[SizzleUnrlsd]

Summary

Phase 1 item "Complete the PyHIR node set" (§3.2) and most of the open PyIR instructions (§6), plus a tolerant --check.

• Acceptance tests first (test: define everyday syntax coverage and tolerant check), implementation follows.
• PyHIR: parameters carry defaults and kinds (positional, keyword, var-positional, var-keyword), functions and classes carry decorators, AugAssign, assignment targets may be attributes, items or unpacked tuples, Tuple/List/Dict literals, BoolOp, chained comparisons (lowered to and), With/WithItem, Assert, keyword-argument unpacking, and HIR_SCHEMA_VERSION. Star arguments stay an explicit diagnostic.
• Scope analysis binds with targets and unpacked names and evaluates defaults and decorators in the enclosing scope; import analysis walks with bodies.
• CFG: a with body is laid out inline between synthetic EnterWith / ExitWith statements; an early exit skips the exit (no exception edges yet).
• PyIR: Call keywords, SetAttr, SetItem, BuildList, BuildTuple, BuildDict, BoolOp, WithEnter, WithExit, Assert; operands and substitution recurse through nested tuples generically. Methods of module-level classes are lowered and named Class.method; other module-level statements are skipped instead of rejected.
• Taint: keyword arguments are sink arguments and propagate like positional ones; list, tuple and dict literals propagate, so subprocess.run(["sh", "-c", cmd]) is caught.
• --check no longer aborts on a function outside the subset: it emits an unsupported-syntax note (severity info) for that function and analyses the others. Plugins see only the analysable functions through PluginContext.functions().

Not in this PR: Try and exception edges, Lambda, Await/Yield, star arguments, nested function definitions (closures), which remain explicit diagnostics.

Part of #25: everything but await and yield, which stay open there with Try, Lambda, star arguments and closures.