Add maintained consumer migration examples

docs/consumers/README.md

@@ -0,0 +1,98 @@
+# Consumer Adoption Guide
+
+ConfigKit removes parser setup, strict decoding, presence bookkeeping, import and
+profile traversal, precedence, provenance, secret lookup, and safe inspection from
+applications. Consumers still own their configuration structs, defaults, semantic
+validation, schema-version policy, CLI parsing, runtime matching and conversion,
+resource checks, remote acquisition, and service initialization.
+
+The maintained [`examples/consumers`](../../examples/consumers) package demonstrates
+four sanitized shapes using only ConfigKit and the Go standard library:
+
+| Shape | Demonstrated fit | Application code deliberately retained |
+| --- | --- | --- |
+| Narratio-like | Fresh defaults, explicit partial imports, artifact maps, recorded inherited defaults, normalization, and source ownership | Artifact meaning and the separate `model_profile` domain field |
+| Notarius-like | Canonical object bindings, a string schema version, strict dynamic options, and `int64` dynamic integers | Catalog selection, allowed option keys, range-checked conversion to runtime `int` |
+| WeatherReporter-like | Defaults-only loading, report maps, canonical module objects, typed option unions, explicit CLI records, and typed secret startup | Report/module compatibility, rejection of explicitly empty domain lists, CLI parsing, and startup ordering |
+| Seriatim-like | Independent strict ordered speaker and autocorrect rule files | First-match and ordered replacement algorithms; no central application configuration file |
+
+The YAML under [`testdata`](../../examples/consumers/testdata) is loaded by the
+executable examples and ordinary tests. It contains no private application data,
+credentials, network calls, or dependency on a sibling checkout.
+
+## Happy path
+
+An application defines ordinary types and passes one explicit source. Optional
+features appear only when the application needs them:
+
+```go
+result, err := configkit.Load[Config](configkit.File(path), configkit.Options[Config]{
+    Definition: rules,
+    Imports:    useDeclaredImports,
+    Profile:    selectedConfigProfile,
+    Overrides:  explicitlySetFlags,
+})
+if err != nil {
+    return err
+}
+return start(result.Config)
+```
+
+Simple consumers use neither imports nor profiles. A complex consumer can opt into
+both without redefining their syntax. ConfigKit profiles are configuration overlays;
+they do not select or replace an application's LLM, model, pipeline, report, or
+execution profile concepts.
+
+Known module catalogs should use canonical object entries with a module identifier
+and typed options. A small union struct is sufficient when the available option
+fields are known; validation selects which fields apply to each module. Runtime-
+selected catalogs may retain `map[string]any`, whose integers are `int64`; applications
+validate keys and ranges and convert only at their runtime boundary. Neither shape
+needs YAML reserialization, a parser hook, a ConfigKit registry, or a generic subtree
+conversion API.
+
+## Intentional migration changes
+
+The examples preserve domain meaning while adopting one configuration convention:
+
+- Explicit empty strings, lists, zeroes, false values, and nulls remain intentional.
+  ConfigKit accepts an empty list structurally; WeatherReporter-shaped validation
+  rejects an explicitly or programmatically supplied empty module/template list as a
+  domain rule. Loaded and constructed values use the same validator.
+- Canonical module and object bindings replace string shorthand. Unknown fields and
+  incompatible option shapes fail at their semantic paths.
+- Schema versions are strings. Consumers with integer versions migrate their files
+  instead of enabling another scalar convention.
+- Integers inside dynamic options are portable `int64` values. Runtime `int`
+  conversion is explicit and range checked.
+- Strict YAML intentionally rejects duplicate keys, aliases, merge keys, unsupported
+  tags/scalars, trailing documents, and unknown typed fields. Diagnostics expose
+  stable classifications and safe paths, not copied parser text.
+- General environment-variable configuration overlays retire. Application CLI
+  parsers translate only explicitly set configuration flags into `Override` records.
+  Separate invocation state remains outside configuration.
+- Credential fields migrate to environment-name `Secret` references. Applications
+  explicitly call `LoadSecretsDir` before `Load` when they choose file bootstrap;
+  blocked empty variables remain blocked, and ordinary `Load` never changes the
+  process environment.
+
+These examples are migration evidence, not completed changes to Narratio, Notarius,
+WeatherReporter, or Seriatim. Updating those repositories, their deployed YAML, CLI
+wiring, runtime catalogs, and operational documentation remains separate downstream
+work.
+
+## Maintained roadmap examples
+
+Every nontrivial API sketch from the feature roadmap has a compiled example or a
+focused behavioral owner:
+
+| Roadmap surface | Maintained owner |
+| --- | --- |
+| `Load`, `NoSource`, validation, versions, resolution, `SecretEnv`, overrides, and explanation | Executable examples in [`example_test.go`](../../example_test.go) |
+| Source/import/profile pipeline rules and artifact defaults | Narratio-shaped executable example and fixture |
+| Canonical module objects and dynamic option handling | WeatherReporter- and Notarius-shaped examples and migration tests |
+| `LoadSecretsDir`, bootstrap reporting, typed lookup, CLI explanation | `Example_weatherStartup` |
+| Results, metadata, diagnostics, effective output, and writer failures | Focused root-package load, provenance, rendering, and explanation tests |
+
+The package-level import-boundary test covers the consumer examples too: supported
+usage names no YAML dependency, parser type, parser option, or parser error chain.