feat(bench): add matrix runner, gamescope and per-session controls

- bench.py: gamescope-headless display (default, 1920x1080; ~2% cost vs
  desktop for isolation from the shared Wayland desktop), --shader,
  --dh, --disable-mods/--add-mods, --world-zip, crash-safe restore
  journal, spectator mode in the plan (elevated cameras fell to the
  sea floor and S4 measured underwater darkness)
- matrix.toml/matrix.py: declarative, resumable B0-B14 runner keyed on
  mods hash (warns when B0 must be re-run)
- build.py: bench-only resource-pack variants (C1-fa, C1-fa-ext,
  emf-lod*-fa, C1-bl); every bench variant pins resourcePacks so packs
  don't leak between sessions; shipped tier output unchanged
- analyze.py: tagged labels use their own block's baseline

analysis/client-perf/proposed-configs/build.py

@@ -190,8 +190,27 @@ BENCH = {
 }
 
 
-def c1(extra):
-    return [DEFAULT, extra]
+# Resource packs (names = zips in the bench instance's resourcepacks/). Every bench
+# variant pins the list: apply_variant.py merges options.txt key by key, so a variant
+# without the key would keep the previous session's packs. Later entries win.
+FA = "file/FreshAnimations_v1.10.4.zip"
+FA_EXT = "file/FA+All_Extensions-v1.8.1.zip"
+BETTER_LEAVES = "file/Better-Leaves-9.6.zip"
+
+
+def packs(*extra):
+    return {"options.txt": {"resourcePacks": json.dumps(["vanilla", "mod_resources", *extra],
+                                                       separators=(",", ":"))}}
+
+
+PACKS_BASE = packs()
+# Keys the bench layers may add to a base that lacks them (the options.txt template
+# has no resourcePacks line; tiers never set it, so shipped output is unaffected).
+ALLOW_NEW = {"options.txt": {"resourcePacks"}}
+
+
+def c1(*extra):
+    return [DEFAULT, PACKS_BASE, *extra]
 
 
 VARIANTS = {
@@ -201,10 +220,10 @@ VARIANTS = {
     "T-mid": ([DEFAULT], False),
     "T-high": ([DEFAULT, HIGH], False),
     # bench: composites
-    "C0": ([], True),
-    "C1": ([DEFAULT], True),
-    "C1-deck": ([DEFAULT, DECK], True),
-    "C1-high": ([DEFAULT, HIGH], True),
+    "C0": ([PACKS_BASE], True),
+    "C1": (c1(), True),
+    "C1-deck": (c1(DECK), True),
+    "C1-high": (c1(HIGH), True),
     # bench: Distant Horizons
     "dh-r256": (c1({"config/DistantHorizons.toml": {(DH_Q, "lodChunkRenderDistanceRadius"): 256}}), True),
     "dh-r192": (c1({"config/DistantHorizons.toml": {(DH_Q, "lodChunkRenderDistanceRadius"): 192}}), True),
@@ -226,6 +245,15 @@ VARIANTS = {
                                                             "modelUpdateFrequency": "Average"}}), True),
     "emf-lod8": (c1({"config/entity_model_features.json": {"animationLODDistance": 8,
                                                            "retainDetailOnLowFps": False}}), True),
+    "C1-fa": (c1(packs(FA)), True),
+    "C1-fa-ext": (c1(packs(FA, FA_EXT)), True),
+    "emf-lod20-fa": (c1({"config/entity_model_features.json": {"animationLODDistance": 20,
+                                                               "modelUpdateFrequency": "Average"}},
+                        packs(FA)), True),
+    "emf-lod8-fa": (c1({"config/entity_model_features.json": {"animationLODDistance": 8,
+                                                              "retainDetailOnLowFps": False}},
+                       packs(FA)), True),
+    "C1-bl": (c1(packs(BETTER_LEAVES)), True),
     "ldl-fancy": (c1({"config/lambdynlights.toml": {("", "mode"): "fancy"}}), True),
     "ldl-fastest": (c1({"config/lambdynlights.toml": {("", "mode"): "fastest",
                                                       ("light_sources", "entities"): False}}), True),
@@ -290,7 +318,8 @@ def apply_kv(text, ov, name, sep, append):
         sval = toml_val(val) if isinstance(val, bool) else str(val)
         rx = re.compile(rf"^{re.escape(key)}{re.escape(sep)}")
         hits = [i for i, ln in enumerate(lines) if rx.match(ln)]
-        if len(hits) > 1 or (not hits and not append):
+        may_add = append if isinstance(append, bool) else key in append
+        if len(hits) > 1 or (not hits and not may_add):
             raise SystemExit(f"{name}: {key}: {len(hits)} matches in base")
         if hits:
             lines[hits[0]] = f"{key}{sep}{sval}"
@@ -327,7 +356,7 @@ def render(layers, name):
     if fmt == "json":
         return apply_json(text, merged, name), merged
     sep = ":" if fmt == "options" else "="
-    return apply_kv(text, merged, name, sep, append), merged
+    return apply_kv(text, merged, name, sep, append or ALLOW_NEW.get(name, set())), merged
 
 
 def main():