[faresobeid]

What

Carries the sampler's logprobs at the sampling-mask ids onto the trace graph.

• SamplingMask gets an optional float32 logprobs array, parallel to ids: the sampler's renormalized logprobs of the kept ids.
• SamplingMask.from_sampling_mask(mask, logprobs=None) decodes logprobs from prime-rl's /generate sampling_mask_logprobs: packed float32, base64 {data, shape, dtype}, the same form as the packed ids, decoded with _decode_packed. response_from_generate passes result.get("sampling_mask_logprobs"). Stock vLLM does not send it, so the per-row mask path has no logprobs.
• Attribution: a mask whose logprobs length differs from ids is not attributed (same rule as a mask whose counts do not match the node's sampled positions).
• Aggregation: Branch.sampling_mask concatenates the logprobs only when every mask on the path has them; otherwise logprobs is None and ids/counts still merge. Nodes without a mask (prompt, replayed prefix) do not count.
• The __nd__ serializer/validator handle every field present on the dataclass. Without logprobs, the serialized form and payload are unchanged.

Payload when present: 4 B per kept id.

Consumer

prime-rl score centering, PrimeIntellect-ai/prime-rl#3794, pins this head. It sends sampling_mask_logprobs packed. Without that consumer this field is unused.

Companion

PrimeIntellect-ai/renderers#170 passes sampling_mask_logprobs (and payload) through. Order: renderers#170 + this PR -> prime-rl#3794.

Validation

• tests/unit/test_graph.py::test_sampling_mask_logprobs_attributed_aggregated_and_round_tripped: branch concat, wire round trip, mixed turns -> None, mismatched length not attributed.
• tests/unit/test_trace.py::test_sampling_mask_from_packed_matches_lists: packed logprobs decode.
• pytest tests/unit/test_graph.py tests/unit/test_trace.py, ruff check, ruff format --check.

Note

Add optional sampler logprobs to SamplingMask

• Adds an optional float32 logprobs array to SamplingMask, parallel to the flattened mask IDs, and SamplingMask.from_sampling_mask now decodes optional packed logprobs (types.py)
• response_from_generate passes generate-result logprobs into the mask when constructing TurnTokens (train.py)
• Branch.sampling_mask concatenates per-node logprobs in ID order; returns None logprobs if any non-empty mask on the branch lacks them (trace.py)
• Attribution now rejects masks whose logprobs length differs from their IDs length, and serialization omits None-valued array fields (graph.py)
• Risk: MessageNode.serialize_sampling_arrays in graph.py changes wire format for masks without logprobs — those fields are now absent rather than encoded

^{Macroscope summarized 8a90f95.}

---

Note

Low Risk
Additive optional field with stricter attribution validation; behavior unchanged when logprobs are absent (e.g. stock vLLM).

Overview
Adds optional sampler logprobs on SamplingMask: a float32 array parallel to flattened mask ids, populated from prime-rl’s packed sampling_mask_logprobs when building turn tokens from /generate.

Trace graph behavior: masks with logprobs length mismatched to ids are no longer attributed to assistant nodes. Branch-level sampling_mask concatenates logprobs across turns only when every attributed mask on the path includes them; otherwise logprobs stays None while ids/counts still merge. Wire serialization now omits unset ndarray fields on SamplingMask (and top_logprobs), so payloads without logprobs stay unchanged.

Unit tests cover packed decode, multi-turn aggregation, mixed turns, round-trip, and rejection of mismatched lengths.

^{Reviewed by Cursor Bugbot for commit 8a90f95. Bugbot is set up for automated code reviews on this repo. Configure here.}

[macroscopeapp]

Approvability

Verdict: Would Approve

Macroscope's review found this PR approvable — This is a localized, backward-compatible addition of optional sampler logprobs, with existing paths preserved and aggregation/serialization covered by tests. An unresolved high-severity comment still flags the wire round-trip area for masks without logprobs, despite the current diff adding absent-field handling and round-trip coverage.

Needs human approval because:

• 1 blocking correctness issue found at or above your repo's Minimum Blocking Severity

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Dismissing prior approval to re-evaluate 1e499fb

Dismissing prior approval to re-evaluate cf6ebfe

The base branch was changed.

[cursor]

Stale Bugbot comment from a previous run.

[macroscopeapp]

🟠 High v1/types.py:223

Masks created without sampler logprobs now fail to round-trip across the env-server wire. The serializer iterates every dataclass field, so it encodes logprobs=None as an object-dtype array, which _decode_ndarray cannot read; omit None fields in serialize_sampling_arrays.

🚀 Reply "fix it for me" or copy this AI Prompt for your agent:

In file @verifiers/v1/types.py around line 223:

Masks created without sampler logprobs now fail to round-trip across the env-server wire. The serializer iterates every dataclass field, so it encodes `logprobs=None` as an object-dtype array, which `_decode_ndarray` cannot read; omit `None` fields in `serialize_sampling_arrays`.

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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