A batch step can name itself with "as" and later steps refer to it with
{"$ref": "name"}, alongside positional {"$step": n}. "field" now takes a
slash path into the result as well as a key, so {"$ref": "copy",
"field": "ids/0"} reaches the first id edit.duplicate returned (the
convention variable.bind uses for fills/0/color; a leading "/" as in
JSON Pointer also works, and a key holding "/" still matches first).
Resolution moves to crates/engine/src/batch.rs (BatchStep, BatchScope),
shared by command.batch, the CLI script runner, the control channel and
the MCP batch tool, which now passes "as" through. Duplicate names fail
before any step runs; unknown, same-step or later names, bad paths and
out-of-range indexes fail the batch with the step, name and full path.
$ref is reserved like $step; nested batches keep their own names.
Fixes#994.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
The outer batch passes a command.batch step on as written, so the inner
steps' `$step` references point at the inner batch's steps. The docs say
that `$step` is a reserved key in step params.
Inside command.batch, `{"$step": n}` anywhere in a step's params is
replaced by the `id` in step n's result before the step runs
(`{"$step": n, "field": "..."}` picks another field). A nested tree,
such as a frame with children, now takes one batch and one undo step,
not one round-trip per level with ids copied between calls by hand.
Malformed references (forward or self, negative or fractional index,
missing or non-string field, extra keys) fail the batch with BadParams
naming the step, and the existing group machinery rolls it back. The
params walk is depth-capped. Steps are journalled with resolved params.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
