Removed @JS protocol support and migrated guidance/tests to @JSClass interfaces.

- `Plugins/BridgeJS/Sources/BridgeJSCore/SwiftToSkeleton.swift` now rejects `@JS protocol` with a clear diagnostic pointing to `@JSClass struct`; updated `ImportTS.swift` messaging accordingly.
- Dropped protocol fixtures/snapshots (`Plugins/BridgeJS/Tests/BridgeJSToolTests/Inputs/Protocol.swift` and related snapshots); README/type-modeling notes now steer interface modeling toward `@JSClass` (`Plugins/BridgeJS/README.md`).
- Rewrote the DocC article to document `@JSClass` interface usage and migration steps (`Sources/JavaScriptKit/Documentation.docc/Articles/BridgeJS/Exporting-Swift/Exporting-Swift-Protocols.md`).
- Removed protocol-based runtime APIs/tests, refreshed JS harness, and regenerated bridge outputs to align (`Tests/BridgeJSRuntimeTests/ExportAPITests.swift`, `Tests/prelude.mjs`, `Tests/BridgeJSRuntimeTests/Generated/*`).

Tests run:
- `swift test --package-path Plugins/BridgeJS`

Author: kateinoigakukun

Plugins/BridgeJS/README.md

@@ -89,7 +89,6 @@ graph LR
 | `@JS enum` (case) | const object + tag type | Copy (integer) | ✅ |
 | `@JS enum` (raw value) | const object + tag type | Copy (raw value) | ✅ |
 | `@JS enum` (associated) | discriminated union | Copy (fields via stacks) | ✅ |
-| `@JS protocol` | `interface` | Reference (wrapper) | ✅ |
 | `Optional<T>` | `T \| null` | Depends on T | ✅ |
 | `(T) -> U` | `(arg: T) => U` | Reference (boxed) | ✅ |
 | `JSObject` | `any` / `object` | Reference | ✅ |
@@ -111,19 +110,7 @@ graph LR
 ## Type Modeling
 
 TypeScript uses [structural subtyping](https://www.typescriptlang.org/docs/handbook/type-compatibility.html), but Swift doesn't directly offer it. We can't map every TypeScript type to Swift, so we made several give-ups and heuristics.
-
-### `interface`
-
-We intentionally don't simulate TS's `interface` with Swift's `protocol` even though they are quite similar for the following reasons:
-
-* Adding a protocol conformance for each `interface` implementation adds binary size cost in debug build because it's not easy to DCE.
-* No straightforward way to represent the use of `interface` type on the return type position of TS function. Which concrete type it should it be?
-* For Embedded Swift, we should avoid use of existential type as much as possible.
-
-Instead of simulating the subtyping-rule with Swift's `protocol`, we represent each `interface` with Swift's struct.
-In this way, we lose implicit type coercion but it makes things simpler and clear.
-
-TBD: Consider providing type-conversion methods to simulate subtyping rule like `func asIface()`
+Use `@JSClass` structs to model JavaScript interfaces that you want to consume from Swift.
 
 ### Anonymous type literals
 

Plugins/BridgeJS/Sources/BridgeJSCore/ImportTS.swift

@@ -884,7 +884,7 @@ extension BridgeType {
                 throw BridgeJSCoreError(
                     """
                     swiftHeapObject '\(className)' is not supported in TypeScript imports.
-                    Swift classes can only be used in @JS protocols where Swift owns the instance.
+                    Pass Swift instances through exported @JS classes or structs instead.
                     """
                 )
             case .exportSwift:

Plugins/BridgeJS/Sources/BridgeJSCore/SwiftToSkeleton.swift

@@ -1422,59 +1422,14 @@ private final class ExportSwiftAPICollector: SyntaxAnyVisitor {
     }
 
     override func visit(_ node: ProtocolDeclSyntax) -> SyntaxVisitorContinueKind {
-        guard let jsAttribute = node.attributes.firstJSAttribute else {
-            return .skipChildren
-        }
-
-        let name = node.name.text
-
-        let namespaceResult = resolveNamespace(from: jsAttribute, for: node, declarationType: "protocol")
-        guard namespaceResult.isValid else {
+        guard node.attributes.firstJSAttribute != nil else {
             return .skipChildren
         }
-        _ = computeExplicitAtLeastInternalAccessControl(
-            for: node,
-            message: "Protocol visibility must be at least internal"
-        )
-
-        let protocolUniqueKey = makeKey(name: name, namespace: namespaceResult.namespace)
-
-        exportedProtocolByName[protocolUniqueKey] = ExportedProtocol(
-            name: name,
-            methods: [],
-            properties: [],
-            namespace: namespaceResult.namespace
-        )
-
-        stateStack.push(state: .protocolBody(name: name, key: protocolUniqueKey))
-
-        var methods: [ExportedFunction] = []
-        for member in node.memberBlock.members {
-            if let funcDecl = member.decl.as(FunctionDeclSyntax.self) {
-                if let exportedFunction = visitProtocolMethod(
-                    node: funcDecl,
-                    protocolName: name,
-                    namespace: namespaceResult.namespace
-                ) {
-                    methods.append(exportedFunction)
-                }
-            } else if let varDecl = member.decl.as(VariableDeclSyntax.self) {
-                _ = visitProtocolProperty(node: varDecl, protocolName: name, protocolKey: protocolUniqueKey)
-            }
-        }
 
-        let exportedProtocol = ExportedProtocol(
-            name: name,
-            methods: methods,
-            properties: exportedProtocolByName[protocolUniqueKey]?.properties ?? [],
-            namespace: namespaceResult.namespace
+        diagnose(
+            node: node,
+            message: "@JS protocol has been removed. Use @JSClass struct to model JavaScript interfaces."
         )
-
-        exportedProtocolByName[protocolUniqueKey] = exportedProtocol
-        exportedProtocolNames.append(protocolUniqueKey)
-
-        stateStack.pop()
-
         return .skipChildren
     }