diff --git a/.github/workflows/performance-ab.yml b/.github/workflows/performance-ab.yml
index 320e11c77..cf9fb8037 100644
--- a/.github/workflows/performance-ab.yml
+++ b/.github/workflows/performance-ab.yml
@@ -30,9 +30,9 @@ on:
   workflow_dispatch:
     inputs:
       duration:
-        description: "warp duration per round"
+        description: "warp duration per round (short by default to fit the double-build budget)"
         required: false
-        default: "30s"
+        default: "12s"
         type: string
       allow_regression:
         description: "Pass the gate despite a FAIL (deliberate tradeoff)"
@@ -69,7 +69,12 @@ jobs:
       (contains(github.event.pull_request.labels.*.name, 'perf-ab') &&
        (github.event.action != 'labeled' || github.event.label.name == 'perf-ab'))
     runs-on: sm-standard-2
-    timeout-minutes: 90
+    # Phase-0 stopgap: the baseline+candidate release double-build alone is
+    # ~65min on this runner, so 90min left no room for a real full-matrix
+    # measurement (the earlier nightly runs only ever failed *before*
+    # measuring). 120min gives the 24-cell short matrix headroom until perf-3
+    # caches the baseline binary and restores a tighter budget.
+    timeout-minutes: 120
     steps:
       - name: Checkout repository
         uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7
@@ -109,7 +114,17 @@ jobs:
         id: ab
         run: |
           set -euo pipefail
-          args=(--baseline-ref origin/main --duration "${{ github.event.inputs.duration || '30s' }}")
+          # Budget note: the baseline+candidate release double-build (~65 min,
+          # cached away later by perf-3) dominates the 90-min job, so the
+          # measurement runs a short warp matrix — duration/rounds/cooldown are
+          # kept small to fit all 24 cells (6 workloads x 2 phases x 2 drive-sync)
+          # under budget rather than dropping cells. --health-timeout 180 outlasts
+          # the server's own 120s startup-readiness budget, which is what the
+          # rig's previous 60s health poll undershot (the first two nightly
+          # failures). perf-6 will recalibrate these once the pipeline is green.
+          duration="${{ github.event.inputs.duration || '12s' }}"
+          args=(--baseline-ref origin/main
+            --duration "$duration" --rounds 2 --cooldown 5 --health-timeout 180)
           if [[ "${{ steps.exempt.outputs.allow_regression }}" == "true" ]]; then
             args+=(--allow-regression --exemption-reason "labeled perf-deliberate-tradeoff / dispatch override")
           fi
@@ -119,7 +134,14 @@ jobs:
           bash scripts/run_hotpath_warp_ab.sh "${args[@]}"
           echo "status=$?" >> "$GITHUB_OUTPUT"
           set -e
-          # Locate the newest gate.md for the comment/artifact steps.
+          # Locate the newest run dir + gate.md for the summary/comment/artifact
+          # steps. On a startup failure there is no gate.md, but the run dir still
+          # holds server-logs/ for diagnosis.
+          # Run dirs are UTC-timestamp names (no special chars); ls is safe here.
+          # shellcheck disable=SC2012
+          run_dir="$(ls -td target/hotpath-ab/*/ 2>/dev/null | head -n1 || true)"
+          echo "run_dir=${run_dir%/}" >> "$GITHUB_OUTPUT"
+          # shellcheck disable=SC2012
           gate_md="$(ls -t target/hotpath-ab/*/gate.md 2>/dev/null | head -n1 || true)"
           echo "gate_md=$gate_md" >> "$GITHUB_OUTPUT"
 
@@ -128,8 +150,49 @@ jobs:
         uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6
         with:
           name: hotpath-warp-ab-${{ github.run_number }}
+          # Includes per-cell median_summary.csv / baseline_compare.csv, gate.md,
+          # and server-logs/ (rustfs.log + startup env per phase) so a failed run
+          # is diagnosable. Short retention: this is churny nightly debug data.
           path: target/hotpath-ab/
           if-no-files-found: warn
+          retention-days: 14
+
+      - name: Write gate summary
+        if: always()
+        run: |
+          set -euo pipefail
+          status="${{ steps.ab.outputs.status }}"
+          gate_md="${{ steps.ab.outputs.gate_md }}"
+          run_dir="${{ steps.ab.outputs.run_dir }}"
+          {
+            echo "## Hotpath warp A/B — run ${{ github.run_number }}"
+            echo
+            if [[ "$status" == "0" ]]; then
+              echo "Rig/gate exit: \`0\` (pass or warn)."
+            else
+              echo "Rig/gate exit: \`${status:-unknown}\` — **FAILED**."
+            fi
+            echo
+            if [[ -n "$gate_md" && -f "$gate_md" ]]; then
+              cat "$gate_md"
+            else
+              echo "No \`gate.md\` produced — the rig failed **before** the gate"
+              echo "(most likely server startup / health). Failing phase(s) below;"
+              echo "full logs in the \`hotpath-warp-ab-${{ github.run_number }}\` artifact."
+              if [[ -n "$run_dir" && -d "$run_dir/server-logs" ]]; then
+                for f in "$run_dir"/server-logs/*.log; do
+                  [[ -f "$f" ]] || continue
+                  echo
+                  echo "<details><summary>$(basename "$f")</summary>"
+                  echo
+                  echo '```'
+                  tail -n 30 "$f"
+                  echo '```'
+                  echo "</details>"
+                done
+              fi
+            fi
+          } >> "$GITHUB_STEP_SUMMARY"
 
       - name: Comment gate result on PR
         if: always() && github.event_name == 'pull_request' && steps.ab.outputs.gate_md != ''
@@ -138,12 +201,19 @@ jobs:
         run: |
           gh pr comment "${{ github.event.pull_request.number }}" --body-file "${{ steps.ab.outputs.gate_md }}"
 
+      # TODO(ci-8/perf-2): scheduled/dispatch failures are currently silent. Once
+      # ci-8 lands the .github/actions/schedule-failure-issue composite action,
+      # perf-2 adds a step here guarded by
+      #   if: failure() && github.event_name != 'pull_request'
+      # that calls it (label perf-nightly-failure, append to an existing open
+      # issue) instead of hand-rolling gh CLI dedup. Do not implement it here.
+
       - name: Enforce gate
         if: always()
         run: |
           status="${{ steps.ab.outputs.status }}"
           if [[ "$status" != "0" ]]; then
-            echo "::error::warp A/B budget gate failed (exit $status). See the PR comment / gate.md artifact." >&2
+            echo "::error::warp A/B budget gate failed (exit $status). See the step summary / PR comment / gate.md artifact." >&2
             exit "$status"
           fi
           echo "warp A/B budget gate passed."
diff --git a/docs/operations/hotpath-warp-ab-runbook.md b/docs/operations/hotpath-warp-ab-runbook.md
index 8bb2f484b..0d5affed9 100644
--- a/docs/operations/hotpath-warp-ab-runbook.md
+++ b/docs/operations/hotpath-warp-ab-runbook.md
@@ -23,6 +23,29 @@ Metric directions: `reqps` (put obj/s) and `throughput` (get MiB/s) are
 higher-is-better; `latency` / p99 (mixed) is lower-is-better. warp is assumed
 pre-installed, as elsewhere in `scripts/`.
 
+## Workload matrix
+
+Six workloads × the drive-sync on/off matrix × baseline/candidate = 24 cells:
+
+| Workload | mode | size | why |
+| --- | --- | --- | --- |
+| `put-4kib` / `get-4kib` | put / get | 4KiB | the #4221 fsync regression size (~-10% @4KiB) — previously invisible |
+| `put-4mib` / `get-4mib` | put / get | 4MiB | bulk obj/s and MiB/s |
+| `get-10mib` | get | 10MiB | the historical large-GET EOF size |
+| `mixed-256k` | mixed | 256KiB | p99 latency |
+
+Sizes are passed to the load driver via `--sizes` (one size per cell); the
+driver's `DEFAULT_SIZES` covers 1KiB..10MiB, so any of those can be added by
+editing `WORKLOADS` in `scripts/run_hotpath_warp_ab.sh`. A 1KiB cell is left
+out for now to keep the nightly matrix under the 90-minute job budget (the
+baseline+candidate double build dominates until perf-3 caches it); re-enable it
+once that lands.
+
+CI runs a **short** warp matrix (`--duration`/`--rounds`/`--cooldown` tuned in
+`.github/workflows/performance-ab.yml`) so all 24 cells fit the budget without
+dropping cells. These params are deliberately noisy-but-fast for the Phase-0
+"keep the pipeline alive" goal; perf-6 recalibrates them.
+
 ## Local mode (quick / CI smoke)
 
 Builds both binaries and runs a throwaway single-node server on local disks.
@@ -94,6 +117,22 @@ cost to restore power-loss durability. For those, run with
 `--allow-regression` (or add the `perf-deliberate-tradeoff` label in CI): the
 FAIL is recorded and rendered as an exempted WARN, and the gate exits 0.
 
+## Diagnosing a failed run
+
+Each phase's server log and its startup environment are written under the run's
+output dir (`target/hotpath-ab/<ts>/server-logs/<phase>-sync-<sync>.{log,env}`)
+and uploaded in the `hotpath-warp-ab-<run>` artifact, so a failure is
+diagnosable after the fact. On a health-check failure the rig also dumps the
+last 50 log lines into the job log and the CI job writes the failing phase (or
+the gate table) into the GitHub step summary.
+
+Readiness polling waits up to `--health-timeout` seconds (default **180**),
+which must outlast the server's own startup-readiness budget
+(`RUSTFS_STARTUP_READINESS_MAX_WAIT_SECS`, default 120s) — a shorter poll on a
+slow shared runner mis-reports a slow cold start as a failure. In local mode the
+rig also fails fast if the server process exits before becoming healthy instead
+of polling out the full budget.
+
 ## Scope note
 
 The gate logic is unit-validated across pass/warn/fail/exempt outcomes; the
diff --git a/scripts/run_hotpath_warp_ab.sh b/scripts/run_hotpath_warp_ab.sh
index 0d1395ec5..d5374ed62 100755
--- a/scripts/run_hotpath_warp_ab.sh
+++ b/scripts/run_hotpath_warp_ab.sh
@@ -41,6 +41,7 @@ DISKS=4
 CONCURRENCY=8
 DURATION="30s"
 ROUNDS=3
+COOLDOWN_SECS=""         # empty -> load driver default; CI passes a short value
 LOCAL_ADDRESS="127.0.0.1:9000"
 ACCESS_KEY="rustfsadmin"
 SECRET_KEY="rustfsadmin"
@@ -57,9 +58,32 @@ SKIP_BUILD="false"
 EXTERNAL_ENDPOINT=""     # set -> external mode (warp targets this cluster)
 DEPLOY_HOOK=""           # external mode: command to deploy a phase's binary
 HEALTH_PATH="/health"
+# Readiness poll budget. The server binds its public listener only after startup
+# converges (erasure-format load + IAM); its own budget is
+# RUSTFS_STARTUP_READINESS_MAX_WAIT_SECS (default 120s). Polling must outlast
+# that, otherwise a slow cold start on a shared CI runner looks like a failure —
+# this is exactly what killed the first two nightly runs (60s poll < 120s
+# startup budget). Default 180s; override with --health-timeout.
+HEALTH_TIMEOUT_SECS=180
 
-# Workloads: name|warp-mode|size. put-4mib obj/s, get-4mib MiB/s, mixed-256k p99.
-WORKLOADS=("put-4mib|put|4MiB" "get-4mib|get|4MiB" "mixed-256k|mixed|256KiB")
+# Workloads: name|warp-mode|size.
+#   put-4kib / get-4kib — the #4221 fsync regression size (~-10% @4KiB), invisible
+#     until now; put-4mib / get-4mib — bulk obj/s & MiB/s; get-10mib — the historical
+#     large-GET EOF size; mixed-256k — p99 latency.
+# Tradeoff: 6 workloads × 2 phases × 2 drive-sync = 24 cells. Until perf-3 caches
+# the baseline binary (the ~65min double build dominates the 90min job), CI keeps
+# the matrix under budget with short warp params (--duration/--rounds/--cooldown
+# passed by the workflow), NOT by dropping cells. A 1KiB cell (optional per
+# perf-1) is deferred until that caching frees wall-clock; re-enable by adding
+# e.g. "put-1kib|put|1KiB" here.
+WORKLOADS=(
+  "put-4kib|put|4KiB"
+  "put-4mib|put|4MiB"
+  "get-4kib|get|4KiB"
+  "get-4mib|get|4MiB"
+  "get-10mib|get|10MiB"
+  "mixed-256k|mixed|256KiB"
+)
 # Durability matrix: label|RUSTFS_DRIVE_SYNC_ENABLE value.
 DRIVE_SYNC_MATRIX=("sync-on|true" "sync-off|false")
 
@@ -87,6 +111,9 @@ Common:
   --concurrency <n>       warp --concurrent (default 8).
   --duration <dur>        warp --duration (default 30s).
   --rounds <n>            Rounds per cell for the median (default 3).
+  --cooldown <n>          Seconds between rounds/sizes, forwarded to the load
+                          driver (default: driver default, 20s).
+  --health-timeout <n>    Seconds to poll readiness after bring-up (default 180).
   --fail-pct <n>          Gate fail budget (default 10).
   --warn-pct <n>          Gate warn budget (default 5).
   --allow-regression      Pass the gate despite a FAIL (deliberate tradeoff).
@@ -109,6 +136,8 @@ while [[ $# -gt 0 ]]; do
     --concurrency) CONCURRENCY="$2"; shift 2 ;;
     --duration) DURATION="$2"; shift 2 ;;
     --rounds) ROUNDS="$2"; shift 2 ;;
+    --cooldown) COOLDOWN_SECS="$2"; shift 2 ;;
+    --health-timeout) HEALTH_TIMEOUT_SECS="$2"; shift 2 ;;
     --fail-pct) FAIL_PCT="$2"; shift 2 ;;
     --warn-pct) WARN_PCT="$2"; shift 2 ;;
     --allow-regression) ALLOW_REGRESSION="true"; shift ;;
@@ -184,7 +213,13 @@ else
 fi
 
 # --- Deployment: bring a phase up, tear it down -----------------------------
+# Server logs live under OUT_DIR (not $DATA_ROOT) so they ride along in the CI
+# artifact and the run is diagnosable after the fact — the missing piece that
+# left the first nightly failures unexplained.
+SERVER_LOG_DIR="$OUT_DIR/server-logs"
+run mkdir -p "$SERVER_LOG_DIR"
 SERVER_PID=""
+SERVER_LOG=""
 tear_down() {
   # Local mode owns the server process; external mode leaves lifecycle to the
   # deploy hook / cluster orchestrator.
@@ -195,14 +230,32 @@ tear_down() {
 }
 trap tear_down EXIT INT TERM
 
+# Dump the tail of the current server log to stderr (job log) so a startup
+# failure is visible without downloading the artifact.
+dump_server_log() {
+  [[ -n "$SERVER_LOG" && -f "$SERVER_LOG" ]] || return 0
+  echo "----- last 50 lines of $SERVER_LOG -----" >&2
+  tail -n 50 "$SERVER_LOG" >&2 || true
+  echo "----------------------------------------" >&2
+}
+
 wait_health() {
   [[ "$DRY_RUN" == "true" ]] && return 0
   local i
-  for ((i = 0; i < 60; i++)); do
+  for ((i = 0; i < HEALTH_TIMEOUT_SECS; i++)); do
+    # Local mode owns the process: if it already exited (port bind failure,
+    # panic, disk-check abort), stop polling and surface the log immediately
+    # instead of waiting out the full budget.
+    if [[ "$EXTERNAL" != "true" && -n "$SERVER_PID" ]] && ! kill -0 "$SERVER_PID" 2>/dev/null; then
+      echo "error: rustfs server (pid $SERVER_PID) exited before becoming healthy after ${i}s" >&2
+      dump_server_log
+      return 1
+    fi
     if curl -fsS "http://${ADDRESS}${HEALTH_PATH}" >/dev/null 2>&1; then return 0; fi
     sleep 1
   done
-  echo "error: endpoint http://${ADDRESS}${HEALTH_PATH} did not become healthy" >&2
+  echo "error: endpoint http://${ADDRESS}${HEALTH_PATH} did not become healthy within ${HEALTH_TIMEOUT_SECS}s" >&2
+  dump_server_log
   return 1
 }
 
@@ -224,12 +277,26 @@ bring_up() {
   local disks=() d
   for ((d = 1; d <= DISKS; d++)); do disks+=("$node_dir/d$d"); done
   run mkdir -p "${disks[@]}"
+  SERVER_LOG="$SERVER_LOG_DIR/$phase-sync-$drive_sync.log"
   if [[ "$DRY_RUN" == "true" ]]; then
     { printf 'DRY-RUN: RUSTFS_DRIVE_SYNC_ENABLE=%s %q server' "$drive_sync" "$bin"
       printf ' %q' "${disks[@]}"; printf '\n'; } >&2
     SERVER_PID="dry-run"
     return 0
   fi
+  # Record the startup environment next to the log so a failed run is
+  # self-explanatory in the artifact.
+  cat >"$SERVER_LOG_DIR/$phase-sync-$drive_sync.env" <<EOF
+phase=$phase
+drive_sync=$drive_sync
+binary=$bin
+address=$ADDRESS
+disks=${disks[*]}
+health_url=http://${ADDRESS}${HEALTH_PATH}
+health_timeout_secs=$HEALTH_TIMEOUT_SECS
+uname=$(uname -a 2>/dev/null || echo unknown)
+warp_version=$("$WARP_BIN" --version 2>/dev/null | head -n1 || echo unknown)
+EOF
   RUSTFS_UNSAFE_BYPASS_DISK_CHECK=true \
   RUSTFS_ADDRESS="$ADDRESS" \
   RUSTFS_ACCESS_KEY="$ACCESS_KEY" \
@@ -237,7 +304,7 @@ bring_up() {
   RUSTFS_REGION="$REGION" \
   RUSTFS_CONSOLE_ENABLE=false \
   RUSTFS_DRIVE_SYNC_ENABLE="$drive_sync" \
-    "$bin" server "${disks[@]}" >"$node_dir/rustfs.log" 2>&1 &
+    "$bin" server "${disks[@]}" >"$SERVER_LOG" 2>&1 &
   SERVER_PID=$!
   wait_health
 }
@@ -254,6 +321,7 @@ measure() {
     --region "$REGION" --sizes "$size" --concurrency "$CONCURRENCY"
     --duration "$DURATION" --rounds "$ROUNDS" --out-dir "$cell"
   )
+  [[ -n "$COOLDOWN_SECS" ]] && args+=(--cooldown-secs "$COOLDOWN_SECS")
   [[ -n "$baseline_csv" ]] && args+=(--baseline-csv "$baseline_csv")
   run "$ENHANCED_BENCH" "${args[@]}"
   echo "$cell"