feat(v1): add Trace.last_reply and adopt it across v1 envs

[xeophon]

Description

Adds Trace.last_reply — the stripped text of the final sampled assistant message (or "" when there are no assistant messages / the last one has no text) — and adopts it across the v1 envs and docs that read the model's final reply as text for scoring/judging.

Every scoring reward that wants "the answer" hand-rolled the same idiom (assistant_messages[-1].content if assistant_messages else "", or the unguarded [-1].content). last_reply is the typed convenience over that, and safe by default — it returns "" instead of IndexError on an empty trace, and AssistantMessage.content is str | None, so the None case is handled too.

Type of Change

• New feature (non-breaking change which adds functionality)
• Test improvement
• Documentation update

What changed

• verifiers/v1/trace.py — new last_reply property (@property, next to assistant_messages): (msgs[-1].content or "").strip() if msgs else "".
• tests/v1/test_trace.py — test_last_reply: newest sampled turn wins (" a1 " then "a2" → "a2"), no turns → "", None content → "".
• v1 envs migrated to trace.last_reply (each previously hand-rolled the guard): reverse-text-v1, gsm8k-v1, glossary-v1, deepwiki-v1, code-golf-v1, scratchpad-v1, wiki-search-v1.
• verifiers/v1/GUIDE.md — the canonical reverse-text reward and two other snippets now use trace.last_reply.
• Not migrated (intentionally): alphabet-sort-v1 iterates every assistant turn ([m.content or "" for m in trace.assistant_messages]); color-codeword-v1 takes the AssistantMessage objects themselves. Neither is "last reply" semantics, so they stay on assistant_messages.

Testing

• New tests have been added to cover the changes — tests/v1/test_trace.py::test_last_reply (passes; full test_trace.py green, 4/4).
• All migrated env tasksets import against the patched source (syntactically + semantically valid against the new Trace.last_reply).
• ruff check clean on all changed files.
• The @pytest.mark.e2e env runs (real model rollouts + runtimes) are not executed locally; the change is a read-only property with no new imports and is covered by the unit test + import check.

Checklist

• My code follows the style guidelines (AGENTS.md)
• I have performed a self-review of my own code
• I have commented my code (docstring on the property; inline rationale in the test)
• I have made corresponding changes to the documentation (GUIDE.md)
• My changes generate no new warnings (ruff clean)

Additional Notes

Companion to the Prime CLI v1 work (PrimeIntellect-ai/prime#766). last_reply is purely additive; the env swaps are behavior-preserving (the only behavioral change is an outer .strip() on the final reply, which is benign for the substring/regex/judge checks these rewards use — and matches what the GUIDE's reverse-text example already did).

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Note

Low Risk
Additive trace helper plus mechanical reward refactors; only scoring input normalization changes (strip / empty-string fallback), with no auth, runtime, or wire-format changes.

Overview
Introduces Trace.last_reply on verifiers/v1/trace.py as the canonical way to read the model’s final sampled assistant text: whitespace-stripped content, or "" when there are no assistant messages or content is None.

Seven v1 tasksets (code-golf, deepwiki, glossary, gsm8k, reverse-text, scratchpad, wiki-search) and verifiers/v1/GUIDE.md examples now use trace.last_reply instead of hand-rolled assistant_messages[-1].content guards.

Scoring and stop hooks therefore get normalized, safe final-reply text (including an outer .strip()); empty traces no longer risk IndexError on [-1].

^{Reviewed by Cursor Bugbot for commit d76f20a. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Add Trace.last_reply property and adopt it across v1 environments

• Adds Trace.last_reply to trace.py as a convenience property returning the last assistant message content, whitespace-stripped, or an empty string when no assistant messages exist.
• Replaces manual trace.assistant_messages[-1].content access in reward functions across all v1 environments (code_golf, deepwiki, glossary, gsm8k, reverse_text, scratchpad, wiki_search) with trace.last_reply.
• Updates the GUIDE.md examples to reflect the new pattern.

^{Macroscope summarized d76f20a.}

[macroscopeapp]

Approvability

Verdict: Approved

Adds a convenience property last_reply to consolidate repeated code patterns across v1 environments. The changes are mechanical adoptions of the new property. The only behavioral difference is adding .strip() to whitespace-trim content, which is appropriate for scoring contexts.

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