feat(selfhost): AST producer — full parser error-recovery markers → 565/597

Replicated every malformed_*_span predicate the reference parser records, so the
producer emits the same recovery markers instead of garbage nodes:
- malformed-field / malformed-generic (struct), malformed-param / malformed-generic
  / malformed-effect (fn): emitters now emit only VALID nodes and the markers are
  appended after them (ast_oracle_dump order) via count helpers mirroring
  parse_fields / parse_params / parse_generic_params / parse_effects.
- Empty type-args (`Map<, T>`) dropped, not dumped (malformed_arg_spans).
- Empty call args (`f(, x)`) → `arg malformed=true` + unknown-expr.
- Match arms without `=>` → malformed-arm, emitted after valid arms.
- Nameless fn (`fn (…)`) → program-level malformed-declaration (section 5, last).
- Control statements: `else` without `{`/`if` → malformed-if; `while {` (no cond)
  and `loop <cond> {` → malformed-loop; `match {` (no scrutinee) → malformed-match.

Name-only params (`fn f(x)`) now emit a valid param with an empty type ref.
Corpus reach: 543 -> 565 / 597 byte-exact (+22), still 0 run-failures. Floor -> 565.
42 samples green (10 new malformed fixtures).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: olwang

crates/rsscript/src/selfhost_parity.rs

@@ -1522,7 +1522,7 @@ const AST_SAMPLE_MIN: usize = 6;
 /// Floor for `ast_parity_corpus` — the number of corpus files whose rss AST dump
 /// already matches the oracle byte-for-byte. Ratchets up as the producer's
 /// coverage grows; a drop signals a regression. (Full parity = files.len().)
-const AST_CORPUS_PARITY_FLOOR: usize = 543;
+const AST_CORPUS_PARITY_FLOOR: usize = 565;
 
 /// Step-2 measurement gate (ignored by default): how many corpus files the rss
 /// producer reproduces byte-for-byte. Not full parity yet — this ratchets a floor

selfhost/astdump.rss

@@ -0,0 +1,25 @@
+// expect: RS0015
+
+fn bad_if(value: read Bool) -> Unit {
+    if value {
+        return Unit
+    } else return Unit
+}
+
+fn bad_loop() -> Unit {
+    loop true {
+        return Unit
+    }
+}
+
+fn bad_while() -> Unit {
+    while {
+        return Unit
+    }
+}
+
+fn bad_match() -> Unit {
+    match {
+        _ => return Unit
+    }
+}

selfhost/samples/ast/mal_control.rss

@@ -0,0 +1,7 @@
+// expect: RS0015
+
+fn main() -> Unit {
+    Log.write(, message: read "hello")
+    Log.write(message: read "hello",, tag: read "demo")
+    return Unit
+}

selfhost/samples/ast/mal_empty_call_arg.rss

@@ -0,0 +1,8 @@
+// expect: RS0015
+fn (value: read String) -> Unit {
+    return Unit
+}
+
+fn main() -> Unit {
+    return Unit
+}

selfhost/samples/ast/mal_fn_decl.rss

@@ -0,0 +1,19 @@
+// expect: RS0015
+
+fn empty_effect_slot(value: read String) -> Unit
+    effects(no_panic,, native)
+{
+    return Unit
+}
+
+fn empty_retains(value: read String) -> Unit
+    effects(retains())
+{
+    return Unit
+}
+
+fn unknown_effect_call(value: read String) -> Unit
+    effects(custom(value))
+{
+    return Unit
+}

selfhost/samples/ast/mal_malformed_effect_declaration.rss

@@ -0,0 +1,5 @@
+// expect: RS0015
+
+fn bad(, path: read Path) -> Unit {
+    return Unit
+}

selfhost/samples/ast/mal_malformed_empty_parameter_declaration.rss

@@ -0,0 +1,9 @@
+// expect: RS0015
+struct Broken {
+    name String
+    value:
+}
+
+fn main() -> Unit {
+    return Unit
+}

selfhost/samples/ast/mal_malformed_field_declaration.rss

@@ -0,0 +1,9 @@
+// expect: RS0015
+
+struct Box<T: Unknown> {
+    value: handle T
+}
+
+fn bad<read T>(value: read String) -> Unit {
+    return Unit
+}

selfhost/samples/ast/mal_malformed_generic_parameter_declaration.rss

@@ -0,0 +1,5 @@
+// expect: RS0015
+
+fn bad(read Path) -> Unit {
+    return Unit
+}