diff --git a/agentfailbench/failures/__init__.py b/agentfailbench/failures/__init__.py
index e69de29..1b9ae30 100644
--- a/agentfailbench/failures/__init__.py
+++ b/agentfailbench/failures/__init__.py
@@ -0,0 +1,5 @@
+"""Failure-injection suites for AgentFailBench."""
+
+from agentfailbench.failures.base import FailureInjector, FailureInjectorRegistry
+
+__all__ = ["FailureInjector", "FailureInjectorRegistry"]
diff --git a/agentfailbench/failures/base.py b/agentfailbench/failures/base.py
new file mode 100644
index 0000000..b295b9c
--- /dev/null
+++ b/agentfailbench/failures/base.py
@@ -0,0 +1,74 @@
+"""Shared failure-injector interface for AgentFailBench suites.
+
+Every failure-injection suite (tool drift, memory, planning, retrieval, data,
+communication — see ``docs/roadmap.md`` Milestone 2) drives an episode through
+the same three lifecycle hooks so a single dispatcher can coordinate
+heterogeneous injectors without depending on their concrete types.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Any, Protocol, runtime_checkable
+
+from runtime.schemas.episode import EnvObservation
+
+
+@runtime_checkable
+class FailureInjector(Protocol):
+    """Lifecycle contract every failure injector must implement.
+
+    ``env`` is typed as ``Any`` on purpose: each suite injects failures into
+    a different environment (customer API today, memory/retrieval stores in
+    later milestones), so the interface stays environment-agnostic.
+    """
+
+    def before_step(self, env: Any, step: int) -> None:
+        """Arm/apply the failure ahead of the upcoming step, if triggered."""
+        ...
+
+    def after_step(self, env: Any, step: int, observation: EnvObservation) -> None:
+        """React to the outcome of a step that just executed."""
+        ...
+
+    def reset(self) -> None:
+        """Return the injector to its pre-trigger state for a fresh episode."""
+        ...
+
+    @property
+    def triggered(self) -> bool:
+        """Whether the injected failure has fired at least once."""
+        ...
+
+
+@dataclass
+class FailureInjectorRegistry:
+    """Registers named injectors and dispatches lifecycle hooks to all of them."""
+
+    _injectors: dict[str, FailureInjector] = field(default_factory=dict)
+
+    def register(self, name: str, injector: FailureInjector) -> None:
+        if name in self._injectors:
+            raise ValueError(f"Duplicate failure injector: {name}")
+        self._injectors[name] = injector
+
+    def get(self, name: str) -> FailureInjector:
+        return self._injectors[name]
+
+    def list_names(self) -> list[str]:
+        return sorted(self._injectors)
+
+    def dispatch_before_step(self, env: Any, step: int) -> None:
+        for injector in self._injectors.values():
+            injector.before_step(env, step)
+
+    def dispatch_after_step(self, env: Any, step: int, observation: EnvObservation) -> None:
+        for injector in self._injectors.values():
+            injector.after_step(env, step, observation)
+
+    def dispatch_reset(self) -> None:
+        for injector in self._injectors.values():
+            injector.reset()
+
+    def any_triggered(self) -> bool:
+        return any(injector.triggered for injector in self._injectors.values())
diff --git a/agentfailbench/failures/tool_drift/__init__.py b/agentfailbench/failures/tool_drift/__init__.py
index 18354af..1b12908 100644
--- a/agentfailbench/failures/tool_drift/__init__.py
+++ b/agentfailbench/failures/tool_drift/__init__.py
@@ -1,5 +1,8 @@
 """ToolDrift suite package."""
 
-from agentfailbench.failures.tool_drift.injector import SemanticDriftInjector
+from agentfailbench.failures.tool_drift.injector import (
+    SemanticDriftInjector,
+    SemanticDriftInjectorAdapter,
+)
 
-__all__ = ["SemanticDriftInjector"]
+__all__ = ["SemanticDriftInjector", "SemanticDriftInjectorAdapter"]
diff --git a/agentfailbench/failures/tool_drift/injector.py b/agentfailbench/failures/tool_drift/injector.py
index 425839d..b5d0baa 100644
--- a/agentfailbench/failures/tool_drift/injector.py
+++ b/agentfailbench/failures/tool_drift/injector.py
@@ -2,9 +2,10 @@
 
 from __future__ import annotations
 
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 
 from agentfailbench.environments.customer_api.env import CustomerApiEnv
+from runtime.schemas.episode import EnvObservation
 
 
 @dataclass
@@ -27,3 +28,30 @@ def triggered(self) -> bool:
 
     def reset(self) -> None:
         self._triggered = False
+
+
+@dataclass
+class SemanticDriftInjectorAdapter:
+    """Adapts :class:`SemanticDriftInjector` to the shared ``FailureInjector`` protocol.
+
+    ``SemanticDriftInjector`` predates the shared interface (``agentfailbench.failures.base``)
+    and only needs a trigger-based ``before_step``/``reset``. This adapter fills in the
+    ``after_step`` hook so the injector can be registered and dispatched alongside future
+    suites without changing its existing behavior.
+    """
+
+    injector: SemanticDriftInjector = field(default_factory=SemanticDriftInjector)
+
+    def before_step(self, env: CustomerApiEnv, step: int) -> None:
+        self.injector.before_step(env, step)
+
+    def after_step(self, env: CustomerApiEnv, step: int, observation: EnvObservation) -> None:
+        """No-op: semantic drift is a one-shot contract flip with no post-step reaction."""
+        del env, step, observation
+
+    def reset(self) -> None:
+        self.injector.reset()
+
+    @property
+    def triggered(self) -> bool:
+        return self.injector.triggered
diff --git a/agentfailbench/runners/episode.py b/agentfailbench/runners/episode.py
index f5c99a6..6f7c1ac 100644
--- a/agentfailbench/runners/episode.py
+++ b/agentfailbench/runners/episode.py
@@ -8,7 +8,11 @@
 
 from agentfailbench.agents.scripted import ScriptedApiAgent
 from agentfailbench.environments.customer_api.env import CustomerApiEnv
-from agentfailbench.failures.tool_drift.injector import SemanticDriftInjector
+from agentfailbench.failures.base import FailureInjectorRegistry
+from agentfailbench.failures.tool_drift.injector import (
+    SemanticDriftInjector,
+    SemanticDriftInjectorAdapter,
+)
 from agentfailbench.models import BenchmarkCaseModel
 from agentfailbench.registry import CaseRegistry
 from baselines.rules.detectors import BaseDetector, DetectionResult, all_detectors
@@ -46,21 +50,27 @@ def _run_traced(
     case: BenchmarkCaseModel,
     *,
     inject_failure: bool,
-) -> tuple[CustomerApiEnv, ScriptedApiAgent, TraceCollector, SemanticDriftInjector]:
+) -> tuple[CustomerApiEnv, ScriptedApiAgent, TraceCollector, SemanticDriftInjectorAdapter]:
     task = build_task(case)
     env = CustomerApiEnv(task=task)
     agent = ScriptedApiAgent(env=env)
-    injector = SemanticDriftInjector(trigger_step=case.failure.trigger_step)
+    injector = SemanticDriftInjectorAdapter(
+        SemanticDriftInjector(trigger_step=case.failure.trigger_step)
+    )
+    injectors = FailureInjectorRegistry()
+    injectors.register("tool_drift.semantic_drift", injector)
     collector = TraceCollector(task_id=case.case_id)
 
     for _ in range(case.task.expected_steps):
         upcoming_step = agent._step + 1
         if inject_failure:
-            injector.before_step(env, upcoming_step)
+            injectors.dispatch_before_step(env, upcoming_step)
         action = agent.next_action()
         if action is None:
             break
         obs = env.step(action)
+        if inject_failure:
+            injectors.dispatch_after_step(env, upcoming_step, obs)
         progress = min(1.0, action.step / case.task.expected_steps)
         collector.record(action, obs, agent.expected_attributes(), progress)
 
diff --git a/tests/unit/test_failure_injector.py b/tests/unit/test_failure_injector.py
new file mode 100644
index 0000000..a1c29f2
--- /dev/null
+++ b/tests/unit/test_failure_injector.py
@@ -0,0 +1,116 @@
+"""Unit tests for the shared failure-injector interface and registry."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+
+import pytest
+
+from agentfailbench.environments.customer_api.env import CustomerApiEnv
+from agentfailbench.failures.base import FailureInjector, FailureInjectorRegistry
+from agentfailbench.failures.tool_drift.injector import (
+    SemanticDriftInjector,
+    SemanticDriftInjectorAdapter,
+)
+from runtime.schemas.episode import EnvObservation, TaskSpec
+
+
+def _make_env() -> CustomerApiEnv:
+    task = TaskSpec(
+        task_id="t-1", objective="update_customer_subscription", environment="customer_service_api"
+    )
+    return CustomerApiEnv(task=task)
+
+
+@dataclass
+class _RecordingInjector:
+    """Minimal stand-in suite used to exercise registration/dispatch in isolation."""
+
+    calls: list[str] = field(default_factory=list)
+    _triggered: bool = False
+
+    def before_step(self, env: object, step: int) -> None:
+        del env
+        self.calls.append(f"before:{step}")
+        self._triggered = True
+
+    def after_step(self, env: object, step: int, observation: EnvObservation) -> None:
+        del env, observation
+        self.calls.append(f"after:{step}")
+
+    def reset(self) -> None:
+        self.calls.append("reset")
+        self._triggered = False
+
+    @property
+    def triggered(self) -> bool:
+        return self._triggered
+
+
+def test_semantic_drift_adapter_satisfies_failure_injector_protocol() -> None:
+    adapter = SemanticDriftInjectorAdapter(SemanticDriftInjector(trigger_step=2))
+    assert isinstance(adapter, FailureInjector)
+
+
+def test_recording_injector_satisfies_failure_injector_protocol() -> None:
+    assert isinstance(_RecordingInjector(), FailureInjector)
+
+
+def test_registry_rejects_duplicate_names() -> None:
+    registry = FailureInjectorRegistry()
+    registry.register("a", _RecordingInjector())
+    with pytest.raises(ValueError):
+        registry.register("a", _RecordingInjector())
+
+
+def test_registry_get_and_list_names() -> None:
+    registry = FailureInjectorRegistry()
+    injector = _RecordingInjector()
+    registry.register("only", injector)
+    assert registry.list_names() == ["only"]
+    assert registry.get("only") is injector
+
+
+def test_registry_dispatches_lifecycle_hooks_to_all_injectors() -> None:
+    registry = FailureInjectorRegistry()
+    first = _RecordingInjector()
+    second = _RecordingInjector()
+    registry.register("first", first)
+    registry.register("second", second)
+    env = _make_env()
+    obs = EnvObservation(success=True)
+
+    registry.dispatch_before_step(env, 1)
+    registry.dispatch_after_step(env, 1, obs)
+    registry.dispatch_reset()
+
+    assert first.calls == ["before:1", "after:1", "reset"]
+    assert second.calls == ["before:1", "after:1", "reset"]
+
+
+def test_registry_any_triggered_reflects_injector_state() -> None:
+    registry = FailureInjectorRegistry()
+    registry.register("only", _RecordingInjector())
+    assert registry.any_triggered() is False
+    registry.dispatch_before_step(_make_env(), 1)
+    assert registry.any_triggered() is True
+
+
+def test_adapter_delegates_to_wrapped_semantic_drift_injector() -> None:
+    inner = SemanticDriftInjector(trigger_step=2)
+    adapter = SemanticDriftInjectorAdapter(inner)
+    env = _make_env()
+
+    adapter.before_step(env, 1)
+    assert adapter.triggered is False
+    assert env.contract_version == "v1"
+
+    adapter.before_step(env, 2)
+    assert adapter.triggered is True
+    assert env.contract_version == "v2"
+
+    adapter.after_step(env, 2, EnvObservation(success=True))  # no-op, must not raise
+
+    adapter.reset()
+    assert adapter.triggered is False
+    assert adapter.injector is inner