Variable resolution can recurse while building global scope

[aaaaaandrew]

Summary

Variable resolution can re-enter the exact same query while constructing the top-level scope used by PHP global declarations. The relevant path is still present on current main in src/type_engine/variable/resolution.rs.

The cycle is:

1. resolve_variable_types starts a forward walk.
2. resolve_variable_in_statements sees global in the file and starts a top-level scope walk.
3. Resolving an RHS call argument requests the same variable resolution.
4. That request starts another top-level scope walk, repeating the cycle.

Minimal fixture

<?php
function capture($input) {
    global $shared;
    $shared = transform($input);
}
$arg = source_value();
$old_global = factory($arg);
$value = consume($old_global);
$value->method();

A semantic consumer resolving the receiver of $value->method() reaches the cycle. The important shape is a file containing global plus top-level call arguments that require variable resolution.

Expected behavior

Resolution should terminate without disabling valid global inference. A re-entrant query cannot contribute information while its outer invocation is still incomplete, so only that exact cycle should be cut.

Possible implementation

Use thread-local RAII guards to track active resolution work:

resolve(key):
    if key is already active:
        return no additional types

    mark key active
    defer unmark key
    perform resolution

The resolution key should include source identity, variable name, cursor offset, and current class. Top-level-scope construction needs a separate source-level guard because it can recursively initiate another resolution before the original scope is complete.

The guard must be ownership-aware: rejecting a nested acquisition must not remove the outer acquisition when the rejected guard is dropped.

Acceptance criteria

• The fixture terminates without stack growth or unbounded work.
• Existing global member resolution remains intact.
• Unrelated variables and cursor positions are not suppressed.
• Guard state is released after normal return and unwinding.
• Repeated resolution on the same thread continues to work.