feat: Versionsstelle als Kompatibilitaetsfrage, Breaking-Change-Vermerk erzwungen (2.5.0)

Files changed:
- CHANGES.md
- INSTALL.md
- VERSION
- instructions/dev/stack-dev/SKILL.md
- instructions/dev/version-parts.md
- tools/CONTRACT.md
- tools/chemenu/commands/docs_verify.py
- tools/chemenu/commands/version_cmd.py
- tools/chemenu/tests/test_docs_verify.py
- tools/chemenu/tests/test_version_cmd.py
- tools/chemenu/version.py

tools/chemenu/commands/docs_verify.py

@@ -473,6 +473,43 @@ def check_migration_for_boundary() -> list[str]:
     ]
 
 
+def check_breaking_change_for_boundary() -> list[str]:
+    """A version that crosses the compatibility boundary must say what breaks.
+
+    Separate from `check_migration_for_boundary`, because the two answer
+    different questions: that one asks whether the *content* has to move, this
+    one whether the operator was told the swap is not drop-in at all. A
+    boundary crossing with an untouched corpus - a renamed feed, artefact,
+    import name or flag - satisfies that check and still leaves every existing
+    instance with something to do by hand.
+
+    Only the newest entry is checked, for the same reason: older crossings are
+    history, and re-reporting them forever would make the check noise.
+    """
+    changes_path = config.ROOT / version_mod.CHANGES_FILENAME
+    version_path = config.ROOT / version_mod.VERSION_FILENAME
+    if not changes_path.is_file() or not version_path.is_file():
+        return []  # already reported by check_version_changelog
+
+    text = changes_path.read_text(encoding="utf-8")
+    current = version_mod.top_changes_version(text)
+    previous = _second_changes_version(text)
+    if current is None or previous is None:
+        return []  # the first versioned entry has no predecessor to cross from
+    if current.compat_key == previous.compat_key:
+        return []
+
+    if version_mod.BREAKING_CHANGE_MARKER in (version_mod.changes_section(text, current) or ""):
+        return []
+
+    return [
+        f"{current} crosses the compatibility boundary from {previous}, so it is not a drop-in "
+        f"replacement - but its {version_mod.CHANGES_FILENAME} entry carries no "
+        f"`{version_mod.BREAKING_CHANGE_MARKER}` line saying what stops working. Add it "
+        "(`version bump --breaking` writes it; see instructions/dev/version-parts.md)"
+    ]
+
+
 @app.command("verify")
 def verify():
     """Check the CLI/README command tables, contract presence, type-form drift, ignore rules, and version/changelog agreement."""
@@ -484,6 +521,7 @@ def verify():
         + check_ignored_content()
         + check_version_changelog()
         + check_migration_for_boundary()
+        + check_breaking_change_for_boundary()
     )
 
     if issues:

tools/chemenu/commands/version_cmd.py

@@ -189,6 +189,11 @@ def bump_command(
     minor: bool = typer.Option(False, "--minor", help="Bump MINOR (resets PATCH)"),
     patch: bool = typer.Option(False, "--patch", help="Bump PATCH"),
     title: str = typer.Option(..., "--title", help="One-line title for the new CHANGES.md entry"),
+    breaking: Optional[str] = typer.Option(
+        None,
+        "--breaking",
+        help="What stops working, for a boundary-crossing bump (recorded in CHANGES.md). Required on one, refused on any other",
+    ),
     no_migration: Optional[str] = typer.Option(
         None,
         "--no-migration",
@@ -203,10 +208,14 @@ def bump_command(
     frontmatter and leaves the prose. `docs verify` afterwards enforces that
     the two agree, so a bump with no entry cannot reach a release.
 
-    A bump that crosses the compatibility boundary additionally requires a
-    migration document for the new version, or `--no-migration "<reason>"`.
-    An instance learning that it must migrate, with nothing telling it how, is
-    the gap this closes."""
+    A bump that crosses the compatibility boundary - one whose new version is
+    not a drop-in replacement, whether or not any content moves - requires
+    `--breaking "<what stops working>"`, and on top of that either a migration
+    document for the new version or `--no-migration "<reason>"`. An instance
+    learning that it must migrate, with nothing telling it what broke or how to
+    cross, is the gap these close. Which part to pass stays a judgment call
+    this command does not make - it enforces only that a crossing says what it
+    costs."""
     selected = [name for name, chosen in (("major", major), ("minor", minor), ("patch", patch)) if chosen]
     if len(selected) != 1:
         fail("Pass exactly one of --major / --minor / --patch")
@@ -239,6 +248,23 @@ def bump_command(
     crossing = new_version.compat_key != current.compat_key
     boundary = " (crosses a compatibility boundary - instances must migrate)" if crossing else ""
 
+    if crossing and not breaking:
+        fail(
+            f"{current} -> {new_version} crosses the compatibility boundary, so it is not a "
+            f"drop-in replacement - re-run with --breaking \"<what stops working, and what an "
+            f"instance must do about it>\".\n"
+            f"If that sentence is hard to write because nothing actually breaks - no hand-work "
+            f"on update, and the old version can still be put back - then the bump is probably "
+            f"not --{selected[0]}."
+        )
+        return
+    if breaking and not crossing:
+        fail(
+            f"--breaking only applies to a bump that crosses the compatibility boundary; "
+            f"{current} -> {new_version} does not."
+        )
+        return
+
     if crossing and not no_migration:
         from chemenu import kb_state
 
@@ -267,6 +293,7 @@ def bump_command(
         version_mod.insert_changes_entry(
             text, new_version, today_iso(), title.strip(), author,
             no_migration_reason=no_migration.strip() if no_migration else None,
+            breaking_reason=breaking.strip() if breaking else None,
         ),
         encoding="utf-8",
     )

tools/chemenu/tests/test_docs_verify.py

@@ -237,6 +237,43 @@ def test_a_migration_document_satisfies_the_check(tmp_path, monkeypatch):
     assert docs_verify.check_migration_for_boundary() == []
 
 
+def test_a_breaking_release_without_a_breaking_note_is_reported(tmp_path, monkeypatch):
+    """A crossing that migrates nothing still leaves hand-work behind, so the
+    migration check passing is not evidence that anyone was told."""
+    from chemenu import version as version_mod
+
+    _boundary_tree(
+        tmp_path, monkeypatch, "2.0.0", "1.4.0",
+        marker=f"{version_mod.MIGRATION_NONE_MARKER} - nothing to change.\n\n",
+    )
+    assert docs_verify.check_migration_for_boundary() == []
+    issues = docs_verify.check_breaking_change_for_boundary()
+    assert any("2.0.0" in issue and "drop-in" in issue for issue in issues)
+
+
+def test_a_compatible_release_needs_no_breaking_note(tmp_path, monkeypatch):
+    _boundary_tree(tmp_path, monkeypatch, "1.5.0", "1.4.0")
+    assert docs_verify.check_breaking_change_for_boundary() == []
+
+
+def test_a_breaking_change_marker_satisfies_the_check(tmp_path, monkeypatch):
+    from chemenu import version as version_mod
+
+    _boundary_tree(
+        tmp_path, monkeypatch, "2.0.0", "1.4.0",
+        marker=f"{version_mod.BREAKING_CHANGE_MARKER} the feed moved.\n\n",
+    )
+    assert docs_verify.check_breaking_change_for_boundary() == []
+
+
+def test_verify_raises_when_a_boundary_has_no_breaking_note(monkeypatch):
+    monkeypatch.setattr(
+        docs_verify, "check_breaking_change_for_boundary", lambda: ["unannounced"]
+    )
+    with pytest.raises(typer.Exit):
+        docs_verify.verify()
+
+
 def test_verify_raises_when_a_boundary_has_no_migration(monkeypatch):
     monkeypatch.setattr(docs_verify, "check_migration_for_boundary", lambda: ["unbridged"])
     with pytest.raises(typer.Exit):

tools/chemenu/tests/test_version_cmd.py

@@ -183,7 +183,7 @@ def test_insert_changes_entry_lands_above_the_newest_entry():
 def test_bump_writes_both_the_version_and_the_changelog_heading(tree):
     version_cmd.bump_command(
         major=False, minor=True, patch=False, title="Something happened",
-        no_migration=None, dry_run=False,
+        breaking=None, no_migration=None, dry_run=False,
     )
     assert (tree / "VERSION").read_text(encoding="utf-8").strip() == "1.1.0"
     changes = (tree / "CHANGES.md").read_text(encoding="utf-8")
@@ -194,7 +194,7 @@ def test_bump_writes_both_the_version_and_the_changelog_heading(tree):
 
 def test_bump_dry_run_writes_nothing(tree):
     version_cmd.bump_command(
-        major=False, minor=False, patch=True, title="Nope", no_migration=None, dry_run=True
+        major=False, minor=False, patch=True, title="Nope", breaking=None, no_migration=None, dry_run=True
     )
     assert (tree / "VERSION").read_text(encoding="utf-8").strip() == "1.0.0"
     assert "1.0.1" not in (tree / "CHANGES.md").read_text(encoding="utf-8")
@@ -207,7 +207,7 @@ def test_bump_demands_exactly_one_part(tree, flags):
     major, minor, patch = flags
     with pytest.raises(typer.Exit):
         version_cmd.bump_command(
-            major=major, minor=minor, patch=patch, title="x", no_migration=None, dry_run=False
+            major=major, minor=minor, patch=patch, title="x", breaking=None, no_migration=None, dry_run=False
         )
     assert (tree / "VERSION").read_text(encoding="utf-8").strip() == "1.0.0"
 
@@ -215,7 +215,7 @@ def test_bump_demands_exactly_one_part(tree, flags):
 def test_bump_refuses_an_empty_title(tree):
     with pytest.raises(typer.Exit):
         version_cmd.bump_command(
-            major=False, minor=False, patch=True, title="   ", no_migration=None, dry_run=False
+            major=False, minor=False, patch=True, title="   ", breaking=None, no_migration=None, dry_run=False
         )
 
 
@@ -227,7 +227,7 @@ def test_bump_refuses_when_the_changelog_is_already_ahead(tree):
     )
     with pytest.raises(typer.Exit):
         version_cmd.bump_command(
-            major=False, minor=False, patch=True, title="x", no_migration=None, dry_run=False
+            major=False, minor=False, patch=True, title="x", breaking=None, no_migration=None, dry_run=False
         )
     assert (tree / "VERSION").read_text(encoding="utf-8").strip() == "1.0.0"
 
@@ -241,7 +241,7 @@ def test_a_boundary_crossing_bump_without_a_migration_is_refused(tree):
     with pytest.raises(typer.Exit):
         version_cmd.bump_command(
             major=True, minor=False, patch=False, title="Breaking",
-            no_migration=None, dry_run=False,
+            breaking="the feed moved", no_migration=None, dry_run=False,
         )
     assert (tree / "VERSION").read_text(encoding="utf-8").strip() == "1.0.0"
 
@@ -255,7 +255,8 @@ def test_a_boundary_crossing_bump_passes_with_a_migration_document(tree):
         encoding="utf-8",
     )
     version_cmd.bump_command(
-        major=True, minor=False, patch=False, title="Breaking", no_migration=None, dry_run=False
+        major=True, minor=False, patch=False, title="Breaking",
+        breaking="every page is retyped", no_migration=None, dry_run=False,
     )
     assert (tree / "VERSION").read_text(encoding="utf-8").strip() == "2.0.0"
 
@@ -263,6 +264,7 @@ def test_a_boundary_crossing_bump_passes_with_a_migration_document(tree):
 def test_no_migration_records_the_reason_in_the_changelog(tree):
     version_cmd.bump_command(
         major=True, minor=False, patch=False, title="Breaking",
+        breaking="the release feed moved",
         no_migration="no distributed instance exists yet", dry_run=False,
     )
     changes = (tree / "CHANGES.md").read_text(encoding="utf-8")
@@ -275,10 +277,50 @@ def test_no_migration_is_refused_on_a_compatible_bump(tree):
     with pytest.raises(typer.Exit):
         version_cmd.bump_command(
             major=False, minor=False, patch=True, title="Fix",
-            no_migration="not needed", dry_run=False,
+            breaking=None, no_migration="not needed", dry_run=False,
         )
 
 
+# --- version bump: the breaking-change note --------------------------------
+
+
+def test_a_boundary_crossing_bump_without_breaking_is_refused(tree):
+    """The corpus question and the drop-in question are independent: a bump
+    can migrate nothing and still leave every instance with hand-work."""
+    with pytest.raises(typer.Exit):
+        version_cmd.bump_command(
+            major=True, minor=False, patch=False, title="Renamed the feed",
+            breaking=None, no_migration="kb/ keeps its shape", dry_run=False,
+        )
+    assert (tree / "VERSION").read_text(encoding="utf-8").strip() == "1.0.0"
+
+
+def test_breaking_records_what_stops_working_in_the_changelog(tree):
+    version_cmd.bump_command(
+        major=True, minor=False, patch=False, title="Renamed the feed",
+        breaking="update_url points at a repo path that no longer exists",
+        no_migration="kb/ keeps its shape", dry_run=False,
+    )
+    changes = (tree / "CHANGES.md").read_text(encoding="utf-8")
+    assert version_mod.BREAKING_CHANGE_MARKER in changes
+    assert "update_url points at a repo path that no longer exists" in changes
+    # The break comes before the migration note: it is what an operator acts on.
+    assert changes.index(version_mod.BREAKING_CHANGE_MARKER) < changes.index(
+        version_mod.MIGRATION_NONE_MARKER
+    )
+
+
+def test_breaking_is_refused_on_a_compatible_bump(tree):
+    """A compatible bump that claims a break is describing itself wrongly -
+    one of the two is a mistake, and the command will not guess which."""
+    with pytest.raises(typer.Exit):
+        version_cmd.bump_command(
+            major=False, minor=True, patch=False, title="New command",
+            breaking="nothing, really", no_migration=None, dry_run=False,
+        )
+    assert (tree / "VERSION").read_text(encoding="utf-8").strip() == "1.0.0"
+
+
 # --- version notes ---------------------------------------------------------
 
 

tools/chemenu/version.py

@@ -10,11 +10,23 @@ ingest into a release.
 
 **Compatibility is read off the leftmost non-zero component**, the rule Cargo's
 caret ranges use: `0.1.3 -> 0.1.4` is safe, `0.1.3 -> 0.2.0` is not, and from
-`1.0.0` on the same rule reads as the familiar "MAJOR means migration". Stating
-it that way is what lets the 0.x era carry the migration signal at all - under
-plain "MAJOR breaks" semantics every 0.x release would be indistinguishable
-from every other, which is exactly the signal update detection needs. Nothing
-about the mechanism changes at 1.0.0.
+`1.0.0` on the same rule reads as the familiar "MAJOR breaks". Stating it that
+way is what lets the 0.x era carry the signal at all - under a rule keyed to
+the MAJOR component alone, every 0.x release would be indistinguishable from
+every other, which is exactly the signal update detection needs. Nothing about
+the mechanism changes at 1.0.0.
+
+What that component answers is **whether the new version is a drop-in
+replacement**: whether an instance can copy the new machinery over itself with
+no hand-work and still put the old version back afterwards. Whether *content*
+must be migrated is a **second, independent question**. It is one way to fail
+the first - but a renamed release feed, artefact, import name, flag or envvar
+fails it too, with `kb/` untouched, which is why `--no-migration` exists at all:
+boundary-crossing bumps that migrate nothing are a real case, not an escape
+hatch. Hence two markers below rather than one - `BREAKING_CHANGE_MARKER`
+records the break, `MIGRATION_NONE_MARKER` records the absence of the
+migration. Which part a change earns stays a judgment call made before the
+bump; this module only enforces that a crossing says what it costs.
 
 Paths are resolved through `config.ROOT` at call time rather than at import,
 because the tests (and `dist export`'s own fixtures) relocate the root.
@@ -64,6 +76,11 @@ _SEMVER_RE = re.compile(r"^\s*v?(\d+)\.(\d+)\.(\d+)\s*$")
 # boundary that needs no content migration. `docs verify` accepts it in place
 # of a migration document, so the exact string is a contract between the two.
 MIGRATION_NONE_MARKER = "**Migration:** none required"
+# Written into every CHANGES.md entry whose version crosses a compatibility
+# boundary, migration or not: the swap is not drop-in, and the operator of an
+# existing instance has to be told what stops working. `docs verify` checks the
+# newest crossing carries it, so this string too is a contract between the two.
+BREAKING_CHANGE_MARKER = "**Breaking Change:**"
 # A changelog entry that names a version. Entries predating versioning start
 # with a date instead and are deliberately not matched - they are history, not
 # a claim about which version the tree is.
@@ -332,15 +349,22 @@ def insert_changes_entry(
     title: str,
     author: str,
     no_migration_reason: Optional[str] = None,
+    breaking_reason: Optional[str] = None,
 ) -> str:
     """Add a heading for `version` above the newest existing entry.
 
     Only the skeleton: heading, date, author, and - when a compatibility
-    boundary is crossed without a migration - the line that says so. The
-    entry's actual content is written afterwards by whoever made the change,
-    which is also why `bump` refuses to invent a title.
+    boundary is crossed - the line saying what breaks, plus the line saying no
+    content has to change where that applies. The entry's actual content is
+    written afterwards by whoever made the change, which is also why `bump`
+    refuses to invent a title.
+
+    The break comes first: it is what an operator reading the release notes has
+    to act on, and the migration line only qualifies it.
     """
     lines = [f"## {version} - {date} - {title}", "", f"**Author:** {author}", ""]
+    if breaking_reason:
+        lines += [f"{BREAKING_CHANGE_MARKER} {breaking_reason}", ""]
     if no_migration_reason:
         lines += [f"{MIGRATION_NONE_MARKER} - {no_migration_reason}", ""]
     entry = "\n".join(lines) + "\n---\n\n"