Add Cobra-backed command parsing

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # Initial CommandKit implementation plan
 
-Status: implementation underway; Stages 1-3 complete and Stages 4-14 pending.
+Status: implementation underway; Stages 1-4 complete and Stages 5-14 pending.
 
 Date: 2026-10-07.
 
@@ -294,7 +294,7 @@ preparation parses supplied values without enforcing omitted required values.
 
 ## Stage 4: implement the internal Cobra adapter
 
-**Status:** pending. **Prerequisite:** Stage 3.
+**Status:** complete. **Prerequisite:** Stage 3.
 
 1. Create `internal/cobra` with neutral tree/flag/operand declarations and fresh
    per-run binding factories. A bridge declaration contains path metadata,
@@ -338,6 +338,12 @@ parser causes without scanning their object graphs.
 unknown flags, boolean spellings, last-wins/repetition, help with missing required
 inputs, and fresh consecutive parses. Confirm the root does not import Cobra/pflag.
 
+**Completion evidence:** internal adapter and root-to-adapter integration tests
+cover command routing, local flags, interspersed operands, `--`, boolean presence
+and explicit false, repeated raw values, help parsing, group failures, and fresh
+parse state. `go test ./...` passes; the root package's direct imports include
+only the internal adapter and not Cobra or pflag.
+
 ## Stage 5: implement invocation and diagnostic delivery
 
 **Status:** pending. **Prerequisite:** Stage 4.