[ASDAlexander77]

Toward building the default library under -mm=own: it had 62 ownership errors in lib.ts. With this PR and ASDAlexander77/TypeScriptCompilerDefaultLib branch own-default-lib, 5 remain (release; 7 with --di). All 5 are in matchAll, String[Symbol.iterator] and Response.constructor. Those are exported functions that keep or borrow a parameter, which needs a separate decision.

@nodrops C declarations (f25aaf8)

• @nodrops declare function f(...) marks a C function that destroys nothing a TypeScript caller can reach. The ownership signature pass resolves a call to it the way it resolves an imported own library's no-drops function. Before this, every body that reached strncmp, boundedCopy and the like counted as "may destroy anything".
• Four own false errors that the library hit:
  • Returning one local on two paths (if (c) return r; return r;) failed for every type. It now moves once on each path.
  • A string concat no longer extends a borrow of its operands (v[i] = v[i] + s).
  • ts.Assert only reads its message.
  • return [...a] now compiles.

@final classes

Spec: tslang/docs/superpowers/specs/2026-10-19-final-classes-design.md. Plan: tslang/docs/superpowers/plans/2026-10-19-final-classes.md.

• No class may extend a @final class. That includes from another module, because __decls keeps @final. @final abstract and @final @cpp are errors.
• Direct calls. A method or accessor of a value whose static type is a @final class is called directly (ThisSymbolRef), not through the vtable. This applies only when the member's class is defined in this module. Members of imported or declared classes keep vtable calls: a static importer can't link a member of a base the library doesn't export. The vtable, interfaces and instanceof are unchanged.
• No posing. An unrelated class that fits a @final class member by member is no longer assignable to it.
• Bugs the direct calls exposed:
  • A method read as a value (const fn = f.m) had no lowering for ThisSymbolRef.
  • Generator methods of exported classes were not exported: the wrapper dropped DllExport/IsPublic.
  • Under own with --di, a cast to null (how --di records a variable narrowed by == null) counted as taking a reference.

Tests

• New compiler tests:
  • final/ error cases.
  • final_dispatch under gc, rc, none and own, AOT and JIT.
  • IR checks for direct and base calls.
  • A -shared export/import pair, including a @static import of a @final class with a non-exported base.
  • A cross-module extends error.
  • Own tests: own_final_*, own_declared_no_drops, own_return_paths, own_string_concat_element, own_null_narrowing_di.
  • test-export-generator-method and test-compile-class-cast-to-final-error.
• Full Release suite: 4714/4714.
• DefaultLib (branch own-default-lib): release gc and rc builds pass tests.ps1, compiled and JIT.

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