fix: load spec YAML as JSON-compatible scalars and reject epoch release versions

scripts/check_release_preflight.py

@@ -70,6 +70,7 @@ def version_failure(value: str) -> str | None:
         return "release version is not PEP 440 compliant"
     if (
         str(version) != value
+        or version.epoch != 0
         or len(version.release) != 3
         or version.is_prerelease
         or version.is_devrelease

src/ml4t/specs/io.py

@@ -4,6 +4,7 @@
 
 import json
 import os
+import re
 import stat
 from collections.abc import Mapping
 from pathlib import Path
@@ -15,6 +16,39 @@
 from .base import ArtifactSpec
 
 _SUPPORTED_SUFFIXES = frozenset({".json", ".yaml", ".yml"})
+_YAML_BOOL_TAG = "tag:yaml.org,2002:bool"
+_YAML_TIMESTAMP_TAG = "tag:yaml.org,2002:timestamp"
+
+
+class _SpecYamlLoader(yaml.SafeLoader):
+    """Load YAML spec payloads as JSON-compatible scalars.
+
+    PyYAML defaults to YAML 1.1. Unquoted ISO dates become ``datetime`` objects,
+    which then crash ``fromisoformat``, and ``yes``/``no``/``on``/``off`` become
+    booleans, so an asset id such as ``NO`` never arrives as the string the
+    contract validates.
+    """
+
+
+def _json_compatible_yaml_resolvers() -> dict[str | None, list[tuple[str, re.Pattern[str]]]]:
+    resolvers: dict[str | None, list[tuple[str, re.Pattern[str]]]] = {}
+    for key, entries in yaml.SafeLoader.yaml_implicit_resolvers.items():
+        kept = [
+            (tag, regexp)
+            for tag, regexp in entries
+            if tag not in {_YAML_BOOL_TAG, _YAML_TIMESTAMP_TAG}
+        ]
+        if kept:
+            resolvers[key] = kept
+    return resolvers
+
+
+_SpecYamlLoader.yaml_implicit_resolvers = _json_compatible_yaml_resolvers()
+_SpecYamlLoader.add_implicit_resolver(
+    _YAML_BOOL_TAG,
+    re.compile(r"^(?:true|True|TRUE|false|False|FALSE)$"),
+    list("tTfF"),
+)
 
 
 def _validated_suffix(path: Path) -> str:
@@ -79,7 +113,7 @@ def read_spec_payload(path_or_mapping: str | Path | Mapping[Any, Any]) -> dict[s
     path = Path(path_or_mapping)
     suffix = _validated_suffix(path)
     with path.open(encoding="utf-8") as f:
-        data = json.load(f) if suffix == ".json" else yaml.safe_load(f)
+        data = json.load(f) if suffix == ".json" else yaml.load(f, Loader=_SpecYamlLoader)
     return _normalize_mapping({} if data is None else data)
 
 

tests/test_release_pipeline.py

@@ -44,7 +44,7 @@
 REPOSITORY_ROOT = Path(__file__).parents[1]
 
 
-@pytest.mark.parametrize("version", ["1.2", "v1.2.3", "1.2.3rc1", "1.2.3+local"])
+@pytest.mark.parametrize("version", ["1.2", "v1.2.3", "1.2.3rc1", "1.2.3+local", "1!1.2.3"])
 def test_release_preflight_rejects_nonstable_versions(version: str) -> None:
     assert version_failure(version) is not None
 

tests/test_spec_io.py

@@ -3,13 +3,16 @@
 import json
 import os
 import stat
+from datetime import UTC, date, datetime
 from pathlib import Path
 
 import pytest
+import yaml
 
 import ml4t.specs.io as spec_io
 from ml4t.specs import (
     ArtifactStorage,
+    CanonicalTargetIntent,
     MarketDataSemantics,
     MarketDataSpec,
     TimestampSemantics,
@@ -103,6 +106,65 @@ def test_read_spec_payload_rejects_non_mapping_documents(
         read_spec_payload(path)
 
 
+def test_read_spec_payload_keeps_json_compatible_yaml_scalars(tmp_path) -> None:
+    intent_path = tmp_path / "intent.yaml"
+    intent_path.write_text(
+        """\
+intent_id: target-1
+decision_time: 2026-08-08T13:00:00+00:00
+information_cutoff: 2026-08-08T12:59:59+00:00
+effective_session: 2026-08-10
+effective_phase: pre_open
+targets:
+- asset: NO
+  measure: weight
+  value: 0.5
+idempotency_key: target-key
+measure: weight
+cash_buffer: 0.05
+rounding: toward_zero
+residual: keep_cash
+reason: rebalance
+lifecycle_version: '1'
+""",
+        encoding="utf-8",
+    )
+    payload = read_spec_payload(intent_path)
+    assert isinstance(payload["decision_time"], str)
+    assert payload["effective_session"] == "2026-08-10"
+    assert payload["targets"][0]["asset"] == "NO"
+    intent = CanonicalTargetIntent.from_mapping(payload)
+    assert intent.decision_time == datetime(2026, 8, 8, 13, 0, tzinfo=UTC)
+    assert intent.information_cutoff == datetime(2026, 8, 8, 12, 59, 59, tzinfo=UTC)
+    assert intent.effective_session == date(2026, 8, 10)
+    assert intent.targets[0].asset == "NO"
+
+    market_path = tmp_path / "market.yaml"
+    market_path.write_text(
+        """\
+artifact_id: prices
+provenance:
+  created_by: no
+semantics:
+  calendar: NYSE
+""",
+        encoding="utf-8",
+    )
+    market = read_spec_payload(market_path)
+    assert market["provenance"]["created_by"] == "no"
+    assert MarketDataSpec.from_mapping(market).provenance.created_by == "no"
+
+    flags = tmp_path / "flags.yaml"
+    flags.write_text("enabled: false\nabsent: null\ncount: 2\ntoken: yes\n", encoding="utf-8")
+    assert read_spec_payload(flags) == {
+        "enabled": False,
+        "absent": None,
+        "count": 2,
+        "token": "yes",
+    }
+    assert yaml.safe_load("asset: NO\n") == {"asset": False}
+
+
 def test_read_spec_payload_normalizes_mapping_keys(tmp_path) -> None:
     path = tmp_path / "numeric-key.yaml"
     path.write_text("1: value\n")