feat(codegen): accept pointer types to any C type in EXTERN

A pseudocode pointer type now counts as a C type, in EXTERN signatures
and as a C-struct field, when it finally points to a non-void C type or a
C struct, as in TYPE PInt = ^C_INT. A pointer cycle such as TYPE P = ^P
and a pointer to a pseudocode type stay rejected.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

7 files changed, 38 insertions, 3 deletions

diff --git a/tests/i/extern-c-struct/expected.txt b/tests/i/extern-c-struct/expected.txt
index dee8467..816b4e3 100644
--- a/tests/i/extern-c-struct/expected.txt
+++ b/tests/i/extern-c-struct/expected.txt
@@ -2,3 +2,5 @@ S 4.500000 5
 G 0.500000 7
 9
 14
+3
+G 9
diff --git a/tests/i/extern-c-struct/lib.c b/tests/i/extern-c-struct/lib.c
index 65080f1..45bb30e 100644
--- a/tests/i/extern-c-struct/lib.c
+++ b/tests/i/extern-c-struct/lib.c
@@ -12,6 +12,14 @@ void scale_sample(struct Sample *s, int k) { s->value *= k; }
 struct Sample *shared_sample(void) { return &shared; }
 int shared_count(void) { return shared.count; }
 
+struct Counter {
+    int *target;
+};
+
+void bump(int *p) { ++*p; }
+void bump_counter(struct Counter *c) { ++*c->target; }
+void get_shared(struct Sample **out) { *out = &shared; }
+
 /* Each argument after n is a struct Sample *, read back with va_arg. */
 int sum_counts(int n, ...) {
     va_list ap;
diff --git a/tests/i/extern-c-struct/notes.md b/tests/i/extern-c-struct/notes.md
index 519e835..494c510 100644
--- a/tests/i/extern-c-struct/notes.md
+++ b/tests/i/extern-c-struct/notes.md
@@ -4,4 +4,4 @@ Human review: pending. Expected output was independently traced by AI, not captu
 
 Basis: compiler extension (EXTERN "C", INCLUDE_OBJ of a user object); a record whose fields are all C types has the layout of the matching C struct.
 
-Trace: the harness compiles `lib.c` with the host C compiler. Sample matches `struct Sample {char; double; int}`, including the padding after the char. S is 'S', 1.5, 5. scale_sample(^S, 3) multiplies the value through the pointer to 4.5 and leaves tag and count alone, so the first line is `S 4.500000 5`. shared_sample returns the address of the static struct in lib.c, initialised to 'G', 0.5, 7, giving `G 0.500000 7`. P^.Count <- 9 writes through that pointer into the C object, so shared_count() returns 9. sum_counts receives P and Q as variadic arguments; pointers are passed unchanged and read back with va_arg(ap, struct Sample *). P points to the shared struct, whose count is now 9, and Q points to S, whose count is 5, so the last line is 9 + 5 = 14.
+Trace: the harness compiles `lib.c` with the host C compiler. Sample matches `struct Sample {char; double; int}`, including the padding after the char. S is 'S', 1.5, 5. scale_sample(^S, 3) multiplies the value through the pointer to 4.5 and leaves tag and count alone, so the first line is `S 4.500000 5`. shared_sample returns the address of the static struct in lib.c, initialised to 'G', 0.5, 7, giving `G 0.500000 7`. P^.Count <- 9 writes through that pointer into the C object, so shared_count() returns 9. sum_counts receives P and Q as variadic arguments; pointers are passed unchanged and read back with va_arg(ap, struct Sample *). P points to the shared struct, whose count is now 9, and Q points to S, whose count is 5, so the last line is 9 + 5 = 14. N starts at 1. bump(^N) receives a PInt, an int * in C, and increments N to 2. Counter matches `struct Counter {int *}`; bump_counter(^C) increments through C.Target, which points to N, giving 3. get_shared(^R) receives a struct Sample ** and stores the address of the shared struct into R, so R^ shows tag G and the count 9 written earlier: `G 9`.
diff --git a/tests/i/extern-c-struct/program.cps b/tests/i/extern-c-struct/program.cps
index bcb7af4..62370d3 100644
--- a/tests/i/extern-c-struct/program.cps
+++ b/tests/i/extern-c-struct/program.cps
@@ -1,4 +1,4 @@
-// Records whose fields are C types pass to C functions through pointer types.
+// Records whose fields are C types, and pointer types to C types, pass to C functions.
 INCLUDE_OBJ "lib.o"
 TYPE Sample
     DECLARE Tag : C_CHAR
@@ -6,13 +6,25 @@ TYPE Sample
     DECLARE Count : C_INT
 ENDTYPE
 TYPE PSample = ^Sample
+TYPE PPSample = ^PSample
+TYPE PInt = ^C_INT
+TYPE Counter
+    DECLARE Target : PInt
+ENDTYPE
+TYPE PCounter = ^Counter
 EXTERN "C" EXTERN_PROCEDURE scale_sample(PSample, C_INT)
 EXTERN "C" EXTERN_FUNCTION shared_sample() RETURNS PSample
 EXTERN "C" EXTERN_FUNCTION shared_count() RETURNS C_INT
 EXTERN "C" EXTERN_FUNCTION sum_counts(C_INT, ...) RETURNS C_INT
+EXTERN "C" EXTERN_PROCEDURE bump(PInt)
+EXTERN "C" EXTERN_PROCEDURE bump_counter(PCounter)
+EXTERN "C" EXTERN_PROCEDURE get_shared(PPSample)
 DECLARE S : Sample
 DECLARE P : PSample
 DECLARE Q : PSample
+DECLARE R : PSample
+DECLARE N : C_INT
+DECLARE C : Counter
 S.Tag <- (C_CHAR)'S'
 S.Value <- (C_DOUBLE)1.5
 S.Count <- (C_INT)5
@@ -24,3 +36,10 @@ P^.Count <- (C_INT)9
 OUTPUT shared_count()
 Q <- ^S
 OUTPUT sum_counts((C_INT)2, P, Q)
+N <- (C_INT)1
+CALL bump(^N)
+C.Target <- ^N
+CALL bump_counter(^C)
+OUTPUT N
+CALL get_shared(^R)
+OUTPUT R^.Tag, " ", R^.Count
diff --git a/tests/iii/extern-struct-rejected/case.json b/tests/iii/extern-struct-rejected/case.json
index cd7a3dd..905d5ad 100644
--- a/tests/iii/extern-struct-rejected/case.json
+++ b/tests/iii/extern-struct-rejected/case.json
@@ -15,6 +15,10 @@
     {
       "reason": "Variadic\\ argument\\ 2\\ to\\ printf\\ uses\\ record\\ Person,\\ which\\ is\\ not\\ a\\ C\\ struct:\\ field\\ Name\\ of\\ Person\\ has\\ type\\ STRING",
       "line": 13
+    },
+    {
+      "reason": "EXTERN\\ parameter\\ 1\\ of\\ srand\\ must\\ be\\ a\\ non\\-void\\ C\\ type\\ \\(got\\ PInteger\\)",
+      "line": 15
     }
   ]
 }
diff --git a/tests/iii/extern-struct-rejected/notes.md b/tests/iii/extern-struct-rejected/notes.md
index 650b420..40e3ab8 100644
--- a/tests/iii/extern-struct-rejected/notes.md
+++ b/tests/iii/extern-struct-rejected/notes.md
@@ -1,5 +1,5 @@
 # extern-struct-rejected
 
-Compiler extension: an EXTERN signature accepts a record, through a pointer type or by value, only as a C struct (every field a C type, a C struct or a pointer type to one). Person has a STRING field, so a pointer to it, Person as a by-value parameter, as a by-value result and as a by-value variadic argument are all rejected and the field is named.
+Compiler extension: an EXTERN signature accepts a record, through a pointer type or by value, only as a C struct (every field a C type, a C struct or a pointer type to either). Person has a STRING field, so a pointer to it, Person as a by-value parameter, as a by-value result and as a by-value variadic argument are all rejected and the field is named. A pointer type counts as a C type only when its pointee does, so a pointer to INTEGER is rejected too.
 
 Require exit 1 and each cause on its EXTERN or call line.
diff --git a/tests/iii/extern-struct-rejected/program.cps b/tests/iii/extern-struct-rejected/program.cps
index ced6fee..80f965f 100644
--- a/tests/iii/extern-struct-rejected/program.cps
+++ b/tests/iii/extern-struct-rejected/program.cps
@@ -11,3 +11,5 @@ EXTERN "C" EXTERN_FUNCTION atoi(C_STRING) RETURNS Person
 EXTERN "C" EXTERN_FUNCTION printf(C_STRING, ...) RETURNS C_INT
 DECLARE Someone : Person
 OUTPUT printf((C_STRING)"%d", Someone)
+TYPE PInteger = ^INTEGER
+EXTERN "C" EXTERN_PROCEDURE srand(PInteger)