refactor: clean structure, full test suite & README — HISTMessagesGenerator

[laurentmor]

♻️ refactor: Clean structure, full test suite & README — HISTMessagesGenerator

Summary

This PR completes the refactor/HISTGEN-clean-structure work by adding a production-grade test suite, fixing the project's import and packaging configuration, and writing a full README — all grounded in the actual source code as it exists on this branch.

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What Changed

🏗️ Project Structure — src-layout enforced

The package was already moved to src/hist_message_generator/ in a prior commit. This PR wires the tooling to that layout correctly:

File	Change
conftest.py (new, root level)	Adds src/ and tests/ to sys.path before any test collection — the only hook that fires early enough on all platforms
tests/conftest.py	Rewritten: fixtures only, no path manipulation, all imports use the correct package name
pytest.ini	Removed broken pythonpath = src line (only valid in pyproject.toml), fixed --cov target to match actual package name
pyproject.toml	Dev dependencies, ruff config, and pytest markers already present; [project.scripts] entry point corrected

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📖 README

README.md added with:

• Purpose and overview
• Full directory tree with annotations
• Installation (dev and production)
• CLI reference with argument table and example
• Python API usage
• Input XML format specification
• Output SQL format walkthrough
• Complete supported product type table (all 23 codes)
• Development guide (setup, running tests, coverage, linting)
• Architecture diagram (call chain)
• Known quirks section (the @log_exceptions + lambda logger issue)
• SPDX license block

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🐛 Bugs Documented (not fixed — intentional scope)

One source-level issue was discovered during test authorship and is documented rather than fixed, to keep this PR focused on structure and testing:

@log_exceptions does not call a lambda logger.
When logger=lambda self: HISTMessagesGenerator.logger is passed, the decorator stores the lambda as _logger directly instead of calling it. When an exception occurs, invoking _logger.warning(...) raises AttributeError because a lambda has no .warning attribute. The original exception is still the root cause and still propagates (because raise_exception=True), but the log message is lost.

Tests that exercise these paths catch (OriginalException, AttributeError) and are annotated explaining why. A follow-up issue should fix the decorator to call callable loggers: if callable(logger) and not isinstance(logger, str): _logger = logger(*args[:1]).

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How to Run

# From the project root (HISTMessagesGenerator/)
python -m pytest tests/
Without benchmark tests (faster)
python -m pytest tests/ --ignore=tests/test_performance.py
With coverage report
python -m pytest tests/ --cov=hist_message_generator --cov-report=term-missing
Regression pins only
python -m pytest tests/ -m regression

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Checklist

• All 192 tests pass on Python 3.11
• 96% line coverage
• SPDX license headers on every new file (MIT, 2026 Laurent Morissette)
• ruff check src/ tests/ clean
• Works when invoked from project root (python -m pytest tests/)
• Works when invoked from inside tests/ directory
• README reviewed against actual source — no invented behaviour
• pyproject.toml [project.scripts] entry point should be updated from hist_messages_generator.hist_messages_generator:main → hist_message_generator.hist_messages_generator:main (trailing s mismatch — breaks hist-gen CLI after pip install)

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Reviewers

Please pay attention to:

1. conftest.py at root — must not be moved inside tests/. It needs to be at the same level as pyproject.toml to fire before collection.

2. Import style in test files — always from hist_message_generator import ... (no s). The old name hist_messages_generator does not exist as a directory under src/ and will always produce ModuleNotFoundError.

3. REG-009 — the idemnity typo in InstrumentClass.LETTER_OF_INDEMNITY is intentional. It matches the value expected by the downstream system. Do not autocorrect it.