Before anything else: read $HOME/.agentic-workflow/toolkit/skills/_preamble.md and follow it (skill index, provider capability map, bootstrap check, session context). Run its Session Close section when this skill finishes.

/new-slice

Adds one use case to a package that /new-package created, exactly as docs/csharp/scaffolds/new-slice.md
specifies (that file is the contract; this skill drives its generator, scripts/scaffold/new-slice.mjs). The recipe
it encodes: test (with compiling stubs) → service → endpoint or CLI command → registration. It leaves exactly one
new red test; everything else stays green.

1. Collect the inputs

Take what the arguments give, then Ask the user for every input still missing.

Input	Flag	Rule
package	--package	an existing src/<Package>/ declared in deps.yaml
slice	--slice	PascalCase, verb first (CheckRepo, StartItem); no existing Features/<Slice>/
behavior	--behavior	snake_case sentence for the first test; the test is <Slice>_<behavior>
surface	--surface	cli, http or none, matching the package's host
command	--command	cli: kebab-case command name (default: the slice in kebab case)
route	--route	http: "<METHOD> /path"; each {name} names a typed id ({itemId} for ItemId; {id} when there is one id)
ids	--ids	new typed ids the request uses, Name:string|Guid|int, names ending in Id; existing ids are reused
ports	--ports	Core port interfaces the service needs; a missing one is created with its fake and contract base. ports + TimeProvider ≤ 5
slice-only	--slice-only	set when other branches scaffold slices into the same package in parallel (Sindri API spec C7, §12)

2. Run the generator

node scripts/scaffold/new-slice.mjs --package <Pkg> --slice <Slice> --behavior <behavior> --surface <cli|http|none> \
  [--command <cmd> | --route "<METHOD> /path/{fooId}"] [--ids FooId:string] [--ports IFooStore] [--slice-only]

Pass --slice-only when other branches scaffold slices into the same package in parallel. It writes the slice's
own files and only its lines in A.cs, IdsJsonContext and PublicAPI.Unshipped.txt, then prints the registration,
table and JSON context lines to add by hand in the branch, and the endpoint or command file to write by hand. A shared
edit or new shared file it would need is refused (NS-SLICE-ONLY), including a missing A.cs, or a missing IdsJsonContext when the slice adds an id:
the phase's contract unit adds those.

It takes a slot of the heavy-job lock itself, writes the files, records the public API lines (every RS0016 symbol the
build reports for Core and Features, Vogen's generated id members included), then runs dotnet build -warnaserror, the unit lane (exactly one
failure: the new test) and dotnet format --verify-no-changes. Any other failure reverts every file it wrote.

Refusals (exit 1, nothing written): NS-PACKAGE, NS-NAME, NS-EXISTS, NS-BEHAVIOR, NS-SURFACE, NS-COMMAND,
NS-ROUTE, NS-IDS, NS-PORTS, NS-DEPS, NS-SLICE-ONLY. Shared logic is never copied from another slice: if the new slice needs
another slice's code, move it into Core first (second use → generalize), then re-run.

3. Commit and hand over

Commit the listed files as test: red <Slice> test (<behavior>) (with --slice-only, also pass on the printed
shared lines), then report the next steps the generator printed:
write the assertion → add the ports to the constructor → implement the service (pure decisions on the domain type in
Core) → add the integration test if the slice touches SQL → run the lane.

Next steps

• /specToProvenPR — take the slice to a proven, review-clean PR
• /new-slice — the next use case