chore: scripts/hammer.sh — flake-hammer for conn-lifecycle discipline

Default run encodes the pre-commit ritual: 35x the lifecycle-sensitive
integration subset (shutdown timeout reaped slowloris streaming chunked
sse stalled), fail-fast, then 3x the full suite. -n/-f override counts,
'-- <words>' overrides the filter. Failing run's output lands in
target/hammer-fail.log.

scripts/hammer.sh

@@ -0,0 +1,59 @@
+#!/usr/bin/env bash
+# Flake hammer: the conn-lifecycle test discipline, in one command.
+#
+# Default (no args) = the full pre-commit ritual for conn-lifecycle changes:
+#   1. N x the lifecycle-sensitive integration subset (fail-fast)
+#   2. M x the full suite (unit + integration + doc)
+#
+# Usage:
+#   scripts/hammer.sh                 # 35x subset + 3x full
+#   scripts/hammer.sh -n 50 -f 5      # override counts
+#   scripts/hammer.sh -n 20 -f 0 -- shutdown sse   # custom filter, skip full runs
+#
+# On failure: stops immediately, output of the failing run is in $LOG.
+
+set -u
+cd "$(dirname "$0")/.."
+export PATH="$HOME/.cargo/bin:$PATH"
+
+N=35
+FULL=3
+SUBSET=(shutdown timeout reaped slowloris streaming chunked sse stalled)
+
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    -n) N="$2"; shift 2 ;;
+    -f) FULL="$2"; shift 2 ;;
+    --) shift; SUBSET=("$@"); break ;;
+    *) echo "unknown arg: $1" >&2; exit 2 ;;
+  esac
+done
+
+LOG=target/hammer-fail.log
+mkdir -p target
+
+echo "== build once =="
+cargo test --no-run --quiet || exit 1
+
+fail() { # $1 = label
+  echo
+  echo "FAILED at $1 — output in $LOG"
+  exit 1
+}
+
+echo "== ${N}x subset: ${SUBSET[*]} =="
+for ((i = 1; i <= N; i++)); do
+  printf '\r  subset %d/%d ' "$i" "$N"
+  cargo test --quiet --test integration -- "${SUBSET[@]}" >"$LOG" 2>&1 \
+    || fail "subset run $i/$N"
+done
+echo
+
+echo "== ${FULL}x full suite =="
+for ((i = 1; i <= FULL; i++)); do
+  printf '  full %d/%d\n' "$i" "$FULL"
+  cargo test --quiet >"$LOG" 2>&1 || fail "full run $i/$FULL"
+done
+
+rm -f "$LOG"
+echo "hammer green: ${N}x subset + ${FULL}x full"