L3 3.0: wire --enable-cp-l3 flag, validation, hash-from-init

server_args: --enable-cp-l3 + --cp-l3-config fields/args. Validation (R1 HIGH-2): do NOT re-gate
the 6 CP storage forbids (they gate on hicache_storage_backend and correctly never fire); instead
assert enable_cp_l3 is mutually exclusive with hicache_storage_backend, requires
enable_cp_shared_physical_l2_hicache, and requires cp_l3_config.
hiradix: self.enable_cp_l3 (CP-only) + cp_l3_store placeholder; compute_node_hash_values now also
fires under enable_cp_l3 (the per-page content hash is L3's key) — clean-boot only (R1 HIGH-3).
Default-off + behavior-neutral; store construction + drain follow.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

python/sglang/srt/mem_cache/hiradix_cache.py

@@ -1041,6 +1041,10 @@ class HiRadixCache(RadixCache):
         self.enable_storage = server_args.hicache_storage_backend is not None
         self.enable_storage_metrics = self.enable_storage and params.enable_metrics
         self.extra_metric_labels = server_args.extra_metric_labels
+        # CP L3 durable floor (disk tier): own content-addressed path, NOT enable_storage. Built on the
+        # pooled shared-L2 (server_args validation already enforced the prerequisites + mutual exclusion).
+        self.enable_cp_l3 = bool(getattr(server_args, "enable_cp_l3", False)) and self._uses_cp_hicache
+        self.cp_l3_store = None  # constructed after the host pool + allocator (slab accessors need them)
 
         (
             extra_config,
@@ -5591,8 +5595,11 @@ class HiRadixCache(RadixCache):
             self._update_leaf_status(node)
             self._update_leaf_status(new_node)
 
-            # Compute hash_value if storage or kv events are enabled
-            if self.enable_storage or self.enable_kv_cache_events:
+            # Compute hash_value if storage or kv events are enabled, or for the CP L3 disk tier (the
+            # per-page content hash is L3's key). Clean-boot only (default-off+additive): a fresh process
+            # with --enable-cp-l3 computes the unbroken parent-chained hash from the root; flipping it at
+            # runtime would leave pre-existing nodes None-seeded (R1 HIGH-3).
+            if self.enable_storage or self.enable_kv_cache_events or self.enable_cp_l3:
                 new_node.hash_value = compute_node_hash_values(new_node, self.page_size)
 
             # Emit BlockStored so the router indexes this block.

python/sglang/srt/server_args.py

@@ -597,6 +597,10 @@ class ServerArgs:
     cp_shared_l2_hugetlbfs_dir: str = "/mnt/huge_2m"
     cp_shared_l2_slab_size_gb: int = 0
     cp_shared_l2_numa_policy: str = "interleave_2m"
+    # L3 durable floor (disk tier), built on the pooled shared-L2. Its own content-addressed path —
+    # NOT the mainline hicache_storage_backend page-op path (which stays disabled under CP).
+    enable_cp_l3: bool = False
+    cp_l3_config: Optional[str] = None
 
     # Hierarchical sparse attention
     enable_hisparse: bool = False
@@ -1000,6 +1004,19 @@ class ServerArgs:
             "hicache_storage_backend in the host-only CP HiCache stage. "
             "Disable hicache_storage_backend or disable CP shared KV."
         )
+        if self.enable_cp_l3:
+            # L3 is a distinct CP content-addressed disk tier, NOT the mainline storage page-op path
+            # (which stays off under CP). The 6 CP storage forbids gate on hicache_storage_backend and
+            # correctly never fire here. One assert keeps the two paths mutually exclusive.
+            assert self.hicache_storage_backend is None, (
+                "enable_cp_l3 is mutually exclusive with hicache_storage_backend: L3 uses its own "
+                "CpL3Store path, not the mainline storage backend. Unset --hicache-storage-backend."
+            )
+            assert self.enable_cp_shared_physical_l2_hicache, (
+                "enable_cp_l3 requires --enable-cp-shared-physical-l2-hicache (L3 spills/reloads the "
+                "pooled shared-L2 objects)."
+            )
+            assert self.cp_l3_config, "enable_cp_l3 requires --cp-l3-config <path>."
         assert not (
             self.enable_nsa_prefill_cp_shared_kv
             and envs.SGLANG_REQ_WAITING_TIMEOUT.get() > 0
@@ -5661,6 +5678,26 @@ class ServerArgs:
                 "strict_local, round_robin."
             ),
         )
+        parser.add_argument(
+            "--enable-cp-l3",
+            action="store_true",
+            default=ServerArgs.enable_cp_l3,
+            help=(
+                "Enable the CP HiCache L3 durable floor (disk tier) on top of the pooled shared-L2. "
+                "Content-addressed, per-rank-by-owner spill/reload. Requires "
+                "--enable-cp-shared-physical-l2-hicache and --cp-l3-config; mutually exclusive with "
+                "--hicache-storage-backend."
+            ),
+        )
+        parser.add_argument(
+            "--cp-l3-config",
+            type=str,
+            default=ServerArgs.cp_l3_config,
+            help=(
+                "Path to the per-machine L3 config (TOML/JSON): disks (paths + budgets), rank->disk "
+                "mapping, backend, index location, PLP gate. See CpL3Config."
+            ),
+        )
 
         # Hierarchical sparse attention
         parser.add_argument(