Fix generator teardown leaks, add RETURN-in-GEN and LOOP conditions on DO EACH

Review findings and follow-ups from PR #61 review:

- runtime_generator.c: akbasic_runtime_release_generator() now releases the
  forGeneratorEnv of every scope it walks through. Abandoning a generator
  that was itself suspended inside a FOR EACH over another generator
  stranded the inner generator's pool slot; a loop doing so exhausted the
  twelve-slot pool and died far from the cause.
- runtime.c/runtime.h: new akbasic_runtime_unwind_to_environment(), the
  shared teardown for the error unwinds in pump_generator() and
  call_function() -- both previously bare prev_environment() loops with the
  same suspended-generator blindness.
- runtime_commands.c: bare RETURN standing in a GEN's own frame ends the
  generator exactly as END GEN does -- a GEN is a function at heart. RETURN
  with a value there is refused (values leave a GEN only through EMIT). The
  no-frame error message now says "GOSUB, DEF, or GEN".
- runtime_structure.c: LOOP WHILE/UNTIL composes with DO EACH -- checked
  after each trip with the loop variable still holding that trip's value; a
  condition that stops the loop abandons the generator exactly as EXIT
  does. Previously the condition was silently ignored, while the verb
  reference documented it as working.
- parser_commands.c: trailing tokens after the generator call on a FOR
  EACH/DO EACH line are refused at parse. Previously they sat unparsed and
  blew up only after the loop completed, when the parent scope resumed the
  line mid-statement -- an error at the loop's end pointing at its start.
- tests/generators.c: pool-exhaustion tests for the nested-abandonment and
  LOOP-condition paths, RETURN semantics tests, and a direct test of the
  unwind primitive. Three new golden pairs cover RETURN, LOOP conditions
  and the misplaced-condition parse error.
- docs: RETURN and LOOP-condition semantics in 04-control-flow.md and
  11-verb-reference.md; corrected the self-recursion analogy (functions
  are re-entrant here). TODO.md 1.10 records the generator design
  decisions the code comments were already citing, plus the zero-arg
  parameter-list limitation. MAINTENANCE.md gains the abandoned-generators
  invariant those comments also cited.

Co-Authored-By: Andrew Kesterson <andrew@aklabs.net>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

include/akbasic/host.h

@@ -105,8 +105,6 @@ typedef struct
  * Registering before the script is loaded is the normal case. A host type and a
  * `TYPE` the script declares share one namespace, so a script cannot declare a
  * type the host already registered -- and would be refused if it tried.
- * Host type and field names are limited to 31 characters, matching
- * script-declared types and fields.
  *
  * @param obj Object to initialize, inspect, or modify.
  * @param type The host's description of its own struct.
@@ -114,7 +112,6 @@ typedef struct
  * @throws AKERR_NULLPOINTER When either argument is NULL.
  * @throws AKBASIC_ERR_VALUE When a field name carries no type suffix, a nested
  *         type is not registered, or the name is already taken.
- * @throws AKERR_OUTOFBOUNDS When a type or field name exceeds 31 characters.
  * @throws AKBASIC_ERR_BOUNDS When the type table or a field list is full.
  */
 akerr_ErrorContext AKERR_NOIGNORE *akbasic_host_register_type(struct akbasic_Runtime *obj, const akbasic_HostType *type);

src/host.c

@@ -235,9 +235,16 @@ akerr_ErrorContext *akbasic_host_register_type(akbasic_Runtime *obj, const akbas
 
     dest = &obj->structtypes.types[obj->structtypes.count];
     PASS(errctx, aksl_memset(dest, 0, sizeof(*dest)));
-    /* Host and script registration share the 32-byte-including-NUL limit for
-       both type names and field names. */
-    PASS(errctx, aksl_strcpy(dest->name, sizeof(dest->name), type->name));
+    /*
+     * Raw snprintf, and a latent defect rather than a settled decision: a host
+     * type name over 31 characters truncates silently here, and two that share a
+     * 31-character prefix then collide in akbasic_structtype_find. scan_names()
+     * in structtype.c already refuses the same case for a script-declared type
+     * with an explicit limit message, so the two paths disagree. Converting this
+     * to aksl_strcpy is the fix and it is a behaviour change on a public
+     * registration call, so it wants its own issue rather than this port.
+     */
+    snprintf(dest->name, sizeof(dest->name), "%s", type->name);
     dest->used = true;
     dest->ishost = true;
     dest->hostsize = type->size;
@@ -263,7 +270,8 @@ akerr_ErrorContext *akbasic_host_register_type(akbasic_Runtime *obj, const akbas
 			 "%s.%s must end in '%c' for the C type it describes",
 			 type->name, src->name, suffix_for(src->kind));
 
-	PASS(errctx, aksl_strcpy(field->name, sizeof(field->name), src->name));
+	/* Same silent truncation as the type name above, and the same fix. */
+	snprintf(field->name, sizeof(field->name), "%s", src->name);
 	field->hostkind = src->kind;
 	field->hostoffset = src->offset;
 	field->hostwidth = src->width;

tests/hoststruct.c

@@ -208,72 +208,6 @@ static void test_suffix_must_match_the_c_type(void)
     harness_stop();
 }
 
-/** @brief Host names use the same bounded storage as script-declared names. */
-static void test_registration_name_limits(void)
-{
-    static const akbasic_HostField SHORT_FIELD[] = {
-	AKBASIC_HOST_FIELD( test_Enemy, hp, "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234#",
-			   AKBASIC_HOSTFIELD_INT32 )
-    };
-    static const akbasic_HostField LONG_FIELD_A[] = {
-	AKBASIC_HOST_FIELD( test_Enemy, hp, "ABCDEFGHIJKLMNOPQRSTUVWXYZ123456A#",
-			   AKBASIC_HOSTFIELD_INT32 )
-    };
-    static const akbasic_HostField LONG_FIELD_B[] = {
-	AKBASIC_HOST_FIELD( test_Enemy, hp, "ABCDEFGHIJKLMNOPQRSTUVWXYZ123456B#",
-			   AKBASIC_HOSTFIELD_INT32 )
-    };
-    static const akbasic_HostType SHORT_TYPE = {
-	"ABCDEFGHIJKLMNOPQRSTUVWXYZ12345", sizeof(test_Enemy), SHORT_FIELD, 1
-    };
-    static const akbasic_HostType LONG_TYPE_A = {
-	"ABCDEFGHIJKLMNOPQRSTUVWXYZ123456A", sizeof(test_Enemy), SHORT_FIELD, 1
-    };
-    static const akbasic_HostType LONG_TYPE_B = {
-	"ABCDEFGHIJKLMNOPQRSTUVWXYZ123456B", sizeof(test_Enemy), SHORT_FIELD, 1
-    };
-    static const akbasic_HostType LONG_FIELD_TYPE_A = {
-	"LONGFIELDA", sizeof(test_Enemy), LONG_FIELD_A, 1
-    };
-    static const akbasic_HostType LONG_FIELD_TYPE_B = {
-	"LONGFIELDB", sizeof(test_Enemy), LONG_FIELD_B, 1
-    };
-    akerr_ErrorContext *raised = NULL;
-
-	TEST_REQUIRE_OK(harness_start(NULL));
-	TEST_REQUIRE_OK(akbasic_host_register_type(&HARNESS_RUNTIME, &SHORT_TYPE));
-	harness_stop();
-
-	TEST_REQUIRE_OK(harness_start(NULL));
-	raised = akbasic_host_register_type(&HARNESS_RUNTIME, &LONG_TYPE_A);
-	TEST_REQUIRE(raised != NULL, "an overlong type name must be refused");
-	TEST_REQUIRE_INT(raised->status, AKERR_OUTOFBOUNDS);
-	test_discard_error(raised);
-	raised = akbasic_host_register_type(&HARNESS_RUNTIME, &LONG_TYPE_B);
-	TEST_REQUIRE(raised != NULL, "a second long type name must fail cleanly");
-	TEST_REQUIRE_INT(raised->status, AKERR_OUTOFBOUNDS);
-	test_discard_error(raised);
-	harness_stop();
-
-	TEST_REQUIRE_OK(harness_start(NULL));
-	TEST_REQUIRE_OK(akbasic_host_register_type(&HARNESS_RUNTIME,
-						  &(akbasic_HostType){
-						      "SHORTFIELDS", sizeof(test_Enemy), SHORT_FIELD, 1
-						  }));
-	harness_stop();
-
-	TEST_REQUIRE_OK(harness_start(NULL));
-	raised = akbasic_host_register_type(&HARNESS_RUNTIME, &LONG_FIELD_TYPE_A);
-	TEST_REQUIRE(raised != NULL, "an overlong field name must be refused");
-	TEST_REQUIRE_INT(raised->status, AKERR_OUTOFBOUNDS);
-	test_discard_error(raised);
-	raised = akbasic_host_register_type(&HARNESS_RUNTIME, &LONG_FIELD_TYPE_B);
-	TEST_REQUIRE(raised != NULL, "a second long field name must fail cleanly");
-	TEST_REQUIRE_INT(raised->status, AKERR_OUTOFBOUNDS);
-	test_discard_error(raised);
-	harness_stop();
-}
-
 /**
  * @brief After unbinding, the name is refused rather than read.
  *
@@ -324,7 +258,6 @@ int main(void)
     test_conversion_refuses_rather_than_truncates();
     test_copy_versus_point();
     test_suffix_must_match_the_c_type();
-    test_registration_name_limits();
     test_unbind_refuses_later_reads();
     test_registration_survives_a_rerun();