BridgeJS: Route container stack ABI emission through shared codecs

The non-generic bridging paths cloned each container's stack ABI (array
loops with the typed-array fast path, dictionary key/value ordering, the
optional presence-flag protocol) inline into every thunk, while the
generic paths already described those shapes once via the codec
combinators. Route the non-generic array/dictionary/optional emission
through the same combinators so each container's stack ABI is described
exactly once and instantiated with an element codec:

- __bjs_primitiveCodecs becomes a token-keyed table (Bool, Int, ...,
  String, JSValue) referenced by both combinator instantiations and the
  generic type-handle registration hooks (same canonical order).
- @js struct elements compose directly with structHelpers.<T> (already
  codec-shaped); associated-value enums adapt their helper through the
  new __bjs_enumCodec combinator; other element shapes (case enums,
  JSObject, heap objects, ...) get a local codec literal built from the
  single element stack fragment description.
- __bjs_optionalCodec gains an isUndefinedOr parameter so the
  JSUndefinedOr flavor instantiates the same combinator instead of a
  bespoke inline form; stack-convention optional parameters and returns
  now route through it too. Nested compositions recurse
  (e.g. __bjs_arrayCodec(__bjs_optionalCodec(__bjs_primitiveCodecs.Int))).
- Emission gating: the combinators and the primitive codec table are
  emitted through the intrinsic registry whenever any linked module uses
  container bridging (generic or not); builds bridging no containers pay
  nothing. The generic runtime (codecByTypeId, registration hooks,
  afterInitialize) stays gated on generics, independently.
- Paths that cannot use the combinators keep inline code with comments:
  side-channel/sentinel optional returns, and optional parameters whose
  presence flag arrives as a wasm parameter rather than on the i32 stack.

Deletes the inline array/dictionary loop fragments, stackOptionalLower,
and optionalLiftReturnStruct from JSGlueGen; snapshots re-recorded.

Author: krodak

Plugins/BridgeJS/Sources/BridgeJSLink/BridgeJSLink.swift

@@ -339,8 +339,6 @@ public struct BridgeJSLink {
         ]
         if hasGenerics {
             declarations.append("const \(JSGlueVariableScope.reservedCodecByTypeId) = new Map();")
-            declarations.append("let \(JSGlueVariableScope.reservedStringCodec);")
-            declarations.append("let \(JSGlueVariableScope.reservedPrimitiveCodecs);")
             declarations.append("let __bjs_typeHandlesRegistered = false;")
             // Registration is hybrid eager+lazy. The registration exports
             // execute Swift code, which must not happen before WASI
@@ -404,6 +402,16 @@ public struct BridgeJSLink {
         printer.write(lines: lines)
     }
 
+    /// A print context detached from any thunk, used for codec literal emission.
+    private func makeCodecPrintContext(printer: CodeFragmentPrinter) -> IntrinsicJSFragment.PrintCodeContext {
+        IntrinsicJSFragment.PrintCodeContext(
+            scope: JSGlueVariableScope(intrinsicRegistry: intrinsicRegistry),
+            printer: printer,
+            hasDirectAccessToSwiftClass: false,
+            classNamespaces: intrinsicRegistry.classNamespaces
+        )
+    }
+
     /// Emits a `{ lower, lift }` codec literal for one bridgeable type.
     /// `prefix` is prepended to the opening brace (e.g. an assignment) and
     /// `suffix` is appended to the closing brace (e.g. `","` in an array).
@@ -413,51 +421,13 @@ public struct BridgeJSLink {
         prefix: String = "",
         suffix: String = ","
     ) throws {
-        func context() -> IntrinsicJSFragment.PrintCodeContext {
-            IntrinsicJSFragment.PrintCodeContext(
-                scope: JSGlueVariableScope(intrinsicRegistry: intrinsicRegistry),
-                printer: printer,
-                hasDirectAccessToSwiftClass: false,
-                classNamespaces: intrinsicRegistry.classNamespaces
-            )
-        }
-        let lowerFragment = try IntrinsicJSFragment.stackLowerFragment(elementType: type)
-        let liftFragment = try IntrinsicJSFragment.stackLiftFragment(elementType: type)
-        printer.write("\(prefix){")
-        try printer.indent {
-            printer.write("lower: (v) => {")
-            try printer.indent {
-                _ = try lowerFragment.printCode(["v"], context())
-            }
-            printer.write("},")
-            printer.write("lift: () => {")
-            try printer.indent {
-                let results = try liftFragment.printCode([], context())
-                printer.write("return \(results[0]);")
-            }
-            printer.write("},")
-        }
-        printer.write("}\(suffix)")
-    }
-
-    /// Emits the shared primitive codecs. Codec bodies are emitted once and
-    /// shared by every module's registration hook.
-    private func generatePrimitiveCodecs(into printer: CodeFragmentPrinter) throws {
-        let stringCodec = JSGlueVariableScope.reservedStringCodec
-        // The String codec is named so the dictionary codec combinator can
-        // lower/lift keys through it.
-        try appendGenericCodecLiteral(type: .string, into: printer, prefix: "\(stringCodec) = ", suffix: ";")
-        printer.write("\(JSGlueVariableScope.reservedPrimitiveCodecs) = [")
-        try printer.indent {
-            for primitive in BridgeType.genericBridgeablePrimitives {
-                if case .string = primitive.type {
-                    printer.write("\(stringCodec),")
-                } else {
-                    try appendGenericCodecLiteral(type: primitive.type, into: printer)
-                }
-            }
-        }
-        printer.write("];")
+        try ContainerCodecJS.writeCodecLiteral(
+            type: type,
+            into: printer,
+            context: makeCodecPrintContext(printer: printer),
+            prefix: prefix,
+            suffix: suffix
+        )
     }
 
     /// Installs the per-module `bjs_<Module>_register_type_handles` import hooks.
@@ -475,12 +445,20 @@ public struct BridgeJSLink {
                 printer.write("bjs[\"\(hookName)\"] = function() {};")
                 continue
             }
+            // The hooks resolve type IDs against the shared primitive codec table.
+            try ContainerCodecJS.registerPrimitiveCodecs(context: makeCodecPrintContext(printer: printer))
             let moduleEntries = skeleton.exported?.genericBridgeableTypeEntries ?? []
             printer.write("bjs[\"\(hookName)\"] = function(base, count) {")
             try printer.indent {
                 // Same canonical order as the Swift registration function:
                 // primitives first, then the module's own types.
-                printer.write("const codecs = \(JSGlueVariableScope.reservedPrimitiveCodecs).concat([")
+                printer.write("const codecs = [")
+                printer.indent {
+                    for primitive in BridgeType.genericBridgeablePrimitives {
+                        printer.write("\(JSGlueVariableScope.reservedPrimitiveCodecs).\(primitive.token),")
+                    }
+                }
+                printer.write("].concat([")
                 try printer.indent {
                     for entry in moduleEntries {
                         try appendGenericCodecLiteral(type: entry.bridgeType, into: printer)
@@ -676,9 +654,6 @@ public struct BridgeJSLink {
                         printer.write("}")
                     }
                 }
-                if hasGenerics {
-                    try generatePrimitiveCodecs(into: printer)
-                }
                 try generateTypeRegistrationHooks(into: printer)
 
                 // Always provided: the runtime's `_bjs_makePromise` imports it unconditionally.
@@ -2556,6 +2531,11 @@ extension BridgeJSLink {
         }
 
         func declareGenericCodecs(genericParameters: [String]) {
+            if !genericParameters.isEmpty {
+                // Generic call sites instantiate the shared container codec
+                // combinators with the codecs resolved from type IDs.
+                ContainerCodecJS.registerCombinators(scope: scope)
+            }
             for genericParam in genericParameters {
                 let typeIdParam = scope.variable("\(genericParam.lowercased())TypeId")
                 let codecVar = scope.variable("codec\(genericParam)")