Install shell completion as an optional command

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # Shell completion implementation plan
 
-Status: Stages 1–2 complete. Stage 3 is next.
+Status: Stages 1–3 complete. Stage 4 is next.
 
 Implement the [shell completion roadmap](completion.md) from baseline
 `2301872`. Follow the stages in order in one sprint. Intermediate stages may
@@ -109,6 +109,8 @@ internal adapter, and neutral metadata package tests pass with `GOWORK=off` and
 
 ## Stage 3: Install completion as an ordinary declaration
 
+Status: complete.
+
 1. Add `func Completion(executable string) Command`. The parameter is the
    executable basename the operator types, independent of the human-readable
    `Identity.Name`. Use a root-only `completion` group with three runnable
@@ -134,6 +136,16 @@ internal adapter, and neutral metadata package tests pass with `GOWORK=off` and
    rollback, late installation, and absence of new reserved names for an app
    that does not install completion.
 
+Completion: added the root-only completion declaration and three script
+commands, with generator output delivered through the invocation reporter.
+Registration validates hidden-query collisions in either order, and the routing
+snapshot reflects committed installation. Tests cover help, quiet output,
+delivery failure, invalid basenames, opt-in behavior, collisions, rollback,
+nesting, and late installation. Fish variable names are adjusted to support
+dotted executable basenames; interactive checks of those names pass in Bash,
+Zsh, and Fish. Root and adapter package tests pass with `GOWORK=off` and
+`GOTOOLCHAIN=local`.
+
 ## Stage 4: Resolve the entered command context
 
 1. Add a private core completion request that separates completed words from