chore: add module, license and repository guides

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

AGENTS.md

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+# AGENTS.md
+
+Go module `go.auvem.com/corestack`. Reading map:
+
+- Build and test: `go build ./...`, `go vet ./...`, `go test -race ./...`; format with `gofmt -w .`.
+- Docs format (the spec `docs check` implements): `docs/docs-format.md`.
+- Check records: `go run ./cmd/docs check`. Create one: `go run ./cmd/docs new adr|plan "Title"`.
+- Decisions live in `docs/adr/`, plans in `docs/plans/`. Records are permanent; never rename them.
+- Dependencies are limited to `go.yaml.in/yaml/v3` and `github.com/yuin/goldmark`.

CLAUDE.md

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+See [AGENTS.md](AGENTS.md).

LICENSE

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+BSD 3-Clause License
+
+Copyright (c) 2026, Elijah Duffy
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+1. Redistributions of source code must retain the above copyright notice, this
+   list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright notice,
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+
+3. Neither the name of the copyright holder nor the names of its
+   contributors may be used to endorse or promote products derived from
+   this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

README.md

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 # corestack go
+
+Shared Go building blocks. The first one is `docs`, a checker for architecture decision records (ADRs) and implementation plans.
+
+## docs
+
+Install:
+
+```sh
+go install go.auvem.com/corestack/cmd/docs@latest
+```
+
+Use, from a repository root:
+
+```sh
+docs new adr "Use Example Queue for background jobs"   # creates docs/adr/<id>.md
+docs new plan "Adopt Example Queue"                    # creates docs/plans/<id>.md
+docs check [--root DIR]                                # prints path:line: message; exit 1 on problems
+```
+
+The format is specified in [docs/docs-format.md](docs/docs-format.md); that document is the complete rule set. Exit status is `0` when every record is valid, `1` when problems are reported and `2` for usage errors.
+
+## Status
+
+No support is guaranteed. Breaking changes, including to the format rules, may happen before 1.0 and are listed in the release notes.
+
+## License
+
+BSD-3-Clause, see [LICENSE](LICENSE).

go.mod

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+module go.auvem.com/corestack
+
+go 1.27.1
+
+require (
+	github.com/yuin/goldmark v1.8.6
+	go.yaml.in/yaml/v3 v3.0.5
+)

go.sum

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+github.com/yuin/goldmark v1.8.6 h1:d0VcaP1sx9GkFVkoW+KtggpGi2KZ965i14b0+bDQST4=
+github.com/yuin/goldmark v1.8.6/go.mod h1:ip/1k0VRfGynBgxOz0yCqHrbZXhcjxyuS66Brc7iBKg=
+go.yaml.in/yaml/v3 v3.0.5 h1:N6y/pJk8buWs9NY5ERU2HSMfm+IuD/OtfdAnq6kESPw=
+go.yaml.in/yaml/v3 v3.0.5/go.mod h1:HVTZu1O7/Vkt2N+BFy8Zza+lnLsABggaTM2ZpNIGuKg=