diff --git a/.vscode/settings.json b/.vscode/settings.json
index 433dee7..09b031d 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -1,5 +1,5 @@
 {
-    "python-envs.defaultEnvManager": "ms-python.python:system",
+    "python-envs.defaultEnvManager": "ms-python.python:venv",
     "python-envs.pythonProjects": [],
     "python.analysis.typeCheckingMode": "strict",
     "python.analysis.generateWithTypeAnnotation": true,
diff --git a/base120.egg-info/SOURCES.txt b/base120.egg-info/SOURCES.txt
index 3dce60a..7b9b10f 100644
--- a/base120.egg-info/SOURCES.txt
+++ b/base120.egg-info/SOURCES.txt
@@ -2,9 +2,11 @@ LICENSE
 README.md
 pyproject.toml
 base120/__init__.py
+base120/observability.py
 base120.egg-info/PKG-INFO
 base120.egg-info/SOURCES.txt
 base120.egg-info/dependency_links.txt
 base120.egg-info/requires.txt
 base120.egg-info/top_level.txt
-tests/test_corpus.py
\ No newline at end of file
+tests/test_corpus.py
+tests/test_observability.py
\ No newline at end of file
diff --git a/base120/observability.py b/base120/observability.py
index 388a6d1..cc19218 100644
--- a/base120/observability.py
+++ b/base120/observability.py
@@ -5,12 +5,14 @@
 Uses standard library only - no runtime dependencies.
 """
 
+from typing import Any, Callable, Iterable, Mapping, Optional, TextIO, cast
+
 import json
 import sys
 from datetime import datetime, timezone
 
 
-def create_event_sink(output=None):
+def create_event_sink(output: Optional[TextIO] = None) -> Callable[[Mapping[str, Any]], None]:
     """
     Create a standard event sink that logs structured JSON events.
     
@@ -26,8 +28,9 @@ def create_event_sink(output=None):
     """
     if output is None:
         output = sys.stdout
+    output = cast(TextIO, output)
         
-    def sink(event):
+    def sink(event: Mapping[str, Any]) -> None:
         try:
             json.dump(event, output)
             output.write('\n')
@@ -41,13 +44,13 @@ def sink(event):
 
 
 def create_validator_event(
-    artifact_id,
-    schema_version,
-    result,
-    error_codes,
-    failure_mode_ids,
-    correlation_id=None
-):
+    artifact_id: str,
+    schema_version: str,
+    result: str,
+    error_codes: Iterable[str],
+    failure_mode_ids: Iterable[str],
+    correlation_id: Optional[str] = None,
+) -> Mapping[str, Any]:
     """
     Create a validator_result event conforming to the observability schema.
     
@@ -62,12 +65,12 @@ def create_validator_event(
     Returns:
         Dict conforming to validator_result event schema
     """
-    event = {
+    event: dict[str, Any] = {
         "event_type": "validator_result",
         "artifact_id": artifact_id,
         "schema_version": schema_version,
         "result": result,
-        "error_codes": error_codes,
+        "error_codes": list(error_codes),
         "failure_mode_ids": sorted(failure_mode_ids),  # Ensure sorted for consistency
         "timestamp": datetime.now(timezone.utc).isoformat()
     }
diff --git a/base120/validators/errors.py b/base120/validators/errors.py
index 32ae3e7..7fbbb00 100644
--- a/base120/validators/errors.py
+++ b/base120/validators/errors.py
@@ -1,14 +1,18 @@
-def resolve_errors(fms: list[str], err_registry: list[dict]) -> list[str]:
+from typing import Any, Mapping, Sequence
+
+
+def resolve_errors(fms: list[str], err_registry: Sequence[Mapping[str, Any]]) -> list[str]:
     # FM30 dominance: escalation suppresses all other errors
     if "FM30" in fms:
         return sorted(
-            entry["id"]
+            str(entry.get("id", ""))
             for entry in err_registry
-            if "FM30" in entry["fm"]
+            if "FM30" in entry.get("fm", [])
         )
 
-    errs = []
+    errs: list[str] = []
     for entry in err_registry:
-        if any(fm in fms for fm in entry["fm"]):
-            errs.append(entry["id"])
+        fm_list = entry.get("fm", [])
+        if any(fm in fms for fm in fm_list):
+            errs.append(str(entry.get("id", "")))
     return sorted(set(errs))
diff --git a/base120/validators/mappings.py b/base120/validators/mappings.py
index 987e6c5..fc1e86c 100644
--- a/base120/validators/mappings.py
+++ b/base120/validators/mappings.py
@@ -1,2 +1,5 @@
-def resolve_failure_modes(subclass: str, mappings: dict) -> list[str]:
-    return mappings.get("mappings", {}).get(subclass, [])
+from typing import Mapping, Sequence
+
+
+def resolve_failure_modes(subclass: str, mappings: Mapping[str, Mapping[str, Sequence[str]]]) -> list[str]:
+    return list(mappings.get("mappings", {}).get(subclass, []))
diff --git a/base120/validators/schema.py b/base120/validators/schema.py
index e786cd2..e06579e 100644
--- a/base120/validators/schema.py
+++ b/base120/validators/schema.py
@@ -1,6 +1,10 @@
+from typing import Any, Mapping
+
+# pyright: reportMissingModuleSource=false
 from jsonschema import Draft202012Validator
 
-def validate_schema(artifact: dict, schema: dict) -> list[str]:
+
+def validate_schema(artifact: Mapping[str, Any], schema: Mapping[str, Any]) -> list[str]:
     validator = Draft202012Validator(schema)
-    errors = list(validator.iter_errors(artifact))
+    errors = list(validator.iter_errors(artifact))  # type: ignore[call-overload]
     return ["ERR-SCHEMA-001"] if errors else []
diff --git a/base120/validators/validate.py b/base120/validators/validate.py
index deb6a04..aae1783 100644
--- a/base120/validators/validate.py
+++ b/base120/validators/validate.py
@@ -1,17 +1,19 @@
+from typing import Any, Callable, Mapping, MutableSequence, Optional, Sequence
+
 from base120.validators.schema import validate_schema
 from base120.validators.mappings import resolve_failure_modes
 from base120.validators.errors import resolve_errors
 
 def validate_artifact(
-    artifact: dict,
-    schema: dict,
-    mappings: dict,
-    err_registry: list[dict],
-    event_sink=None
+    artifact: Mapping[str, Any],
+    schema: Mapping[str, Any],
+    mappings: Mapping[str, Any],
+    err_registry: Sequence[Mapping[str, Any]],
+    event_sink: Optional[Callable[[Mapping[str, Any]], None]] = None,
 ) -> list[str]:
 
-    errs = []
-    fms = []
+    errs: MutableSequence[str] = []
+    fms: list[str] = []
 
     # 1. Schema validation
     errs.extend(validate_schema(artifact, schema))
@@ -22,7 +24,7 @@ def validate_artifact(
         return sorted(set(errs))
 
     # 2. Subclass → FM
-    subclass = artifact.get("class")
+    subclass = str(artifact.get("class", ""))
     fms = resolve_failure_modes(subclass, mappings)
 
     # 3. FM → ERR
@@ -34,7 +36,12 @@ def validate_artifact(
     return sorted(set(errs))
 
 
-def _emit_event(artifact, error_codes, failure_mode_ids, event_sink):
+def _emit_event(
+    artifact: Mapping[str, Any],
+    error_codes: Sequence[str],
+    failure_mode_ids: Sequence[str],
+    event_sink: Optional[Callable[[Mapping[str, Any]], None]],
+) -> None:
     """
     Emit validator_result event if event_sink is provided.
     
@@ -54,7 +61,7 @@ def _emit_event(artifact, error_codes, failure_mode_ids, event_sink):
             schema_version="v1.0.0",
             result=result,
             error_codes=sorted(set(error_codes)),
-            failure_mode_ids=failure_mode_ids
+            failure_mode_ids=list(failure_mode_ids),
         )
         
         event_sink(event)
diff --git a/tests/test_corpus.py b/tests/test_corpus.py
index a96a581..7dc0062 100644
--- a/tests/test_corpus.py
+++ b/tests/test_corpus.py
@@ -15,7 +15,7 @@
 with open(ROOT / "registries" / "err.json") as f:
     ERR_REGISTRY = json.load(f)["registry"]
 
-def load_json(path):
+def load_json(path: str | Path):
     with open(path) as f:
         return json.load(f)
 
diff --git a/tests/test_observability.py b/tests/test_observability.py
index f12f1e1..cdc74c1 100644
--- a/tests/test_observability.py
+++ b/tests/test_observability.py
@@ -7,6 +7,7 @@
 import json
 from pathlib import Path
 from io import StringIO
+from typing import Any, Mapping
 
 from base120.validators.validate import validate_artifact
 from base120.observability import create_event_sink, create_validator_event
@@ -130,7 +131,7 @@ def test_backward_compatibility_without_event_sink():
 
 def test_event_emission_failure_does_not_propagate():
     """Errors during event emission do not affect validation."""
-    def failing_sink(event):
+    def failing_sink(event: Mapping[str, Any]) -> None:
         raise Exception("Event emission failed!")
     
     artifact = {
@@ -159,13 +160,16 @@ def test_unknown_artifact_id():
         "instance": "test",
         "models": ["FM1"]
     }
-    
+
     errors = validate_artifact(artifact, SCHEMA, MAPPINGS, ERR_REGISTRY, event_sink=event_sink)
-    
+    assert errors == ["ERR-SCHEMA-001"], "Missing id should fail schema validation"
+
     output.seek(0)
     event = json.loads(output.read().strip())
     
     assert event["artifact_id"] == "unknown"
+    assert event["result"] == "failure"
+    assert "ERR-SCHEMA-001" in event["error_codes"]
 
 
 def test_create_validator_event_with_correlation_id():