Implement canonical projection and detached copies

docs/roadmap/implementation.md

@@ -2,7 +2,7 @@
 
 ## Status and ownership
 
-Status: implementation in progress; Stages 1–4 are complete and later stages are
+Status: implementation in progress; Stages 1–5 are complete and later stages are
 pending.
 
 Audience: a `gpt-5.6-terra` coding agent implementing one stage per prompt, in
@@ -512,7 +512,30 @@ Acceptance:
 
 ## Stage 5 — Implement canonical projection and detached copies
 
-Status: pending.
+Status: complete.
+
+Completion evidence (2026-09-06):
+
+- Added descriptor-driven canonical typed projection and independently owned cloning
+  in [`projection.go`](../../projection.go), without YAML serialization or a second
+  binding model. Zero values, nil/empty distinctions, exact integers, destination-
+  precision finite floats, durations, text scalars, dynamic concrete values, and
+  recursive acyclic objects retain their configuration meaning.
+- Added active-graph cycle detection, private depth/node enforcement, safe custom
+  codec and dynamic-type failures, zeroing of ignored state, reconstruction of text
+  scalars into fresh instances, and non-preservation of shared pointer identity.
+- Added canonical-tree structural comparison with semantic mapping additions,
+  removals and replacements, cross-kind replacement, and whole-sequence atomicity.
+  The [current ownership contract](../config.md#typed-projection-and-ownership) and
+  component inventory now own the implemented behavior.
+- Focused tests mutate every source alias after cloning, cover nil versus empty,
+  wide integers, duration/text canonicalization, recursive acyclic values and cycles,
+  unsupported dynamic types, non-finite floats, value-free codec failures, inline
+  physical members/conflicts, projection bounds, ignored state, and meaningful
+  comparison paths without index-wise sequence matching. 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; defaults and typed decoding
+  remain later work.
 
 Read: feature [ownership](initial.md#recorded-resolution-and-validation) and
 [type/projection contract](initial.md#supported-types-and-projection).