scripts: archive obsolete one-off shell/python scripts to legacy/ (D2, D3)

D2: run_benchmark.sh and run_experiments.sh still pass --time-scale and
--max-inflight-sessions to the replayer, but those flags were removed when
the project moved to trace-driven dispatch. The scripts cannot run as-is.

D3: ~25 ad-hoc analyze_* / compare_* / profile_* / final_* scripts and a
handful of single-experiment run_*.sh point at /home/admin/cpfs paths,
deleted output directories, or a sampled trace file that no longer exists.
Keep them in scripts/legacy/ for historical reference; the scripts that
remain in scripts/ (analyze_trace, analyze_breakdown, analyze_cache_hit,
analyze_eviction, compare_results, compute_roofline, sample_trace,
analyze_agentic_patterns, simulate_cache_policies, plus launch_*.sh,
gpu_monitor.sh, bench.sh) cover the current workflow.

Adds scripts/legacy/README.md to document the archival policy.

scripts/legacy/run_lmetric_ab.sh

@@ -0,0 +1,56 @@
+#!/bin/bash
+# A/B comparison: linear (session-sticky) vs lmetric (OSDI'26, no affinity).
+# Wraps bench.sh for guaranteed fresh state between experiments.
+#
+# Usage:
+#   bash scripts/run_lmetric_ab.sh                    # defaults: 200 req
+#   bash scripts/run_lmetric_ab.sh --requests 1000    # override request count
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PROJECT_DIR="$(dirname "$SCRIPT_DIR")"
+VENV="${VENV_PATH:-$PROJECT_DIR/.venv/bin}"
+TS=$(date +%Y%m%d_%H%M%S)
+
+echo "================================================================"
+echo "  A/B: Linear vs LMetric routing policy"
+echo "  $(date)"
+echo "================================================================"
+
+echo ""
+echo "=== Experiment 1/2: Linear (session-sticky) ==="
+bash "$SCRIPT_DIR/bench.sh" --tag "ab_linear_${TS}" --mode baseline --policy linear "$@"
+
+echo ""
+echo "=== Experiment 2/2: LMetric (no affinity) ==="
+bash "$SCRIPT_DIR/bench.sh" --tag "ab_lmetric_${TS}" --mode baseline --policy lmetric "$@"
+
+echo ""
+echo "================================================================"
+echo "  Results comparison"
+echo "================================================================"
+"$VENV/python" -c "
+import json
+
+def summarize(path):
+    rows = [json.loads(l) for l in open(path)]
+    ok = [r for r in rows if not r.get('error')]
+    p = lambda v,q: sorted(v)[min(int(q*len(v)),len(v)-1)] if v else 0
+    ttfts = [r['ttft_s'] for r in ok if r.get('ttft_s')]
+    tpots = [r['tpot_s'] for r in ok if r.get('tpot_s') and r['tpot_s']>0]
+    e2es = [r['latency_s'] for r in ok]
+    return len(ok), len(rows), p(ttfts,.5), p(ttfts,.9), p(tpots,.9), p(e2es,.5)
+
+lin = summarize('$PROJECT_DIR/outputs/ab_linear_${TS}/metrics.jsonl')
+lm = summarize('$PROJECT_DIR/outputs/ab_lmetric_${TS}/metrics.jsonl')
+
+fmt = '  %-20s OK=%3d/%3d  TTFT50=%7.3f  TTFT90=%7.3f  TPOT90=%6.4f  E2E50=%7.3f'
+print(fmt % ('Linear', *lin))
+print(fmt % ('LMetric', *lm))
+print()
+for name, i in [('TTFT50',2),('TTFT90',3),('TPOT90',4),('E2E50',5)]:
+    d = (lm[i] - lin[i]) / lin[i] * 100 if lin[i] else 0
+    print('  %s delta: %+.1f%%' % (name, d))
+"
+
+echo ""
+echo "Done at $(date)"