release: bump version to 0.3.1 and update CHANGELOG.md

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: DaoTwenty

CHANGELOG.md

@@ -11,6 +11,12 @@ section above `[Unreleased]` before tagging.
 
 ## [Unreleased]
 
+## [0.3.1] - 2026-07-06
+
+### Added
+- **Token Diagnostics:** Opt-in `TokenLogger` for `SamplingSession` — per-token JSONL logs capturing token id/type/value, the grammar-masked T=1 distribution (log-prob, entropy, top-5 alternatives), grammar-collapse events, per-step summaries (context size, token budget, velocity mode) and per-bar summaries of the decoded result. No behavior change when no logger is attached. Also warns when the context window is nearly full and late tracks would be silently truncated.
+- **Replay Scoring:** `SamplingSession.score_from_tokens()` — teacher-forced log-probability of a previously generated token sequence under the session's context, applying the same grammar legality masks used at sampling time. Enables cross-conditional scoring (score a generation made under conditioning A against conditioning B) without re-sampling. Sequences longer than the model's positional window are scored with a sliding window; generation paths are untouched.
+
 ## [0.3.0] - 2026-07-06
 
 ### Added

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "scikit_build_core.build"
 
 [project]
 name            = "midigpt"
-version         = "0.3.0"
+version         = "0.3.1"
 description     = "GPT-2 transformer for symbolic music generation"
 readme          = "README.md"
 license         = { text = "MIT" }

src/python/midigpt/__init__.py

@@ -15,7 +15,7 @@
     except (ValueError, AttributeError):
         pass
 
-__version__ = "0.3.0"
+__version__ = "0.3.1"
 __all__ = [
     "Bar",
     "Note",