Clarify collection contracts and migration docs

docs/consumers/pkg-promptkit.md

@@ -252,7 +252,7 @@ for _, difference := range differences {
 ```
 
 See the [`ConfigurationInspection.Diff` GoDoc](../../configuration_inspection.go)
-and ConfigKit's [v0.7.0 effective-configuration diff guidance](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.7.0/docs/config.md#effective-configuration-diffs)
+and ConfigKit's [v0.8.0 effective-configuration diff guidance](https://gitea.maximumdirect.net/eric/ConfigKit/src/tag/v0.8.0/docs/config.md#effective-configuration-diffs)
 for the exact comparison contract. The operation compares only frozen effective
 configuration values: it does not reread external files or compare their
 contents, resolved credential contents, later execution preparation, or
@@ -637,24 +637,16 @@ are keys in configuration, not registrations. Choose caller underlays in
 fallback-to-operator-to-programmatic order; use `Sources.Main` for one final
 highest-priority input.
 
-Move embedded `id` and `version` fields into keyed `profiles` and `prompts`
-maps; convert `base_profile` to ConfigKit `extends`. IDs and references are
-exact literal keys, without trimming. A supplied zero, false, or empty string
-is now distinguishable from omission; null can clear or suppress an inherited
-field according to the [field table](../formats.md#defaults-and-overrides).
-Maps merge recursively across inheritance and layers. `{}` does not clear an
-inherited map: use null to clear the whole map. At request time, a literal
-`extra_params["extends"]` is ordinary provider data, not an inheritance
-instruction; a nonempty request ExtraParams map replaces configured params.
-Changing a model or backend does not clear unrelated explicit fields, though
-backend-derived defaults are applied after inheritance to the final backend.
-
-Invalid final definitions, including unused ones, now fail `NewEngine`; only
-request-dependent failures remain at preparation or execution. Prompt text
-and static templates are captured at construction, not automatically reloaded
-between runs. Replace the engine to pick up changed definitions or message
-files. The [format reference](../formats.md) owns exact field and presence
-rules; the maintained examples show complete runnable workflows.
+Move embedded IDs into keyed `profiles` and `prompts` maps; each prompt ID now
+contains one installed definition, with any descriptive `version` label inside
+that definition. Convert `base_profile` to ConfigKit `extends`. For the current
+collection identity mapping, ID-only prompt selection, and required
+caller-owned choices, see the
+[configuration migration guide](configuration-migration.md). Exact current
+format, reference, inheritance, and presence semantics belong to the
+[framework format reference](../formats.md). Prompt text and static templates
+are captured at construction, not automatically reloaded between runs. Replace
+the engine to pick up changed definitions or message files.
 
 ### Choose A Profile Ownership Model
 
@@ -662,8 +654,9 @@ Supply backend and profile definitions through the configuration sources your
 application selects. PromptKit does not install provider catalogs or built-in
 profile inventories; conventional backend ID constants are names only. Define
 the model, endpoint, credentials lookup, and settings that your application
-intends to support. Profiles may inherit another configured profile using an
-exact ID, and caller-selected source layers determine the final values. The
+intends to support. A profile may inherit a sibling profile by its local key in
+the same root or collection mapping; its backend reference uses the exact
+configured identity. Caller-selected source layers determine the final values. The
 [format reference](../formats.md) describes the definition fields and
 composition rules.