fix(release): version detection accepts manifest variants, never crashes the sweep

_pyproject_version read pyproject.toml with no error handling, so a
non-Python project failed the release-manager cycle every interval
forever. _project_version now probes pyproject.toml, package.json,
Cargo.toml, then a bare VERSION file; missing or unparseable manifests
are skipped and no manifest degrades to an empty version.

roboco/services/release_readiness.py

@@ -12,11 +12,15 @@ gate state) is layered on top of these primitives in Task 3.
 
 from __future__ import annotations
 
+import json
 import re
 import subprocess
 from dataclasses import dataclass, field
 from pathlib import Path
-from typing import Any, Literal
+from typing import TYPE_CHECKING, Any, Literal
+
+if TYPE_CHECKING:
+    from collections.abc import Callable
 
 BumpKind = Literal["major", "minor", "patch"]
 
@@ -439,12 +443,49 @@ def _run_git(root: Path, args: list[str]) -> str:
     return result.stdout
 
 
-def _pyproject_version(root: Path) -> str:
-    text = (root / "pyproject.toml").read_text(encoding="utf-8")
-    match = re.search(r'^version\s*=\s*"([^"]+)"', text, re.MULTILINE)
+_TOML_VERSION_RE = re.compile(r'^version\s*=\s*"([^"]+)"', re.MULTILINE)
+
+
+def _toml_version(path: Path) -> str:
+    match = _TOML_VERSION_RE.search(path.read_text(encoding="utf-8"))
     return match.group(1) if match else ""
 
 
+def _package_json_version(path: Path) -> str:
+    version = json.loads(path.read_text(encoding="utf-8")).get("version")
+    return version if isinstance(version, str) else ""
+
+
+def _version_file_version(path: Path) -> str:
+    lines = path.read_text(encoding="utf-8").strip().splitlines()
+    return lines[0].strip() if lines else ""
+
+
+_VERSION_PROBES: tuple[tuple[str, Callable[[Path], str]], ...] = (
+    ("pyproject.toml", _toml_version),
+    ("package.json", _package_json_version),
+    ("Cargo.toml", _toml_version),
+    ("VERSION", _version_file_version),
+)
+
+
+def _project_version(root: Path) -> str:
+    """Current version from the repo's own manifest — first probe that
+    yields one wins (pyproject.toml, package.json, Cargo.toml, VERSION).
+
+    Missing or unparseable manifests are skipped, never raised: a non-Python
+    layout must degrade to "" (readiness reports the gap) instead of
+    crashing the release-manager sweep every cycle."""
+    for name, probe in _VERSION_PROBES:
+        try:
+            version = probe(root / name)
+        except (OSError, ValueError):
+            continue
+        if version:
+            return version
+    return ""
+
+
 def _last_tag(root: Path) -> str | None:
     tag = _run_git(root, ["describe", "--tags", "--abbrev=0"]).strip()
     return tag or None
@@ -607,7 +648,7 @@ def gather_snapshot(
     (the ``tag_drift`` gap). None ⇒ degenerate/unsplit project, baseline stays
     ``last_tag`` (unchanged behavior).
     """
-    version = _pyproject_version(root)
+    version = _project_version(root)
     tag = _last_tag(root)
     prod_tip = _rev_parse(root, f"origin/{prod_branch}") if prod_branch else None
     last_tag_sha = _rev_parse(root, f"{tag}^{{commit}}") if tag else None

tests/unit/services/test_release_readiness.py

@@ -14,6 +14,7 @@ from roboco.services.release_readiness import (
     CommitInfo,
     _commits_since,
     _draft_changelog,
+    _project_version,
     _run_git,
     classify_changes,
     derive_bump,
@@ -164,3 +165,41 @@ def test_draft_changelog_falls_back_to_transcription_without_curation() -> None:
     draft = _draft_changelog("0.25.0", changes, "2026-07-15", empty)
     assert "### Added" in draft
     assert "- shiny thing" in draft
+
+
+# --------------------------------------------------------------------------- #
+# _project_version — manifest-variant probing, never raises on a non-Python
+# layout (a missing/unparseable manifest must not crash the readiness sweep).
+# --------------------------------------------------------------------------- #
+
+
+def test_project_version_reads_pyproject(tmp_path: Path) -> None:
+    (tmp_path / "pyproject.toml").write_text('version = "1.2.3"\n', encoding="utf-8")
+    assert _project_version(tmp_path) == "1.2.3"
+
+
+def test_project_version_falls_back_to_package_json(tmp_path: Path) -> None:
+    (tmp_path / "package.json").write_text('{"version": "4.5.6"}', encoding="utf-8")
+    assert _project_version(tmp_path) == "4.5.6"
+
+
+def test_project_version_falls_back_to_cargo_toml(tmp_path: Path) -> None:
+    (tmp_path / "Cargo.toml").write_text(
+        '[package]\nname = "x"\nversion = "7.8.9"\n', encoding="utf-8"
+    )
+    assert _project_version(tmp_path) == "7.8.9"
+
+
+def test_project_version_falls_back_to_version_file(tmp_path: Path) -> None:
+    (tmp_path / "VERSION").write_text("2.0.0\n", encoding="utf-8")
+    assert _project_version(tmp_path) == "2.0.0"
+
+
+def test_project_version_empty_when_no_manifest(tmp_path: Path) -> None:
+    assert _project_version(tmp_path) == ""
+
+
+def test_project_version_skips_unparseable_manifest(tmp_path: Path) -> None:
+    (tmp_path / "package.json").write_text("{not json", encoding="utf-8")
+    (tmp_path / "VERSION").write_text("3.1.4\n", encoding="utf-8")
+    assert _project_version(tmp_path) == "3.1.4"