[dev-belly]

GET /reports/{name}?directory=... previously treated the caller-selected directory as its allowed root, so a readable HTML file anywhere on the server could be returned. Select the report root at server startup with TRADEFORGE_REPORT_ROOT (default artifacts/reports), and allow requests to choose only relative subdirectories within it.

Reject absolute and parent paths, Windows drive/UNC/stream syntax, filename path components, and resolved symlink escapes. Generated HTML reports remain available through the default endpoint and valid subdirectories; the guide documents the new directory semantics.

Validation:

• Windows Python 3.12: API and HTML report tests: 48 passed, 2 skipped. The two real symlink cases require Windows symlink privileges unavailable to this user; the tests run without that skip on Linux CI.
• Ruff lint/format, API mypy, architecture checks and whitespace checks pass.
• The same readable HTML file outside the configured root returns 200 before the change and 400 after it.
• A subprocess test starts the API with a custom server-owned root and serves a generated report through the default route.