Implements ScanType::PlcControlLogic — the missing piece for PlcSps targets,
which previously classified but ran no scan.
New `pipeline::plc`:
- A real IEC 61131-3 Structured Text front end: lexer + recursive-descent parser
→ AST (POUs, typed VAR sections, statements, expressions). Tolerant recovery so
odd constructs never sink a file.
- PLCopen XML extractor: pulls each ST POU's interface vars + `<ST>` body and
reconstructs equivalent ST, so raw `.st` files and PLCopen projects share one
analysis path.
- Eight semantic, guard-aware rules over the AST → findings: hardcoded
credentials, default/weak passwords, safety-interlock/watchdog bypass, array
indexed by unvalidated input, division without a zero-guard (suppressed when an
enclosing `IF <d> <> 0` proves it), insecure comm (auth/encryption disabled),
and cleartext OT protocol ports, plus unstructured JMP. Each carries CWE +
remediation.
- `PlcControlLogicScanner` (Scanner impl) walks the project tree and emits
`Finding`s (dedup fingerprint, file, line, severity).
Wired into `run_target_pipeline`: when the scan plan includes PlcControlLogic,
`run_plc_scan` ingests the PlcProject artifact, analyzes it, and persists the
findings (findings_count handled by run_target).
Demo fixtures under examples/plc-demo/ (a vulnerable pump-station `.st` + a
PLCopen `conveyor.xml`). Tests: parser, all-rules-fire, guarded-clean-is-quiet,
and an end-to-end tree scan — 5 passing.
Adds `roxmltree` (read-only XML) for PLCopen parsing.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
