Remove the completed step 4 migration roadmap

docs/roadmap/implementation.md

@@ -1,62 +0,0 @@
-# Migration Step 4 Implementation Plan
-
-## Status
-
-Complete as of 2026-07-28. The public-facade adapter boundary and its
-post-implementation remediation are fully revalidated.
-
-## Objective
-
-This plan completed the target state in the
-[Step 4 public-facade adapter roadmap](step4.md) without changing the intended
-CLI, HTTP, or public Go contracts.
-
-The [accepted split decision](../adr/0002-split-promptkit-from-scriptorium.md)
-owns the long-term Promptkit/Scriptorium boundary. The
-[testing policy](../policy/testing.md) governs test value and ownership. The
-[documentation policy](../policy/documentation.md) governs completion
-bookkeeping and canonical ownership.
-
-## Constraints
-
-- Keep this work in the Scriptorium repository. Do not modify the sibling
-  Promptkit repository or infer that Migration Step 5 is complete merely from
-  its local presence.
-- Preserve the public `ArtifactReader`, error sentinel, CLI, HTTP, containment,
-  artifact-size, formatting, timeout, credential, and redaction contracts.
-- Do not add compatibility shims, begin framework extraction, change the module
-  path, or add dependencies.
-- Keep tests deterministic, offline, independent of machine MIME databases,
-  and focused at the narrowest stable owner.
-- Preserve unrelated working-tree changes.
-
-## Completed Work
-
-The original implementation established the Step 4 boundary:
-
-- the root facade now exposes `ArtifactReader` and `WithArtifactReader`, copies
-  mutable artifact bodies, handles nil responses, and exposes the two specific
-  public request-error identities required by HTTP;
-- the restricted artifact reader and its containment and byte-limit policy now
-  belong to the HTTP adapter and use public artifact types;
-- prepared-run formatting and CLI `run` and `render` consume public prepared,
-  request, and result values;
-- the HTTP handler consumes a local interface expressed in public types, and
-  CLI `serve` injects the restricted reader into the public engine;
-- the legacy restricted framework reader was removed, current-behavior
-  documentation was reconciled, and an initial dependency guard was added; and
-- the initial validation pass covered the full suite, vet, build, race and
-  repeated tests, maintained examples, configuration loading, links, and
-  whitespace.
-
-The post-implementation remediation is also complete:
-
-- public error mapping retains collaborator identities while adding the active
-  operation's public category;
-- HTTP artifact MIME coverage uses a built-in media type while retaining the
-  unknown-extension fallback check;
-- the dependency guard recursively scans production adapter and formatter
-  sources and rejects descendants of forbidden framework package families; and
-- the final validation passed full and repeated tests, vet, a temporary-output
-  build, race checks, maintained examples, both maintained configuration files,
-  import and link inspection, and whitespace validation.