Record agreed namespace default composition

docs/roadmap/promptkit-v0.19.0.md

@@ -194,8 +194,9 @@ output-contract overrides and appended-message controls.
 
 Design independent prompt, profile, and backend defaults together. Native
 `WithNamespaces` replaces all defaults on its new view; it has no partial-update
-semantics. Omission must therefore have a deliberate meaning when a loader
-already returns a scoped engine (OD-3).
+semantics. Under the agreed OD-3 design, opt-in selectors combine explicitly
+declared suite defaults with supplied overrides; they do not infer defaults
+from a loader's engine view.
 
 Qualified IDs pass through native selection unchanged. Captured references,
 configuration inspection, and namespace/collection inventories retain their
@@ -366,8 +367,11 @@ Default tests remain offline and independent of real credentials.
   Resolve and cover duplicate-name precedence across the two input forms.
 - [ ] Output-contract override and appended-message flags remain outside this
   adoption, with their operator use cases retained in future work.
-- [ ] Namespace defaults, explicit clearing, qualified selections, and catalog
-  filters are forwarded according to the selected design.
+- [ ] Opt-in namespace selectors combine declared suite defaults with supplied
+  fields in one native view update. Omission preserves each declared default;
+  explicit empty values clear only the selected default. Qualified selections
+  and catalog filters retain their native meanings. Custom scoped loaders remain
+  usable without the option.
 - [ ] The full configuration suite retains six subcommands. Explanation
   discovery and validation diagnostics are modes of existing commands, with
   capability-aware help and selected mode/flag combination checks.
@@ -582,18 +586,27 @@ general-purpose request-building API follows from these CLI choices.
 
 ### OD-3: Namespace flags and loader defaults
 
-**Recommendation:** make the standard namespace selectors opt-in with explicit
-suite-owned namespace defaults. Compose supplied fields with those defaults,
-then apply one native `WithNamespaces` call. Loaders using this option leave
-default selection to that adapter. This gives omission and explicit empty
-values predictable meanings without trying to read private engine state.
-Without the option, existing scoped loaders continue as before.
+**Agreed:** make the standard namespace selectors opt-in with explicit
+application-supplied defaults for prompts, profiles, and backends in the suite.
+`ckprompt` combines those defaults with the supplied CLI fields, then applies
+one native `WithNamespaces` call. Loaders using this option leave namespace
+default selection to that adapter rather than relying on hidden engine-view
+state. Without the option, existing scoped loaders continue as before.
 
-**Alternative:** pass presence-aware namespace choices to an acquisition
-callback and let the application combine them with its existing loader defaults.
-This accommodates applications whose defaults depend on domain input, but adds
-consumer wiring and makes consistent behavior less automatic. Either design
-must account for the native API replacing all three defaults at once.
+Omitting a selector preserves its declared default. Supplying a namespace
+replaces that default for the invocation; supplying an explicitly empty value
+clears it. Each resource type is independent. For example, overriding the
+prompt namespace must preserve the declared profile and backend defaults.
+Qualified resource IDs pass through unchanged. Catalog namespace filters remain
+separate from these resource-resolution defaults.
+
+The standard option owns composition instead of requiring an application
+callback to merge every selection. Applications needing custom namespace
+selection can retain their own loading behavior without enabling the option.
+
+**Remaining design:** select exact flag names, scoped convenience aliases,
+and applicability to individual commands. These details are not settled by
+agreement on default composition.
 
 ### OD-4: Configuration path and metadata presentation