[Bugifx] Missing Renderer for fastokens mode

[tjtanaa]

Purpose

Fix error of #41741

(APIServer pid=8195)   File "/app/vllmaitercheck/vllmnew/vllm/renderers/registry.py", line 87, in renderer_from_config
(APIServer pid=8195)     return RENDERER_REGISTRY.load_renderer(renderer_mode, config, tokenizer)
(APIServer pid=8195)            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
(APIServer pid=8195)   File "/app/vllmaitercheck/vllmnew/vllm/renderers/registry.py", line 68, in load_renderer
(APIServer pid=8195)     renderer_cls = self.load_renderer_cls(renderer_mode)
(APIServer pid=8195)                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
(APIServer pid=8195)   File "/app/vllmaitercheck/vllmnew/vllm/renderers/registry.py", line 55, in load_renderer_cls
(APIServer pid=8195)     raise ValueError(f"No renderer registered for {renderer_mode=!r}.")
(APIServer pid=8195) ValueError: No renderer registered for renderer_mode='fastokens'.

Test Plan

Evaluate Qwen3-8B

#!/bin/bash

vllm serve Qwen/Qwen3-8B --tokenizer-mode fastokens \
--port 8001 \
2>&1 | tee -a serverqwen38bfastokens.log

#!/bin/bash

MODEL=Qwen/Qwen3-8B 
lm_eval --model local-completions --model_args model=$MODEL,base_url=http://0.0.0.0:8001/v1/completions,num_concurrent=100,max_retries=10,max_gen_toks=2048,timeout=60000,trust_remote_code=True --batch_size auto --tasks gsm8k --num_fewshot 5 --output_path . 2>&1 | tee -a eval.log

Test Result

Qwen3-8B

local-completions ({'model': 'Qwen/Qwen3-8B', 'base_url': 'http://0.0.0.0:8001/v1/completions', 'num_concurrent': 100, 'max_retries': 10, 'max_gen_toks': 2048, 'timeout': 60000}), gen_kwargs: ({}), limit: None, num_fewshot: 5, batch_size: auto
|Tasks|Version|     Filter     |n-shot|  Metric   |   |Value |   |Stderr|
|-----|------:|----------------|-----:|-----------|---|-----:|---|-----:|
|gsm8k|      3|flexible-extract|     5|exact_match|_  |0.8969|_  |0.0084|
|     |       |strict-match    |     5|exact_match|_  |0.8976|_  |0.0083|

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Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

[gemini-code-assist]

Code Review

This pull request adds "fastokens" to the renderer registry in vllm/renderers/registry.py, mapping it to the HfRenderer. There are no review comments to address, and I have no feedback to provide.

[claude]

Claude Code Review

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