fix: metadata["boundary"] documents trial 0 on all code paths

[AlexanderFengler]

Closes #315

What was wrong

• With multi-row θ, the sequential flexbound kernels returned the scratch boundary buffer in full-return metadata — i.e. the last trial's boundary — while metadata["trajectory"] (and the per-trial arrays t, z, ...) described trial 0.
• 4 parallel dispatcher kernels already returned boundaries_all_np[0], so metadata["boundary"] silently depended on the code path (n_threads) taken.

The fix

• Every flexbound kernel now recomputes the trial-0 boundary into the existing scratch buffer immediately before metadata assembly (19 sites across ddm_models, sequential_models, race_models, levy_models, ornstein_models, parallel_models).
• No signature or shape changes; a no-op for single-trial calls; the already-correct dispatcher sites and addm are untouched.

Tests

• New tests/test_metadata_boundary_trial0.py: one model per touched kernel family (angle, weibull_cdf, ddm_seq2_angle_no_bias, race_no_bias_angle_4, levy_angle, ornstein_angle, ddm_par2_angle_no_bias), asserting (1) multi-trial boundary == single-row trial-0 boundary, (2) reversed row order flips the result (contract is "first row", not coincidence), (3) n_threads=1 vs n_threads=4 give identical boundary metadata. 17/21 of these fail on current main.

Docs

• simulator() docstring now states the contract: with full metadata, boundary and trajectory describe trial 0 (first row of θ); per-trial parameter arrays remain full-length. Previously last-trial on sequential paths.

Downstream

• HSSM's model-cartoon single-row workaround (plot_model_cartoon: reduce each posterior draw to one θ vector (correctness follow-up to #1124) HSSM#1125) stays valid; no downstream changes required.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes

  • Corrected full-output metadata so boundary and trajectory information consistently describe the first trial.
  • Ensured sequential and parallel simulations report matching boundary metadata.
  • Prevented boundary metadata errors when simulations contain no trials.

• Documentation

  • Clarified that full-output boundary and trajectory fields refer to trial 0, while per-trial parameters remain unchanged.

• Tests

  • Added regression coverage across simulator types, including multi-trial results and reordered parameter sets.

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Review details

⚙️ Run configuration

Configuration used: defaults

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Run ID: ba717a9c-a82e-4b9c-9938-59ed8d77a6bd

📥 Commits

Reviewing files that changed from the base of the PR and between 913ba05 and 43391b8.

📒 Files selected for processing (1)

• pyproject.toml

📝 Walkthrough

Walkthrough

The simulator kernels now recompute full-result metadata boundaries from trial 0 parameters when trials exist. The simulator documentation defines trial 0 scope for boundary and trajectory metadata. Regression tests cover multiple kernel families and execution modes.

Changes

Metadata boundary alignment

Layer / File(s)	Summary
Kernel metadata boundary reconciliation src/cssm/ddm_models.pyx, src/cssm/levy_models.pyx, src/cssm/ornstein_models.pyx, src/cssm/parallel_models.pyx, src/cssm/race_models.pyx, src/cssm/sequential_models.pyx	Full metadata paths recompute boundary from trial 0 parameters when n_trials > 0.
Metadata contract and regression validation ssms/basic_simulators/simulator.py, tests/test_metadata_boundary_trial0.py	The documentation defines trial 0 metadata scope. Tests verify trial ordering, model-specific boundaries, and sequential versus parallel consistency.

Estimated code review effort: 2 (Simple) | ~15 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the primary change: metadata boundary now consistently documents trial 0 across all code paths.
Linked Issues check	✅ Passed	The changes satisfy issue #315 by aligning boundary metadata with trial 0 across kernels, documenting the contract, and adding regression tests.
Out of Scope Changes check	✅ Passed	All code, documentation, and test changes directly support the trial-0 metadata consistency objective in issue #315.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch 315-boundary-metadata-trial0

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Flag	Coverage Δ
unittests	94.08% <ø> (ø)

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Files with missing lines	Coverage Δ
ssms/basic_simulators/simulator.py	89.53% <ø> (ø)

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