ConfigKit/docs/development.md

# Development

Start here when contributing to ConfigKit. Read the task-specific owners below
before making changes. The [component overview](internal/overview.md) maps
implementation responsibilities; the [configuration contract](config.md) owns
public behavior.

## Initial orientation

1. Inspect the working tree and preserve unrelated changes.
2. Use the Policy Reading Guide below to select applicable policies.
3. Read the contract and internal documents applicable to the task.
4. Inspect the relevant implementation and behavioral tests before changing them.

## Policy Reading Guide

| Policy | Read before… |
| --- | --- |
| [Policy set provenance](policy/meta.md) | Adopting policies, checking upstream revisions, or updating the adopted policy set. |
| [Agents](policy/agents.md) | Recommending, planning, or implementing repository changes. |
| [Architecture](policy/architecture.md) | Planning or changing Go library code or its structure. |
| [Testing](policy/testing.md) | Selecting validation for code changes, or adding, changing, removing, or evaluating tests. |
| [Documentation](policy/documentation.md) | Writing, revising, or reorganizing documentation. |
| [OSS](policy/oss.md) | Adding or updating dependencies or incorporated third-party material, or changing licensing or attribution. |
| [Release](policy/release.md) | Preparing or publishing a release, changing release procedures, or making versioning and compatibility decisions. |

- Read applicable policies before making decisions they govern; multiple policies
  may apply.
- Select policies using the task triggers above. Follow cross-references to
  relevant sections when needed to resolve a concrete question.
- Reuse policies already available in context; reread when changed or no longer
  available.
- Expand reading when the task's scope expands.
- When revising a policy itself, read that policy and any provisions elsewhere
  affected by the revision.

## Task-specific reading guide

| Task | Read |
| --- | --- |
| Repository orientation or component responsibility | [Component overview](internal/overview.md) |
| Documentation changes | The owning document |
| Licensing, dependencies, attribution, or release-document changes | [Project grant](../COPYRIGHT) and [attribution](oss/attribution.md); release changes also follow the release procedure |
| Architecture decisions or future work | [Deferred scope](roadmap/deferred.md) and relevant ADRs listed below |
| Code and test changes | The owning contract and tests from the map below |
| Examples or copyable assets | The owning implemented contract and [consumer adoption guide](consumers/README.md) |
| Release preparation | [Release procedure](release.md) |

Accepted decisions:

- [Separate composition and overlay](adr/0001-separate-composition-and-overlay.md)
- [Own YAML semantics behind a private parser boundary](adr/0002-own-yaml-semantics.md)
- [Preserve presence and record application resolution](adr/0003-preserve-presence-and-resolution-history.md)
- [Secret references and explicit bootstrap](adr/0004-secret-references-and-explicit-bootstrap.md)
- [Explicit overrides and safe explanation](adr/0005-explicit-overrides-and-safe-explanation.md)
- [Keep the public facade root-owned](adr/0006-public-facade.md)
- [Compare frozen effective configuration snapshots](adr/0010-effective-configuration-diff.md)

For cross-cutting changes, follow every applicable row. Completed implementation
and remediation plans are preserved in Git history at `cb5b435`; use current
contracts and the component overview for ongoing work. For example:

```sh
git show cb5b435:docs/roadmap/remediation.md
```

Release-candidate, publication, and verification work follows the operational
[release procedure](release.md). Its module-selected ReleaseKit `publish`
invocation validates the committed candidate and publishes only the intended
tag; those release checks remain distinct from the everyday development check.

The completed string-and-integer schema-version implementation and remediation
records are preserved in Git history at `244104f`. The
[configuration contract](config.md#application-schema-versions) owns current behavior.

The completed source-origins and public-facade roadmaps, implementation plan, and
resolved review findings are preserved in Git history at `5760614`, for example
`git show 5760614:docs/roadmap/remediation.md`. The earlier source-origins staged
plan remains at `28e7fc5:docs/roadmap/implementation.md`. Current resolution
behavior belongs to the [configuration contract](config.md#recorded-application-resolution),
and current facade ownership belongs to the [component overview](internal/overview.md).

## Baseline validation

The completed filesystem-source and underlay roadmap, original feature request,
implementation plan, and resolved remediation record are preserved in Git history
at `b604aa1` under `docs/roadmap/`. Current behavior belongs to the
[configuration contract](config.md#layered-loading). Built-in sibling
inheritance is now part of the [configuration contract](config.md#sibling-inheritance).
The completed request, roadmap, plan, and resolved review findings are preserved
in Git history at `83c59ea` under `docs/roadmap/`.

The completed overlay rename plan and release-workflow simplification record are
preserved in Git history at `73ce6e9` under `docs/roadmap/`. Current overlay
behavior belongs to the [configuration contract](config.md#selected-overlays),
and release operations belong to the [release procedure](release.md).

The completed ReleaseKit adoption, startup performance request and experiments,
benchmark evidence, performance audit, implementation plan, and remediation
record are preserved in Git history at `8e91a2b` under `docs/roadmap/`. For example:

```sh
git show 8e91a2b:docs/roadmap/startup-benchmark.md
```

Remaining optimization candidates belong to
[deferred scope](roadmap/deferred.md#deferred-performance-experiments).

Install the Go version required by `go.mod` or a compatible newer toolchain.
Acquire declared dependencies explicitly before entering an offline
development or validation environment:

```sh
go mod download
```

Run the everyday check with Bash 3.2 or newer and Git:

```sh
./scripts/check.sh
```

[The script](../scripts/check.sh) runs from the repository root regardless of the
invocation directory. It checks Go formatting without rewriting files, checks
staged/unstaged and untracked whitespace, then runs `go test ./...`,
`go vet ./...`, and `go build ./...`, stopping on the first failure. It uses the
installed Go toolchain by default, honors an explicit `GOTOOLCHAIN`, and disables
dependency downloads. Acquire dependencies and any selected toolchain beforehand.
Format reported Go files with `gofmt -w <files>`.

The default suite includes executable examples, maintained consumer fixtures,
local documentation-link checks, and the dependency import-boundary check.
It must stay deterministic and runnable without network access or credentials.
Still inspect new/untracked content and review paths, examples, ownership, and
current-versus-planned claims; automated checks do not replace content review.

Use focused checks while iterating, with validation proportionate to the change
under the testing policy. Documentation-only work normally needs the local-link
check below and whitespace review; behavior-bearing examples and commands also
need execution. Use `go test -race ./...` for ownership or concurrency changes.
The [release procedure](release.md#4-publish-the-committed-candidate) performs
its selected validation through one `publish` invocation. The everyday checker
remains a development gate and is not a separate release prerequisite. CI never
gates a release.

## Task-to-test map

Commands run from the repository root after dependency acquisition. These are
starting points for focused iteration; run the everyday check before handing off
code changes. Use the component overview to find the corresponding implementation.

| Task | Behavioral test owners | Focused command |
| --- | --- | --- |
| YAML syntax, diagnostics, parser limits | [Adapter tests](../internal/yaml/parse_test.go), [source translation](../internal/engine/parse_test.go) | `go test ./internal/yaml` and `go test ./internal/engine -run '^TestParseSource'` |
| File/reader access, imports, globs, containment | [Sources](../internal/engine/source_test.go), [FIFO](../internal/engine/source_fifo_test.go), [imports](../internal/engine/imports_test.go), [globs](../internal/engine/glob_test.go) | `go test ./internal/engine -run 'Source\|Import\|Glob\|Filesystem\|Nonregular\|RegularFile'` |
| Native filesystem and mapping sources | [Native acquisition](../internal/engine/native_filesystem_test.go), [filesystem facade](../facade_filesystem_test.go), [mapping facade](../facade_mapping_test.go) | `go test ./internal/engine -run 'NativeFilesystem'` and `go test . -run 'TestFacade'` |
| Composition, selected overlays, CLI precedence | [Composition](../internal/engine/compose_test.go), [overlay](../internal/engine/overlay_test.go), [selected overlays](../internal/engine/selected_overlay_test.go), [overrides](../internal/engine/override_test.go) | `go test ./internal/engine -run 'Compose\|Overlay\|Override'` |
| Sibling inheritance, provenance, history, sensitivity | [Expansion](../internal/engine/inheritance_test.go), [destination scopes](../internal/engine/inheritance_walk_test.go), [origins](../internal/engine/inheritance_origin_test.go), [history](../internal/engine/inheritance_history_test.go), [secrets](../internal/engine/inheritance_secret_test.go), [public loading](../facade_inheritance_test.go) | `go test ./internal/engine -run 'Inheritance\|Inherited'` and `go test . -run '^TestFacadeInheritance\|^TestFacadeInheritedSecrets'` |
| Layered loading and source equivalence | [Grouped lifecycle](../internal/engine/load_request_test.go), [layered facade](../facade_layered_test.go), [equivalence](../facade_equivalence_test.go) | `go test ./internal/engine -run '^TestGrouped'`, `go test . -run '^TestFacadeLayered'`, and `go test . -run '^TestEquivalentSourceForms'` |
| Schema, defaults, projection, cloning | [Schema](../internal/engine/schema_test.go), [decoding](../internal/engine/decode_test.go), [projection](../internal/engine/projection_test.go) | `go test ./internal/engine -run 'Schema\|Decode\|Projection\|Clone\|Inline\|CompareDocument'` |
| Lifecycle, resolution, validation, callback ownership | [Loading](../internal/engine/load_test.go), [resolution](../internal/engine/resolution_test.go), [validation](../internal/engine/validation_test.go), [ownership](../internal/engine/callback_ownership_test.go), [independence](../internal/engine/independence_test.go) | `go test ./internal/engine -run 'Load\|Resolution\|Validation\|Validator\|Hook\|Callback\|Parallel'` |
| Paths, metadata, provenance | [Paths](../internal/engine/path_test.go), [metadata](../internal/engine/metadata_test.go), [provenance](../internal/engine/provenance_test.go) | `go test ./internal/engine -run 'Path\|Metadata\|Provenance\|Queries'` |
| Passive resource contexts | [Engine contexts](../internal/engine/resource_context_test.go), [public contexts](../facade_resource_context_test.go) | `go test ./internal/engine -run 'Resource'` and `go test . -run 'SourceContext'` |
| Secrets, bootstrap, redaction, explanation | [References](../internal/engine/secret_reference_test.go), [bootstrap](../internal/engine/secrets_test.go), [rendering](../internal/engine/render_test.go), [explanation](../internal/engine/explain_test.go) | `go test ./internal/engine -run 'Secret\|Bootstrap\|Effective\|Explain\|Explanation\|History\|Sensitivity'` |
| Effective configuration diff | [Engine comparison and masking tests](../internal/engine/diff_test.go), [engine operation tests](../internal/engine/diff_operation_test.go), [root facade tests](../facade_diff_test.go), and [consumer examples](../examples/consumers/diff_test.go) | `go test ./internal/engine -run 'Diff|Explain|History|Secret|Independent'`, `go test . -run 'Diff|FacadeInspection|PublicFacadeBoundary|DependencyImportBoundary'`, `go test ./examples/consumers`, and `go test . -run '^ExampleDiff$'` |
| Consumer examples and migration fixtures | [Consumer tests](../examples/consumers/consumers_test.go), [native and layered examples](../examples/consumers/layered_test.go), [API examples](../example_test.go) | `go test ./examples/consumers` and `go test . -run '^Example'` |
| Assembly and layered scaling evidence | [Assembly benchmarks](../internal/engine/assembly_bench_test.go), [layered benchmarks](../internal/engine/underlay_bench_test.go) | `go test ./internal/engine -run '^$' -bench '^BenchmarkUnderlay' -benchmem`; repeat with `^BenchmarkCompose` and `^BenchmarkOverlay` |
| Inheritance scaling evidence | [Expansion benchmarks](../internal/engine/inheritance_bench_test.go) | `go test ./internal/engine -run '^$' -bench '^BenchmarkInheritance' -benchmem` |
| Documentation links and dependency isolation | [Link checks](../documentation_test.go), [import boundary](../import_boundary_test.go), [public boundary](../public_boundary_test.go) | `go test . -run 'TestLocalDocumentationLinks\|TestDependencyImportBoundary\|TestPublicFacadeBoundary'` |
| Development check behavior | [Development checker test](../development_check_test.go) | `go test . -run '^TestDevelopmentCheckHandlesFilenamesAndStopsOnFailure$'` |
| Release profile wiring | [Release profile test](../releasekit_profile_test.go) | `go test . -run '^TestReleaseKitProfile$'` |

## Fuzz validation

Run the bounded fuzz targets independently from the repository root. These exact
commands keep each campaign short and constrain concurrent workers:

```sh
go test ./internal/engine -run='^$' -fuzz='^FuzzParsePath$' -fuzztime=30s -parallel=2
go test ./internal/yaml -run='^$' -fuzz='^FuzzParseDocument$' -fuzztime=30s -parallel=2
go test ./internal/engine -run='^$' -fuzz='^FuzzCompositionAndOverlay$' -fuzztime=30s -parallel=2
```