[Bugfix][ROCm] Fix DeepSeek V4 DSpark probabilistic startup

[tuukkjs]

Purpose

DeepSeek V4 DSpark uses a full-vocabulary draft model, so draft token ids are already target token ids and no draft-to-target remapping is needed. The CUDA implementation exposes this by defining draft_id_to_target_id = None, but the ROCm platform implementation was missing the same marker.

The shared DSpark speculator reads model.draft_id_to_target_id when draft_sample_method="probabilistic" to decide whether reduced-vocabulary draft logits need scattering into target-vocabulary columns. On ROCm, the missing attribute causes probabilistic DeepSeek V4 DSpark startup to fail with:

AttributeError: 'DSparkDeepseekV4ForCausalLM' object has no attribute 'draft_id_to_target_id'

This PR adds the full-vocabulary marker to the ROCm DeepSeek V4 DSpark class.

Duplicate-Work Check

No open PR seems to address this ROCm omission.

Test Plan

Validate on ROCm with DeepSeek V4 Flash DSpark using draft_sample_method="probabilistic".

Test Result

ROCm serving validation:

Model: deepseek-ai/DeepSeek-V4-Flash-0731
Speculative config: {"method":"dspark","num_speculative_tokens":5,"draft_sample_method":"probabilistic"}
Result: server started successfully and completed a random 8192-input / 512-output benchmark.
Acceptance rate: 43.19%
Acceptance length: 3.16
Per-position acceptance: 73.01%, 57.06%, 37.42%, 27.61%, 20.86%

AI assitance was used for this PR.

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

[AndreasKaratzas]

/ci run

[github-actions]

✅ Triggered Buildkite CI #82508 for commit 4166b8d698bc.

[tuukkjs]

@tjtanaa would you have time to review this one-line fix? It seems draft_sample_method="probabilistic" is not working atm on ROCm.