Stop textually splicing variable values into expression source in ControlFlowAutoResolver._safe_eval

[jeremymanning]

Verified on main today.

Evidence

src/orchestrator/control_flow/auto_resolver.py:712:

resolved_expr = self._replace_variables(expr_to_eval, context)

The expression string is rewritten as text, substituting variable values, before being evaluated.

Why this is wrong

This is the same defect class that produced the original eval() bug documented in core/expressions.py: substituting names as text corrupts unrelated substrings. A context variable named a rewrites the a inside max(...). The result is silent, incorrect evaluation — not an error.

It is no longer an RCE vector (names now resolve from context inside the constrained evaluator), so this is a correctness bug, not a security one. But it is the last surviving instance of the pattern.

Proposed fix

Delete _replace_variables from this path and pass context to evaluate_expression(expr, context) directly — the evaluator already resolves names from a context mapping, which is precisely what this code is hand-rolling incorrectly.

Acceptance criteria

• _safe_eval performs no textual substitution
• A test proves max(a, 10) with {"a": 3} returns 10, not a corrupted expression
• Existing auto_resolver tests still pass