recursion-cycle: de-conflate leaf-nominal identity from structural self-containment (un-spurious-Box leaf types; supersedes #5624)

[gunbai-bot]

What

De-conflate a leaf nominal's own identity from structural self-containment in the recursion-cycle dependency extraction, so opaque/alias/branded leaf types (Symbol, Char, Email, Url, Path-class, type parameters …) are no longer spuriously marked recursive and spuriously Box-wrapped in emitted Rust.

Root cause (by execution)

detect_type_cycles_kahn marks a type recursive if its deps contain its own name (self_ref). node_type_deps returns a leaf nominal's own name as a "dependency" (Symbol deps=[Symbol]) — because type Symbol (opaque), type Email = String (alias), type Char = Int where brand(...) (branded) all resolve to their own nominal identity. That self-name is the type's identity, not a structural dependency, so kahn over-marks every such leaf as recursive → spurious Box<…> in emit (the cargo-green E0308 class).

The kahn algorithm and import handling are correct; only the dependency-extraction input conflated identity with structural self-containment.

Fix

At the dependency-extraction call site (all_deps_map, both build_type_env copies): a binding whose resolved form is a bare leaf (NoConnective, 0 children) and whose deps are exactly [own_name] contributes no self-dependency. Genuine structural recursion (GrammarExpr, whose self-name comes from variant children) flows the unchanged structural path and stays marked. node_type_deps and the kahn algorithm are unchanged; no filter, no import-union, no resolve-stage change.

• src/v1/04_infer.dag: helper deps_excluding_leaf_self + both fold sites (authority)
• src/v1/stage0/src/v1_compiler_infer.rs: hand-mirror (both sites, inline)

Validation (by execution)

Apples-to-apples on identical sources (dsl-first compile-clean closure, --dependency-pool-index primary-precedence):

• No net-new diagnostics: 486 files / 0 diagnostics before and after.
• Box win: Box< 445 → 308 (−137); Box::new 258 → 123 (−135).
• Smoking gun: 50 marks dropped — all leaf nominals + type-params; 0 newly marked; genuine recursion (GrammarExpr/GrammarProduction/GrammarRoot/Node/FreeMonoid/CoreNode) preserved.
• target_model_runtime_import_repro 4/4 PASS (cross-module field access intact).
• anthropic non-regression green; realization_reconcile green (no change — this fix is narrower than the abandoned v3 lever).
• Red-on-revert: reverting restores the 445/258 boxes.

Supersedes #5624 (the v3 filter+union lever, refuted by execution).

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