Add reusable CI preparation operations

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # ReleaseKit audit implementation plan
 
-Status: Stages 1–7 complete; Stage 8 next.
+Status: Stages 1–8 complete; Stage 9 next.
 Baseline: `e4be7fa` (2026-10-06). The [audit](audit.md) records the evidence,
 product goals, and selected direction. This document owns implementation order
 and completion criteria for that work.
@@ -412,6 +412,18 @@ uses the repository and preparation environment and propagates failure and
 cancellation. Keep default tests offline with a local module cache or a small
 Go-command fixture; no live module server is needed.
 
+**Completed:** The root facade now exposes `PrepareTaggedCheckout` and
+`PrepareBuildDependencies`. Checkout preparation fetches an explicit tag
+refspec, compares the peeled commit with the expected full object ID, and
+detaches only after a match; tests cover default and selected remotes, wrong
+commits, conflicting local edits and tags, and input rejection before fetch.
+Dependency preparation runs `go mod download` with workspace discovery off and
+the local Go toolchain, preserving caller proxy, private-module, and cache
+settings; subprocess fixtures verify repository selection, failure details,
+and cancellation without network access. GoDoc, the delivery consumer guide,
+and the internal inventory describe effects and ownership. The full offline
+suite, API boundary check, and documentation whitespace checks pass.
+
 ## Stage 9 — Add the shared CI delivery command
 
 **Covers:** the shared command portion of F6.