refactor: derive the milestone bounds from the registry

The highest supported milestone was spelled out in six places across four
files: range(1, 7) and default="m6" in test_cli.py, the same pair in
test_milestones_dosboxx.py, and through=6 in both registry.py and suite.py.
Registering M7 meant finding all six, and missing one failed silently.

Derive MAX_MILESTONE and MILESTONES from CASES instead, and move the mN
selector parser to registry.milestone_number so the pytest module stops
carrying its own copy. Adding cases for a new milestone is now enough for
ferro-test to accept --through/--only for it.

No behaviour change: MAX_MILESTONE evaluates to 6, ferro-test still advertises
{m1..m6} with default m6, and the case snapshot is unchanged.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BScg8CF1sAAM2zVHAu5zvW

src/ferrolang_vm/registry.py

@@ -187,7 +187,22 @@ CASES: list[Case] = [
         "okstatic", "oktemp", "oktrim", "okwcall")],
 ]
 
-def all_cases(*, through: int = 6, only: int | None = None) -> list[Case]:
+MAX_MILESTONE: int = max(case.milestone for case in CASES)
+MILESTONES: tuple[str, ...] = tuple(f"m{number}"
+                                    for number in range(1, MAX_MILESTONE + 1))
+
+
+def milestone_number(name: str) -> int:
+    """Parse an ``mN`` selector against the milestones the registry knows about."""
+    if not name.startswith("m") or not name[1:].isdigit():
+        raise ValueError(f"invalid milestone: {name}")
+    value = int(name[1:])
+    if value not in range(1, MAX_MILESTONE + 1):
+        raise ValueError(f"unsupported milestone: {name}")
+    return value
+
+
+def all_cases(*, through: int = MAX_MILESTONE, only: int | None = None) -> list[Case]:
     if only is not None:
         return [case for case in CASES if case.milestone == only]
     return [case for case in CASES if case.milestone <= through]

src/ferrolang_vm/test_cli.py

@@ -7,9 +7,7 @@ import sys
 from pathlib import Path
 
 from .dosboxx import DosboxError, setup
-
-
-MILESTONES = tuple(f"m{number}" for number in range(1, 7))
+from .registry import MAX_MILESTONE, MILESTONES
 
 
 def main() -> int:
@@ -23,8 +21,9 @@ def main() -> int:
                          help="confirm acceptance of the Sybase Open Watcom Public License")
     run = commands.add_parser("run", help="build once and run milestone pytest cases")
     selection = run.add_mutually_exclusive_group()
-    selection.add_argument("--through", choices=MILESTONES, default="m6",
-                           help="run cumulatively through this milestone (default: m6)")
+    selection.add_argument("--through", choices=MILESTONES, default=f"m{MAX_MILESTONE}",
+                           help="run cumulatively through this milestone "
+                                f"(default: m{MAX_MILESTONE})")
     selection.add_argument("--only", choices=MILESTONES,
                            help="run only this milestone's cases")
     run.add_argument("-v", "--verbose", action="store_true", help="show every pytest case")

tools/tests/test_milestones_dosboxx.py

@@ -6,23 +6,13 @@ import warnings
 import pytest
 
 from ferrolang_vm.dosboxx import SuiteRun, run_suite
-from ferrolang_vm.registry import all_cases
+from ferrolang_vm.registry import MAX_MILESTONE, all_cases, milestone_number
 from ferrolang_vm.suite import Case
 
-
-def _number(name: str) -> int:
-    if not name.startswith("m") or not name[1:].isdigit():
-        raise ValueError(f"invalid milestone: {name}")
-    value = int(name[1:])
-    if value not in range(1, 7):
-        raise ValueError(f"unsupported milestone: {name}")
-    return value
-
-
 ONLY = os.environ.get("FERRO_TEST_ONLY")
 CASES = all_cases(
-    through=_number(os.environ.get("FERRO_TEST_THROUGH", "m6")),
-    only=_number(ONLY) if ONLY else None,
+    through=milestone_number(os.environ.get("FERRO_TEST_THROUGH", f"m{MAX_MILESTONE}")),
+    only=milestone_number(ONLY) if ONLY else None,
 )