Close non-last parameter types of function templates

[coord-e]

Fixes #235.

FunctionTemplateTypeBuilder::build gave a non-last parameter's type the scope of the parameters before it. Nothing in that type carries a template except an enum's type arguments, which TemplateTypeBuilder::build refines via build_refined, so for a parameter whose type contains a generic enum the scope leaked into the resulting type and left it open.

BasicBlockType::params holds the enclosing function's arguments, and analyze::basic_block instantiates each of them against the caller's variable through assert_closed. A generic enum in any parameter but the last one therefore aborted with unexpected variable as soon as the body had a block needing its own precondition:

fn get_or(o: Option<i64>, d: i64) -> i64 {
    match o { Some(x) => x, None => d }
}

This builds such a parameter without the scope. The last parameter's own type is already built that way inside build_refined — only its refinement is scoped — so the two paths now agree.

The alternative repair sketched in the issue (carrying the enum-argument templates through the basic-block parameter instead of calling assert_closed) is not taken here: the scope only ever reached enum type arguments, incidentally, and it never reached the last parameter's type at all, so dropping it is the smaller and more consistent change.

Testing

• tests/ui/{pass,fail}/option_param_order.rs: the get_or shape above, with the fail file breaking only the None-case assertion. Both ICE (exit 101) on main and pass here.
• All 13 rows of the issue's isolation table verify as safe, including the &self-method shape, and the three soundness spot-checks it lists are still rejected as Unsat.
• cargo test: 326 UI tests, 2 doc-tests passing; cargo fmt --check clean.

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Generated by Claude Code

[Copilot]

Pull request overview

Closes generic-enum refinements in non-last function parameters, preventing assert_closed panics during branching analysis.

Changes:

• Builds non-last parameter types without leaking the function-template scope.
• Adds paired UI tests covering successful and unsatisfiable Option parameter cases.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/refine/template.rs	Builds nested templates with an empty scope and converts the resulting closed type.
tests/ui/pass/option_param_order.rs	Verifies correct branching with a non-last Option parameter.
tests/ui/fail/option_param_order.rs	Confirms an invalid assertion remains rejected.

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