fix(ci): address PR #35 review comments

- Document non-blocking receive contract in perf_bench.rs docstring,
  confirming no TCP deadlock race (Hoshe #1, critical)
- Make shadowcast parser order-independent — flush on new config header
  instead of requiring Recursive after Symmetric (Hoshe #2)
- Fix p95 calculation: use floor(0.95*(N-1)) nearest-rank instead of
  ceil(0.95*N)-1 which was off-by-one at N=50 (Hoshe #4)
- Error on --compare when no baseline file exists (Hoshe #5)
- Add D-031 10tps assumption comment to TICK_BUDGET_US (Tyre #1)
- Strengthen snapshot assertion: require warmup + half measurement
  window instead of warmup + 1 (Tyre #2)
- Regenerate baseline with corrected p95 (356µs, was 526µs)

Hoshe #3 (.PHONY) was already addressed — perf-baseline is in the
.PHONY declaration on Makefile line 10.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tooling/perf-baseline

@@ -22,7 +22,8 @@ ROOT = Path(__file__).resolve().parent.parent
 PERF_DIR = ROOT / "tests" / "perf"
 BASELINE_FILE = PERF_DIR / "baseline.json"
 
-# Tick budget from D-026
+# Tick budget from D-026: 100ms per tick at 10 tps floor (D-031).
+# If tick rate changes, update this constant.
 TICK_BUDGET_US = 100_000  # 100ms
 
 
@@ -95,6 +96,9 @@ def run_shadowcast_benchmark():
             line,
         )
         if m:
+            # New config block — flush previous if complete
+            if current.get("map_size"):
+                configs.append(current)
             current = {
                 "map_size": int(m.group(1)),
                 "density": m.group(3),
@@ -113,11 +117,12 @@ def run_shadowcast_benchmark():
         if m:
             current["recursive_total_ms"] = float(m.group(1))
             current["recursive_per_call_us"] = float(m.group(2))
-            if current.get("map_size"):
-                configs.append(current)
-            current = {}
             continue
 
+    # Flush last config
+    if current.get("map_size"):
+        configs.append(current)
+
     return {"configs": configs} if configs else None
 
 
@@ -252,6 +257,10 @@ def main():
         if compare_mode and regressions:
             print(f"\n{len(regressions)} regression(s) detected.")
             return 1
+    elif compare_mode:
+        print(f"\nERROR: --compare requires a saved baseline at {BASELINE_FILE.relative_to(ROOT)}")
+        print("Run `make perf-baseline` first to create one.")
+        return 1
 
     if compare_mode:
         return 0