feat(A4): adopt the strict parse — stray identifiers are a parse error

The batch-4 hazard (stray identifiers silently no-op — a typo'd map
is silently wrong) is closed: the corpus gate passed (295/295
strict-clean after maps#207's stray-'s' fix), so comment_item no
longer consumes bare identifiers.

The batch-4/5 vectors flip accordingly:
- stray identifiers now raise Isc::ParseError (was: silent no-op)
-  is likewise rejected — the strict parse revealed it
  only ever executed by accident (noop + the case directive). The
  sanctioned spelling is the bare stage directive, which the vector
  now pins.

Also fixes the run_rule documentation gap: stdlib functions are stage
directives, never run targets.

Author: ronaldtse

lib/interscript/isc/grammar/concerns/stages.rb

@@ -25,10 +25,11 @@ module Stages
               whitespace?
           end
 
-          # Comments and stray identifiers are silently consumed.
+          # Comments are consumed; stray identifiers are a parse error
+          # (WO87/A4 strict-parse ruling: the corpus is 295/295 strict-clean,
+          # so a typo'd map can no longer silently no-op).
           rule(:comment_item) do
-            (str("#") >> (str("\n").absent? >> any).repeat).as(:comment) |
-              identifier.as(:noop)
+            (str("#") >> (str("\n").absent? >> any).repeat).as(:comment)
           end
 
           # Bare rule directly in a stage body (not wrapped in sequence/parallel).

spec/isc/semantics_spec.rb

@@ -228,10 +228,17 @@ def system_map(id, body)
     ISC
   end
 
-  it "rules: run <stdlib-name> dispatches the stdlib function" do
-    with_map("tst-fn-1.isc", system_map(51, "stage main { run downcase }")) do
+  it "rules: stdlib string functions are stage DIRECTIVES (downcase), not run targets" do
+    # The strict parse revealed `run downcase` only ever worked by
+    # accident (noop + case-directive). The sanctioned spelling is the
+    # bare directive.
+    with_map("tst-fn-1.isc", system_map(51, "stage main { downcase }")) do
       expect(Interscript.transliterate("tst-fn-1", "AbC")).to eq("abc")
     end
+    with_map("tst-fn-1b.isc", system_map(51, "stage main { run downcase }")) do
+      expect { Interscript.transliterate("tst-fn-1b", "AbC") }
+        .to raise_error(Interscript::Isc::ParseError)
+    end
   end
 
   it "rules: stage-level case directives run at their position, on the whole string" do
@@ -249,15 +256,14 @@ def system_map(id, body)
     end
   end
 
-  it "rules: stray identifiers are consumed as no-ops — pinned as a hazard" do
-    # HAZARD (A4 follow-up): `run nosuchfunction` drops BOTH identifiers
-    # at parse time and the stage becomes empty — a typo'd map is
-    # silently wrong. Ruled normative-for-now (legacy .imp corpus
-    # tolerance, grammar/concerns/stages.rb comment_item); the stricter
-    # parse is an open item tracked in the IS-1 v2 text, gated on a
-    # clean parse of the full 293-map corpus across all three compilers.
+  it "rules: stray identifiers are a PARSE ERROR (the strict-parse ruling, A4 adopted)" do
+    # The batch-4 hazard (silent no-op) is CLOSED: the corpus gate
+    # passed (295/295 strict-clean after the odni-prs stray-'s' fix,
+    # maps#207), so the grammar rejects stray identifiers — a typo'd
+    # map fails loudly instead of being silently wrong.
     with_map("tst-fn-4.isc", system_map(54, "stage main { run nosuchfunction parallel { sub { from \"a\" to \"b\" } } }")) do
-      expect(Interscript.transliterate("tst-fn-4", "a")).to eq("b")
+      expect { Interscript.transliterate("tst-fn-4", "a") }
+        .to raise_error(Interscript::Isc::ParseError)
     end
   end
 end