Add semantic paths and safe diagnostics

docs/roadmap/implementation.md

@@ -2,7 +2,7 @@
 
 ## Status and ownership
 
-Status: implementation in progress; Stage 1 is complete and later stages are
+Status: implementation in progress; Stages 1–2 are complete and later stages are
 pending.
 
 Audience: a `gpt-5.6-terra` coding agent implementing one stage per prompt, in
@@ -333,7 +333,25 @@ Acceptance:
 
 ## Stage 2 — Implement semantic paths and safe diagnostic records
 
-Status: pending.
+Status: complete.
+
+Completion evidence (2026-09-06):
+
+- Implemented immutable key/index paths, strict JSON Pointer parsing, canonical
+  spelling, parsed numeric-token preservation, and private traversal intent in
+  [`path.go`](../../path.go).
+- Implemented detached metadata/provenance records and empty/unknown query behavior
+  in [`records.go`](../../records.go) and [`metadata.go`](../../metadata.go).
+- Implemented canonical diagnostic ordering, related-location normalization,
+  control-safe rendering, short/error writer propagation, and defensive
+  `LoadError` access in [`diagnostic.go`](../../diagnostic.go). No raw values,
+  parser errors, source parsing, or loading surface was introduced.
+- Added focused tests for escaped slash/tilde/empty/dotted/numeric keys, literal
+  dot/percent tokens, malformed escapes, builder immutability, detached nested
+  records, `errors.As`, ordering independence, control escaping, and failing/short
+  writers. Verified `go test ./...`, `go vet ./...`, `go build ./...`, and
+  `git diff --check` with Go 1.26.7 on linux/amd64. No deviations were required;
+  metadata population and configuration lifecycle behavior remain later work.
 
 Read: feature [paths](initial.md#paths-and-presence),
 [diagnostics](initial.md#provenance-diagnostics-and-redaction), public metadata API.