- Introduced canonical `*** Cell` headers with `t:` and `rst` attributes in eval prompts, schema, and docs.
- Updated parser and grammar to parse `*** Cell` blocks, stop on `*** End`/next header/EOF, and handle invalid `rst` with errors.
- Added quote-aware attribute tokenizers and split HTML eval parsing into `Cell` and legacy `Begin` handlers with `py` defaults.
- Expanded parsing behavior and tests for `rst` booleans, title aliases, abort boundaries, and stray-line skips between cells.
- Updated parseEvalInput to verify begin-cell markers before dereferencing regex matches.
- Skipped stray non-marker lines between and after cells, preserving valid cells when model output is noisy.
- Added eval parse regression tests for stray content and trailing chatter, and kept abort-line handling explicit.
- Replaced `===== ... =====` eval cell headers with `*** Begin ` / `*** End ` markers; legacy format remains renderable in HTML exports.
- Replaced hashline patch grammar with `*** Begin Patch` / `*** End Patch` envelope; old inputs without the envelope are still accepted.
- Extracted `sniffEvalLanguage` into a shared `sniff.ts` module reused by the parser and tool.
- Added `docs/ERRATA-GPT5-HARMONY.md` and `scripts/session-stats/harmony_backtest.py` documenting and backtesting the GPT-5 Harmony-header leak defect.
- Added a unified eval framework with parser grammar, backend interfaces, and JS/Python execution result types.
- Added eval tool docs and updated prompts for fenced cells, `eval.py`/`eval.js`, and fallback behavior.
- Replaced the built-in `python` tool with `eval` across registry, rendering, interactive modes, and tool settings.
- Migrated Python execution runtime from `src/ipy` to `src/eval/py`, renamed state fields, and removed legacy introspection.
- Refactored browser tooling from in-process VM helpers to worker-managed tab supervisors and protocol transport.
- Added eval parser fallback and JS tool-bridge tests, updated imports, and removed obsolete python-mode suites.
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