ffi 2.16a green: parser + AST + sema for #jni_env(env) { body }

New `hash_jni_env` lexer token; `parsePrimary` dispatches to a small
`parseJniEnvBlock` that consumes `(env) { body }` and returns a new
`JniEnvBlock` AST node (env_expr + body block).

Sema's analyzeNode arm recurses into env + body inside a pushed
scope; findNodeAtOffset descends through both children for go-to-
definition.

Lowering treats it as a syntactic wrapper around the block: env is
evaluated for side effects, body lowers as a normal block. The TL
push/pop semantics (synthesizing the env stack so `#jni_call`'s env
arg can become optional) land in 2.16b.

`expectSemicolonAfter` recognises `jni_env_block` as block-form so
statement-position uses don't need a trailing `;` — matches `if` /
`while` / `for` / bare blocks.

Test runs through the block body and prints expected output; xfail
snapshot flips to green. 127/127 examples green.

src/parser.zig

@@ -1558,6 +1558,7 @@ pub const Parser = struct {
             .while_expr => false,
             .for_expr => false,
             .block => false,
+            .jni_env_block => false,
             else => true,
         };
         if (needs_semi) {
@@ -2187,6 +2188,9 @@ pub const Parser = struct {
             .hash_objc_call, .hash_jni_call, .hash_jni_static_call => {
                 return try self.parseFfiIntrinsicCall();
             },
+            .hash_jni_env => {
+                return try self.parseJniEnvBlock();
+            },
             else => {
                 return self.fail("unexpected token in expression");
             },
@@ -2198,6 +2202,27 @@ pub const Parser = struct {
     /// `#jni_static_call(T)(class, "name", "(Sig)R", args...)`. The
     /// return type sits in the first parens; the actual call args
     /// follow in the second.
+    fn parseJniEnvBlock(self: *Parser) anyerror!*Node {
+        const start = self.current.loc.start;
+        self.advance(); // skip `#jni_env`
+
+        try self.expect(.l_paren);
+        const env_expr = try self.parseExpr();
+        try self.expect(.r_paren);
+
+        // Body is a brace-delimited block. The `-> ?T` annotation for
+        // exception bubbling lands with step 2.15 / 2.16 follow-ups.
+        if (self.current.tag != .l_brace) {
+            return self.fail("expected '{' after '#jni_env(env)'");
+        }
+        const body = try self.parseBlock();
+
+        return try self.createNode(start, .{ .jni_env_block = .{
+            .env = env_expr,
+            .body = body,
+        } });
+    }
+
     fn parseFfiIntrinsicCall(self: *Parser) anyerror!*Node {
         const start = self.current.loc.start;
         const kind: ast.FfiIntrinsicKind = switch (self.current.tag) {