Wildcard + fixed_values surfaces are binding PRODUCERS, not consumers
— they don't read upstream \$var. Combine + derivation + assembler do
(template interpolation is their reason to exist).
Adds VarOutOfSurfaceError to engine.syntax.types + extends SurfaceKind
literal with "fixed_values". _resolve_var checks surface membership
in _VAR_SURFACES_ALLOWED frozenset; out-of-surface refs warn + render
literal \$name in lenient mode (existing default), raise in strict
mode (used by tests + dev mode).
Lenient strategy means workflows saved before this cycle keep
resolving — the warning surfaces in toast / conflict scanner without
crashing the queue.
Test fixture adjustments document the new contract:
- tests/syntax/test_resolve.py default surface flips wildcard -> combine
(these tests cover VAR resolution mechanics, not surface gating)
- tests/syntax/test_determinism.py corpus single_var + var_in_text
cases use surface=combine
- tests/engine/modules/test_wildcard_handler.py:
* test_resolve_var_substitution_in_option renamed to
test_resolve_var_in_option_renders_literal_warns + asserts new
lenient path
* test_resolve_pinned_mode_resolves_inline_syntax swaps \$color for
a {red|red} alternation that DOES resolve on wildcard surface
Surface gating tests live in tests/engine/syntax/test_resolve_var_surface.py
covering all 5 surfaces + lenient vs strict modes + internal-key skip.
