Index backend commands for path lookup

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # Performance implementation plan
 
-Status: implementation in progress; Stages 1–3 are complete, Stages 4–11 have not started.
+Status: implementation in progress; Stages 1–4 are complete, Stages 5–11 have not started.
 
 Date: 2026-10-09.
 
@@ -376,7 +376,7 @@ construction; text requests retain their report semantics and formatting errors.
 
 ## Stage 4: index backend declarations and traverse parents
 
-**Status:** not started. **Prerequisite:** Stage 3.
+**Status:** complete. **Prerequisite:** Stage 3.
 
 **Files:** [adapter](../../internal/cobra/parse.go),
 [adapter tests](../../internal/cobra/parse_test.go), relevant benchmarks, and
@@ -402,7 +402,30 @@ parse and dispatch benchmarks.
 **Completion:** declaration lookup uses the index and ancestry traversal is
 proportional to selected depth after backend construction.
 
-**Evidence:** pending.
+**Evidence:** `go test -mod=readonly -count=1 ./internal/cobra .` passed with
+the common offline environment settings. The focused test covers a 24-level
+path, 128 siblings, root selection, unknown help/usage paths, and exact help and
+usage resolution. Existing exact-path and parse failure tests remain in place.
+
+Measurements used Go 1.26.8, linux/amd64, Linux 6.17.0-41-generic, Intel Core
+i5-7260U CPU @ 2.20 GHz, based on source revision `628dc78` with this stage's
+changes in the working tree. The five-sample adapter command was
+`GOWORK=off GOTOOLCHAIN=local GOPROXY=off GONOPROXY=none GOSUMDB=off go test -mod=readonly -run '^$' -bench '^BenchmarkPerformanceParse$' -benchmem -benchtime=200ms -count=5 ./internal/cobra`;
+the dispatch command used the same flags with `-bench
+'^BenchmarkPerformanceDispatch$' .`. Both passed. Raw outputs are in
+`/tmp/commandkit-performance-parse-after-stage4.txt` and
+`/tmp/commandkit-performance-dispatch-after-stage4.txt`.
+
+Adapter shallow/wide Parse measured 149,426–171,199 ns/op,
+242,936 B/op, and 1,705 allocs/op, compared with baseline 150,918–171,598
+ns/op, 242,936 B/op, and 1,705 allocs/op. Deep Parse measured 90,608–104,770
+ns/op, 119,536 B/op, and 826 allocs/op, compared with baseline 86,282–109,697
+ns/op, 119,920 B/op, and 827 allocs/op. Timings overlap; deep parsing saves
+384 B and one allocation. End-to-end dispatch allocations remain effectively
+unchanged across the measured cases. Timing variation, including deep-help
+outliers, is substantial, so these runs do not support an end-to-end speedup
+claim. The comparison isolates the selected-path lookup change while backend
+tree construction remains in each parse.
 
 ## Stage 5: scan YAML preambles without splitting documents