refactor(drivers): rename the layout axis to partition

[fujibee]

Renames the driver axis layout to partition on integration/remote.

shared and per-team answer how the store is divided, and that is all the axis decides. "layout" covers that and much else — the word is already in this tree for tmux panes, on-disk transcript shapes, screen copy, and install structure — so an axis named after it reads as any of them.

Hard rename, no compatibility shim: integration/remote is unreleased, so nothing in the wild is keyed on the old name.

What changed

The driver directory (scripts/drivers/layout/ → scripts/drivers/partition/), the drivers.partition config key, the axis argument passed to the registry, partition_store_relpath and the load helper, and the prose describing the axis.

scripts/lib/driver-registry.sh needed nothing structural — it takes the axis as a parameter and never named this one. Only a sentence of prose there mentioned the axis by name.

Finding the sites took four passes, and that is the interesting part

A single grep would have got this wrong in both directions.

1. Path, config-key, and function-prefix greps — seven files.
2. Reading the loader rather than grepping it added two more: api.sh and rename-team.sh pass the axis as a bare word (agmsg_driver_for_team layout …), which no layout_-prefix pattern matches.
3. A full-tree sweep then found a JSON literal in remote.sh (json_object('layout', 'per-team')) and several tests that spell the key inline as "drivers":{"layout":…} — neither matches drivers.layout.
4. The bare word layout matches 49 files, nearly all of them unrelated. Those were classified by reading, not replaced.

Every remaining layout under scripts/, tests/, and server/ is the ordinary word: tmux panes, CLI-internal transcript shapes, a pre-1.1.0 install structure, field counts.

Tests

bats tests/test_storage.bats tests/test_migrate_team_store.bats tests/test_team.bats tests/test_remote.bats tests/test_remote_forget.bats — 186/187.

The one failure, connect: a keyed team fails closed when the remote disallows age-v1, is not from this change: it fails identically on unmodified integration/remote. Verified by running it on a clean worktree of the base before concluding that.

The axis's own tests pass, including a team on the per-team partition moves, and only that team and an unknown partition is an error, not a fallback.

After landing

Local dogfood installs carry drivers.layout in their team config and need a forget-and-pull or a reinstall to pick up the new key.

[fujibee]

Operational note for anyone migrating an existing install past this rename.

Update the install first, migrate the config second. In that order the new code reads drivers.partition and everything resolves. In the reverse order — config rewritten while the old code is still in place — the old code looks for drivers.layout, does not find it, and falls back to the default shared. That fallback is silent: no error, no warning, just a team quietly resolving to the shared store instead of its own.

This was hit in practice while migrating local installs, not reasoned about after the fact. The rename itself is fine either way; it is only the window between the two steps that bites, and only in one direction.

Worth stating because the failure has no symptom at the point it happens. A team that has moved to its own store and then resolves to the shared one does not error — it reads a store that exists and is populated, just not the one it owns.