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[None][fix] Warmup: no generation shapes on a context-only KV cache - #21343

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Nov 2, 2026
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longlee0622 merged 2 commits into
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@longlee0622 longlee0622 commented Oct 30, 2026 •

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A disaggregated context worker with a context-only cache (KDA context-only state or the context-only FP4 MLA cache
from #20888) cannot build generation warmup requests, so create_warmup_request returns None for them. The
attention-JIT warmup and the autotuner warmup still proposed generation shapes. Under DWDP (Kimi K3 CTX workers)
WarmupAgreement cannot confirm a unanimous skip and turns that None into a fatal RuntimeError at startup.

The two warmups now leave out generation shapes up front when the KV cache manager is context-only
(is_context_only_kv_cache). The property is the same on every rank of a role, so no
cross-rank agreement is needed.

Tests: test_attention_warmup_leaves_out_generation_shapes_on_context_only_cache and
test_autotuner_warmup_leaves_out_generation_shape_on_context_only_cache (DWDP agreement, both context-only flags;
fail on main with the RuntimeError above).

Evidence: Kimi K3 NVFP4-KV disagg CTX (DWDP16) workers on the K3 branch start and serve with this change (startup
smoke of all four AgentX cases, GSM8K 96.06 run 2931122).

🤖 Generated with Claude Code

Dev Engineer Review

No current review findings were supplied, so severity counts are unavailable. The provided change summary reports that generation warmup shapes are omitted for context-only KV caches. The implementation diff was not available for verification.

QA Engineer Review

The reported tests cover KDA and FP4 MLA context-only caches, non-context-only behavior, and attention and autotuner warmup counts. Test results and test-list status are unavailable. Coverage verdict: needs follow-up.

Per-File QA Perspective

  • tensorrt_llm/_torch/pyexecutor/engine/runners/decoder/warmup.py: Verify that context-only caches omit generation shapes in the affected warmup paths and that other cache types retain existing behavior.
  • tests/unittest/_torch/pyexecutor/engine/runners/decoder/test_warmup.py: The reported tests cover cache flags and warmup request counts. CI and manual-QA test-list status is unavailable.

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  • tensorrt_llm/_torch/pyexecutor/engine/runners/decoder/warmup.py
  • tests/unittest/_torch/pyexecutor/engine/runners/decoder/test_warmup.py

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Walkthrough

Warmup shape generation now excludes generation requests for context-only KV caches. The change covers maximum-shape, one-token, attention JIT, and autotuner configurations. Tests verify request shapes and forward-call counts for context-only and other cache types.

Changes

Warmup Shape Selection

Layer / File(s) Summary
Maximum and general warmup shapes
tensorrt_llm/_torch/pyexecutor/engine/runners/decoder/warmup.py, tests/unittest/_torch/pyexecutor/engine/runners/decoder/test_warmup.py
Maximum-shape and one-token configurations include generation shapes only when the cache is not context-only. Parameterized tests check both cache types.
Attention warmup shape selection
tensorrt_llm/_torch/pyexecutor/engine/runners/decoder/warmup.py, tests/unittest/_torch/pyexecutor/engine/runners/decoder/test_warmup.py
Attention warmup omits generation and mixed context-and-generation shapes for context-only caches. Tests check submitted requests and forward-call counts.
Autotuner warmup shape selection
tensorrt_llm/_torch/pyexecutor/engine/runners/decoder/warmup.py, tests/unittest/_torch/pyexecutor/engine/runners/decoder/test_warmup.py
Autotuner warmup omits generation configurations for context-only caches. Tests check submitted requests and forward-call counts.

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Suggested reviewers: lori-ren, zhaoyuanh-nvidia, yihuilu512

Merge Risk: Minimal · previous review e4028

The affected warmup paths no longer propose generation shapes for context-only caches. No introduced merge-blocking risk remains.

Pre-merge checks: Passed 4 · Failed 1

Failed Failed checks: 1 warning

Check name Status Explanation Resolution
Docstring Coverage Warning Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documenta… Write docstrings for the functions missing them to satisfy the coverage threshold.
Passed Passed checks: 4 passed
Check name Status Explanation
Title check Passed The title is concise, specific, and accurately describes the main change: preventing generation warmup shapes on context-only KV caches.
Description check Passed The description clearly explains the issue, the solution, affected warmups, test coverage, and validation evidence. It does not reproduce the template headings or checklist, but it contains the requir…
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The description clearly explains the issue, the solution, affected warmups, test coverage, and validation evidence. It does not reproduce the template headings or checklist, but it contains the required information and is mostly complete.

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Write docstrings for the functions missing them to satisfy the coverage threshold.

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Follow-up Comments

Outside diff Exclude generation shapes from the general warmup plan.

337-337: Major · Stability & Availability · Heavy lift

Exclude generation shapes from the general warmup plan.

Pure FP4 MLA context-only managers can enter general warmup because the entry guard excludes only MambaHybridCacheManager. The general plan still includes (1, 1) and the maximum generation shape. create_warmup_request returns None for those shapes. Under DWDP, no allgather can confirm that peers also skip the batch, so should_run_warmup_batch raises during startup.

Apply the context-only predicate to both general-warmup shape lists. Add a scheduled-warmup regression test that asserts no generation shape is requested for either context-only flag.

Suggested fix
     def _get_full_general_warmup_requests(
         self, resource_manager: ResourceManager
     ) -> list[tuple[int, int]]:
         """
         Returns the ordered warmup configs for torch.compile specialization.
@@
         Covers 1-token (0-1 graph specialization), max-shape (best triton autotuning),
         and small-context (2-token path) cases.
         """
+        supports_generation = not is_context_only_kv_cache(
+            resource_manager.get_resource_manager(ResourceManagerType.KV_CACHE_MANAGER)
+        )
         max_configs = self._get_max_shape_warmup_requests(resource_manager)
+        if not supports_generation:
+            max_configs = [config for config in max_configs if config[1] == 0]
         # Specialize for 1 token pure ctx and pure gen
-        one_token_configs = [(1, 0), (1, 1)]
+        one_token_configs = [(1, 0)]
+        if supports_generation:
+            one_token_configs.append((1, 1))

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Review comment at
@tensorrt_llm/_torch/pyexecutor/engine/runners/decoder/warmup.py at line 337:
Update _get_full_general_warmup_requests to apply the context-only KV-cache
predicate to both general warmup shape lists, excluding generation shapes from
max-shape configs and one-token configs. Add a scheduled-warmup regression test
that verifies no generation shape is requested for either context-only flag.

Source: Path instructions


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  • tensorrt_llm/_torch/pyexecutor/engine/runners/decoder/warmup.py
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Runtime part looks right for the attention and autotuner phases; one question inline on the general/memory-pool warmups, which still propose generation shapes on a context-only cache.

@longlee0622
longlee0622 force-pushed the user/jonasl/k3-fix-k3-nvfp4kv-runtime branch from 573c9f9 to e402832 Compare November 2, 2026 02:58

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Thanks, my comment is addressed: _get_max_shape_warmup_requests now covers both phases and (1, 1) is dropped. LGTM.

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Automatically added "ci: full pre-merge approved" because this PR has satisfied the required GitHub review approvals. Unresolved review conversations and other required checks remain independent merge requirements.

A disaggregated context server with a context-only cache (KDA context-only
state, context-only FP4 MLA cache) cannot build generation warmup requests,
so create_warmup_request returns None for them. Under DWDP (Kimi K3 CTX)
the warmup agreement cannot confirm a unanimous skip and turns that None
into a fatal error. The attention-JIT and autotuner warmups now leave out
the generation shapes up front when the cache is context-only; that
property is the same on every rank of the role.

Signed-off-by: Jonas Li <6110159+longlee0622@users.noreply.github.com>
…ol phases on a context-only KV cache

A context-only KV cache that is not a Mamba hybrid manager (e.g. a pure-MLA
model on Fp4MlaKVCacheManagerV2 with the context-only FP4 MLA cache) passes
can_run_general_warmup, so the general warmup and the memory-pool
pre-population still proposed generation shapes: (1, 1) and
(max_batch_size, max_batch_size). create_warmup_request returns None for them,
and under DWDP should_run_warmup_batch turns that into a fatal error.

_get_max_shape_warmup_requests now returns the context shape only on a
context-only cache, which covers both phases, and the general plan drops (1, 1).

Signed-off-by: Jonas Li <6110159+longlee0622@users.noreply.github.com>
@longlee0622
longlee0622 force-pushed the user/jonasl/k3-fix-k3-nvfp4kv-runtime branch from e402832 to f2fc07d Compare November 2, 2026 03:14
@longlee0622
longlee0622 enabled auto-merge (squash) November 2, 2026 03:15
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/bot run --disable-fail-fast

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PR_Github #81891 [ run ] triggered by Bot. Commit: f2fc07d Link to invocation

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PR_Github #81891 [ run ] completed with state SUCCESS. Commit: f2fc07d
/LLM/main/L0_MergeRequest_PR pipeline #67540 completed with status: 'SUCCESS'
Pipeline passed with automatic retried tests. Check the rerun report for details.

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@longlee0622
longlee0622 merged commit 4fe736f into NVIDIA:main Nov 2, 2026
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@longlee0622
longlee0622 deleted the user/jonasl/k3-fix-k3-nvfp4kv-runtime branch November 2, 2026 07:30
yizhang-nv added a commit to yizhang-nv/TensorRT-LLM that referenced this pull request Nov 9, 2026
…e guided decoder

A capturable guided decoder (guided decoding together with one-model
speculative decoding: MTP, Eagle3 one-model, the external drafters such as
DFlash and DSpark, or SA) turned the whole general warmup off, though it
rules out only the warmup's generation requests: the autotuner already
runs its context step with the decoder installed. Without the general
warmup, the autotuner's max-token step was the engine's first forward.
What a first forward creates lazily, including the attention-DP group's
NCCL communicator (allocated through cuMem, outside the torch caching
allocator, so it cannot reclaim the cache), then came in the middle of the
autotuner's exploration with torch's cache full.

Any model served with guided decoding and one of those drafters takes
this path. It ran memory profiling out of memory while bringing up
Mistral Large 4 (NVFP4 DEP4 at 1M context with the DSpark draft and
xgrammar): rank 0 ran out of memory in the autotuner's max-token step,
and the other ranks failed to allocate NCCL memory through cuMem. Without
guided decoding, where the general warmup and its release run ahead of
the autotuner, the same configuration profiles at a peak of 238.6 GiB per
rank.

The general warmup now runs its context requests in that case, followed
by the same release as before, so the first forward and the release come
ahead of the autotuner, as they do without guided decoding. The extra
phase decision is agreed across ranks like can_run_general_warmup, which
is already rank-uniform when it is taken.

Test: test_guided_decoder_runs_the_context_warmup_before_the_autotuner
installs a guided decoder and checks that the general warmup runs with
context-only shapes (including the max-token one), followed by the MoE
workspace release, the cache release and then the autotuner.

Split out of NVIDIA#21693 (Mistral Large 4 merge-back); originally GitLab
a2d3872e7b, rebased onto main's warmup after NVIDIA#21343.

Signed-off-by: Yi Zhang <187001205+yizhang-nv@users.noreply.github.com>
yizhang-nv added a commit to yizhang-nv/TensorRT-LLM that referenced this pull request Nov 9, 2026
…e guided decoder

A capturable guided decoder (guided decoding together with one-model
speculative decoding: MTP, Eagle3 one-model, the external drafters such as
DFlash and DSpark, or SA) turned the whole general warmup off, though it
rules out only the warmup's generation requests: the autotuner already
runs its context step with the decoder installed. Without the general
warmup, the autotuner's max-token step was the engine's first forward.
What a first forward creates lazily, including the attention-DP group's
NCCL communicator (allocated through cuMem, outside the torch caching
allocator, so it cannot reclaim the cache), then came in the middle of the
autotuner's exploration with torch's cache full.

Any model served with guided decoding and one of those drafters takes
this path. It ran memory profiling out of memory while bringing up
Mistral Large 4 (NVFP4 DEP4 at 1M context with the DSpark draft and
xgrammar): rank 0 ran out of memory in the autotuner's max-token step,
and the other ranks failed to allocate NCCL memory through cuMem. Without
guided decoding, where the general warmup and its release run ahead of
the autotuner, the same configuration profiles at a peak of 238.6 GiB per
rank.

The general warmup now runs its context requests in that case, followed
by the same release as before, so the first forward and the release come
ahead of the autotuner, as they do without guided decoding. The extra
phase decision is agreed across ranks like can_run_general_warmup, which
is already rank-uniform when it is taken.

Test: test_guided_decoder_runs_the_context_warmup_before_the_autotuner
installs a guided decoder and checks that the general warmup runs with
context-only shapes (including the max-token one), followed by the MoE
workspace release, the cache release and then the autotuner.

Split out of NVIDIA#21693 (Mistral Large 4 merge-back); originally GitLab
a2d3872e7b, rebased onto main's warmup after NVIDIA#21343.

Signed-off-by: Yi Zhang <187001205+yizhang-nv@users.noreply.github.com>
yizhang-nv added a commit to yizhang-nv/TensorRT-LLM that referenced this pull request Nov 10, 2026
…e guided decoder

A capturable guided decoder (guided decoding together with one-model
speculative decoding: MTP, Eagle3 one-model, the external drafters such as
DFlash and DSpark, or SA) turned the whole general warmup off, though it
rules out only the warmup's generation requests: the autotuner already
runs its context step with the decoder installed. Without the general
warmup, the autotuner's max-token step was the engine's first forward.
What a first forward creates lazily, including the attention-DP group's
NCCL communicator (allocated through cuMem, outside the torch caching
allocator, so it cannot reclaim the cache), then came in the middle of the
autotuner's exploration with torch's cache full.

Any model served with guided decoding and one of those drafters takes
this path. It ran memory profiling out of memory while bringing up
Mistral Large 4 (NVFP4 DEP4 at 1M context with the DSpark draft and
xgrammar): rank 0 ran out of memory in the autotuner's max-token step,
and the other ranks failed to allocate NCCL memory through cuMem. Without
guided decoding, where the general warmup and its release run ahead of
the autotuner, the same configuration profiles at a peak of 238.6 GiB per
rank.

The general warmup now runs its context requests in that case, followed
by the same release as before, so the first forward and the release come
ahead of the autotuner, as they do without guided decoding. The extra
phase decision is agreed across ranks like can_run_general_warmup, which
is already rank-uniform when it is taken.

The general warmup skips a shape that runs a single rank out of memory
and goes on to a smaller one. With the decoder installed, input
preparation has already queued that shape's batch for the decoder's host
functions, so the abandoned batch would stay at the head of the queue and
every later forward, the first real guided request included, would be
served the batch before its own. The recovery now waits for the decoder's
stream, so that no host function of the failed forward is still pending,
and drops the queued batches and both request snapshots
(CapturableGuidedDecoder.reset_warmup_state). A failed reset stops the
warmup, and a distributed forward still re-raises the out-of-memory error.

Tests: test_guided_decoder_runs_the_context_warmup_before_the_autotuner
installs a guided decoder and checks that the general warmup runs with
context-only shapes (including the max-token one), followed by the MoE
workspace release, the cache release and then the autotuner.
test_general_warmup_oom_restores_guided_batch_queue fails a shape before
and after its host function is submitted and checks that the next guided
request is served its own batch. test_general_warmup_oom_policy and
test_general_warmup_aborts_if_guided_state_cannot_be_reset cover when the
reset runs and that its failure stops the warmup.

Split out of NVIDIA#21693 (Mistral Large 4 merge-back); originally GitLab
a2d3872e7b, rebased onto main's warmup after NVIDIA#21343.

Signed-off-by: Yi Zhang <187001205+yizhang-nv@users.noreply.github.com>
yizhang-nv added a commit to yizhang-nv/TensorRT-LLM that referenced this pull request Nov 11, 2026
…e guided decoder

A capturable guided decoder (guided decoding together with one-model
speculative decoding: MTP, Eagle3 one-model, the external drafters such as
DFlash and DSpark, or SA) turned the whole general warmup off, though it
rules out only the warmup's generation requests: the autotuner already
runs its context step with the decoder installed. Without the general
warmup, the autotuner's max-token step was the engine's first forward.
What a first forward creates lazily, including the attention-DP group's
NCCL communicator (allocated through cuMem, outside the torch caching
allocator, so it cannot reclaim the cache), then came in the middle of the
autotuner's exploration with torch's cache full.

Any model served with guided decoding and one of those drafters takes
this path. It ran memory profiling out of memory while bringing up
Mistral Large 4 (NVFP4 DEP4 at 1M context with the DSpark draft and
xgrammar): rank 0 ran out of memory in the autotuner's max-token step,
and the other ranks failed to allocate NCCL memory through cuMem. Without
guided decoding, where the general warmup and its release run ahead of
the autotuner, the same configuration profiles at a peak of 238.6 GiB per
rank.

The general warmup now runs its context requests in that case, followed
by the same release as before, so the first forward and the release come
ahead of the autotuner, as they do without guided decoding. The extra
phase decision is agreed across ranks like can_run_general_warmup, which
is already rank-uniform when it is taken.

The general warmup skips a shape that runs a single rank out of memory
and goes on to a smaller one. With the decoder installed, input
preparation has already queued that shape's batch for the decoder's host
functions, so the abandoned batch would stay at the head of the queue and
every later forward, the first real guided request included, would be
served the batch before its own. The recovery now waits for the decoder's
stream, so that no host function of the failed forward is still pending,
and drops the queued batches and both request snapshots
(CapturableGuidedDecoder.reset_warmup_state). A failed reset stops the
warmup, and a distributed forward still re-raises the out-of-memory error.

Tests: test_guided_decoder_runs_the_context_warmup_before_the_autotuner
installs a guided decoder and checks that the general warmup runs with
context-only shapes (including the max-token one), followed by the MoE
workspace release, the cache release and then the autotuner.
test_general_warmup_oom_restores_guided_batch_queue fails a shape before
and after its host function is submitted and checks that the next guided
request is served its own batch. test_general_warmup_oom_policy and
test_general_warmup_aborts_if_guided_state_cannot_be_reset cover when the
reset runs and that its failure stops the warmup.

Split out of NVIDIA#21693 (Mistral Large 4 merge-back); originally GitLab
a2d3872e7b, rebased onto main's warmup after NVIDIA#21343.

Signed-off-by: Yi Zhang <187001205+yizhang-nv@users.noreply.github.com>
hanjingtian pushed a commit to yizhang-nv/TensorRT-LLM that referenced this pull request Nov 11, 2026
…e guided decoder

A capturable guided decoder (guided decoding together with one-model
speculative decoding: MTP, Eagle3 one-model, the external drafters such as
DFlash and DSpark, or SA) turned the whole general warmup off, though it
rules out only the warmup's generation requests: the autotuner already
runs its context step with the decoder installed. Without the general
warmup, the autotuner's max-token step was the engine's first forward.
What a first forward creates lazily, including the attention-DP group's
NCCL communicator (allocated through cuMem, outside the torch caching
allocator, so it cannot reclaim the cache), then came in the middle of the
autotuner's exploration with torch's cache full.

Any model served with guided decoding and one of those drafters takes
this path. It ran memory profiling out of memory while bringing up
Mistral Large 4 (NVFP4 DEP4 at 1M context with the DSpark draft and
xgrammar): rank 0 ran out of memory in the autotuner's max-token step,
and the other ranks failed to allocate NCCL memory through cuMem. Without
guided decoding, where the general warmup and its release run ahead of
the autotuner, the same configuration profiles at a peak of 238.6 GiB per
rank.

The general warmup now runs its context requests in that case, followed
by the same release as before, so the first forward and the release come
ahead of the autotuner, as they do without guided decoding. The extra
phase decision is agreed across ranks like can_run_general_warmup, which
is already rank-uniform when it is taken.

The general warmup skips a shape that runs a single rank out of memory
and goes on to a smaller one. With the decoder installed, input
preparation has already queued that shape's batch for the decoder's host
functions, so the abandoned batch would stay at the head of the queue and
every later forward, the first real guided request included, would be
served the batch before its own. The recovery now waits for the decoder's
stream, so that no host function of the failed forward is still pending,
and drops the queued batches and both request snapshots
(CapturableGuidedDecoder.reset_warmup_state). A failed reset stops the
warmup, and a distributed forward still re-raises the out-of-memory error.

Tests: test_guided_decoder_runs_the_context_warmup_before_the_autotuner
installs a guided decoder and checks that the general warmup runs with
context-only shapes (including the max-token one), followed by the MoE
workspace release, the cache release and then the autotuner.
test_general_warmup_oom_restores_guided_batch_queue fails a shape before
and after its host function is submitted and checks that the next guided
request is served its own batch. test_general_warmup_oom_policy and
test_general_warmup_aborts_if_guided_state_cannot_be_reset cover when the
reset runs and that its failure stops the warmup.

Split out of NVIDIA#21693 (Mistral Large 4 merge-back); originally GitLab
a2d3872e7b, rebased onto main's warmup after NVIDIA#21343.

Signed-off-by: Yi Zhang <187001205+yizhang-nv@users.noreply.github.com>
yizhang-nv added a commit to yizhang-nv/TensorRT-LLM that referenced this pull request Nov 12, 2026
…e guided decoder

A capturable guided decoder (guided decoding together with one-model
speculative decoding: MTP, Eagle3 one-model, the external drafters such as
DFlash and DSpark, or SA) turned the whole general warmup off, though it
rules out only the warmup's generation requests: the autotuner already
runs its context step with the decoder installed. Without the general
warmup, the autotuner's max-token step was the engine's first forward.
What a first forward creates lazily, including the attention-DP group's
NCCL communicator (allocated through cuMem, outside the torch caching
allocator, so it cannot reclaim the cache), then came in the middle of the
autotuner's exploration with torch's cache full.

Any model served with guided decoding and one of those drafters takes
this path. It ran memory profiling out of memory while bringing up
Mistral Large 4 (NVFP4 DEP4 at 1M context with the DSpark draft and
xgrammar): rank 0 ran out of memory in the autotuner's max-token step,
and the other ranks failed to allocate NCCL memory through cuMem. Without
guided decoding, where the general warmup and its release run ahead of
the autotuner, the same configuration profiles at a peak of 238.6 GiB per
rank.

The general warmup now runs its context requests in that case, followed
by the same release as before, so the first forward and the release come
ahead of the autotuner, as they do without guided decoding. The extra
phase decision is agreed across ranks like can_run_general_warmup, which
is already rank-uniform when it is taken.

The general warmup skips a shape that runs a single rank out of memory
and goes on to a smaller one. With the decoder installed, input
preparation has already queued that shape's batch for the decoder's host
functions, so the abandoned batch would stay at the head of the queue and
every later forward, the first real guided request included, would be
served the batch before its own. The recovery now waits for the decoder's
stream, so that no host function of the failed forward is still pending,
and drops the queued batches and both request snapshots
(CapturableGuidedDecoder.reset_warmup_state). A failed reset stops the
warmup, and a distributed forward still re-raises the out-of-memory error.

Tests: test_guided_decoder_runs_the_context_warmup_before_the_autotuner
installs a guided decoder and checks that the general warmup runs with
context-only shapes (including the max-token one), followed by the MoE
workspace release, the cache release and then the autotuner.
test_general_warmup_oom_restores_guided_batch_queue fails a shape before
and after its host function is submitted and checks that the next guided
request is served its own batch. test_general_warmup_oom_policy and
test_general_warmup_aborts_if_guided_state_cannot_be_reset cover when the
reset runs and that its failure stops the warmup.

Split out of NVIDIA#21693 (Mistral Large 4 merge-back); originally GitLab
a2d3872e7b, rebased onto main's warmup after NVIDIA#21343.

Signed-off-by: Yi Zhang <187001205+yizhang-nv@users.noreply.github.com>
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