diff --git a/src/agent_env/task_step/__init__.py b/src/agent_env/task_step/__init__.py
index 626cea566..dd249d93b 100644
--- a/src/agent_env/task_step/__init__.py
+++ b/src/agent_env/task_step/__init__.py
@@ -1,7 +1,7 @@
 """TaskStep module for AgentEnv."""
 
 from agent_env.env.env import DeployedEnv
-from .context import DeployedAgent, PromptResponse, TaskStepContext
+from .context import DeployedAgent, PromptResponse, StepContextError, TaskStepContext
 from .task_step import TaskStep
 from .task_steps import AddSkillsTaskStep, AgentPromptResponseVerifierTaskStep, BuildMcpCliTaskStep, CombineUniverseVerdictsStep, DeployAgentTaskStep, DeployEnvTaskStep, EnvOutcomeVerifierTaskStep, LoadArtifactTaskStep, ModifyEnvToolAccessStep, PromptAgentTaskStep, RubricsVerifierTaskStep, ScoreAggregator, ValidationGateAggregatorStep, VerifyCoreA2AProtocolStep, VerifyCoreEnvironmentProtocolStep, VerifyEnvironmentCardStep, VerifyMCPEnvAssessmentStep, VerifyMCPToolSchemaTaskStep, VerifySpecConformanceTaskStep, VerifyUniverseLoadExportRoundtripStep, VerifyA2AAgentCardStep, VerifyA2AAgentMCPStep, VerifyA2ASkillConfigStep, VerifyA2ATrajectoryStep
 from .task_steps.verifiers.judge_utils.judge_output_format import JudgeOutputFormat, get_judge_output_format_spec
@@ -14,6 +14,7 @@
     "get_judge_output_format_spec",
     "PromptResponse",
     "ScoreAggregator",
+    "StepContextError",
     "TaskStepContext",
     "TaskStep",
     "AddSkillsTaskStep",
diff --git a/src/agent_env/task_step/context.py b/src/agent_env/task_step/context.py
index e6d541bae..082a3d736 100644
--- a/src/agent_env/task_step/context.py
+++ b/src/agent_env/task_step/context.py
@@ -14,6 +14,12 @@
 
 HEARTBEAT_KEY = "_heartbeat_fn"
 
+
+class StepContextError(RuntimeError):
+    """The run's context can't satisfy a step: something the step needs from an earlier step is missing, or
+    something it would create is already there. Running the step again on the same context fails the same
+    way, so a runner should not retry it."""
+
 _REDACTED_KEYS = {
     "litellm_api_key", "judge_litellm_api_key", "usersim_api_key", "remote_tokens", "cf_access_client_secret",
     HEARTBEAT_KEY,
diff --git a/src/agent_env/task_step/task_steps/add_skills.py b/src/agent_env/task_step/task_steps/add_skills.py
index f8fccc3d5..019b02a27 100644
--- a/src/agent_env/task_step/task_steps/add_skills.py
+++ b/src/agent_env/task_step/task_steps/add_skills.py
@@ -15,7 +15,7 @@
 from agentenv_protocol.client import children, find_extension_method
 
 from agent_env.config import get_config
-from agent_env.task_step.context import DeployedAgent, TaskStepContext
+from agent_env.task_step.context import DeployedAgent, StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.entity.scopes import FieldScope
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
@@ -261,7 +261,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
             raise ValueError("; ".join(problems))
         agent = next((a for a in context.deployed_agents if a.agent_name == self.agent_name), None)
         if agent is None:
-            raise RuntimeError(f"Agent '{self.agent_name}' not found in context.deployed_agents")
+            raise StepContextError(f"Agent '{self.agent_name}' not found in context.deployed_agents")
         if agent.instance_id is None:
             raise RuntimeError(f"Agent '{self.agent_name}' is missing instance_id; cannot resolve deployment")
 
diff --git a/src/agent_env/task_step/task_steps/collect_artifacts.py b/src/agent_env/task_step/task_steps/collect_artifacts.py
index c55923a6a..b440a5ce0 100644
--- a/src/agent_env/task_step/task_steps/collect_artifacts.py
+++ b/src/agent_env/task_step/task_steps/collect_artifacts.py
@@ -80,7 +80,7 @@
 from agent_env.config import get_config
 from agent_env.env.gateway.constants import EXT_STEP_URI
 from agent_env.store.ids import derive_path_id, is_local_id, validate_local_id
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 from agent_env.task_step.task_steps.sandbox_utils.sandbox_utils import find_agent_container
@@ -650,7 +650,7 @@ def _resolve_cua_env(self, context):
         DeployedEnv metadata, so its presence authoritatively marks a CUA env."""
         deployed_env = next((d for d in context.deployed_envs if d.env_id == self.env_id), None)
         if deployed_env is None:
-            raise RuntimeError(
+            raise StepContextError(
                 f"Env '{self.env_id}' not found in context.deployed_envs — cannot collect artifacts via controller"
             )
         if _CUA_ENV_METADATA_MARKER not in (deployed_env.metadata or {}):
@@ -758,7 +758,7 @@ async def _collect_via_agent_container(self, context, store, artifact_id, versio
 
         agent = next((a for a in context.deployed_agents if a.agent_name == self.agent_name), None)
         if agent is None:
-            raise RuntimeError(f"Agent '{self.agent_name}' not found in context.deployed_agents")
+            raise StepContextError(f"Agent '{self.agent_name}' not found in context.deployed_agents")
         if not agent.sandbox_id:
             raise RuntimeError(f"Agent '{self.agent_name}' has no sandbox_id — cannot collect artifacts")
 
@@ -804,7 +804,7 @@ async def _collect_via_vm_host(self, context, store, artifact_id, version):
             (sb for sb in context.deployed_sandboxes if sb.sandbox_name == self.sandbox_name), None
         )
         if ds is None:
-            raise RuntimeError(
+            raise StepContextError(
                 f"Sandbox '{self.sandbox_name}' not found in context.deployed_sandboxes"
             )
 
@@ -862,7 +862,7 @@ async def _collect_via_sandbox_container(self, context, store, artifact_id, vers
             (s for s in context.deployed_sandboxes if s.sandbox_name == self.sandbox_name), None
         )
         if deployed is None:
-            raise RuntimeError(
+            raise StepContextError(
                 f"Sandbox '{self.sandbox_name}' not found in context.deployed_sandboxes"
             )
 
diff --git a/src/agent_env/task_step/task_steps/configure_scheduled_checks.py b/src/agent_env/task_step/task_steps/configure_scheduled_checks.py
index aa46f4f5c..e46bdc979 100644
--- a/src/agent_env/task_step/task_steps/configure_scheduled_checks.py
+++ b/src/agent_env/task_step/task_steps/configure_scheduled_checks.py
@@ -18,7 +18,7 @@
 from agent_env.env.gateway.constants import EXT_NOTIFICATIONS_URI
 from agent_env.env.gateway.notifications import DEFAULT_MAX_ACTIVE, DEFAULT_MIN_INTERVAL
 from agent_env.entity.refs import EntityRef
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 
 logger = logging.getLogger(__name__)
@@ -77,7 +77,7 @@ def from_dict(cls, data: dict) -> ConfigureScheduledChecksTaskStep:
     async def execute(self, context: TaskStepContext) -> TaskStepContext:
         deployed = next((d for d in context.deployed_envs if d.env_id == self.env_id), None)
         if deployed is None:
-            raise RuntimeError(f"Env '{self.env_id}' not found in context.deployed_envs")
+            raise StepContextError(f"Env '{self.env_id}' not found in context.deployed_envs")
         if not deployed.supports(EXT_NOTIFICATIONS_URI, "config"):
             raise RuntimeError(f"Env '{self.env_id}' runs a gateway without {EXT_NOTIFICATIONS_URI}; redeploy it on a "
                                "gateway image that has it.")
diff --git a/src/agent_env/task_step/task_steps/deploy_agent.py b/src/agent_env/task_step/task_steps/deploy_agent.py
index cbacdc804..c95b198ff 100644
--- a/src/agent_env/task_step/task_steps/deploy_agent.py
+++ b/src/agent_env/task_step/task_steps/deploy_agent.py
@@ -40,7 +40,7 @@
     sandbox_request_headers_for_url,
 )
 from agent_env.providers.sandbox_providers.sandbox import NetworkPolicy
-from agent_env.task_step.context import DeployedAgent, TaskStepContext
+from agent_env.task_step.context import DeployedAgent, StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.entity.scopes import FieldScope
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
@@ -356,13 +356,13 @@ async def _execute(self, context: TaskStepContext, deployed_agents: list) -> Tas
 
         existing = next((a for a in context.deployed_agents if a.agent_name == self.agent_name), None)
         if existing is not None:
-            raise RuntimeError(f"Agent with name '{self.agent_name}' is already deployed")
+            raise StepContextError(f"Agent with name '{self.agent_name}' is already deployed")
 
         linked_sandbox = None
         if self.sandbox_name:
             ds = next((s for s in context.deployed_sandboxes if s.sandbox_name == self.sandbox_name), None)
             if ds is None:
-                raise RuntimeError(
+                raise StepContextError(
                     f"Sandbox '{self.sandbox_name}' not found in context.deployed_sandboxes; "
                     f"deploy it with DeploySandboxTaskStep before this step"
                 )
diff --git a/src/agent_env/task_step/task_steps/deploy_env.py b/src/agent_env/task_step/task_steps/deploy_env.py
index 1ff00eaa3..96a669f65 100644
--- a/src/agent_env/task_step/task_steps/deploy_env.py
+++ b/src/agent_env/task_step/task_steps/deploy_env.py
@@ -11,7 +11,7 @@
 from agent_env.config import get_config
 from agent_env.env.gateway import GatewayMode
 from agent_env.env.store import update_env_instance_metadata
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.entity.scopes import FieldScope
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
@@ -155,7 +155,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
 
         existing = next((d for d in context.deployed_envs if d.env_id == self.env_id), None)
         if existing is not None:
-            raise RuntimeError(f"Env '{self.env_id}' is already deployed")
+            raise StepContextError(f"Env '{self.env_id}' is already deployed")
 
         env = Env.get(self.env_id, self.env_version)
         user_overrides = context.metadata.get("user_overrides", {})
diff --git a/src/agent_env/task_step/task_steps/deploy_human_agent.py b/src/agent_env/task_step/task_steps/deploy_human_agent.py
index a262ebc79..b7719d1c9 100644
--- a/src/agent_env/task_step/task_steps/deploy_human_agent.py
+++ b/src/agent_env/task_step/task_steps/deploy_human_agent.py
@@ -10,7 +10,7 @@
 
 import httpx
 
-from agent_env.task_step.context import DeployedAgent, TaskStepContext
+from agent_env.task_step.context import DeployedAgent, StepContextError, TaskStepContext
 from agent_env.entity.scopes import FieldScope
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 
@@ -60,7 +60,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
                 "only one human agent is allowed per task"
             )
         if any(a.agent_name == self.agent_name for a in context.deployed_agents):
-            raise RuntimeError(f"Agent with name '{self.agent_name}' is already deployed")
+            raise StepContextError(f"Agent with name '{self.agent_name}' is already deployed")
 
         if self.a2a_url:
             url = self.a2a_url
diff --git a/src/agent_env/task_step/task_steps/deploy_sandbox.py b/src/agent_env/task_step/task_steps/deploy_sandbox.py
index 6e8bce2f4..bb833ab40 100644
--- a/src/agent_env/task_step/task_steps/deploy_sandbox.py
+++ b/src/agent_env/task_step/task_steps/deploy_sandbox.py
@@ -8,7 +8,7 @@
 from agent_env.artifact.artifacts.docker_image import pull_problem
 from agent_env.providers.sandbox_providers.chained_sandbox_provider import skip_refusing
 from agent_env.providers.sandbox_providers.sandbox import NetworkPolicy
-from agent_env.task_step.context import DeployedSandbox, TaskStepContext
+from agent_env.task_step.context import DeployedSandbox, StepContextError, TaskStepContext
 from agent_env.entity.scopes import FieldScope
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 from agent_env.attribution import deploy_attribution
@@ -113,7 +113,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
         from agent_env.providers.sandbox_providers.sandbox_provider import build_sandbox_provider, get_sandbox_provider
 
         if any(s.sandbox_name == self.sandbox_name for s in context.deployed_sandboxes):
-            raise RuntimeError(f"Sandbox '{self.sandbox_name}' is already deployed")
+            raise StepContextError(f"Sandbox '{self.sandbox_name}' is already deployed")
 
         user_overrides = context.metadata.get("user_overrides") or {}
         # Moves only deploy_sandbox steps: deploy_env and deploy_agent read env_sandbox and agent_sandbox.
diff --git a/src/agent_env/task_step/task_steps/env_card_validator/verify_env_card.py b/src/agent_env/task_step/task_steps/env_card_validator/verify_env_card.py
index 890048177..63bd1e7c2 100644
--- a/src/agent_env/task_step/task_steps/env_card_validator/verify_env_card.py
+++ b/src/agent_env/task_step/task_steps/env_card_validator/verify_env_card.py
@@ -5,7 +5,7 @@
 import logging
 from typing import ClassVar, Optional
 
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 
@@ -48,7 +48,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
 
         deployed = next((d for d in context.deployed_envs if d.env_id == self.env_id), None)
         if deployed is None:
-            raise RuntimeError(f"Env '{self.env_id}' not found in context.deployed_envs")
+            raise StepContextError(f"Env '{self.env_id}' not found in context.deployed_envs")
 
         card = None
         error = None
diff --git a/src/agent_env/task_step/task_steps/env_card_validator/verify_env_core_protocol.py b/src/agent_env/task_step/task_steps/env_card_validator/verify_env_core_protocol.py
index 20d25ea43..20a92ff0b 100644
--- a/src/agent_env/task_step/task_steps/env_card_validator/verify_env_core_protocol.py
+++ b/src/agent_env/task_step/task_steps/env_card_validator/verify_env_core_protocol.py
@@ -9,7 +9,7 @@
 from agentenv_protocol import METHOD_ADD, METHOD_GET, METHOD_RESET, RPC_PATH
 from agentenv_protocol import client as protocol_v1
 
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 
@@ -54,7 +54,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
 
         deployed = next((d for d in context.deployed_envs if d.env_id == self.env_id), None)
         if deployed is None:
-            raise RuntimeError(f"Env '{self.env_id}' not found in context.deployed_envs")
+            raise StepContextError(f"Env '{self.env_id}' not found in context.deployed_envs")
 
         card = None
         try:
diff --git a/src/agent_env/task_step/task_steps/install_agent.py b/src/agent_env/task_step/task_steps/install_agent.py
index 6fdd517a9..edebd8b2b 100644
--- a/src/agent_env/task_step/task_steps/install_agent.py
+++ b/src/agent_env/task_step/task_steps/install_agent.py
@@ -33,7 +33,7 @@
     trust_env,
 )
 from agent_env.store.base import NotFoundError
-from agent_env.task_step.context import DeployedAgent, TaskStepContext
+from agent_env.task_step.context import DeployedAgent, StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 
@@ -226,7 +226,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
 
         existing = next((a for a in context.deployed_agents if a.agent_name == self.agent_name), None)
         if existing is not None:
-            raise RuntimeError(f"Agent with name '{self.agent_name}' is already deployed")
+            raise StepContextError(f"Agent with name '{self.agent_name}' is already deployed")
 
         if self.container_name is not None:
             containers = context.metadata.get("deployed_docker_containers", [])
@@ -246,7 +246,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
 
         ds = next((s for s in context.deployed_sandboxes if s.sandbox_name == self.sandbox_name), None)
         if ds is None:
-            raise RuntimeError(f"Sandbox '{self.sandbox_name}' not found in context.deployed_sandboxes")
+            raise StepContextError(f"Sandbox '{self.sandbox_name}' not found in context.deployed_sandboxes")
         if ds.sandbox_mode != SANDBOX_MODE_VM:
             raise RuntimeError(
                 f"InstallAgent requires a VM-mode sandbox; '{self.sandbox_name}' is mode={ds.sandbox_mode!r}"
diff --git a/src/agent_env/task_step/task_steps/load_artifact.py b/src/agent_env/task_step/task_steps/load_artifact.py
index e2f4a8c55..1762baaf0 100644
--- a/src/agent_env/task_step/task_steps/load_artifact.py
+++ b/src/agent_env/task_step/task_steps/load_artifact.py
@@ -18,7 +18,7 @@
 from agent_env.providers.sandbox_providers.local_docker.provider import LocalSandbox
 from agent_env.providers.sandbox_providers.sandbox import into_container
 from agent_env.providers.sandbox_providers.sandbox_provider import reachable_url
-from agent_env.task_step.context import DeployedAgent, TaskStepContext
+from agent_env.task_step.context import DeployedAgent, StepContextError, TaskStepContext
 from agent_env.task_step.preflight import stored_env
 from agent_env.entity.refs import EntityRef
 from agent_env.entity.scopes import FieldScope
@@ -322,7 +322,7 @@ def _resolve_step_artifact(context: TaskStepContext, step_id: str) -> Optional[d
                 continue
             ref = extract(entry)
             return {"id": ref["id"], "version": ref.get("version")} if ref else None
-        raise RuntimeError(
+        raise StepContextError(
             f"No artifact recorded by step '{step_id}'. Ensure a step that produces "
             f"one (e.g. `collect_artifacts`, `snapshot_env`) ran with that id before "
             f"this load step."
@@ -447,7 +447,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
         if self.env_id is not None:
             deployed = self._deployed_env(context)
             if deployed is None:
-                raise RuntimeError(f"Env '{self.env_id}' not found in context.deployed_envs")
+                raise StepContextError(f"Env '{self.env_id}' not found in context.deployed_envs")
 
         inputs = self._resolve_inputs(context)
         resolved_artifacts = inputs.artifacts
@@ -474,7 +474,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
                     )
             ds = next((s for s in context.deployed_sandboxes if s.sandbox_name == self.sandbox_name), None)
             if ds is None:
-                raise RuntimeError(f"Sandbox '{self.sandbox_name}' not found in context.deployed_sandboxes")
+                raise StepContextError(f"Sandbox '{self.sandbox_name}' not found in context.deployed_sandboxes")
             provider = (
                 build_sandbox_provider(ds.sandbox_type) if ds.sandbox_type else get_sandbox_provider()
             )
@@ -545,7 +545,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
                 else:
                     agent = next((a for a in context.deployed_agents if a.agent_name == self.agent_name), None)
                     if agent is None or not agent.instance_id:
-                        raise RuntimeError(f"Agent '{self.agent_name}' not found in context.deployed_agents (or missing instance_id)")
+                        raise StepContextError(f"Agent '{self.agent_name}' not found in context.deployed_agents (or missing instance_id)")
                     deployed_agent = get_a2a_agent_instance_store().get(agent.instance_id)
                     destination = (destination_path or "/tmp/file_artifacts").rstrip("/") or "/"
                     files = await A2AAgent.load_file_artifact_universe(
@@ -582,7 +582,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
                     else:
                         agent = next((a for a in context.deployed_agents if a.agent_name == self.agent_name), None)
                         if agent is None or not agent.sandbox_id:
-                            raise RuntimeError(
+                            raise StepContextError(
                                 f"Agent '{self.agent_name}' not found in context.deployed_agents (or missing sandbox_id)"
                             )
                         provider = (
@@ -641,7 +641,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
                     raise RuntimeError("env_id is required when loading a CliArtifact (for gateway_url)")
                 agent = next((a for a in context.deployed_agents if a.agent_name == self.agent_name), None)
                 if agent is None or not agent.instance_id:
-                    raise RuntimeError(f"Agent '{self.agent_name}' not found in context.deployed_agents (or missing instance_id)")
+                    raise StepContextError(f"Agent '{self.agent_name}' not found in context.deployed_agents (or missing instance_id)")
                 deployed_agent = get_a2a_agent_instance_store().get(agent.instance_id)
                 gateway_url = require_gateway_url(deployed, "Installing a CliArtifact")
                 # A local sandbox's host is this machine, which reaches the gateway as it was issued.
@@ -664,7 +664,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
             else:
                 agent = next((a for a in context.deployed_agents if a.agent_name == self.agent_name), None)
                 if agent is None or not agent.sandbox_id:
-                    raise RuntimeError(f"Agent '{self.agent_name}' not found in context.deployed_agents (or missing sandbox_id)")
+                    raise StepContextError(f"Agent '{self.agent_name}' not found in context.deployed_agents (or missing sandbox_id)")
                 provider = (
                     build_sandbox_provider(agent.sandbox_type)
                     if agent.sandbox_type
diff --git a/src/agent_env/task_step/task_steps/mcp_cli_builder/build_mcp_cli.py b/src/agent_env/task_step/task_steps/mcp_cli_builder/build_mcp_cli.py
index 23c0f22d3..afab39ad8 100644
--- a/src/agent_env/task_step/task_steps/mcp_cli_builder/build_mcp_cli.py
+++ b/src/agent_env/task_step/task_steps/mcp_cli_builder/build_mcp_cli.py
@@ -19,7 +19,7 @@
 from agent_env.env import Env
 from agent_env.env.env import require_gateway_url, website_child
 from agent_env.store.ids import derive_id
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef, RefRole
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 from agent_env.task_step.thread_work import finish_on_thread
@@ -160,7 +160,7 @@ def from_dict(cls, data: dict) -> BuildMcpCliTaskStep:
     async def execute(self, context: TaskStepContext) -> TaskStepContext:
         deployed = next((d for d in context.deployed_envs if d.env_id == self.env_id), None)
         if deployed is None:
-            raise RuntimeError(f"Env '{self.env_id}' not found in context.deployed_envs")
+            raise StepContextError(f"Env '{self.env_id}' not found in context.deployed_envs")
         gateway_url = require_gateway_url(deployed, "build_mcp_cli")  # the CLI it generates talks to the gateway
 
         env = Env.get(self.env_id, deployed.env_version)
diff --git a/src/agent_env/task_step/task_steps/mcp_env_validator/verify_mcp_env_assessment.py b/src/agent_env/task_step/task_steps/mcp_env_validator/verify_mcp_env_assessment.py
index 6030ceaef..72ba54990 100644
--- a/src/agent_env/task_step/task_steps/mcp_env_validator/verify_mcp_env_assessment.py
+++ b/src/agent_env/task_step/task_steps/mcp_env_validator/verify_mcp_env_assessment.py
@@ -6,7 +6,7 @@
 import logging
 from typing import Any, ClassVar, Optional
 
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 
@@ -45,7 +45,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
 
         prompt_response = next((pr for pr in context.prompt_responses if pr.prompt_id == self.prompt_id), None)
         if prompt_response is None:
-            raise RuntimeError(f"PromptResponse with prompt_id='{self.prompt_id}' not found in context")
+            raise StepContextError(f"PromptResponse with prompt_id='{self.prompt_id}' not found in context")
 
         if prompt_response.error_type:
             logger.warning(f"Skipping assessment: prompt had error_type={prompt_response.error_type}")
@@ -55,7 +55,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
 
         deployed = next((d for d in context.deployed_envs if d.env_id == self.env_id), None)
         if deployed is None:
-            raise RuntimeError(f"Env '{self.env_id}' not found in context.deployed_envs")
+            raise StepContextError(f"Env '{self.env_id}' not found in context.deployed_envs")
         env = Env.get(self.env_id, deployed.env_version)
         env.update_metadata({**env.metadata, "mcp_tool_correctness_validation": result})
 
diff --git a/src/agent_env/task_step/task_steps/mcp_env_validator/verify_mcp_tool_schema.py b/src/agent_env/task_step/task_steps/mcp_env_validator/verify_mcp_tool_schema.py
index c5e5c42e6..1a7df4f06 100644
--- a/src/agent_env/task_step/task_steps/mcp_env_validator/verify_mcp_tool_schema.py
+++ b/src/agent_env/task_step/task_steps/mcp_env_validator/verify_mcp_tool_schema.py
@@ -9,7 +9,7 @@
 from mcp import ClientSession
 from mcp.client.streamable_http import streamable_http_client
 
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 
@@ -122,7 +122,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
 
         deployed = next((d for d in context.deployed_envs if d.env_id == self.env_id), None)
         if deployed is None:
-            raise RuntimeError(f"Env '{self.env_id}' not found in context.deployed_envs")
+            raise StepContextError(f"Env '{self.env_id}' not found in context.deployed_envs")
 
         mcp_url = deployed.mcp_url
         logger.info(f"Connecting to MCP at {mcp_url} to verify tool schemas")
diff --git a/src/agent_env/task_step/task_steps/mcp_env_validator/verify_spec_conformance.py b/src/agent_env/task_step/task_steps/mcp_env_validator/verify_spec_conformance.py
index 8a61e84dc..9787c3ae5 100644
--- a/src/agent_env/task_step/task_steps/mcp_env_validator/verify_spec_conformance.py
+++ b/src/agent_env/task_step/task_steps/mcp_env_validator/verify_spec_conformance.py
@@ -27,7 +27,7 @@
 from mcp.client.streamable_http import streamable_http_client
 
 from agent_env.env import legacy_protocol
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 from agent_env.task_step.task_steps.mcp_env_validator.verify_mcp_tool_schema import (
@@ -405,7 +405,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
 
         deployed = next((d for d in context.deployed_envs if d.env_id == self.env_id), None)
         if deployed is None:
-            raise RuntimeError(f"Env '{self.env_id}' not found in context.deployed_envs")
+            raise StepContextError(f"Env '{self.env_id}' not found in context.deployed_envs")
 
         env = Env.get(self.env_id, deployed.env_version)
         environment_name = env.environment_name
diff --git a/src/agent_env/task_step/task_steps/modify_env_tool_access.py b/src/agent_env/task_step/task_steps/modify_env_tool_access.py
index 589da671a..4e71d2f21 100644
--- a/src/agent_env/task_step/task_steps/modify_env_tool_access.py
+++ b/src/agent_env/task_step/task_steps/modify_env_tool_access.py
@@ -7,7 +7,7 @@
 
 from agent_env.env.gateway import TOOL_DISABLE_ACTION, TOOL_ENABLE_ACTION
 from agent_env.env.gateway.constants import EXT_DISABLE_TOOL_URI, EXT_ENABLE_TOOL_URI
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 
@@ -62,7 +62,7 @@ def from_dict(cls, data: dict) -> ModifyEnvToolAccessStep:
     async def execute(self, context: TaskStepContext) -> TaskStepContext:
         deployed = next((d for d in context.deployed_envs if d.env_id == self.env_id), None)
         if deployed is None:
-            raise RuntimeError(f"Env '{self.env_id}' not found in context.deployed_envs")
+            raise StepContextError(f"Env '{self.env_id}' not found in context.deployed_envs")
         body = await deployed.invoke(_TOOL_ACCESS_URIS[self.action], self.action, {"role": self.role, "tools": self.tools})
         logger.info(f"{self.action} role={self.role!r} tools={self.tools} on env={self.env_id}: {body}")
         context.metadata.setdefault("tool_access_changes", []).append({
diff --git a/src/agent_env/task_step/task_steps/multienv_validator/verify_universe_roundtrip.py b/src/agent_env/task_step/task_steps/multienv_validator/verify_universe_roundtrip.py
index 9e8274beb..585c2a945 100644
--- a/src/agent_env/task_step/task_steps/multienv_validator/verify_universe_roundtrip.py
+++ b/src/agent_env/task_step/task_steps/multienv_validator/verify_universe_roundtrip.py
@@ -12,7 +12,7 @@
 from agent_env.env.env_artifact_store import EnvArtifactType, get_env_artifact_store
 from agent_env.artifact.store import artifact_write_lock
 from agent_env.store.ids import derive_id, fs_safe, is_local_id
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 
@@ -101,7 +101,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
         # Phase 1: Resolve deployed env and universe artifact
         deployed = next((d for d in context.deployed_envs if d.env_id == self.env_id), None)
         if deployed is None:
-            raise RuntimeError(f"Env '{self.env_id}' not found in context.deployed_envs")
+            raise StepContextError(f"Env '{self.env_id}' not found in context.deployed_envs")
         env = Env.get(deployed.env_id, deployed.env_version)
         env = await type(env).from_deployed_env(deployed)
         universe = EnvironmentUniverseArtifact.get(self.universe_artifact_id, self.universe_artifact_version)
diff --git a/src/agent_env/task_step/task_steps/prompt_agent.py b/src/agent_env/task_step/task_steps/prompt_agent.py
index c11fb716b..c0b986b00 100644
--- a/src/agent_env/task_step/task_steps/prompt_agent.py
+++ b/src/agent_env/task_step/task_steps/prompt_agent.py
@@ -35,7 +35,7 @@
 )
 from agent_env.store import DuplicateKeyError, get_config
 from agent_env.store.object_store import ObjectStore
-from agent_env.task_step.context import DeployedAgent, PromptResponse, TaskStepContext
+from agent_env.task_step.context import DeployedAgent, PromptResponse, StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.entity.scopes import FieldScope
 from agent_env.task_step.task_step import RetryConfig, TaskStep, TaskStepDependency
@@ -452,7 +452,7 @@ async def _converse(
     ) -> TaskStepContext:
         agent = next((a for a in context.deployed_agents if a.agent_name == self.agent_name), None)
         if agent is None:
-            raise RuntimeError(f"Agent with name '{self.agent_name}' not found in context.deployed_agents")
+            raise StepContextError(f"Agent with name '{self.agent_name}' not found in context.deployed_agents")
         target_url = agent.a2a_url or agent.api_url
         user_sim = next((a for a in context.deployed_agents if a.agent_name == self.user_agent_name), None)
         user_url = self.user_a2a_url or (
diff --git a/src/agent_env/task_step/task_steps/register_agent_triggers.py b/src/agent_env/task_step/task_steps/register_agent_triggers.py
index 64074b983..05171c26f 100644
--- a/src/agent_env/task_step/task_steps/register_agent_triggers.py
+++ b/src/agent_env/task_step/task_steps/register_agent_triggers.py
@@ -9,7 +9,7 @@
 import httpx
 
 from agent_env.a2a_agent.a2a_agent import A2AAgent
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 
@@ -76,7 +76,7 @@ def from_dict(cls, data: dict) -> RegisterAgentTriggersStep:
     async def execute(self, context: TaskStepContext) -> TaskStepContext:
         agent = next((a for a in context.deployed_agents if a.agent_name == self.agent_name), None)
         if agent is None:
-            raise RuntimeError(f"Agent '{self.agent_name}' not found in context.deployed_agents")
+            raise StepContextError(f"Agent '{self.agent_name}' not found in context.deployed_agents")
         card = agent.a2a_card or {}
         ext = A2AAgent.find_extension(card, A2AAgent.EXT_TRIGGERS)
         if ext is None:
diff --git a/src/agent_env/task_step/task_steps/register_env_triggers.py b/src/agent_env/task_step/task_steps/register_env_triggers.py
index 237f77259..6229a59e4 100644
--- a/src/agent_env/task_step/task_steps/register_env_triggers.py
+++ b/src/agent_env/task_step/task_steps/register_env_triggers.py
@@ -23,7 +23,7 @@
     TRIGGER_WEBSITE,
     TRIGGER_WEBSITE_OP,
 )
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 
@@ -131,7 +131,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
             raise RuntimeError("; ".join(problems))
         deployed = next((d for d in context.deployed_envs if d.env_id == self.env_id), None)
         if deployed is None:
-            raise RuntimeError(f"Env '{self.env_id}' not found in context.deployed_envs")
+            raise StepContextError(f"Env '{self.env_id}' not found in context.deployed_envs")
         body: dict = {"triggers": self.triggers}
         if self.watch_roles is not None:
             body["watch_roles"] = self.watch_roles
@@ -227,7 +227,7 @@ def _await_failure(self, seen: dict[str, Optional[str]], state: dict, stuck: lis
     def _executor_config(self, context: TaskStepContext, deployed: DeployedEnv, agent_name: str) -> dict:
         agent = next((a for a in context.deployed_agents if a.agent_name == agent_name), None)
         if agent is None:
-            raise RuntimeError(f"Executor agent '{agent_name}' not found in context.deployed_agents")
+            raise StepContextError(f"Executor agent '{agent_name}' not found in context.deployed_agents")
         if not agent.role:
             raise RuntimeError(
                 f"Executor agent '{agent_name}' was deployed without an explicit role; "
diff --git a/src/agent_env/task_step/task_steps/run_code.py b/src/agent_env/task_step/task_steps/run_code.py
index 6695a0e18..2652f4f01 100644
--- a/src/agent_env/task_step/task_steps/run_code.py
+++ b/src/agent_env/task_step/task_steps/run_code.py
@@ -42,7 +42,7 @@
 from agent_env.env.env import DeployedSandboxEnv, require_sandbox
 from agent_env.env.envs.computer.utils import inside
 from agent_env.providers.sandbox_providers.sandbox import into_container
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 
@@ -406,7 +406,7 @@ def _deployed_env(self, context: TaskStepContext) -> DeployedSandboxEnv:
         if deployed is not None:
             deployed = require_sandbox(deployed, "run_code on the env's host")
         if deployed is None or not deployed.sandbox_id:
-            raise RuntimeError(
+            raise StepContextError(
                 f"Env '{self.env_id}' not found in context.deployed_envs "
                 "(or missing sandbox_id)"
             )
@@ -457,7 +457,7 @@ async def _sandbox_target(self, context: TaskStepContext) -> _ExecTarget:
             (s for s in context.deployed_sandboxes if s.sandbox_name == self.sandbox_name), None
         )
         if deployed is None:
-            raise RuntimeError(f"Sandbox '{self.sandbox_name}' not found in context.deployed_sandboxes")
+            raise StepContextError(f"Sandbox '{self.sandbox_name}' not found in context.deployed_sandboxes")
         provider = (
             build_sandbox_provider(deployed.sandbox_type)
             if deployed.sandbox_type
@@ -487,7 +487,7 @@ async def _agent_target(self, context: TaskStepContext) -> _ExecTarget:
             (a for a in context.deployed_agents if a.agent_name == self.agent_name), None
         )
         if agent is None or not agent.sandbox_id:
-            raise RuntimeError(
+            raise StepContextError(
                 f"Agent '{self.agent_name}' not found in context.deployed_agents "
                 "(or missing sandbox_id)"
             )
diff --git a/src/agent_env/task_step/task_steps/run_docker_container.py b/src/agent_env/task_step/task_steps/run_docker_container.py
index 15280d4db..6d8269170 100644
--- a/src/agent_env/task_step/task_steps/run_docker_container.py
+++ b/src/agent_env/task_step/task_steps/run_docker_container.py
@@ -11,7 +11,7 @@
 from urllib.parse import urlparse
 
 from agent_env.artifact.artifacts.docker_image import DockerImageArtifact
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.entity.scopes import FieldScope
 from agent_env.providers.sandbox_providers.sandbox import SANDBOX_LABEL, port_bindings
@@ -177,7 +177,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
             None,
         )
         if ds is None:
-            raise RuntimeError(
+            raise StepContextError(
                 f"Sandbox '{self.sandbox_name}' not found in context.deployed_sandboxes; "
                 f"deploy it with DeploySandboxTaskStep before this step"
             )
diff --git a/src/agent_env/task_step/task_steps/sync_env_clock.py b/src/agent_env/task_step/task_steps/sync_env_clock.py
index 040c958c2..b4c92793e 100644
--- a/src/agent_env/task_step/task_steps/sync_env_clock.py
+++ b/src/agent_env/task_step/task_steps/sync_env_clock.py
@@ -19,7 +19,7 @@
 from agentenv_protocol import client as protocol_v1
 
 from agent_env.env.gateway.constants import EXT_CLOCK_URI
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 
@@ -124,7 +124,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
 
         deployed = next((d for d in context.deployed_envs if d.env_id == self.env_id), None)
         if deployed is None:
-            raise RuntimeError(f"Env '{self.env_id}' not found in context.deployed_envs")
+            raise StepContextError(f"Env '{self.env_id}' not found in context.deployed_envs")
         try:
             await deployed.invoke(EXT_CLOCK_URI, "set_time",
                                   {"virtual_time": self.armed_virtual_time, "virtual_seconds_per_real_second": self.virtual_seconds_per_real_second},
diff --git a/src/agent_env/task_step/task_steps/verifiers/agent_prompt_response_verifier.py b/src/agent_env/task_step/task_steps/verifiers/agent_prompt_response_verifier.py
index a4fb779f2..7d868f330 100644
--- a/src/agent_env/task_step/task_steps/verifiers/agent_prompt_response_verifier.py
+++ b/src/agent_env/task_step/task_steps/verifiers/agent_prompt_response_verifier.py
@@ -21,7 +21,7 @@
 import uuid
 from typing import ClassVar, Optional
 
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 from agent_env.task_step.task_steps.verifiers.scoring import ScoreAggregator, aggregate_score
 
@@ -81,7 +81,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
             None,
         )
         if prompt_response is None:
-            raise RuntimeError(f"PromptResponse with prompt_id='{self.prompt_id}' not found in context")
+            raise StepContextError(f"PromptResponse with prompt_id='{self.prompt_id}' not found in context")
 
         if prompt_response.error_type:
             logger.warning(
diff --git a/src/agent_env/task_step/task_steps/verifiers/env_outcome_verifier.py b/src/agent_env/task_step/task_steps/verifiers/env_outcome_verifier.py
index 51f0c7213..5e45774af 100644
--- a/src/agent_env/task_step/task_steps/verifiers/env_outcome_verifier.py
+++ b/src/agent_env/task_step/task_steps/verifiers/env_outcome_verifier.py
@@ -13,7 +13,7 @@
 from typing import ClassVar, Optional
 
 from agent_env.config import get_config
-from agent_env.task_step.context import PromptResponse, TaskStepContext
+from agent_env.task_step.context import PromptResponse, StepContextError, TaskStepContext
 from agent_env.entity.refs import EntityRef
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 from agent_env.task_step.task_steps.verifiers.run_context import load_run_context
@@ -108,7 +108,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
 
         deployed = next((d for d in context.deployed_envs if d.env_id == self.env_id), None)
         if deployed is None:
-            raise RuntimeError(f"Env '{self.env_id}' not found in context.deployed_envs")
+            raise StepContextError(f"Env '{self.env_id}' not found in context.deployed_envs")
 
         artifact = FileArtifact.get(self.file_artifact_id, self.file_artifact_version)
         verifier_bytes = await asyncio.to_thread(artifact.load)
@@ -151,7 +151,7 @@ def _graded_prompt(self, context: TaskStepContext) -> Optional[PromptResponse]:
             return context.prompt_responses[-1] if context.prompt_responses else None
         prompt_response = next((pr for pr in context.prompt_responses if pr.prompt_id == self.prompt_id), None)
         if prompt_response is None:
-            raise RuntimeError(f"PromptResponse with prompt_id='{self.prompt_id}' not found in context")
+            raise StepContextError(f"PromptResponse with prompt_id='{self.prompt_id}' not found in context")
         return prompt_response
 
 
diff --git a/src/agent_env/task_step/task_steps/verifiers/rubrics_verifier.py b/src/agent_env/task_step/task_steps/verifiers/rubrics_verifier.py
index 443e86103..915fca57e 100644
--- a/src/agent_env/task_step/task_steps/verifiers/rubrics_verifier.py
+++ b/src/agent_env/task_step/task_steps/verifiers/rubrics_verifier.py
@@ -20,7 +20,7 @@
 from agent_env.config import get_config
 from agent_env.config.model import ModelParam
 from agent_env.providers.sandbox_providers.sandbox import into_container
-from agent_env.task_step.context import PromptResponse, TaskStepContext, dual_keyed
+from agent_env.task_step.context import PromptResponse, StepContextError, TaskStepContext, dual_keyed
 from agent_env.task_step.task_steps.verifiers.judge_utils.judge_output_format import (
     SCREENSHOT_GROUNDING,
     JudgeOutputFormat,
@@ -636,7 +636,7 @@ def _resolved_criteria(self, context: TaskStepContext) -> list[dict]:
     async def execute(self, context: TaskStepContext) -> TaskStepContext:
         prompt_response = next((pr for pr in context.prompt_responses if pr.prompt_id == self.prompt_id), None)
         if prompt_response is None:
-            raise RuntimeError(f"PromptResponse with prompt_id='{self.prompt_id}' not found in context")
+            raise StepContextError(f"PromptResponse with prompt_id='{self.prompt_id}' not found in context")
         overrides_for_step = self.step_param_overrides(context)
         grade_up_to_turn = (
             _validated_turn(overrides_for_step["grade_up_to_turn"])
@@ -744,7 +744,7 @@ async def execute(self, context: TaskStepContext) -> TaskStepContext:
             if self.agent_name is not None:
                 agent = next((a for a in context.deployed_agents if a.agent_name == self.agent_name), None)
                 if agent is None:
-                    raise RuntimeError(f"Agent '{self.agent_name}' not found in context.deployed_agents")
+                    raise StepContextError(f"Agent '{self.agent_name}' not found in context.deployed_agents")
                 if not agent.sandbox_id:
                     raise RuntimeError(f"Agent '{self.agent_name}' has no sandbox_id")
                 judge_a2a_url = agent.a2a_url or agent.api_url
diff --git a/src/agent_env/task_step/task_steps/verifiers/run_container_unit_tests_verifier.py b/src/agent_env/task_step/task_steps/verifiers/run_container_unit_tests_verifier.py
index 61c3c4838..ab8cb2e96 100644
--- a/src/agent_env/task_step/task_steps/verifiers/run_container_unit_tests_verifier.py
+++ b/src/agent_env/task_step/task_steps/verifiers/run_container_unit_tests_verifier.py
@@ -50,7 +50,7 @@
     registered_sandbox_provider_classes,
 )
 from agent_env.store.ids import derive_id, is_local_id, key_segment, validate_local_id
-from agent_env.task_step.context import TaskStepContext, dual_keyed
+from agent_env.task_step.context import StepContextError, TaskStepContext, dual_keyed
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 from agent_env.task_step.task_steps.run_code import _DriverTarget
 
@@ -395,7 +395,7 @@ async def _container_sandbox(self, context: TaskStepContext):
             )
         ds = next((s for s in context.deployed_sandboxes if s.sandbox_name == self.sandbox_name), None)
         if ds is None:
-            raise RuntimeError(f"Sandbox '{self.sandbox_name}' not found in context.deployed_sandboxes")
+            raise StepContextError(f"Sandbox '{self.sandbox_name}' not found in context.deployed_sandboxes")
 
         provider = (
             build_sandbox_provider(ds.sandbox_type) if ds.sandbox_type else get_sandbox_provider()
@@ -439,7 +439,7 @@ def _computer(self, context: TaskStepContext) -> _DriverTarget:
         timeout."""
         deployed = next((d for d in context.deployed_envs if d.env_id == self.env_id), None)
         if deployed is None:
-            raise RuntimeError(f"Env '{self.env_id}' not found in context.deployed_envs")
+            raise StepContextError(f"Env '{self.env_id}' not found in context.deployed_envs")
         deployed = require_sandbox(deployed, "Running a verifier in an env")
         if missing := inside.missing(deployed):
             raise RuntimeError(f"env '{self.env_id}' doesn't serve {', '.join(missing)}, which running a verifier in "
diff --git a/src/agent_env/task_step/task_steps/verifiers/verify_sandbox.py b/src/agent_env/task_step/task_steps/verifiers/verify_sandbox.py
index 9144fbc58..5d5776b34 100644
--- a/src/agent_env/task_step/task_steps/verifiers/verify_sandbox.py
+++ b/src/agent_env/task_step/task_steps/verifiers/verify_sandbox.py
@@ -35,7 +35,7 @@
     get_agent_sandbox_provider,
     get_sandbox_provider,
 )
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.task_step.task_step import TaskStep, TaskStepDependency
 from agent_env.task_step.task_steps.sandbox_utils.sandbox_utils import find_agent_container
 from agent_env.task_step.task_steps.verifiers.scoring import ScoreAggregator, aggregate_score
@@ -194,7 +194,7 @@ async def _agent_sandbox(self, context: TaskStepContext):
             None,
         )
         if agent is None:
-            raise RuntimeError(f"Agent '{self.agent_name}' not found in context.deployed_agents")
+            raise StepContextError(f"Agent '{self.agent_name}' not found in context.deployed_agents")
         if not agent.sandbox_id:
             raise RuntimeError(f"Agent '{self.agent_name}' has no sandbox_id")
         provider = (
@@ -210,7 +210,7 @@ async def _deployed_sandbox(self, context: TaskStepContext):
             None,
         )
         if deployed is None:
-            raise RuntimeError(
+            raise StepContextError(
                 f"Sandbox '{self.sandbox_name}' not found in context.deployed_sandboxes "
                 f"(deployed: {[s.sandbox_name for s in context.deployed_sandboxes]})"
             )
diff --git a/tst/unit/task_step/deploy_human_agent_test.py b/tst/unit/task_step/deploy_human_agent_test.py
index 8d604af2b..98ec3c308 100644
--- a/tst/unit/task_step/deploy_human_agent_test.py
+++ b/tst/unit/task_step/deploy_human_agent_test.py
@@ -7,7 +7,7 @@
 import pytest
 
 from agent_env.config.errors import ConfigError
-from agent_env.task_step.context import DeployedAgent, TaskStepContext
+from agent_env.task_step.context import DeployedAgent, StepContextError, TaskStepContext
 from agent_env.task_step.registry import get_task_step_registry
 from agent_env.task_step.task_steps.deploy_human_agent import DeployHumanAgentTaskStep
 
@@ -94,7 +94,7 @@ async def test_execute_explicit_a2a_url_is_verbatim():
 async def test_execute_rejects_duplicate_agent_name():
     context = TaskStepContext(deployed_agents=[DeployedAgent(agent_name="human", api_url="http://x")])
     step = DeployHumanAgentTaskStep(id="t.dh", version=None, agent_name="human")
-    with pytest.raises(RuntimeError, match="already deployed"):
+    with pytest.raises(StepContextError, match="already deployed"):
         await step.execute(context)
 
 
diff --git a/tst/unit/task_step/test_load_artifact_overrides.py b/tst/unit/task_step/test_load_artifact_overrides.py
index bc8bd98c8..9d0ad2f0d 100644
--- a/tst/unit/task_step/test_load_artifact_overrides.py
+++ b/tst/unit/task_step/test_load_artifact_overrides.py
@@ -10,7 +10,7 @@
 
 import pytest
 
-from agent_env.task_step.context import TaskStepContext
+from agent_env.task_step.context import StepContextError, TaskStepContext
 from agent_env.task_step.task_steps.load_artifact import LoadArtifactTaskStep
 
 
@@ -119,7 +119,7 @@ def test_collected_missing_entry_still_raises(self):
         step = LoadArtifactTaskStep(
             id="load", version=None, agent_name="agent", collected_artifacts_step_id="collect",
         )
-        with pytest.raises(RuntimeError, match="No artifact recorded by step 'collect'"):
+        with pytest.raises(StepContextError, match="No artifact recorded by step 'collect'"):
             step._resolve_inputs(_ctx())
 
 
diff --git a/tst/unit/task_step/test_run_code.py b/tst/unit/task_step/test_run_code.py
index a972dd17a..b21f10b7f 100644
--- a/tst/unit/task_step/test_run_code.py
+++ b/tst/unit/task_step/test_run_code.py
@@ -25,7 +25,7 @@
 from agent_env.env.env import DeployedEnv, DeployedGatewayEnv, DeployedSandboxEnv, EnvNeedsSandbox
 from agent_env.providers.sandbox_providers.local_docker.provider import LocalSandbox
 from agent_env.providers.sandbox_providers.sandbox import Sandbox, VmSandbox
-from agent_env.task_step.context import DeployedAgent, DeployedSandbox, TaskStepContext
+from agent_env.task_step.context import DeployedAgent, DeployedSandbox, StepContextError, TaskStepContext
 from agent_env.task_step.task_steps import run_code as _run_code_module
 from tst.unit.computer_home import CARD, TOKEN, Computer
 from tst.unit.event_loop_probe import on_event_loop
@@ -492,7 +492,7 @@ async def test_sandbox_target_honors_the_sandboxs_type():
 
 @pytest.mark.asyncio
 async def test_sandbox_target_names_a_sandbox_the_run_never_deployed():
-    with pytest.raises(RuntimeError, match="^Sandbox 'ghost' not found in context.deployed_sandboxes$"):
+    with pytest.raises(StepContextError, match="^Sandbox 'ghost' not found in context.deployed_sandboxes$"):
         await _step(sandbox_name="ghost")._sandbox_target(_sandbox_context())
 
 
diff --git a/tst/unit/task_step/test_step_context_error.py b/tst/unit/task_step/test_step_context_error.py
new file mode 100644
index 000000000..0767cc44e
--- /dev/null
+++ b/tst/unit/task_step/test_step_context_error.py
@@ -0,0 +1,62 @@
+"""A step that finds the run's context can't satisfy it raises StepContextError, which a runner does not
+retry: running the step again on the same context fails the same way."""
+
+import ast
+import re
+from pathlib import Path
+
+import pytest
+
+import agent_env.task_step.task_steps as task_steps
+
+_CONTEXT_FAILURE = re.compile(
+    r"not found in context\.deployed_(envs|agents|sandboxes)|' is already deployed"
+    r"|^PromptResponse with prompt_id=.* not found in context|^No artifact recorded by step"
+)
+
+
+def _message_text(node: ast.expr) -> str:
+    """The literal text of a message, with each formatted value as ``{}``."""
+    if isinstance(node, ast.Constant) and isinstance(node.value, str):
+        return node.value
+    if isinstance(node, ast.JoinedStr):
+        return "".join(_message_text(part) if isinstance(part, ast.Constant) else "{}" for part in node.values)
+    return ""
+
+
+def _plain_context_raises(source: str) -> list[int]:
+    """The lines of ``source`` raising a context failure as a plain RuntimeError."""
+    return [
+        node.lineno
+        for node in ast.walk(ast.parse(source))
+        if isinstance(node, ast.Raise)
+        and isinstance(node.exc, ast.Call)
+        and isinstance(node.exc.func, ast.Name)
+        and node.exc.func.id == "RuntimeError"
+        and node.exc.args
+        and _CONTEXT_FAILURE.search(_message_text(node.exc.args[0]))
+    ]
+
+
+@pytest.mark.parametrize(
+    "source",
+    [
+        """raise RuntimeError(f"Env '{env_id}' not found in context.deployed_envs")""",
+        """raise RuntimeError(f'Agent {name!r} not found in context.deployed_agents')""",
+        """raise RuntimeError(\n    f"Sandbox '{name}' not found "\n    "in context.deployed_sandboxes"\n)""",
+        """raise RuntimeError("No artifact recorded by step 'collect'")""",
+    ],
+    ids=["double-quoted", "single-quoted", "split", "plain-string"],
+)
+def test_the_guard_sees_a_context_failure_however_it_is_written(source):
+    assert _plain_context_raises(source) == [1]
+
+
+def test_no_step_raises_a_context_failure_as_a_plain_runtime_error():
+    root = Path(task_steps.__file__).parent
+    found = [
+        f"{path.relative_to(root)}:{line}"
+        for path in sorted(root.rglob("*.py"))
+        for line in _plain_context_raises(path.read_text())
+    ]
+    assert found == [], "raise StepContextError (agent_env.task_step.context) for these instead"