diff --git a/backend/druks/api/artifacts.py b/backend/druks/api/artifacts.py
index 79b33d38..8924da9f 100644
--- a/backend/druks/api/artifacts.py
+++ b/backend/druks/api/artifacts.py
@@ -2,6 +2,7 @@
 
 from druks.api.schemas import ArtifactContent
 from druks.database import db_session
+from druks.durable.exceptions import AgentCallNotFound
 from druks.durable.models import AgentCall, Artifact
 
 router = APIRouter(prefix="/api/artifacts", tags=["artifacts"])
@@ -14,8 +15,11 @@ async def get_artifact(artifact_id: str) -> ArtifactContent:
     artifact = db_session().get(Artifact, artifact_id)
     if not artifact:
         raise HTTPException(status.HTTP_404_NOT_FOUND, "artifact not found")
-    call = AgentCall.get(artifact.agent_call_id)
-    path = call.get_file_path(artifact.path) if call else None
+    try:
+        call = AgentCall.get(artifact.agent_call_id)
+    except AgentCallNotFound as error:
+        raise HTTPException(status.HTTP_404_NOT_FOUND, "artifact content missing") from error
+    path = call.get_file_path(artifact.path)
     if not path:
         raise HTTPException(status.HTTP_404_NOT_FOUND, "artifact content missing")
     return ArtifactContent(kind=artifact.kind, title=artifact.title, content=path.read_text())
diff --git a/backend/druks/durable/exceptions.py b/backend/druks/durable/exceptions.py
index 083b3eca..ba107202 100644
--- a/backend/druks/durable/exceptions.py
+++ b/backend/druks/durable/exceptions.py
@@ -15,6 +15,11 @@ class WorkflowError(Exception):
     pass
 
 
+class AgentCallNotFound(Exception):
+    def __init__(self, agent_call_id: str) -> None:
+        super().__init__(f"No agent call {agent_call_id}.")
+
+
 class GateTimeout(FatalError):
     code = "gate_timeout"
 
diff --git a/backend/druks/durable/models.py b/backend/druks/durable/models.py
index b0743af1..7b5e54b2 100644
--- a/backend/druks/durable/models.py
+++ b/backend/druks/durable/models.py
@@ -28,6 +28,7 @@
     RunState,
     WorkflowEvent,
 )
+from druks.durable.exceptions import AgentCallNotFound
 from druks.harnesses.artifacts import normalize_token_usage
 from druks.models import Base
 from druks.notifications.models import Notification
@@ -490,8 +491,11 @@ def fail(cls, engine, *, call_id: str, error: BaseException) -> None:
             session.commit()
 
     @classmethod
-    def get(cls, agent_call_id: str) -> "AgentCall | None":
-        return db_session().get(cls, agent_call_id)
+    def get(cls, agent_call_id: str) -> "AgentCall":
+        call = db_session().get(cls, agent_call_id)
+        if not call:
+            raise AgentCallNotFound(agent_call_id)
+        return call
 
     @classmethod
     def list_for_run(cls, run_id: str) -> list["AgentCall"]:
diff --git a/backend/druks/durable/reads.py b/backend/druks/durable/reads.py
index ce560fde..f4b14e5f 100644
--- a/backend/druks/durable/reads.py
+++ b/backend/druks/durable/reads.py
@@ -12,6 +12,7 @@
 from druks.durable.live import keepalive_comment, serialize_model_event
 
 from .enums import RunState
+from .exceptions import AgentCallNotFound
 from .models import AgentCall, Artifact, Run
 from .schemas import (
     AgentCallFiles,
@@ -34,8 +35,9 @@
 
 
 def get_agent_call_files(call_id: str) -> AgentCallFiles | None:
-    call = AgentCall.get(call_id)
-    if not call:
+    try:
+        call = AgentCall.get(call_id)
+    except AgentCallNotFound:
         return
     return AgentCallFiles.from_call(call, Artifact.get_for_call(call.id))
 
@@ -196,14 +198,14 @@ async def stream_transcript(
     last_keepalive = 0.0
     while True:
         with session_scope(engine):
-            call = AgentCall.get(call_id)
-            path = call.get_stream_path(stream) if call else None
-            summary = AgentCallResponse.model_validate(call) if call else None
-
-        if not summary:
-            # Unknown (or deleted) call: nothing will ever arrive — close the
-            # stream instead of keepaliving forever.
-            return
+            try:
+                call = AgentCall.get(call_id)
+            except AgentCallNotFound:
+                # Unknown (or deleted) call: nothing will ever arrive — close the
+                # stream instead of keepaliving forever.
+                return
+            path = call.get_stream_path(stream)
+            summary = AgentCallResponse.model_validate(call)
 
         if path and path.exists():
             size = path.stat().st_size
diff --git a/backend/druks/extensions/base.py b/backend/druks/extensions/base.py
index 15442dd4..1f5ffe0b 100644
--- a/backend/druks/extensions/base.py
+++ b/backend/druks/extensions/base.py
@@ -332,6 +332,7 @@ def _get_transcript_routes(cls) -> "APIRouter":
         from druks.api.dependencies import EngineDep
         from druks.durable import reads
         from druks.durable.enums import AgentCallStatus
+        from druks.durable.exceptions import AgentCallNotFound
         from druks.durable.live import SSE_HEADERS
         from druks.durable.models import AgentCall
         from druks.durable.schemas import AgentCallFiles, TranscriptChunk
@@ -358,9 +359,10 @@ async def get_transcript(
                 raise HTTPException(
                     status.HTTP_400_BAD_REQUEST, f"limit must be in 1..{max_limit}."
                 )
-            call = AgentCall.get(call_id)
-            if not call:
-                raise HTTPException(status.HTTP_404_NOT_FOUND, "Run not found.")
+            try:
+                call = AgentCall.get(call_id)
+            except AgentCallNotFound as error:
+                raise HTTPException(status.HTTP_404_NOT_FOUND, "Run not found.") from error
             if call.live_status == AgentCallStatus.RUNNING:
                 response.headers["Cache-Control"] = "no-store"
             else:
@@ -393,9 +395,10 @@ async def get_file(
             file_name: str,
             disposition: Literal["inline", "attachment"] = "inline",
         ) -> FileResponse:
-            call = AgentCall.get(call_id)
-            if not call:
-                raise HTTPException(status.HTTP_404_NOT_FOUND, "Agent call not found.")
+            try:
+                call = AgentCall.get(call_id)
+            except AgentCallNotFound as error:
+                raise HTTPException(status.HTTP_404_NOT_FOUND, "Agent call not found.") from error
             resolved = call.get_file_path(file_name)
             if not resolved:
                 raise HTTPException(status.HTTP_404_NOT_FOUND, "File not found for this call.")
diff --git a/backend/druks/mcp/gateway/routes.py b/backend/druks/mcp/gateway/routes.py
index 53036906..c3e0bdca 100644
--- a/backend/druks/mcp/gateway/routes.py
+++ b/backend/druks/mcp/gateway/routes.py
@@ -2,7 +2,8 @@
 
 from druks.accounts.dependencies import current_account
 from druks.accounts.models import Account
-from druks.mcp.gateway import schemas, services
+from druks.durable import exceptions as durable_exceptions
+from druks.mcp.gateway import exceptions, schemas, services
 
 # Docstrings here are the derived tool descriptions and operation_id is the
 # tool name — renaming one is a break, never a refactor side effect.
@@ -49,7 +50,10 @@ async def answer_gate(run_id: str, body: schemas.AnswerGateRequest) -> schemas.G
 async def get_agent_call(call_id: str) -> schemas.AgentCallDetailResponse:
     """One agent call's metadata with bounded transcript and stderr tails and
     an artifact chunk."""
-    return services.get_agent_call(call_id)
+    try:
+        return services.get_agent_call(call_id)
+    except durable_exceptions.AgentCallNotFound as error:
+        raise exceptions.AgentCallNotFound(call_id) from error
 
 
 @router.get(
diff --git a/backend/druks/mcp/gateway/services.py b/backend/druks/mcp/gateway/services.py
index 67608850..e6da8898 100644
--- a/backend/druks/mcp/gateway/services.py
+++ b/backend/druks/mcp/gateway/services.py
@@ -4,6 +4,7 @@
 from druks.api.exceptions import RunNotFound
 from druks.core.utils.time import operator_local_day
 from druks.database import db_session
+from druks.durable import exceptions as durable_exceptions
 from druks.durable.enums import RunState
 from druks.durable.models import AgentCall, Artifact, Run
 from druks.durable.reads import read_slice
@@ -72,8 +73,6 @@ async def answer_gate(
 
 def get_agent_call(call_id: str) -> schemas.AgentCallDetailResponse:
     call = AgentCall.get(call_id)
-    if not call:
-        raise exceptions.AgentCallNotFound(call_id)
     layout = call.artifact_layout
     return schemas.AgentCallDetailResponse(
         run_id=call.run_id,
@@ -89,8 +88,11 @@ def get_agent_call(call_id: str) -> schemas.AgentCallDetailResponse:
 def _artifact_content(artifact: Artifact | None) -> schemas.ArtifactContent | None:
     if not artifact:
         return
-    call = AgentCall.get(artifact.agent_call_id)
-    path = call.get_file_path(artifact.path) if call else None
+    try:
+        call = AgentCall.get(artifact.agent_call_id)
+    except durable_exceptions.AgentCallNotFound:
+        return
+    path = call.get_file_path(artifact.path)
     if not path:
         return
     return schemas.ArtifactContent(
diff --git a/backend/tests/test_agent_routes.py b/backend/tests/test_agent_routes.py
index fab8849f..4dd54437 100644
--- a/backend/tests/test_agent_routes.py
+++ b/backend/tests/test_agent_routes.py
@@ -113,6 +113,17 @@ def test_agent_errors_share_one_shape(client: TestClient, druks_db):
     assert body["retryable"] is True
 
 
+def test_missing_agent_call_returns_wire_error(client: TestClient):
+    response = client.get("/api/agent-calls/no-such-call")
+
+    assert response.status_code == 404
+    assert response.json() == {
+        "code": "AGENT_CALL_NOT_FOUND",
+        "message": "No agent call no-such-call.",
+        "retryable": False,
+    }
+
+
 def test_get_gate_then_answer_roundtrip(client: TestClient, druks_db, resume_spy):
     note = Note.create(body="answer gate")
     run = _park(druks_db, note)
diff --git a/backend/tests/test_agent_services.py b/backend/tests/test_agent_services.py
index ba70d2f3..9d3d1fc3 100644
--- a/backend/tests/test_agent_services.py
+++ b/backend/tests/test_agent_services.py
@@ -8,9 +8,10 @@
 from druks.accounts.models import Account
 from druks.api import runs
 from druks.api.exceptions import RunNotActive, RunNotFailed, RunNotFound, SubjectBusy
+from druks.durable import exceptions as durable_exceptions
 from druks.durable.engine import run_queue
 from druks.durable.enums import WorkflowEvent
-from druks.durable.models import Artifact, Run
+from druks.durable.models import AgentCall, Artifact, Run
 from druks.durable.reads import read_slice
 from druks.mcp.gateway import exceptions, services
 from druks.testing import seed_call, seed_dbos_status
@@ -203,6 +204,12 @@ async def test_answer_gate_error_taxonomy(druks_db, resume_spy):
 # ---- agent calls ----------------------------------------------------------
 
 
+def test_agent_call_get_raises_for_missing_call(druks_db):
+    with pytest.raises(durable_exceptions.AgentCallNotFound) as error:
+        AgentCall.get("no-such-call")
+    assert str(error.value) == "No agent call no-such-call."
+
+
 def test_get_agent_call_serves_bounded_tails(druks_db):
     from conftest import finish_agent_run, seed_note_agent_run
 
@@ -226,7 +233,7 @@ def test_get_agent_call_serves_bounded_tails(druks_db):
     assert detail.artifact is not None
     assert detail.artifact.content == "a" * 4096
 
-    with pytest.raises(exceptions.AgentCallNotFound):
+    with pytest.raises(durable_exceptions.AgentCallNotFound):
         services.get_agent_call("no-such-call")
 
 
diff --git a/backend/tests/test_api_runs.py b/backend/tests/test_api_runs.py
index 64efd02f..ca3a86e6 100644
--- a/backend/tests/test_api_runs.py
+++ b/backend/tests/test_api_runs.py
@@ -147,6 +147,16 @@ def test_transcript_missing_file_returns_eof(
     assert data["text"] == ""
 
 
+def test_transcript_range_missing_call_returns_404(client: TestClient):
+    response = client.get(
+        "/api/field_notes/transcripts/no-such-call",
+        params={"stream": "stdout"},
+    )
+
+    assert response.status_code == 404
+    assert response.json() == {"error": "HTTP_404", "detail": "Run not found."}
+
+
 def test_transcript_stream_emits_chunk_then_finishes(
     client: TestClient,
     tmp_path: Path,
@@ -199,6 +209,20 @@ def test_get_file_serves_inventory_paths(
     assert response.json() == {"ok": True}
 
 
+def test_file_inventory_missing_call_returns_404(client: TestClient):
+    response = client.get("/api/field_notes/transcripts/no-such-call/files")
+
+    assert response.status_code == 404
+    assert response.json() == {"error": "HTTP_404", "detail": "Agent call not found."}
+
+
+def test_file_download_missing_call_returns_404(client: TestClient):
+    response = client.get("/api/field_notes/transcripts/no-such-call/files/output.json")
+
+    assert response.status_code == 404
+    assert response.json() == {"error": "HTTP_404", "detail": "Agent call not found."}
+
+
 def test_get_file_rejects_path_traversal(
     client: TestClient,
     tmp_path: Path,