allium check: status reachability ignores ensures clauses inside if/else branches

[abalmus-celonis]

Version: allium 3.5.0 (language versions: 1, 2, 3), installed via brew tap juxt/allium && brew install allium.

Bug: allium check's allium.status.unreachableValue diagnostic does not recognize ensures: clauses nested inside if/else branches as valid assignments, even though allium parse shows the AST correctly captures them as IfBlock items.

Repro (widget.allium):

-- allium: 3

entity Widget {
    status: pending | approved | rejected

    transitions status {
        pending -> approved
        pending -> rejected
        terminal: approved, rejected
    }
}

rule Decide {
    when: Decide(widget, ok)

    if ok:
        ensures: widget.status = approved
    else:
        ensures: widget.status = rejected
}

Actual: allium check widget.allium reports:

Status 'approved' in entity 'Widget' is never assigned by any rule ensures clause.
Status 'rejected' in entity 'Widget' is never assigned by any rule ensures clause.

Expected: both statuses should be recognized as reachable, since they are assigned by Decide (conditionally). Confirmed via allium parse widget.allium that the AST correctly contains both ensures: widget.status = approved and ensures: widget.status = rejected inside the IfBlock's two branches — so this looks like a gap in the reachability analysis pass specifically, not the parser.

Impact: any rule that assigns a status conditionally (a very common pattern — e.g. approve/reject outcomes depending on a guard) produces false-positive "unreachable status" warnings for every branch, which drowns out real reachability findings (we ran into this distilling a real spec with 3 conditional branches; all 5 conditionally-assigned statuses were flagged, alongside 1 genuine issue elsewhere).