fix(conformance): pass absolute --report-path so run.sh is CWD-robust

run.sh exited non-zero (breaking the L2 gate) when invoked from the repo root:
chainsaw's config report.path is relative (_artifacts), so it resolved against
$PWD and failed to write ('open _artifacts/chainsaw-report.xml: no such file')
even though all tests passed. Pass --report-path ${ARTIFACTS} (absolute) +
mkdir -p first. Verified: R-NET-01 from repo root now exits 0 with report written.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

conformance/run.sh

@@ -137,8 +137,14 @@ run_chainsaw() {
 
   log "Running Chainsaw over ${#dirs[@]} test dir(s) with pinned ${CHAINSAW_VERSION}"
   # Chainsaw writes JUnit per config/chainsaw-config.yaml (report.* under _artifacts).
+  # --report-path is passed ABSOLUTE (overriding the config's relative `_artifacts`) so the report
+  # write succeeds regardless of the caller's CWD — otherwise chainsaw's relative path resolves
+  # against $PWD and fails ("open _artifacts/chainsaw-report.xml: no such file") when run.sh is
+  # invoked from the repo root instead of conformance/.
+  mkdir -p "${ARTIFACTS}"
   chainsaw test \
     --config "${CONF_ROOT}/config/chainsaw-config.yaml" \
+    --report-path "${ARTIFACTS}" \
     "${test_dir_args[@]}"
 
   # Normalize whatever chainsaw named the report to a stable path CI collects.