Resolve concatenation in the html-safety check, and empty the baseline

[abrignoni]

Port of ALEAPP #1045. Every baselined entry in this core turned out to be a false positive rather than an unescaped sink, so the baseline goes to zero.

The checker gap

It did not resolve + chains at all, so an accumulator read as unknown even when every write to it was escaped:

agg = agg + f'<td>{esc(value)}</td>'   # escaped, but reported as unknown
agg = agg + '</table>'                  # concat with a tool-owned literal

It now resolves a concatenation when both sides resolve, with the self-reference terminating through the existing seen set. Accumulate-then-emit is how most of these builders work, so this was the single largest source of noise.

This does not weaken the check. The regression probe includes an unescaped accumulator concat, and it is still caught.

media_to_html

source was assigned four times and then emitted. The final write was safe_local_path() and nothing read it earlier, so the function was correct — but a name counts as safe only when every assignment to it is, because this check does not order assignments.

The escaped values now bind to their own names, safe_source and safe_filename. That makes the safety local and obvious to a reader as much as to the checker, which is the better shape regardless of tooling.

Validation

• py_compile clean; lint_changed reports no new warnings
• unit tests OK; PluginLoader loads every plugin
• the check exits 0 with 0 baselined, and still exits 1 on injected probes — including an unescaped accumulator concat

🤖 Generated with Claude Code