docs(sglang): correct session radix availability (ai-dynamo#11241)

Signed-off-by: Ishan Dhanani <ishandhanani@gmail.com>

Author: ishandhanani

components/src/dynamo/sglang/CLAUDE.md

@@ -313,10 +313,11 @@ text-to-video-diffusion.sh  # 1-2 GPUs - Text-to-video (Wan2.1)
   Always slice with an offset, don't assume per-chunk logprobs.
 - **Zombie GPU processes**: `sgl_diffusion::scheduler` spawns a child process that
   survives parent kill. Always check `nvidia-smi` after teardown.
-- **Session radix cache**: SGLang 0.5.14+ provides session-aware radix ownership
-  without an opt-in flag. The handler passes `agent_context.session_id` to SGLang
-  as `session_params.id`. Agent KV hints are forwarded as metadata but are not
-  acted on by the SGLang backend. This path does not create router affinity.
+- **Session identity**: SGLang 0.5.14 does not support passive session-aware radix
+  ownership. Do not pass `agent_context.session_id` as `session_params.id`;
+  SGLang treats that field as an explicit session lifecycle and rejects IDs that
+  were not created through `open_session`. Session headers remain available for
+  tracing and router affinity.
 
 For troubleshooting (CuDNN, config.json errors, OOM, disagg connectivity), see
 `docs/backends/sglang/sglang-examples.md#troubleshooting`.

components/src/dynamo/sglang/request_handlers/handler_base.py

@@ -669,9 +669,6 @@ def __init__(
         self.serving_mode = config.serving_mode
         self.use_sglang_tokenizer = config.dynamo_args.use_sglang_tokenizer
         self.enable_trace = getattr(config.server_args, "enable_trace", False)
-        self.enable_session_radix_cache = getattr(
-            config.server_args, "enable_session_radix_cache", False
-        )
 
         if engine is not None:
             self.input_param_manager = InputParamManager(
@@ -1019,16 +1016,6 @@ def _get_input_param(self, request: Dict[str, Any]) -> Dict[str, Any]:
             "prompt" if isinstance(request_input, str) else "input_ids": request_input
         }
 
-    def _session_id(self, request: Dict[str, Any]) -> Optional[str]:
-        if not self.enable_session_radix_cache:
-            return None
-        session_id = (request.get("agent_context") or {}).get("session_id")
-        return session_id if isinstance(session_id, str) and session_id else None
-
-    def _session_kwargs(self, request: Dict[str, Any]) -> Dict[str, Any]:
-        session_id = self._session_id(request)
-        return {"session_params": {"id": session_id}} if session_id else {}
-
     @staticmethod
     def _get_guided_decoding_params(
         guided_decoding: Optional[Dict[str, Any]],

components/src/dynamo/sglang/request_handlers/llm/decode_handler.py

@@ -395,7 +395,6 @@ async def generate(
                 external_trace_header=trace_header,
                 rid=trace_id,
                 data_parallel_rank=dp_rank,
-                **self._session_kwargs(request),
                 lora_path=lora_path,
                 **logprob_kwargs,
                 **self._priority_kwargs(priority),
@@ -463,7 +462,6 @@ async def generate(
                 external_trace_header=trace_header,
                 rid=trace_id,
                 data_parallel_rank=dp_rank,
-                **self._session_kwargs(request),
                 lora_path=lora_path,
                 **logprob_kwargs,
                 **self._priority_kwargs(priority),

components/src/dynamo/sglang/request_handlers/llm/prefill_handler.py

@@ -166,7 +166,6 @@ async def generate(
             external_trace_header=trace_header,
             rid=trace_id,
             data_parallel_rank=dp_rank,
-            **self._session_kwargs(inner_request),
             lora_path=lora_path,
             **self._priority_kwargs(priority),
         )

components/src/dynamo/sglang/tests/test_sglang_frontend_decoding.py

@@ -97,7 +97,6 @@ async def no_cancellation_monitor(*args, **kwargs):
 
     handler._get_input_param = lambda req: {"input_ids": req.get("token_ids", [])}
     handler._resolve_lora = lambda req: None
-    handler._session_kwargs = lambda req: {}
     handler._priority_kwargs = lambda priority: {}
 
     return handler

docs/backends/sglang/agents.md

@@ -2,10 +2,10 @@
 # SPDX-FileCopyrightText: Copyright (c) 2025-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 # SPDX-License-Identifier: Apache-2.0
 title: SGLang for Agentic Workloads
-subtitle: Priority scheduling and session-aware radix KV for agentic serving
+subtitle: Priority scheduling and KV cache tuning for agentic serving
 ---
 
-This guide covers SGLang-specific configuration for agentic serving with Dynamo. It explains which SGLang engine flags to enable, how Dynamo's [agent hints](../../components/frontend/nvext.md#agent-hints) map to SGLang behavior, and how to tag radix KV by session.
+This guide covers SGLang-specific configuration for agentic serving with Dynamo. It explains which SGLang engine flags to enable, how Dynamo's [agent hints](../../components/frontend/nvext.md#agent-hints) map to SGLang behavior, and how session headers interact with SGLang 0.5.14.
 
 ## Overview
 
@@ -111,23 +111,14 @@ for chunk in response:
         print(chunk.choices[0].delta.content, end="")
 ```
 
-## Session Radix Cache
+## Session Identity
 
-SGLang can tag ordinary evictable radix KV with the normalized agent session ID without pinning requests to a worker or creating a separate streaming-session lifecycle.
+Dynamo normalizes agent headers such as `X-Dynamo-Session-ID` for request tracing and router affinity. SGLang 0.5.14 does not support passive session-aware radix ownership, so the Dynamo worker does not attach this ID to SGLang generate requests.
 
-> **Availability:** Session-aware radix ownership is built into SGLang 0.5.14 and later; no opt-in server argument is required.
+> [!NOTE]
+> SGLang 0.5.14's `session_params` belongs to its explicit session lifecycle and requires a session created through `open_session`. It is not a passive KV ownership tag.
 
-Launch the worker with:
-
-```bash
-python -m dynamo.sglang \
-  --model-path <model> \
-  --radix-eviction-policy priority
-```
-
-Dynamo reads session identity from agent headers such as `X-Dynamo-Session-ID` and passes it to SGLang on every generate request. `X-Dynamo-Session-Final: true` is normalized into an internal KV eviction hint and forwarded with the agent context, but the SGLang backend does not act on that hint in this release.
-
-The radix entries remain normally evictable. Session-aware radix ownership does not create router affinity; a configured router can independently use `X-Dynamo-Session-ID` for router-local affinity.
+The `--radix-eviction-policy priority` flag controls priority-based KV eviction only; it does not tag radix entries by session. `X-Dynamo-Session-Final: true` is normalized into an internal KV eviction hint, but the SGLang backend does not act on that hint in this release.
 
 ## Quickstart
 
@@ -138,7 +129,7 @@ bash examples/backends/sglang/launch/agg_agent.sh \
   --model-path zai-org/GLM-4.7-Flash --tp 2
 ```
 
-Agent providers send session headers directly; no body-level lifecycle object is needed.
+Agent providers send session headers directly for tracing and router affinity; no body-level lifecycle object is needed.
 
 ## See Also
 

docs/backends/sglang/sglang-chat-processor.md

@@ -151,4 +151,4 @@ Key differences:
 
 - **[Tool Calling](../../tool-calling/README.md)**: General tool calling guide
 - **[Reference Guide](sglang-reference-guide.md)**: Full SGLang backend reference
-- **[Agentic Workloads](agents.md)**: Priority scheduling and session-aware radix KV
+- **[Agentic Workloads](agents.md)**: Priority scheduling and KV cache tuning

docs/components/frontend/nvext.md

@@ -229,4 +229,4 @@ When the client requests response metadata via `extra_fields`, the response incl
 | [Session IDs](../../agents/session-ids.md) | Passive session identity |
 | [Agent Tracing](../../agents/agent-tracing.md) | JSONL request traces, inferred tool-call metadata, and harness tool-event ingestion |
 | [Agent Hints](../../agents/agent-hints.md) | Per-request serving hints for routing, scheduling, and cache behavior |
-| [SGLang for Agentic Workloads](../../backends/sglang/agents.md) | SGLang engine flags for priority scheduling, eviction policies, and session-aware radix tagging |
+| [SGLang for Agentic Workloads](../../backends/sglang/agents.md) | SGLang engine flags for priority scheduling and KV eviction policies |

docs/digest/agentic-inference/agentic-inference.md

@@ -170,7 +170,7 @@ Making blocks globally available solves the sharing problem, but does not solve
 
 The general design pattern is to attach zero or more retention directives to a request or token range. Blocks without directives follow the default LRU path with zero overhead. The evictor becomes a two-structure system: an LRU free list for unprioritized blocks (O(1), unchanged) and a priority queue for annotated blocks. Dynamo's public agent surface exposes the priority part today through `nvext.agent_hints.priority`; TTL or per-token-range retention directives are future API work.
 
-Anthropic's prompt caching lets you mark prefixes as cacheable on their infrastructure. Dynamo does not currently expose the same semantics as a self-hosted `nvext.cache_control` TTL pinning API. The supported production path is priority-driven: `nvext.agent_hints.priority` can influence router queueing and, when the backend enables it, engine scheduling and priority-aware cache eviction. SGLang can additionally tag ordinary evictable radix KV by session.
+Anthropic's prompt caching lets you mark prefixes as cacheable on their infrastructure. Dynamo does not currently expose the same semantics as a self-hosted `nvext.cache_control` TTL pinning API. The supported production path is priority-driven: `nvext.agent_hints.priority` can influence router queueing and, when the backend enables it, engine scheduling and priority-aware cache eviction.
 
 The next step is connecting richer retention directives with the distributed cache. Today, priority and session metadata are local serving signals, not a cluster-wide per-block TTL lease. Extending retention semantics across HiCache/KVBM's shared storage tier would let the harness mark a block once and have its priority, lifetime, and placement intent travel with it through the write-through path. Combined with the prefetch hooks described above, this gives the harness end-to-end lifecycle control across the full memory hierarchy.
 

examples/backends/sglang/launch/_test_agg.sh

@@ -8,7 +8,6 @@
 #
 # Same shape as agg_router.sh (2 workers, KV routing, KV events) but with:
 #   - --enable-hierarchical-cache              -> HiCache row populates
-#   - session-aware radix ownership             -> session-tagged radix KV
 #   - --enable-metrics-for-all-schedulers      -> per-scheduler metrics
 #   - --enable-mfu-metrics                     -> model FLOPs utilization
 #   - --mem-fraction-static 0.92               -> larger KV pool per worker
@@ -104,7 +103,6 @@ Topology:
 
 Features enabled for full Grafana coverage:
   - hierarchical KV cache (host RAM tier)        -> HiCache row
-  - session radix cache                          -> session-tagged evictable KV
   - per-scheduler metrics + MFU metrics
   - mem-fraction-static=$MEM_FRACTION, max-running-requests=$MAX_RUNNING
   - page-size=$PAGE_SIZE, chunked-prefill-size=$CHUNKED_PREFILL