diff --git a/codex-rs/app-server/src/request_processors/thread_attachments.rs b/codex-rs/app-server/src/request_processors/thread_attachments.rs
index 2cdaaeca65..40d8850897 100644
--- a/codex-rs/app-server/src/request_processors/thread_attachments.rs
+++ b/codex-rs/app-server/src/request_processors/thread_attachments.rs
@@ -284,7 +284,10 @@ fn thread_attachment_store_error(
         ThreadStoreError::ThreadNotFound { thread_id } => {
             invalid_params(format!("thread not found: {thread_id}"))
         }
-        error @ (ThreadStoreError::Conflict { .. } | ThreadStoreError::Internal { .. }) => {
+        error @ (ThreadStoreError::Conflict { .. }
+        | ThreadStoreError::Retryable { .. }
+        | ThreadStoreError::OutcomeUnknown { .. }
+        | ThreadStoreError::Internal { .. }) => {
             internal_error(format!("failed to process {operation}: {error}"))
         }
     }
diff --git a/codex-rs/app-server/src/request_processors/thread_processor_tests.rs b/codex-rs/app-server/src/request_processors/thread_processor_tests.rs
index f1bd1bfe92..a42e06dc9d 100644
--- a/codex-rs/app-server/src/request_processors/thread_processor_tests.rs
+++ b/codex-rs/app-server/src/request_processors/thread_processor_tests.rs
@@ -1,3 +1,44 @@
+use codex_app_server_protocol::JSONRPCErrorError;
+use codex_thread_store::ThreadStoreError;
+use pretty_assertions::assert_eq;
+
+#[test]
+fn storage_failure_classification_does_not_change_mutation_error_policy() {
+    for error in [
+        ThreadStoreError::Internal {
+            message: "retryable conflict; outcome unknown".to_owned(),
+        },
+        ThreadStoreError::Retryable {
+            message: "store temporarily unavailable".to_owned(),
+        },
+        ThreadStoreError::OutcomeUnknown {
+            message: "connection lost after write".to_owned(),
+        },
+    ] {
+        let mapped = super::thread_store_mutation_error("archive", error.clone());
+        let expected = JSONRPCErrorError {
+            code: -32603,
+            message: format!("failed to archive session: {error}"),
+            data: None,
+        };
+        assert_eq!(mapped, expected);
+    }
+
+    assert_eq!(
+        super::thread_store_mutation_error(
+            "archive",
+            ThreadStoreError::Conflict {
+                message: "writer already active".to_owned(),
+            },
+        ),
+        JSONRPCErrorError {
+            code: -32600,
+            message: "writer already active".to_owned(),
+            data: None,
+        },
+    );
+}
+
 mod thread_list_cwd_filter_tests {
     use super::super::normalize_thread_list_cwd_filters;
     use codex_app_server_protocol::ThreadListCwdFilter;
diff --git a/codex-rs/app-server/src/request_processors/thread_sections.rs b/codex-rs/app-server/src/request_processors/thread_sections.rs
index 6491b3bc78..31f5b3f7e4 100644
--- a/codex-rs/app-server/src/request_processors/thread_sections.rs
+++ b/codex-rs/app-server/src/request_processors/thread_sections.rs
@@ -224,6 +224,8 @@ fn thread_section_store_error(
         ThreadStoreError::InvalidRequest { message } => invalid_params(message),
         error @ (ThreadStoreError::ThreadNotFound { .. }
         | ThreadStoreError::Conflict { .. }
+        | ThreadStoreError::Retryable { .. }
+        | ThreadStoreError::OutcomeUnknown { .. }
         | ThreadStoreError::Internal { .. }) => {
             let action = operation
                 .strip_prefix("threadSection/")
diff --git a/codex-rs/core/src/agent/control/runtime_tests.rs b/codex-rs/core/src/agent/control/runtime_tests.rs
index 2884575ab3..2fc7e07108 100644
--- a/codex-rs/core/src/agent/control/runtime_tests.rs
+++ b/codex-rs/core/src/agent/control/runtime_tests.rs
@@ -91,13 +91,22 @@ async fn report_display_includes_safe_cause_without_raw_error_payload() {
         .expect("teardown should be admitted")
         .into_teardown_guard("session_startup", Some(thread_id));
     let raw_payload = "sensitive thread-store error payload";
-    let error = ThreadStoreError::Internal {
-        message: raw_payload.to_owned(),
-    };
-    teardown.record_shutdown_failure(
-        "discard_persistence",
-        crate::thread_manager::thread_store_error_kind(&error),
-    );
+    for error in [
+        ThreadStoreError::Internal {
+            message: raw_payload.to_owned(),
+        },
+        ThreadStoreError::Retryable {
+            message: raw_payload.to_owned(),
+        },
+        ThreadStoreError::OutcomeUnknown {
+            message: raw_payload.to_owned(),
+        },
+    ] {
+        teardown.record_shutdown_failure(
+            "discard_persistence",
+            crate::thread_manager::thread_store_error_kind(&error),
+        );
+    }
     let shutdown = runtime.request_shutdown();
     teardown.complete();
 
@@ -109,7 +118,7 @@ async fn report_display_includes_safe_cause_without_raw_error_payload() {
     assert_eq!(
         displayed,
         format!(
-            "agent tree shutdown did not complete cleanly: tree_id={}, failures=[{{operation=session_startup, phase=discard_persistence, thread_id={thread_id}, reason=operation_failed, error_kind=thread_store_internal}}]; omitted_failures=0",
+            "agent tree shutdown did not complete cleanly: tree_id={}, failures=[{{operation=session_startup, phase=discard_persistence, thread_id={thread_id}, reason=operation_failed, error_kind=thread_store_internal}}, {{operation=session_startup, phase=discard_persistence, thread_id={thread_id}, reason=operation_failed, error_kind=thread_store_retryable}}, {{operation=session_startup, phase=discard_persistence, thread_id={thread_id}, reason=operation_failed, error_kind=thread_store_outcome_unknown}}]; omitted_failures=0",
             report.tree_id,
         )
     );
diff --git a/codex-rs/core/src/session_rollout_init_error.rs b/codex-rs/core/src/session_rollout_init_error.rs
index 7e62462add..68581e217d 100644
--- a/codex-rs/core/src/session_rollout_init_error.rs
+++ b/codex-rs/core/src/session_rollout_init_error.rs
@@ -19,6 +19,8 @@ pub(crate) fn map_session_init_error(err: &anyhow::Error, codex_home: &Path) ->
             }
             ThreadStoreError::ThreadNotFound { .. }
             | ThreadStoreError::InvalidRequest { .. }
+            | ThreadStoreError::Retryable { .. }
+            | ThreadStoreError::OutcomeUnknown { .. }
             | ThreadStoreError::Internal { .. } => {}
         }
     }
@@ -65,3 +67,7 @@ fn map_rollout_io_error(io_err: &std::io::Error, codex_home: &Path) -> Option<Co
         "{hint} (underlying error: {io_err})"
     )))
 }
+
+#[cfg(test)]
+#[path = "session_rollout_init_error_tests.rs"]
+mod tests;
diff --git a/codex-rs/core/src/session_rollout_init_error_tests.rs b/codex-rs/core/src/session_rollout_init_error_tests.rs
new file mode 100644
index 0000000000..f49993e5d5
--- /dev/null
+++ b/codex-rs/core/src/session_rollout_init_error_tests.rs
@@ -0,0 +1,62 @@
+//! Checks that storage classifications retain the existing session startup failure policy.
+
+use super::map_session_init_error;
+use codex_protocol::ThreadId;
+use codex_protocol::error::CodexErrorDetails;
+use codex_thread_store::ThreadStoreError;
+use pretty_assertions::assert_eq;
+use std::path::Path;
+
+#[test]
+fn storage_failures_remain_fatal_during_session_initialization() {
+    for error in [
+        ThreadStoreError::ThreadNotFound {
+            thread_id: ThreadId::new(),
+        },
+        ThreadStoreError::InvalidRequest {
+            message: "invalid request".to_owned(),
+        },
+        ThreadStoreError::Internal {
+            message: "retryable conflict; outcome unknown".to_owned(),
+        },
+        ThreadStoreError::Retryable {
+            message: "store temporarily unavailable".to_owned(),
+        },
+        ThreadStoreError::OutcomeUnknown {
+            message: "connection lost after write".to_owned(),
+        },
+    ] {
+        let wrapped = anyhow::Error::new(error.clone()).context("opening persistence");
+        let mapped = map_session_init_error(&wrapped, Path::new("codex-home"));
+        let CodexErrorDetails::Fatal(message) = mapped.details() else {
+            panic!("storage failure must remain fatal during startup: {mapped}");
+        };
+        assert_eq!(
+            message,
+            &format!("Failed to initialize session: opening persistence: {error}")
+        );
+    }
+}
+
+#[test]
+fn conflict_and_unsupported_keep_their_session_initialization_categories() {
+    let conflict = anyhow::Error::new(ThreadStoreError::Conflict {
+        message: "writer already active".to_owned(),
+    })
+    .context("opening persistence");
+    let mapped = map_session_init_error(&conflict, Path::new("codex-home"));
+    assert!(
+        matches!(mapped.details(), CodexErrorDetails::InvalidRequest(message)
+        if message == "writer already active")
+    );
+
+    let unsupported = anyhow::Error::new(ThreadStoreError::Unsupported {
+        operation: "create_thread",
+    })
+    .context("opening persistence");
+    let mapped = map_session_init_error(&unsupported, Path::new("codex-home"));
+    assert!(
+        matches!(mapped.details(), CodexErrorDetails::UnsupportedOperation(message)
+        if message == "create_thread is not supported yet")
+    );
+}
diff --git a/codex-rs/core/src/thread_manager/shutdown.rs b/codex-rs/core/src/thread_manager/shutdown.rs
index cfa4af1ca6..e622f41024 100644
--- a/codex-rs/core/src/thread_manager/shutdown.rs
+++ b/codex-rs/core/src/thread_manager/shutdown.rs
@@ -17,6 +17,8 @@ pub(crate) fn thread_store_error_kind(error: &ThreadStoreError) -> &'static str
         ThreadStoreError::InvalidRequest { .. } => "thread_store_invalid_request",
         ThreadStoreError::Conflict { .. } => "thread_store_conflict",
         ThreadStoreError::Unsupported { .. } => "thread_store_unsupported",
+        ThreadStoreError::Retryable { .. } => "thread_store_retryable",
+        ThreadStoreError::OutcomeUnknown { .. } => "thread_store_outcome_unknown",
         ThreadStoreError::Internal { .. } => "thread_store_internal",
     }
 }
diff --git a/codex-rs/thread-store/src/error.rs b/codex-rs/thread-store/src/error.rs
index bc5e8ed7c4..d0ab6d8826 100644
--- a/codex-rs/thread-store/src/error.rs
+++ b/codex-rs/thread-store/src/error.rs
@@ -16,7 +16,11 @@ pub(crate) fn reject_paginated_history_mode(
 }
 
 /// Error type shared by thread-store implementations.
-#[derive(Debug, thiserror::Error)]
+///
+/// Implementations must explicitly distinguish known transient failures from writes whose
+/// outcome is unknown. These categories carry information only: the operation owner decides
+/// whether and how to recover, and no variant automatically triggers a retry.
+#[derive(Clone, Debug, thiserror::Error)]
 pub enum ThreadStoreError {
     /// The requested thread does not exist in this store.
     #[error("thread {thread_id} not found")]
@@ -32,7 +36,7 @@ pub enum ThreadStoreError {
         message: String,
     },
 
-    /// The operation conflicted with current store state.
+    /// The operation conflicted with current store state. This alone does not imply retryability.
     #[error("thread-store conflict: {message}")]
     Conflict {
         /// User-facing explanation of the conflict.
@@ -46,10 +50,37 @@ pub enum ThreadStoreError {
         operation: &'static str,
     },
 
+    /// A transient failure for which retrying the operation is safe.
+    ///
+    /// For a write, the implementation must know the failed attempt did not commit. Otherwise
+    /// use [`Self::OutcomeUnknown`]. Retry scheduling and limits belong to the operation owner.
+    #[error("thread-store retryable error: {message}")]
+    Retryable {
+        /// User-facing explanation of the transient failure.
+        message: String,
+    },
+
+    /// A write failed to report a definitive outcome and may already have committed.
+    ///
+    /// The operation owner must reconcile the stored state or use an idempotent replay strategy
+    /// before retrying. This must not be treated as an ordinary retryable failure.
+    #[error("thread-store write outcome unknown: {message}")]
+    OutcomeUnknown {
+        /// User-facing explanation of why the write outcome is uncertain.
+        message: String,
+    },
+
     /// Catch-all for implementation failures that do not fit a more specific category.
+    ///
+    /// This includes unclassified failures: callers must not infer retryability or whether a
+    /// write committed from this variant or its message.
     #[error("thread-store internal error: {message}")]
     Internal {
         /// User-facing explanation of the implementation failure.
         message: String,
     },
 }
+
+#[cfg(test)]
+#[path = "error_tests.rs"]
+mod tests;
diff --git a/codex-rs/thread-store/src/error_tests.rs b/codex-rs/thread-store/src/error_tests.rs
new file mode 100644
index 0000000000..4b56fa89bc
--- /dev/null
+++ b/codex-rs/thread-store/src/error_tests.rs
@@ -0,0 +1,23 @@
+//! Verifies conservative classification at the shared storage error boundary.
+
+use super::ThreadStoreError;
+use pretty_assertions::assert_eq;
+
+#[test]
+fn unclassified_sqlx_failures_remain_internal() {
+    for error in [
+        sqlx::Error::PoolTimedOut,
+        sqlx::Error::Io(std::io::Error::new(
+            std::io::ErrorKind::ConnectionReset,
+            "connection lost after write",
+        )),
+        sqlx::Error::Protocol("retryable conflict; outcome unknown".to_owned()),
+    ] {
+        let expected = format!("failed to access thread history: {error}");
+        let error = ThreadStoreError::from(error);
+        let ThreadStoreError::Internal { message } = error else {
+            panic!("unclassified SQLx failure must remain internal: {error:?}");
+        };
+        assert_eq!(message, expected);
+    }
+}