fix: retain safe Workdir open authorization and response failure causes

Keep bounded reasons and derived failure stages separate from public classification. Reject provider-authored raw error text on transport decoding. Preserve identity mismatch when cleanup fails and retain its handle for explicit close without opening again. Add signed Runtime HTTP, Registry/API logging, remote mismatch, authorization no-dispatch and deferred fault coverage. Focused tests and Workdir suite pass; full-source validation follows T773 audit contract merge.

crates/workdir/src/http.rs

@@ -375,12 +375,14 @@ impl WorkdirTransportError {
         use WorkdirTransportErrorCode as Code;
         let error = match self.code {
             Code::NotFound => WorkdirError::NotFound("<remote>".into()),
-            Code::Conflict => WorkdirError::Conflict(self.message),
+            Code::Conflict => WorkdirError::Conflict(
+                "The target file's content or existence changed since it was last observed; read the file again before retrying".into(),
+            ),
             Code::OutcomeUnknown => WorkdirError::OutcomeUnknown(
                 "Workdir operation may have effects; inspect before retrying".into(),
             ),
-            Code::Unsupported => WorkdirError::UnsupportedOperation(self.message),
-            Code::InvalidRequest => WorkdirError::InvalidArgument(self.message),
+            Code::Unsupported => WorkdirError::UnsupportedOperation("Workdir operation is not supported".into()),
+            Code::InvalidRequest => WorkdirError::InvalidArgument("Workdir operation request is invalid".into()),
             Code::Denied => WorkdirError::Denied(crate::WorkdirDenial {
                 reason: self.denial_reason,
                 // Provider-authored text is not trusted diagnostic data.
@@ -409,12 +411,12 @@ impl WorkdirTransportError {
                 target: "<remote-target>".into(),
             },
             Code::UnknownCommand => WorkdirError::UnknownCommand("<remote>".to_string()),
-            Code::Unavailable => WorkdirError::Unavailable(self.message),
+            Code::Unavailable => WorkdirError::Unavailable("Workdir session is unavailable".into()),
             Code::Io => WorkdirError::Io {
                 path: "<remote>".into(),
-                source: std::io::Error::other(self.message),
+                source: std::io::Error::other("Workdir I/O operation failed"),
             },
-            Code::Transport => WorkdirError::Transport(self.message),
+            Code::Transport => WorkdirError::Transport("Workdir transport failed".into()),
             Code::Internal => WorkdirError::OperationFailed,
         };
         let error = if let Some(reason) = self.failure_reason {
@@ -549,7 +551,8 @@ mod client {
             if opened.workdir_id.as_str() != workdir_id.as_str() {
                 return Err(WorkdirError::Unavailable(
                     "Runtime opened a session for a different Workdir".to_string(),
-                ));
+                )
+                .with_failure_reason(crate::WorkdirFailureReason::SessionIdentityMismatch));
             }
             Ok(Self {
                 client,
@@ -608,6 +611,7 @@ mod client {
             WorkdirError::Unavailable(format!(
                 "Runtime returned a mismatched Workdir operation result; expected {expected}"
             ))
+            .with_failure_reason(crate::WorkdirFailureReason::OperationResultMismatch)
         }
     }
 
@@ -770,7 +774,8 @@ mod client {
                 }
                 Ok(_) if mutation => Err(WorkdirError::OutcomeUnknown(
                     "mismatched response after checkout mutation".into(),
-                )),
+                )
+                .with_failure_reason(crate::WorkdirFailureReason::OperationResultMismatch)),
                 Ok(_) => Err(Self::mismatch("checkout_execute")),
                 Err(error)
                     if mutation

crates/workdir/src/lib.rs

@@ -414,6 +414,24 @@ pub enum WorkdirFailureReason {
     HttpTransfer,
     HttpResponseInvalid,
     HttpResponseTooLarge,
+    OperationResultMismatch,
+    SessionIdentityMismatch,
+    SessionOpenTaskFailed,
+    SessionOpenFailed,
+    AuthorizationMissing,
+    AuthorizationStale,
+    AuthorizationUnavailable,
+    SigningIdentityUnavailable,
+    AuthorizationSignFailed,
+    RuntimeStopped,
+    RuntimeStateUnavailable,
+    RuntimeBackendUnavailable,
+    RuntimeOwnerMismatch,
+    RuntimeInvalidRequest,
+    WorkingDirectoryNotFound,
+    WorkingDirectoryNotActive,
+    WorkingDirectoryRecordInvalid,
+    WorkingDirectoryAccessUnavailable,
 }
 
 impl WorkdirFailureReason {
@@ -427,6 +445,83 @@ impl WorkdirFailureReason {
             Self::HttpTransfer => "http_transfer",
             Self::HttpResponseInvalid => "http_response_invalid",
             Self::HttpResponseTooLarge => "http_response_too_large",
+            Self::OperationResultMismatch => "operation_result_mismatch",
+            Self::SessionIdentityMismatch => "session_identity_mismatch",
+            Self::SessionOpenTaskFailed => "session_open_task_failed",
+            Self::SessionOpenFailed => "session_open_failed",
+            Self::AuthorizationMissing => "authorization_missing",
+            Self::AuthorizationStale => "authorization_stale",
+            Self::AuthorizationUnavailable => "authorization_unavailable",
+            Self::SigningIdentityUnavailable => "signing_identity_unavailable",
+            Self::AuthorizationSignFailed => "authorization_sign_failed",
+            Self::RuntimeStopped => "runtime_stopped",
+            Self::RuntimeStateUnavailable => "runtime_state_unavailable",
+            Self::RuntimeBackendUnavailable => "runtime_backend_unavailable",
+            Self::RuntimeOwnerMismatch => "runtime_owner_mismatch",
+            Self::RuntimeInvalidRequest => "runtime_invalid_request",
+            Self::WorkingDirectoryNotFound => "working_directory_not_found",
+            Self::WorkingDirectoryNotActive => "working_directory_not_active",
+            Self::WorkingDirectoryRecordInvalid => "working_directory_record_invalid",
+            Self::WorkingDirectoryAccessUnavailable => "working_directory_access_unavailable",
+        }
+    }
+
+    /// The observed failing boundary, not a dispatch or effects assertion.
+    pub const fn stage(self) -> WorkdirFailureStage {
+        use WorkdirFailureStage as Stage;
+        match self {
+            Self::SessionClosed => Stage::Session,
+            Self::ProviderUnavailable => Stage::Provider,
+            Self::CommandTerminalMissing => Stage::Command,
+            Self::HttpTimeout | Self::HttpConnect | Self::HttpTransfer => Stage::Http,
+            Self::HttpResponseInvalid
+            | Self::HttpResponseTooLarge
+            | Self::OperationResultMismatch => Stage::ResponseValidation,
+            Self::SessionIdentityMismatch
+            | Self::SessionOpenTaskFailed
+            | Self::SessionOpenFailed
+            | Self::WorkingDirectoryNotFound
+            | Self::WorkingDirectoryNotActive
+            | Self::WorkingDirectoryRecordInvalid
+            | Self::WorkingDirectoryAccessUnavailable => Stage::SessionOpen,
+            Self::AuthorizationMissing
+            | Self::AuthorizationStale
+            | Self::AuthorizationUnavailable
+            | Self::SigningIdentityUnavailable
+            | Self::AuthorizationSignFailed => Stage::AuthorizationPreparation,
+            Self::RuntimeStopped
+            | Self::RuntimeStateUnavailable
+            | Self::RuntimeBackendUnavailable
+            | Self::RuntimeOwnerMismatch
+            | Self::RuntimeInvalidRequest => Stage::Runtime,
+        }
+    }
+}
+
+/// Internal operational boundary derived only from a bounded reason.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum WorkdirFailureStage {
+    Session,
+    Provider,
+    Command,
+    Http,
+    ResponseValidation,
+    SessionOpen,
+    AuthorizationPreparation,
+    Runtime,
+}
+
+impl WorkdirFailureStage {
+    pub const fn as_str(self) -> &'static str {
+        match self {
+            Self::Session => "session",
+            Self::Provider => "provider",
+            Self::Command => "command",
+            Self::Http => "http",
+            Self::ResponseValidation => "response_validation",
+            Self::SessionOpen => "session_open",
+            Self::AuthorizationPreparation => "authorization_preparation",
+            Self::Runtime => "runtime",
         }
     }
 }

crates/workdir/tests/failure_diagnostics.rs

@@ -83,3 +83,34 @@ fn provider_cannot_inject_free_text_failure_reason() {
         .is_err()
     );
 }
+
+#[test]
+fn provider_authored_operational_messages_never_enter_error_display_or_debug() {
+    for code in [
+        Code::Conflict,
+        Code::OutcomeUnknown,
+        Code::Unsupported,
+        Code::InvalidRequest,
+        Code::Unavailable,
+        Code::Io,
+        Code::Transport,
+        Code::Internal,
+    ] {
+        let wire = serde_json::json!({
+            "code": code, "message":"/host/private command-secret body-secret proof-secret key-secret Authorization: Bearer bearer-secret",
+            "failure_reason": "session_open_task_failed"
+        });
+        let decoded: WorkdirTransportError = serde_json::from_value(wire).unwrap();
+        let error = decoded.into_workdir_error();
+        for text in [
+            format!("{error}"),
+            format!("{error:?}"),
+            serde_json::to_string(&WorkdirTransportError::from_workdir_error(&error)).unwrap(),
+        ] {
+            assert!(!text.contains("secret"), "{text}");
+            assert!(!text.contains("/host/private"), "{text}");
+        }
+        assert_eq!(error.failure_reason(), Some(Reason::SessionOpenTaskFailed));
+        assert_eq!(WorkdirTransportError::from_workdir_error(&error).code, code);
+    }
+}

crates/workdir/tests/remote_denial_reasons.rs

@@ -216,3 +216,106 @@ async fn remote_checkout_diagnostics_preserve_mutation_outcome_and_read_failures
         }
     }
 }
+
+#[tokio::test]
+async fn mismatched_http_results_keep_cause_and_mutation_uncertainty() {
+    use workdir::{
+        CheckoutOperation, CheckoutRequest, CommandHandle, CommandOutputRequest,
+        WorkdirFailureReason as Failure,
+    };
+    for case in ["variant", "bytes", "mutation", "identity"] {
+        let listener = TcpListener::bind("127.0.0.1:0").unwrap();
+        let address = listener.local_addr().unwrap();
+        let server = thread::spawn(move || {
+            reply(
+                &listener,
+                "200 OK",
+                if case == "identity" {
+                    r#"{"session_id":"s","workdir_id":"wrong-secret","capabilities":{"bits":63}}"#
+                } else {
+                    r#"{"session_id":"s","workdir_id":"w","capabilities":{"bits":63}}"#
+                },
+            );
+            if case != "identity" {
+                let result = if case == "bytes" {
+                    serde_json::json!({"operation":"command_output","result":{
+                        "chunks": [], "next_cursor": 123, "terminal": null
+                    }})
+                } else {
+                    serde_json::to_value(
+                        workdir::http::WorkdirSessionOperationResult::CommandCancel,
+                    )
+                    .unwrap()
+                };
+                reply(&listener, "200 OK", &result.to_string());
+            }
+        });
+        let opened = RemoteWorkdirSession::open(
+            reqwest::Client::builder()
+                .no_proxy()
+                .timeout(Duration::from_secs(5))
+                .build()
+                .unwrap(),
+            format!("http://{address}").parse().unwrap(),
+            "request-secret",
+            Workdir::new("w").id().clone(),
+            OpenWorkdirSessionRequest::default(),
+        )
+        .await;
+        let error = if case == "identity" {
+            opened.unwrap_err()
+        } else {
+            let remote = opened.unwrap();
+            match case {
+                "variant" => remote
+                    .stat(StatRequest {
+                        path: WorkdirPath::new("file-secret").unwrap(),
+                    })
+                    .await
+                    .unwrap_err(),
+                "bytes" => remote
+                    .command_output(CommandOutputRequest {
+                        handle: CommandHandle("command-secret".into()),
+                        cursor: 0,
+                        limit: 16,
+                        wait: false,
+                    })
+                    .await
+                    .unwrap_err(),
+                "mutation" => remote
+                    .checkout_execute(CheckoutRequest {
+                        target: WorkdirPath::new("file-secret").unwrap(),
+                        validator: vec![1],
+                        operation: CheckoutOperation::Write {
+                            content: b"body-secret".to_vec(),
+                            expected_hash: [0; 32],
+                        },
+                    })
+                    .await
+                    .unwrap_err(),
+                _ => unreachable!(),
+            }
+        };
+        server.join().unwrap();
+        let expected = if case == "identity" {
+            Failure::SessionIdentityMismatch
+        } else {
+            Failure::OperationResultMismatch
+        };
+        assert_eq!(error.failure_reason(), Some(expected), "{case}: {error:?}");
+        let transport = WorkdirTransportError::from_workdir_error(&error);
+        assert_eq!(
+            transport.code,
+            if case == "mutation" {
+                Code::OutcomeUnknown
+            } else {
+                Code::Unavailable
+            }
+        );
+        let wire = serde_json::to_string(&transport).unwrap();
+        assert!(!wire.contains("secret"), "{wire}");
+        assert!(!format!("{error:?}").contains("secret"));
+        let forwarded = transport.into_workdir_error();
+        assert_eq!(forwarded.failure_reason(), Some(expected));
+    }
+}

crates/worker-runtime/src/http_server.rs

@@ -2187,7 +2187,25 @@ impl RuntimeHttpWorkdirError {
     }
 
     fn runtime(error: RuntimeError) -> Self {
-        match error {
+        use workdir::WorkdirFailureReason as Reason;
+        let reason = match &error {
+            RuntimeError::WorkingDirectory(diagnostic) => match diagnostic.code.as_str() {
+                "working_directory_not_found" => Reason::WorkingDirectoryNotFound,
+                "working_directory_not_active" => Reason::WorkingDirectoryNotActive,
+                "working_directory_record_invalid" => Reason::WorkingDirectoryRecordInvalid,
+                "working_directory_repository_access_unavailable" => {
+                    Reason::WorkingDirectoryAccessUnavailable
+                }
+                _ => Reason::SessionOpenFailed,
+            },
+            RuntimeError::RuntimeStopped => Reason::RuntimeStopped,
+            RuntimeError::StatePoisoned => Reason::RuntimeStateUnavailable,
+            RuntimeError::ExecutionBackendUnavailable { .. } => Reason::RuntimeBackendUnavailable,
+            RuntimeError::WorkspaceOwnerMismatch { .. } => Reason::RuntimeOwnerMismatch,
+            RuntimeError::InvalidRequest(_) => Reason::RuntimeInvalidRequest,
+            _ => Reason::SessionOpenFailed,
+        };
+        let mut response = match error {
             RuntimeError::WorkingDirectory(diagnostic)
                 if diagnostic.code == "working_directory_not_found" =>
             {
@@ -2200,7 +2218,9 @@ impl RuntimeHttpWorkdirError {
                 WorkdirTransportErrorCode::Unavailable,
                 "Workdir session is unavailable",
             ),
-        }
+        };
+        response.payload.failure_reason = Some(reason);
+        response
     }
 }
 
@@ -2222,6 +2242,7 @@ impl IntoResponse for RuntimeHttpWorkdirError {
                 status = self.status.as_u16(),
                 code = self.payload.code.as_str(),
                 failure_reason = reason.as_str(),
+                failure_stage = reason.stage().as_str(),
                 "Workdir provider operation failed"
             );
         }
@@ -2434,6 +2455,7 @@ pub enum RuntimeHttpServerError {
 #[cfg(test)]
 mod tests {
     mod command_transport_tests;
+    mod runtime_workdir_failure_tests;
     #[cfg(feature = "fs-store")]
     mod session_material_tests;
 

crates/worker-runtime/src/http_server/tests/runtime_workdir_failure_tests.rs

@@ -0,0 +1,528 @@
+//! Session-open integration through the production signed router, Runtime owner/binding
+//! checks, HTTP DTO and tracing boundary. Only the execution backend is replaced
+//! for deterministic lookup/open faults and inert owner-binding Worker fixtures;
+//! no handler, middleware or grant is replaced. Runs in the normal http-server lib
+//! suite with isolated loopback sockets.
+
+use super::*;
+use crate::working_directory::WorkingDirectoryDiagnostic;
+use std::io::{self, Write};
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::time::Duration;
+
+const OPEN_PATH: &str = "/v1/working-directories/private-workdir-marker/sessions";
+const PRIVATE_DIAGNOSTIC: &str = concat!(
+    "raw-runtime-error-marker /private/host-path-marker ",
+    "command=private-command-marker contents=private-file-marker ",
+    "proof=private-proof-marker Authorization: Bearer private-header-marker ",
+    "working_directory_not_found authorization_stale runtime_stopped",
+);
+const PRIVATE_MARKERS: &[&str] = &[
+    "raw-runtime-error-marker",
+    "/private/host-path-marker",
+    "private-command-marker",
+    "private-file-marker",
+    "private-proof-marker",
+    "private-header-marker",
+    "private-workdir-marker",
+    "private-owner-marker",
+];
+
+#[derive(Clone, Default)]
+struct LogCapture(Arc<Mutex<Vec<u8>>>);
+
+impl Write for LogCapture {
+    fn write(&mut self, bytes: &[u8]) -> io::Result<usize> {
+        self.0.lock().unwrap().extend_from_slice(bytes);
+        Ok(bytes.len())
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        Ok(())
+    }
+}
+
+impl LogCapture {
+    fn subscriber(&self) -> impl tracing::Subscriber + Send + Sync + 'static {
+        let writer = self.clone();
+        tracing_subscriber::fmt()
+            .with_ansi(false)
+            .without_time()
+            .with_max_level(tracing::Level::WARN)
+            .with_writer(move || writer.clone())
+            .finish()
+    }
+
+    fn take(&self) -> String {
+        String::from_utf8(std::mem::take(&mut *self.0.lock().unwrap())).unwrap()
+    }
+}
+
+fn assert_private_absent(text: &str) {
+    for marker in PRIVATE_MARKERS {
+        assert!(
+            !text.contains(marker),
+            "private input escaped error boundary"
+        );
+    }
+}
+
+fn assert_failure_log(log: &str, status: StatusCode, code: &str, reason: &str, stage: &str) {
+    let events: Vec<_> = log
+        .lines()
+        .filter(|line| line.contains("workdir_provider_failure"))
+        .collect();
+    assert_eq!(events.len(), 1, "one diagnostic per failed request: {log}");
+    let event = events[0];
+    for field in [
+        "WARN".to_string(),
+        "worker_runtime::workdir".to_string(),
+        format!("status={}", status.as_u16()),
+        format!("code=\"{code}\""),
+        format!("failure_reason=\"{reason}\""),
+        format!("failure_stage=\"{stage}\""),
+    ] {
+        assert!(event.contains(&field), "missing {field}: {event}");
+    }
+    assert_private_absent(log);
+}
+
+fn assert_failure_body(body: &str, code: &str, message: &str, reason: &str) {
+    assert_private_absent(body);
+    // Exact safe transport vocabulary; raw diagnostics and stage are not wire fields.
+    assert_eq!(
+        serde_json::from_str::<serde_json::Value>(body).unwrap(),
+        serde_json::json!({"code": code, "message": message, "failure_reason": reason}),
+    );
+}
+
+struct Harness {
+    server: tokio::task::JoinHandle<()>,
+    client: reqwest::Client,
+    base: String,
+    identity: RuntimeIdentityMaterial,
+    trust: WorkspaceIssuerTrustRecord,
+}
+
+impl Drop for Harness {
+    fn drop(&mut self) {
+        self.server.abort();
+    }
+}
+
+impl Harness {
+    async fn new(runtime: Runtime) -> Self {
+        let identity = RuntimeIdentityMaterial::generate("runtime-failure-test-key").unwrap();
+        let trust = workspace_trust(&identity);
+        let app = runtime_http_router_with_workspace_auth(
+            runtime,
+            None,
+            workspace_test_auth(vec![trust.clone()]),
+        );
+        let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
+        let base = format!("http://{}", listener.local_addr().unwrap());
+        let server = tokio::spawn(async move {
+            axum::serve(listener, app).await.unwrap();
+        });
+        Self {
+            server,
+            client: reqwest::Client::builder()
+                .no_proxy()
+                .timeout(Duration::from_secs(5))
+                .build()
+                .unwrap(),
+            base,
+            identity,
+            trust,
+        }
+    }
+
+    async fn send(
+        &self,
+        claims: &WorkspaceCapabilityClaims,
+        body: Vec<u8>,
+        workspace: &str,
+    ) -> (StatusCode, String, String) {
+        let token = issue_workspace_capability_token(&self.identity.signing_key().unwrap(), claims)
+            .unwrap();
+        let response = self
+            .client
+            .post(format!("{}{OPEN_PATH}", self.base))
+            .bearer_auth(&token)
+            .header(header::CONTENT_TYPE, "application/json")
+            .header(RUNTIME_WORKSPACE_SCOPE_HEADER, workspace)
+            .header("x-private-test-header", "private-header-marker")
+            .body(body)
+            .send()
+            .await
+            .unwrap();
+        let status = StatusCode::from_u16(response.status().as_u16()).unwrap();
+        let headers = format!("{:?}", response.headers());
+        let body = response.text().await.unwrap();
+        assert_private_absent(&headers);
+        for output in [&body, &headers] {
+            assert!(!output.contains(&token), "signed bearer token leaked");
+            assert!(
+                !output.contains(&self.identity.private_key),
+                "signing key leaked"
+            );
+        }
+        (status, body, token)
+    }
+
+    async fn open(&self) -> (StatusCode, String, String) {
+        let body = serde_json::to_vec(&OpenWorkdirSessionRequest::default()).unwrap();
+        let claims = signed_claims(&self.trust, "POST", OPEN_PATH, &body);
+        self.send(&claims, body, "workspace-a").await
+    }
+}
+
+#[derive(Clone, Copy)]
+enum FailureAt {
+    Lookup,
+    Open,
+}
+
+struct FailingBackend {
+    at: FailureAt,
+    code: &'static str,
+    lookups: AtomicUsize,
+    opens: AtomicUsize,
+}
+
+impl FailingBackend {
+    fn runtime(at: FailureAt, code: &'static str) -> (Runtime, Arc<Self>) {
+        let backend = Arc::new(Self {
+            at,
+            code,
+            lookups: AtomicUsize::new(0),
+            opens: AtomicUsize::new(0),
+        });
+        let runtime =
+            Runtime::with_execution_backend(RuntimeOptions::default(), backend.clone()).unwrap();
+        (runtime, backend)
+    }
+
+    fn failure(&self) -> WorkingDirectoryDiagnostic {
+        WorkingDirectoryDiagnostic::rejected(self.code, PRIVATE_DIAGNOSTIC)
+    }
+}
+
+impl WorkerExecutionBackend for FailingBackend {
+    fn backend_id(&self) -> &str {
+        "runtime-failure-test"
+    }
+
+    fn spawn_worker(&self, request: WorkerExecutionSpawnRequest) -> WorkerExecutionSpawnResult {
+        AcceptingBackend.spawn_worker(request)
+    }
+
+    fn dispatch_input(&self, worker: &WorkerRef, input: WorkerInput) -> WorkerExecutionResult {
+        AcceptingBackend.dispatch_input(worker, input)
+    }
+
+    fn stop_worker(&self, worker: &WorkerRef) -> WorkerExecutionResult {
+        AcceptingBackend.stop_worker(worker)
+    }
+
+    fn working_directory(
+        &self,
+        id: &str,
+    ) -> Result<WorkingDirectoryStatus, WorkingDirectoryDiagnostic> {
+        self.lookups.fetch_add(1, Ordering::SeqCst);
+        match self.at {
+            FailureAt::Lookup => Err(self.failure()),
+            FailureAt::Open => Ok(WorkingDirectoryStatus {
+                summary: crate::catalog::WorkingDirectorySummary {
+                    working_directory_id: id.into(),
+                    display_name: None,
+                    repository_id: "repository-test".into(),
+                    creation_selector: None,
+                    creation_ref: None,
+                    creation_tree: None,
+                    current_selector: None,
+                    current_ref: None,
+                    current_tree: None,
+                    observed_at_epoch_seconds: None,
+                    materializer_kind: crate::catalog::MaterializerKind::RuntimeGitClone,
+                    cleanup_target: None,
+                    status: crate::catalog::WorkingDirectoryStatusKind::Active,
+                    cleanliness: None,
+                    occupied_by: None,
+                },
+            }),
+        }
+    }
+
+    fn open_workdir_session(
+        &self,
+        _: &str,
+    ) -> Result<WorkdirSessionHandle, WorkingDirectoryDiagnostic> {
+        self.opens.fetch_add(1, Ordering::SeqCst);
+        Err(self.failure())
+    }
+}
+
+// Current-thread execution keeps the server tasks inside the thread-local tracing
+// capture across awaits, without replacing the process-global subscriber.
+#[tokio::test(flavor = "current_thread")]
+async fn signed_http_session_open_preserves_runtime_availability_and_owner_failures() {
+    let capture = LogCapture::default();
+    let _guard = tracing::subscriber::set_default(capture.subscriber());
+    tracing::callsite::rebuild_interest_cache();
+    tokio::time::timeout(Duration::from_secs(15), async {
+        let stopped = Runtime::new_memory();
+        stopped.stop_runtime().unwrap();
+        let (owned, backend) = FailingBackend::runtime(FailureAt::Lookup, "must_not_reach_backend");
+        let mut request = task_request("bind owner");
+        request.config_bundle = None;
+        request.memory_settings.as_mut().unwrap().workspace_id = "workspace-a".into();
+        owned
+            .create_worker_scoped(
+                &RuntimeWorkspaceScope::new("workspace-a", "private-owner-marker"),
+                request,
+            )
+            .unwrap();
+        for (runtime, status, code, message, reason) in [
+            (
+                stopped,
+                StatusCode::SERVICE_UNAVAILABLE,
+                "unavailable",
+                "Workdir session is unavailable",
+                "runtime_stopped",
+            ),
+            (
+                Runtime::new_memory(),
+                StatusCode::SERVICE_UNAVAILABLE,
+                "unavailable",
+                "Workdir session is unavailable",
+                "runtime_backend_unavailable",
+            ),
+            (
+                owned,
+                StatusCode::NOT_FOUND,
+                "not_found",
+                "Workdir session was not found",
+                "runtime_owner_mismatch",
+            ),
+        ] {
+            let harness = Harness::new(runtime).await;
+            capture.take();
+            let (actual, body, token) = harness.open().await;
+            assert_eq!(actual, status);
+            assert_failure_body(&body, code, message, reason);
+            let log = capture.take();
+            assert_failure_log(&log, status, code, reason, "runtime");
+            assert!(!log.contains(&token));
+            assert!(!log.contains(&harness.identity.private_key));
+        }
+        assert_eq!(backend.lookups.load(Ordering::SeqCst), 0);
+        assert_eq!(backend.opens.load(Ordering::SeqCst), 0);
+    })
+    .await
+    .expect("bounded Runtime failure HTTP requests");
+}
+
+#[tokio::test(flavor = "current_thread")]
+async fn signed_http_session_open_allowlists_diagnostic_codes_without_guessing_unknown_causes() {
+    let capture = LogCapture::default();
+    let _guard = tracing::subscriber::set_default(capture.subscriber());
+    tracing::callsite::rebuild_interest_cache();
+    tokio::time::timeout(Duration::from_secs(20), async {
+        for (diagnostic, reason) in [
+            ("working_directory_not_found", "working_directory_not_found"),
+            (
+                "working_directory_not_active",
+                "working_directory_not_active",
+            ),
+            (
+                "working_directory_record_invalid",
+                "working_directory_record_invalid",
+            ),
+            (
+                "working_directory_repository_access_unavailable",
+                "working_directory_access_unavailable",
+            ),
+            // Plausible provider text/code is not evidence of a typed cause.
+            ("authorization_stale", "session_open_failed"),
+            (
+                "working_directory_not_found_private-proof-marker",
+                "session_open_failed",
+            ),
+        ] {
+            for at in [FailureAt::Lookup, FailureAt::Open] {
+                let (runtime, backend) = FailingBackend::runtime(at, diagnostic);
+                let harness = Harness::new(runtime).await;
+                capture.take();
+                let (status, body, token) = harness.open().await;
+                let (expected, code, message) = if diagnostic == "working_directory_not_found" {
+                    (
+                        StatusCode::NOT_FOUND,
+                        "not_found",
+                        "Workdir session was not found",
+                    )
+                } else {
+                    (
+                        StatusCode::SERVICE_UNAVAILABLE,
+                        "unavailable",
+                        "Workdir session is unavailable",
+                    )
+                };
+                assert_eq!(status, expected, "{diagnostic}");
+                assert_failure_body(&body, code, message, reason);
+                let log = capture.take();
+                assert_failure_log(&log, status, code, reason, "session_open");
+                assert!(!log.contains(&token));
+                assert!(!log.contains(&harness.identity.private_key));
+                assert_eq!(backend.lookups.load(Ordering::SeqCst), 1, "no hidden retry");
+                assert_eq!(
+                    backend.opens.load(Ordering::SeqCst),
+                    usize::from(matches!(at, FailureAt::Open)),
+                );
+            }
+        }
+    })
+    .await
+    .expect("bounded diagnostic fault matrix");
+}
+
+#[tokio::test(flavor = "current_thread")]
+async fn signed_http_session_open_rejects_bad_capability_scope_and_owner_binding_before_backend() {
+    let capture = LogCapture::default();
+    let _guard = tracing::subscriber::set_default(capture.subscriber());
+    tracing::callsite::rebuild_interest_cache();
+    tokio::time::timeout(Duration::from_secs(15), async {
+        let (runtime, backend) =
+            FailingBackend::runtime(FailureAt::Open, "working_directory_record_invalid");
+        let mut request = task_request("foreign workspace binding");
+        request.config_bundle = None;
+        request.memory_settings.as_mut().unwrap().workspace_id = "other-workspace".into();
+        let foreign_worker = runtime
+            .create_worker_scoped(
+                &RuntimeWorkspaceScope::new("other-workspace", "https://backend.test"),
+                request,
+            )
+            .unwrap()
+            .worker_ref;
+        let harness = Harness::new(runtime).await;
+        for case in ["permission", "body", "workspace", "owner_binding"] {
+            let body = if case == "owner_binding" {
+                serde_json::to_vec(&OpenWorkdirSessionRequest {
+                    owner_worker_id: Some(foreign_worker.worker_id.to_string()),
+                })
+                .unwrap()
+            } else {
+                b"{}".to_vec()
+            };
+            let mut claims = signed_claims(&harness.trust, "POST", OPEN_PATH, &body);
+            if case == "permission" {
+                claims.operation = "workers:read".into();
+            }
+            if case == "workspace" {
+                claims.issuer_workspace_id = "other-workspace".into();
+            }
+            let sent = if case == "body" {
+                b"{ }".to_vec()
+            } else {
+                body
+            };
+            capture.take();
+            let (status, body, token) = harness.send(&claims, sent, "workspace-a").await;
+            assert_eq!(
+                status,
+                if case == "owner_binding" {
+                    StatusCode::NOT_FOUND
+                } else {
+                    StatusCode::UNAUTHORIZED
+                },
+                "{case}",
+            );
+            assert_private_absent(&body);
+            let log = capture.take();
+            assert_private_absent(&log);
+            assert!(!log.contains(&token));
+            assert!(!log.contains(&harness.identity.private_key));
+            if case == "owner_binding" {
+                assert_failure_body(
+                    &body,
+                    "not_found",
+                    "Workdir session was not found",
+                    "working_directory_not_found",
+                );
+                assert_failure_log(
+                    &log,
+                    status,
+                    "not_found",
+                    "working_directory_not_found",
+                    "session_open",
+                );
+            } else {
+                let wire: serde_json::Value = serde_json::from_str(&body).unwrap();
+                assert_eq!(wire["error"]["code"], "unauthorized");
+                assert!(
+                    !log.contains("workdir_provider_failure"),
+                    "auth rejection is not a provider fault",
+                );
+            }
+        }
+        assert_eq!(backend.lookups.load(Ordering::SeqCst), 0);
+        assert_eq!(backend.opens.load(Ordering::SeqCst), 0);
+    })
+    .await
+    .expect("bounded authorization rejection requests");
+}
+
+#[tokio::test(flavor = "current_thread")]
+async fn runtime_error_response_keeps_raw_details_private_and_unclassified_causes_generic() {
+    let capture = LogCapture::default();
+    let _guard = tracing::subscriber::set_default(capture.subscriber());
+    tracing::callsite::rebuild_interest_cache();
+    for (error, status, code, message, reason, stage) in [
+        (
+            RuntimeError::ExecutionBackendUnavailable {
+                message: PRIVATE_DIAGNOSTIC.into(),
+            },
+            StatusCode::SERVICE_UNAVAILABLE,
+            "unavailable",
+            "Workdir session is unavailable",
+            "runtime_backend_unavailable",
+            "runtime",
+        ),
+        (
+            RuntimeError::StatePoisoned,
+            StatusCode::SERVICE_UNAVAILABLE,
+            "unavailable",
+            "Workdir session is unavailable",
+            "runtime_state_unavailable",
+            "runtime",
+        ),
+        (
+            RuntimeError::InvalidRequest(PRIVATE_DIAGNOSTIC.into()),
+            StatusCode::BAD_REQUEST,
+            "invalid_request",
+            "Workdir operation request is invalid",
+            "runtime_invalid_request",
+            "runtime",
+        ),
+        (
+            RuntimeError::StoreCorrupt {
+                operation: "session_open",
+                path: PathBuf::from("/private/host-path-marker"),
+                message: PRIVATE_DIAGNOSTIC.into(),
+            },
+            StatusCode::SERVICE_UNAVAILABLE,
+            "unavailable",
+            "Workdir session is unavailable",
+            "session_open_failed",
+            "session_open",
+        ),
+    ] {
+        capture.take();
+        let response = RuntimeHttpWorkdirError::runtime(error).into_response();
+        assert_eq!(response.status(), status);
+        let bytes = to_bytes(response.into_body(), 16384).await.unwrap();
+        let body = std::str::from_utf8(&bytes).unwrap();
+        assert_failure_body(body, code, message, reason);
+        assert_failure_log(&capture.take(), status, code, reason, stage);
+    }
+}

crates/worker-runtime/src/worker_backend/deferred_workdir.rs

@@ -66,13 +66,32 @@ impl DeferredWorkdirSession {
         let open = self.open.clone();
         let session = tokio::task::spawn_blocking(move || open())
             .await
-            .map_err(|_| WorkdirError::Unavailable("Workdir session opener failed".into()))?
-            .map_err(WorkdirError::Unavailable)?;
+            .map_err(|_| {
+                WorkdirError::Unavailable("Workdir session opener failed".into())
+                    .with_failure_reason(WorkdirFailureReason::SessionOpenTaskFailed)
+            })?
+            .map_err(|_| {
+                // The opener's string contract cannot prove a more specific cause.
+                WorkdirError::Unavailable("Workdir session could not be opened".into())
+                    .with_failure_reason(WorkdirFailureReason::SessionOpenFailed)
+            })?;
         if session.workdir().id() != self.workdir.id() {
-            session.close().await?;
-            return Err(WorkdirError::Unavailable(
-                "Workdir session identity mismatch".into(),
-            ));
+            if let Err(error) = session.close().await {
+                // Retain a failed-close owner for explicit close; never use it.
+                state.closed = true;
+                state.session = Some(session);
+                tracing::warn!(
+                    target: "worker_runtime::workdir",
+                    event = "workdir_session_identity_cleanup_failed",
+                    failure_reason = error.failure_reason().map(WorkdirFailureReason::as_str),
+                    denial_reason = error.denial_reason().map(WorkdirDenialReason::as_str),
+                    "Mismatched Workdir session cleanup failed"
+                );
+            }
+            return Err(
+                WorkdirError::Unavailable("Workdir session identity mismatch".into())
+                    .with_failure_reason(WorkdirFailureReason::SessionIdentityMismatch),
+            );
         }
         if let Some(mut source) = session.subscribe_command_events() {
             let events = self.events.clone();
@@ -224,10 +243,16 @@ mod tests {
             },
         );
         assert_eq!(attempts.load(Ordering::SeqCst), 0);
+        let failed = session.read(read_request()).await.unwrap_err();
         assert!(matches!(
-            session.read(read_request()).await,
-            Err(WorkdirError::Unavailable(_))
+            failed.classification_source(),
+            WorkdirError::Unavailable(_)
         ));
+        assert_eq!(
+            failed.failure_reason(),
+            Some(WorkdirFailureReason::SessionOpenFailed)
+        );
+        assert_eq!(attempts.load(Ordering::SeqCst), 1);
         assert_eq!(
             session.read(read_request()).await.unwrap().bytes,
             b"restored"
@@ -253,4 +278,126 @@ mod tests {
         );
         session.close().await.unwrap();
     }
+
+    #[tokio::test]
+    async fn opener_task_and_open_errors_keep_distinct_safe_causes() {
+        for panic in [false, true] {
+            let attempts = Arc::new(AtomicUsize::new(0));
+            let observed = attempts.clone();
+            let session = DeferredWorkdirSession::handle(
+                "saved",
+                WorkdirSessionCapabilities::READ_ONLY,
+                move || {
+                    observed.fetch_add(1, Ordering::SeqCst);
+                    if panic {
+                        panic!(
+                            "/host/private bearer-secret command-secret proof-secret key-secret"
+                        );
+                    }
+                    Err("/host/private bearer-secret command-secret proof-secret key-secret".into())
+                },
+            );
+            let error = session.read(read_request()).await.unwrap_err();
+            assert_eq!(attempts.load(Ordering::SeqCst), 1);
+            let reason = if panic {
+                WorkdirFailureReason::SessionOpenTaskFailed
+            } else {
+                WorkdirFailureReason::SessionOpenFailed
+            };
+            assert_eq!(error.failure_reason(), Some(reason));
+            assert_eq!(reason.stage().as_str(), "session_open");
+            let transport = workdir::http::WorkdirTransportError::from_workdir_error(&error);
+            assert_eq!(transport.code.http_status(), 503);
+            assert!(
+                !serde_json::to_string(&transport)
+                    .unwrap()
+                    .contains("secret")
+            );
+            assert!(!format!("{error:?}").contains("secret"));
+            session.close().await.unwrap();
+            assert_eq!(attempts.load(Ordering::SeqCst), 1);
+        }
+    }
+
+    #[derive(Debug)]
+    struct MismatchedSession {
+        workdir: Workdir,
+        closes: Arc<AtomicUsize>,
+        fail_close: bool,
+    }
+
+    macro_rules! mismatched_session {
+        ($( $method:ident($request:ident: $request_type:ty) -> $result:ty; )*) => {
+            #[async_trait]
+            impl WorkdirSession for MismatchedSession {
+                fn workdir(&self) -> &Workdir { &self.workdir }
+                fn capabilities(&self) -> WorkdirSessionCapabilities { WorkdirSessionCapabilities::READ_ONLY }
+                $(async fn $method(&self, _: $request_type) -> Result<$result, WorkdirError> {
+                    panic!("mismatched session must never be used");
+                })*
+                async fn close(&self) -> Result<(), WorkdirError> {
+                    let attempt = self.closes.fetch_add(1, Ordering::SeqCst);
+                    if self.fail_close && attempt == 0 {
+                        Err(WorkdirError::Transport("/host/private key-secret".into())
+                            .with_failure_reason(WorkdirFailureReason::HttpTransfer))
+                    } else { Ok(()) }
+                }
+            }
+        };
+    }
+    mismatched_session! {
+        stat(request: StatRequest) -> StatResult;
+        read(request: ReadRequest) -> ReadResult;
+        write(request: WriteRequest) -> WriteResult;
+        edit(request: EditRequest) -> EditResult;
+        list(request: ListRequest) -> ListResult;
+        glob(request: GlobRequest) -> GlobResult;
+        grep(request: GrepRequest) -> GrepResult;
+        start_command(request: CommandRequest) -> CommandHandle;
+        command_status(handle: CommandHandle) -> CommandStatus;
+        command_output(request: CommandOutputRequest) -> CommandOutput;
+        cancel_command(handle: CommandHandle) -> ();
+    }
+
+    #[tokio::test]
+    async fn identity_mismatch_preserves_primary_cause_and_failed_close_owner() {
+        for fail_close in [false, true] {
+            let closes = Arc::new(AtomicUsize::new(0));
+            let raw: WorkdirSessionHandle = Arc::new(MismatchedSession {
+                workdir: Workdir::new("wrong-secret"),
+                closes: closes.clone(),
+                fail_close,
+            });
+            let attempts = Arc::new(AtomicUsize::new(0));
+            let observed = attempts.clone();
+            let session = DeferredWorkdirSession::handle(
+                "saved",
+                WorkdirSessionCapabilities::READ_ONLY,
+                move || {
+                    observed.fetch_add(1, Ordering::SeqCst);
+                    Ok(raw.clone())
+                },
+            );
+            let error = session.read(read_request()).await.unwrap_err();
+            assert_eq!(
+                error.failure_reason(),
+                Some(WorkdirFailureReason::SessionIdentityMismatch)
+            );
+            assert!(!format!("{error:?}").contains("secret"));
+            assert_eq!(closes.load(Ordering::SeqCst), 1);
+            if fail_close {
+                assert!(matches!(
+                    session.read(read_request()).await,
+                    Err(WorkdirError::SessionClosed)
+                ));
+                assert_eq!(attempts.load(Ordering::SeqCst), 1);
+            }
+            session.close().await.unwrap();
+            assert_eq!(
+                closes.load(Ordering::SeqCst),
+                if fail_close { 2 } else { 1 }
+            );
+            assert_eq!(attempts.load(Ordering::SeqCst), 1);
+        }
+    }
 }

crates/workspace-server/src/hosts.rs

@@ -3995,12 +3995,27 @@ impl WorkdirHttpAuthorization for RemoteWorkdirAuthorization {
                 return authorizer
                     .issue_async(method, path_and_query, operation, None, body)
                     .await
-                    .map_err(|error| WorkdirError::Unavailable(error.message));
+                    .map_err(|error| {
+                        use workdir::WorkdirFailureReason as Reason;
+                        let reason = match error.code.as_str() {
+                            "workspace_runtime_authorization_stale" => Reason::AuthorizationStale,
+                            "workspace_signing_identity_unavailable" => {
+                                Reason::SigningIdentityUnavailable
+                            }
+                            "workspace_runtime_authorization_sign_failed" => {
+                                Reason::AuthorizationSignFailed
+                            }
+                            _ => Reason::AuthorizationUnavailable,
+                        };
+                        WorkdirError::Unavailable("Workdir authorization is unavailable".into())
+                            .with_failure_reason(reason)
+                    });
             }
             authorization.fallback_bearer_token.ok_or_else(|| {
                 WorkdirError::Unavailable(
                     "remote Runtime does not have bearer authorization configured".to_string(),
                 )
+                .with_failure_reason(workdir::WorkdirFailureReason::AuthorizationMissing)
             })
         })
     }

crates/workspace-server/src/hosts/tests/workspace_auth_tests.rs

@@ -315,3 +315,71 @@ async fn capability_claims_must_match_current_workspace_identity_before_signing(
         .unwrap();
     verify(&fixture.verifier(), &token).unwrap();
 }
+
+#[tokio::test]
+async fn remote_workdir_authorization_failures_keep_safe_reason_without_dispatch_or_fallback() {
+    use workdir::WorkdirFailureReason as Reason;
+    use workdir::http::{OpenWorkdirSessionRequest, RemoteWorkdirSession, WorkdirTransportError};
+    for case in ["stale", "missing_material", "missing_authorization"] {
+        let fixture = Fixture::new().await;
+        if case == "stale" {
+            fixture
+                .store
+                .revoke_workspace_runtime_binding(WORKSPACE, RUNTIME, "revoked")
+                .unwrap();
+        } else if case == "missing_material" {
+            fixture
+                .materials
+                .delete(&fixture.identity.private_material_ref)
+                .unwrap();
+        }
+        let listener = std::net::TcpListener::bind("127.0.0.1:0").unwrap();
+        listener.set_nonblocking(true).unwrap();
+        let authorization = RemoteWorkdirAuthorization {
+            workspace_authorization: (case != "missing_authorization")
+                .then(|| fixture.authorizer.clone()),
+            fallback_bearer_token: (case != "missing_authorization")
+                .then(|| "bearer-secret".into()),
+        };
+        let error = RemoteWorkdirSession::open_with_authorization(
+            reqwest::Client::builder().no_proxy().build().unwrap(),
+            format!("http://{}", listener.local_addr().unwrap())
+                .parse()
+                .unwrap(),
+            Arc::new(authorization),
+            workdir::Workdir::new("workdir-secret").id().clone(),
+            OpenWorkdirSessionRequest::default(),
+        )
+        .await
+        .unwrap_err();
+        let reason = match case {
+            "stale" => Reason::AuthorizationStale,
+            "missing_material" => Reason::AuthorizationUnavailable,
+            _ => Reason::AuthorizationMissing,
+        };
+        assert_eq!(error.failure_reason(), Some(reason));
+        assert_eq!(reason.stage().as_str(), "authorization_preparation");
+        let transport = WorkdirTransportError::from_workdir_error(&error);
+        assert_eq!(transport.code.http_status(), 503);
+        assert_eq!(transport.message, "Workdir session is unavailable");
+        assert!(
+            !serde_json::to_string(&transport)
+                .unwrap()
+                .contains("secret")
+        );
+        let debug = format!("{error:?}");
+        for secret in [
+            "secret",
+            "workspace-signing/",
+            "private material",
+            "Authorization:",
+            "Bearer ",
+        ] {
+            assert!(!debug.contains(secret), "{case}: {debug}");
+        }
+        assert!(
+            matches!(listener.accept(), Err(error) if error.kind() == std::io::ErrorKind::WouldBlock),
+            "authorization failure sent HTTP or fell back"
+        );
+    }
+}

crates/workspace-server/src/server.rs

@@ -13506,6 +13506,7 @@ async fn log_failed_api_response(request: Request, next: Next) -> Response {
             request_token_id_hash = context.and(request_token_id_hash.as_deref()),
             denial_reason = error.and_then(|error| error.denial_reason).map(|reason| reason.as_str()),
             failure_reason = error.and_then(|error| error.failure_reason).map(|reason| reason.as_str()),
+            failure_stage = error.and_then(|error| error.failure_reason).map(|reason| reason.stage().as_str()),
             status = event.status,
             kind = event.kind.unwrap_or("unknown"),
             message = event.message.unwrap_or(""),
@@ -36942,8 +36943,9 @@ impl ApiErrorLog {
         log.denial_reason = error.denial_reason;
         log.failure_reason = error.failure_reason;
         if log.workdir_log.is_some() {
-            // Existing public API details are unchanged; do not copy request-derived
-            // alias/handle text or session-open errors into operational diagnostics.
+            // Public classification and arbitrary diagnostic text are not safe
+            // operational causes. Keep only the separately typed reason/stage;
+            // never infer a reason by parsing request- or provider-authored text.
             log.kind = format!("workdir_session_operation_api_{}", status.as_u16());
             // This can also fail after a command was dispatched. Do not claim
             // a pre-dispatch refusal or absence of effects in the safe message.

crates/workspace-server/src/server/tests/api_logging_tests.rs

@@ -605,6 +605,10 @@ async fn generated_workdir_provider_errors_preserve_response_and_log_details() {
         workdir::WorkdirFailureReason::SessionClosed,
         workdir::WorkdirFailureReason::CommandTerminalMissing,
         workdir::WorkdirFailureReason::HttpTimeout,
+        workdir::WorkdirFailureReason::OperationResultMismatch,
+        workdir::WorkdirFailureReason::SessionOpenTaskFailed,
+        workdir::WorkdirFailureReason::AuthorizationStale,
+        workdir::WorkdirFailureReason::RuntimeStopped,
     ] {
         let request = runtime_source_request(
             &identity,
@@ -653,6 +657,7 @@ async fn generated_workdir_provider_errors_preserve_response_and_log_details() {
         );
         assert_eq!(events.len(), 1, "{events:?}");
         assert_eq!(events[0]["failure_reason"], reason.as_str());
+        assert_eq!(events[0]["failure_stage"], reason.stage().as_str());
         assert_eq!(events[0]["operation"], "command_output");
         assert_eq!(events[0]["workdir_stage"], "provider_dispatch");
         let log = serde_json::to_string(&events).unwrap();
@@ -1249,3 +1254,54 @@ async fn non_api_workspace_paths_are_not_logged_as_ticket_api_errors() {
     assert_eq!(status, StatusCode::BAD_REQUEST);
     assert!(events.is_empty());
 }
+
+#[tokio::test]
+async fn session_open_failure_causes_survive_registry_api_conversion_without_raw_diagnostics() {
+    use workdir::WorkdirFailureReason as Reason;
+    for reason in [
+        Reason::SessionOpenFailed,
+        Reason::SessionOpenTaskFailed,
+        Reason::SessionIdentityMismatch,
+        Reason::AuthorizationStale,
+        Reason::AuthorizationUnavailable,
+        Reason::RuntimeStopped,
+        Reason::WorkingDirectoryRecordInvalid,
+        Reason::OperationResultMismatch,
+    ] {
+        let mut fixture = manual_worker_assignment_fixture().await;
+        fixture.runtime.workdir_session_factory = Some(Arc::new(move |_| {
+            Err(workdir::WorkdirError::Unavailable(
+                "/host/private body-secret proof-secret key-secret credential-secret".into(),
+            )
+            .with_failure_reason(reason))
+        }));
+        fixture
+            .api
+            .runtime
+            .register_or_replace(fixture.runtime.clone());
+        let identity =
+            worker_runtime::auth::RuntimeIdentityMaterial::generate(&fixture.worker.runtime_id)
+                .unwrap();
+        configure_runtime_request_auth(&mut fixture.api, &identity, &fixture.worker.runtime_id);
+        let path = format!("/api/w/{TEST_WORKSPACE_ID}/workers/self/workdir-session/operations");
+        let request = runtime_source_request(&identity, Some(&fixture.worker.worker_id), "POST", &path, serde_json::to_vec(&json!({
+            "target_workdir": "checkout",
+            "operation": {"operation": "read", "request": {"path":"README.md", "offset":0, "limit":10, "max_bytes":1024}}
+        })).unwrap());
+        let (status, body, events) =
+            request_with_logs(build_router(fixture.api.clone()), request).await;
+        assert_eq!(status, StatusCode::BAD_GATEWAY, "{body}");
+        assert_eq!(
+            body["message"],
+            "workdir_session_open_failed: Workdir session is unavailable"
+        );
+        assert!(body.get("failure_reason").is_none(), "{body}");
+        assert!(!body.to_string().contains("secret"));
+        assert_eq!(events.len(), 1, "{events:?}");
+        assert_eq!(events[0]["workdir_stage"], "session_open");
+        assert_eq!(events[0]["failure_reason"], reason.as_str());
+        assert_eq!(events[0]["failure_stage"], reason.stage().as_str());
+        assert_eq!(events[0]["message"], "Workdir operation failed");
+        assert_eq!(events[0]["diagnostics"], "[]");
+    }
+}