test: port 989_lib_byteid to ww; birth test/testenv + test/byteid

test/testenv (package testenv) is the shared plumbing for ww-native
test drivers — subprocess launch with captured output, file IO, string
search, byte-sorted directory listing, scratch ownership — lifted from
the proven package_test.ww idiom; a utility, not a framework.

test/byteid/libbyteid_test.ww carries every assertion of the retired C
carrier: the 44-entry roster (fixtures + sentinel-guarded import probes
+ the zero-dep root-only build), both-stage sep builds with the
resolved-unit proof, per-package .s concat compare with the empty-concat
guard, the ID/DIVERGE/WWREJECT pin discipline, and the lib/ corpus
completeness scan (negative-verified against a planted un-enrolled
module). Concat order strengthened from shell-glob to explicit
byte-lexicographic. The roster fills by cursor-driven field writes
because append() rejects struct-call-result sources (#34).

Byteid carriers 11 -> 10; docs counts move; test-byteid runs the ww
test via the wwtest/ pattern with WW_TEST_REPO.

docs/test-system-v2.md

@@ -36,8 +36,8 @@ The live declarative compiler corpus has 1,495 fixtures and 2,990 C/WW cells:
 338 expected rejections (314 shared and 24 stage-specific), 17 compile-only
 successes, 198 exit-zero programs, and 942 explicit-exit programs.
 
-134 native C carriers remain. They are partitioned exactly once as five
-in-process units, 11 byte/artifact gates, six bootstrap gates, one platform
+133 native C carriers remain. They are partitioned exactly once as five
+in-process units, 10 byte/artifact gates, six bootstrap gates, one platform
 gate, and 111 residual compiler, package-layout, ABI, diagnostic-observer,
 driver, linker, or FFI gates. Rows migrated to fixtures or native `@test`
 owners were removed from those carriers; there is no compatibility execution
@@ -46,11 +46,15 @@ was a cstage-vs-wwstage `.s` byte-compare of sources now living in the
 corpus were retired into the blanket `test-data-byteid` comparator (the
 last 13 had their remaining inline sources added as fixtures first); the
 survivors observe something the blanket cannot: assembly patterns, symbol
-tables, `.wwi` round-trips, or the wwstage-driver leg. Wwstage-driver-leg byte identity (`ww_ww` versus `ww`
-over the emitted `.s` set) has one owner, `989_lib_byteid`, whose unit
-sweep spans lib test fixtures, import probes, and a zero-dep root-only
-build; the former 815/940/951 driver-parity carriers were folded into it,
-their content identity already owned by their corpus twins.
+tables, `.wwi` round-trips, or the wwstage-driver leg. Wwstage-driver-leg
+byte identity (`ww_ww` versus `ww` over the emitted `.s` set) has one
+owner, now ww-native: `test/byteid/libbyteid_test.ww` on the
+`test/testenv` helper package, whose unit sweep spans the 44-entry lib
+roster (test fixtures, sentinel-guarded import probes, a zero-dep
+root-only build) plus the lib/ completeness scan; the former 815/940/951
+driver-parity carriers were folded into it, their content identity
+already owned by their corpus twins, and the native `989_lib_byteid.c`
+carrier retired with the port.
 
 ## Carrier endgame