@endo/immutable-arraybuffer@2.0.0

Major Changes

• #3308 4da9a99 Thanks @kriskowal! - Drop the immutable-ArrayBuffer pseudo-prototype.

  Emulated immutable ArrayBuffers produced by @endo/immutable-arraybuffer now inherit directly from ArrayBuffer.prototype rather than from an intermediate prototype. Object.getPrototypeOf(immuAB) === ArrayBuffer.prototype for both emulated immutable and genuine buffers; the brand check is the new immutable accessor on ArrayBuffer.prototype installed by the shim.

  The [Symbol.toStringTag] slot is preserved as an own property on each emulated immutable buffer (not on the shared prototype), so Object.prototype.toString.call(immuAB) continues to return '[object ImmutableArrayBuffer]' (as in master) while genuine ArrayBuffers continue to read as '[object ArrayBuffer]'. This keeps concordance (and any other downstream consumer that sniffs the toStringTag to decide whether the value is a genuine exotic) from misrouting an emulated immutable through Node's Buffer.from, which throws because the emulated immutable is not an exotic object.

  @endo/immutable-arraybuffer is now a side-effect-only package: its sole public export is ./shim.js. The index.js and the package's . entry are removed; the previously exported names (isBufferImmutable, sliceBufferToImmutable, optTransferBufferToImmutable) are no longer reachable from outside the package. Callers detect immutability via the ArrayBuffer.prototype.immutable accessor (or Object.prototype.toString.call(buffer) === '[object ImmutableArrayBuffer]' when the shim has not been loaded) and convert via buffer.sliceToImmutable(...) and buffer.transferToImmutable(...) on the prototype. The break is a major bump for the @endo/immutable-arraybuffer package.

  @endo/bytes's to-immutable.js imports @endo/immutable-arraybuffer/shim.js (triggering the shim install) and calls buffer.sliceToImmutable(...) on ArrayBuffer.prototype instead of the previously exported sliceBufferToImmutable free function.

  The shim's install policy is now detect-then-skip rather than warn-and-overwrite: the Immutable ArrayBuffer proposal has reached stage 3, so any prior installation (native or previously loaded shim) wins. If 'sliceToImmutable' in ArrayBuffer.prototype is already true when the shim loads, the shim does nothing.

  ses drops the %ImmutableArrayBufferPrototype% permits entry, which no longer has a referent. The three permits lines inside %ArrayBufferPrototype% that declare the shim-installed methods (transferToImmutable, sliceToImmutable, immutable) stay as-is.

  @endo/pass-style's byteArray brand check no longer routes through an intermediate prototype; it consults the immutable accessor on ArrayBuffer.prototype directly. The check also tolerates the [Symbol.toStringTag] own-property on emulated immutable buffers and verifies that its value is a non-enumerable data property with a string value.