CB-WP-0006 T04: withdraw AM-4c; and fix where AM-6 is measured

AM-4c is withdrawn from the acceptance table and retained as a reported
diagnostic. GameKernel §5a carries the argument.

The ratio has no monotone better direction. INTENT's rule is "own the
semantics, assimilate the implementation": rising can mean owning
semantics properly or reimplementing what should have been assimilated;
falling can mean leverage or dependency bloat. A target requires knowing
which way is better. It is also redundant — AM-4a/AM-4b bound the
denominator and AM-2 bounds own-source density, so AM-4c is a ratio of two
already-targeted quantities.

Measured at withdrawal: 1,426 own lines per 100k third-party (shipped),
1,107 (dev). make dep-weight now prints both, labelled diagnostic — the
row was never actually reported before.

M-D1-MUT keeps AM-4c in its denominator on purpose and says so in the
output. Dropping it would move the score 7/14 -> 7/13 without enforcing
anything: a score improved by deleting the question.

Decided before Phase B deliberately, since ADR-0005 predicts own-source
growth that will move this ratio; deciding after would be the retarget
§Step 4 forbids.

A T01 correction found here. The AM-6 gate failed inside `make all` at
38,753 ev/s against 341,280 in isolation — a 9x drop, because cargo test
runs binaries and threads concurrently. A throughput assertion inside a
parallel harness measures contention, not throughput. T01's measurement
was valid; its gate placement was not.

Fixed by running it only where valid — #[ignore] plus `make am6` in
release with --test-threads=1, now 2.0M ev/s at 20.2x headroom — and not
by lowering the target, which T01 forbade. My first attempt did drift that
way, adding a debug "sanity floor" of 50,000, and was backed out: a second
threshold is still a second chance to tune.

The mutation then went SURVIVED on the first run after the move. 4,000
black_box iterations were calibrated against debug's 3.4x headroom and are
invisible against release's 20x. Raised to 100,000; back to red. A weak
mutation is not a fixed property of a row — it can become weak when the
row's measurement conditions change.

Tier S (amends one row, creates no capability), chaos d4=2, no override.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Makefile

@@ -24,7 +24,7 @@ TOOLS := $(REPO)/tools
 # Every cargo recipe runs at the repo root; the shell does not persist cd.
 IN_REPO := cd $(REPO) &&
 
-.PHONY: check test sim bench bench-test coverage dep-weight cost cost-test cost-pin cost-budget cost-mix loop-lint self-tests env-test task-done status facts-check facts-gen mutation-check size-metrics runtime-metrics build-time loc all
+.PHONY: check test sim bench bench-test coverage dep-weight cost cost-test cost-pin cost-budget cost-mix loop-lint self-tests env-test task-done status facts-check facts-gen mutation-check size-metrics runtime-metrics build-time am6 loc all
 
 ## fmt + clippy (deny warnings) + HashMap deny-lint
 check:
@@ -42,6 +42,13 @@ dep-weight:
 coverage:
 	$(PY) $(TOOLS)/rule-coverage.py
 
+# AM-6 gate. Runs in RELEASE, where headroom is ~24x; the same assertion
+# in debug has ~3.4x and flaked under load. The target is unchanged — only
+# where it is measured.
+am6:
+	$(IN_REPO) $(CARGO) test --release -p games-ground --all-features \
+	  am6_throughput -- --ignored --nocapture --test-threads=1
+
 # AM-9 peak RSS (fast, gated). AM-5 needs a clean build — see build-time.
 runtime-metrics:
 	$(PY) $(TOOLS)/runtime-metrics.py --fast
@@ -157,4 +164,4 @@ loc:
 		printf '%-28s %s\n' $$d "$$(find $$d/src -name '*.rs' | xargs cat | grep -vcE '^\s*(//|$$)')"; \
 	done
 
-all: check test sim coverage size-metrics runtime-metrics dep-weight self-tests env-test facts-check loop-lint bench-test
+all: check test sim coverage size-metrics runtime-metrics am6 dep-weight self-tests env-test facts-check loop-lint bench-test