Decode typed configuration over defaults

docs/roadmap/implementation.md

@@ -2,7 +2,7 @@
 
 ## Status and ownership
 
-Status: implementation in progress; Stages 1–5 are complete and later stages are
+Status: implementation in progress; Stages 1–6 are complete and later stages are
 pending.
 
 Audience: a `gpt-5.6-terra` coding agent implementing one stage per prompt, in
@@ -564,7 +564,31 @@ Acceptance:
 
 ## Stage 6 — Decode scalar and container values over defaults
 
-Status: pending.
+Status: complete.
+
+Completion evidence (2026-09-06):
+
+- Added schema-driven typed decoding in [`decode.go`](../../decode.go), starting
+  from the Stage 5 detached clone and returning only private typed state, input
+  presence, projected baseline/final trees, and per-path default/base origins.
+- Implemented recursive mapping retention, atomic sequence replacement, exact array
+  lengths, pointer-object zero allocation versus non-nil retention, nullable-shape
+  clearing, strict nested map values, inline-map decoding, and unknown-field errors.
+- Added checked destination-width integers and floats, dynamic `int64`/`float64`,
+  named scalars, duration strings, paired text codecs, safe value-free failures, and
+  collection of independent decode errors at original semantic paths/coordinates.
+  The [current configuration contract](../config.md#defaults-and-typed-decoding) and
+  component inventory now own this behavior.
+- Adapted Narratio's fresh-default, presence, strict nested-type, and repeated-load
+  cases, replacing custom YAML hooks and pointer/zero guesses with tree-derived
+  presence; explicit empty and null are retained and equal-valued input is explicit.
+  Focused coverage includes the defaults operation table, new/existing map entries,
+  empty mappings/sequences, nil/non-nil pointer objects, default isolation, numeric
+  range and coercion failures, integer durations, inline collisions, nested unknown
+  fields, coordinates, safe codec failures, and independent repeated results.
+  Verified `go test ./...`, `go vet ./...`, `go build ./...`, `go mod tidy -diff`,
+  and `git diff --check` with Go 1.26.7 on linux/amd64. No deviations were required;
+  public loading and schema-version checks remain later work.
 
 Read: feature [defaults/null](initial.md#static-defaults-and-null) and typed decoding.