fix: script/test conditional-verbose-rerun with -cover (closes #59)

script/test now runs the suite quietly first (with -race and -cover, 30s timeout) and re-runs it with -v only when that run fails, then exits non-zero. This is the pattern REPO_POLICIES.md mandates; before, every green run printed full per-test output.

What a reader would trip over: the whole compound command is passed as one string to run_with_cgo_deps, so it behaves the same on the host path and under the nix-shell fallback. -cover is on the first run only; the verbose rerun exists for diagnostics.

Disclosure: no test was written for the wrapper script itself; the failure path was exercised by hand by author and reviewer.
Disclosure: the nix-shell fallback is kept; moving tests into Docker belongs to #101 and #104.

Model: opus-4-8 (implementation, review); fable-5-1 (landing message)

script/test

@@ -17,7 +17,11 @@ run_with_cgo_deps() {
 main() {
     cd "$ROOT"
     echo "Running tests..."
-    run_with_cgo_deps "CGO_ENABLED=1 go test -timeout 30s -race -v ./..."
+    # Run without -v first for clean output on success; on failure rerun
+    # with -v for full diagnostics, then exit non-zero (REPO_POLICIES.md
+    # conditional-verbose-rerun pattern). The first run already proved the
+    # tests broken, so the build fails even if the rerun happens to pass.
+    run_with_cgo_deps "CGO_ENABLED=1 go test -timeout 30s -race -cover ./... || { echo '--- Rerunning with -v for details ---'; CGO_ENABLED=1 go test -timeout 30s -race -v ./...; exit 1; }"
 }
 
 main "$@"