stack ultimately rebases onto — usually main or master. sm needs to know which branch that is so it can render the tree, prune merged work, and pick the right base when no parent is recorded.

Auto-detection

On the first sm command in a fresh repo, trunk is detected in this order:

1. The branch pointed to by origin/HEAD (what git remote set-head origin --auto produces).
2. main, if it exists locally.
3. master, if it exists locally.

The result is persisted to .git/config:

[stac-man]
    trunk = main

After the first run, sm reads this key directly — no detection cost.

Overriding

If your team's trunk is something else (develop, trunk, …), set it manually:

git config --local stac-man.trunk develop

That's the only way to change it. sm deliberately doesn't expose a flag for this — trunk is a per-repo setting that should rarely change.

What "trunk" means in each command

Command	Trunk's role
sm create	Default parent for a new branch made off trunk.
sm log	Root of the rendered tree.
sm restack	Stops walking up at trunk; trunk itself is never rewritten.
sm sync	Fast-forwarded against origin/<trunk>; merged stack-mates are deleted; survivors restacked.
sm submit	Default base for branches whose parent IS trunk.
sm doctor	Reports trunk + tracked-branch count first; flags branches whose parent isn't reachable from trunk.

Trunk vs. parent

Trunk is one specific branch in the repo. Parent is per-branch metadata — every tracked branch has a parent (which may or may not be trunk). A branch sitting directly on trunk has parent = trunk; a branch deeper in the stack has parent = some other tracked branch.

What trunk is NOT

• Not necessarily the default branch on GitHub. They line up by convention but sm reads its own stac-man.trunk key, not GitHub's default.
• Not protected by sm. If you want force-push protection on trunk, that's a git push setting / GitHub branch protection rule. sm will not push to trunk on your behalf.
• Not a "stack" of size one. Trunk is the floor of every stack, not part of it.