Plan filesystem sources and underlays

docs/policy/architecture.md

@@ -108,6 +108,22 @@ must never run implicitly as part of configuration loading.
 Remote data can enter through application-supplied input without introducing a
 network provider into the library.
 
+## Loading Lifecycle
+
+Configuration loading is a synchronous, complete-on-return operation. A successful
+load provides the final configuration and inspection metadata after the configured
+processing and validation phases complete. A failed load reports diagnostics and
+returns no usable partial result. The normal application pattern is one load near
+startup; applications may explicitly initiate additional loads.
+
+ConfigKit releases its library-owned loading handles before returning and remains
+inactive until the application explicitly invokes it again. It performs no
+background watching, refresh, or mutation of published results. Caller-owned
+resources and application callback effects remain the caller's responsibility.
+The [configuration contract](../config.md#completion-and-resource-lifetime) owns
+the precise completion and ownership behavior. The proposed decision record is
+[ADR 0008](../adr/0008-complete-on-return-loading.md).
+
 ## Public API And Dependency Direction
 
 Keep one small, coherent public surface for the supported lifecycle. Simple
@@ -136,9 +152,20 @@ framework on this library.
 
 ## Configuration Integrity
 
-Composition and intentional overlay are distinct operations. Composition must
-not silently become last-wins override through file ordering. The decision and
-alternatives are recorded in [ADR 0001](../adr/0001-separate-composition-and-overlay.md).
+Within a configuration tier, independent contributions use strict composition:
+shared mappings combine recursively, while overlapping non-mapping definitions
+are conflicts, including equal values. Between precedence tiers, intentional
+overlay combines mappings recursively, retains omitted lower-priority children,
+and replaces other present values according to the existing overlay rules.
+Tier precedence is explicit; traversal order within a tier establishes stable
+reporting, not permission to override. The distinction and its rationale are
+recorded in [ADR 0001](../adr/0001-separate-composition-and-overlay.md).
+
+The main document and its imports currently form the strictly composed base
+tier. Input-specific constraints, including CLI path rules and opt-in version
+ownership, remain part of the configuration contract. Consistent combination
+semantics do not require identical acquisition or lifetime behavior from every
+source kind.
 
 ConfigKit must define supported YAML semantics explicitly rather than inherit
 parser defaults. Processing order and diagnostics must be deterministic for the