Effective gate treats missing coverage totals as 0% and can pass without measurements #15

Found while reviewing the architecture documentation. Verified against upstream HEAD d99515b87bbe1dde89984403e9c330d640fc5d33 using synthetic report archives and the real generate_coverage_html CLI (no gate/justification mocks).

The effective coverage path converts missing/unparseable/zero HTML totals to a numeric 0% report. The gate treats this as an evaluated percentage. At the default threshold it exits 1; at threshold 0 it exits 0, although there are no usable measurements. The raw LCOV path rejects zero instrumented lines with exit 2.

Reproduction

Create a report zip containing html_report/index.html with no parseable LLVM Totals row, an empty html_report/style.css, and lcov_report/lcov.dat with LF:0 and LH:0. Supply a valid empty YAML:

version: 1
justifications: []

Run the real generate_coverage_html CLI with --yaml:

• COVERAGE_THRESHOLD=100: warning about unparseable totals, effective 0%, exit 1.
• COVERAGE_THRESHOLD=0: same warning, effective 0%, exit 0.

Without YAML the zero-line LCOV yields exit 2.

Expected

Unavailable measurements must produce exit 2 for every threshold, including 0. Validate usable totals before constructing/accepting an effective gate value. Cover missing/malformed HTML totals and zero instrumented lines in both HTML backends.

This violates tool_req__coverage_gate_exit_codes and tool_req__coverage_gate_no_verdict.

Relevant code

• Effective totals and zero-denominator fallback
• Gate reads only the effective percentage