diff --git a/backend/crates/gateway-admin/src/model/account_groups.rs b/backend/crates/gateway-admin/src/model/account_groups.rs
index 65949ed76..c56310bde 100644
--- a/backend/crates/gateway-admin/src/model/account_groups.rs
+++ b/backend/crates/gateway-admin/src/model/account_groups.rs
@@ -38,7 +38,8 @@ pub struct AccountGroupAccountSummary {
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct AccountGroupCapacity {
     pub used_slots: Option<u64>,
-    pub total_slots: u64,
+    /// `None` 表示可用账号中存在不限制并发的账号。
+    pub total_slots: Option<u64>,
 }
 
 /// Successful, downstream-committed USD request costs for group accounts.
@@ -55,7 +56,7 @@ pub struct AccountGroupMemberFact {
     pub group_id: AccountGroupId,
     pub account_id: String,
     pub status: AccountStatusFacts,
-    pub total_slots: u64,
+    pub total_slots: Option<u64>,
 }
 
 /// Lightweight group reference embedded in account and client-key views.
diff --git a/backend/crates/gateway-admin/src/model/observability.rs b/backend/crates/gateway-admin/src/model/observability.rs
index 4aecffeed..717341444 100644
--- a/backend/crates/gateway-admin/src/model/observability.rs
+++ b/backend/crates/gateway-admin/src/model/observability.rs
@@ -992,7 +992,8 @@ pub struct DashboardWireAttribute {
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct DashboardCapacity {
     pub max_concurrent_per_account: u64,
-    pub total_slots: u64,
+    /// `None` 表示可用账号池不限制并发。
+    pub total_slots: Option<u64>,
     pub used_slots: Option<u64>,
     pub available_slots: Option<u64>,
 }
diff --git a/backend/crates/gateway-admin/src/use_case/account_groups.rs b/backend/crates/gateway-admin/src/use_case/account_groups.rs
index 7cbfbbb0c..4bb571c7c 100644
--- a/backend/crates/gateway-admin/src/use_case/account_groups.rs
+++ b/backend/crates/gateway-admin/src/use_case/account_groups.rs
@@ -231,8 +231,8 @@ fn project_group_runtime(
                     })
                 })
             },
-            total_slots: available_ids.iter().fold(0_u64, |sum, account_id| {
-                sum.saturating_add(slots_by_account.get(*account_id).copied().unwrap_or(0))
+            total_slots: available_ids.iter().try_fold(0_u64, |sum, account_id| {
+                Some(sum.saturating_add(slots_by_account.get(*account_id).copied().flatten()?))
             }),
         };
     }
diff --git a/backend/crates/gateway-admin/src/use_case/observability.rs b/backend/crates/gateway-admin/src/use_case/observability.rs
index f79558bd1..6535331dc 100644
--- a/backend/crates/gateway-admin/src/use_case/observability.rs
+++ b/backend/crates/gateway-admin/src/use_case/observability.rs
@@ -207,27 +207,25 @@ impl DefaultObservabilityService {
         }
         let wire_profiles = self.providers.dashboard_wire_profiles(&configurations);
         let max_concurrent_per_account = u64::from(settings.max_concurrent_per_account);
-        let total_slots = runtime_slots.as_ref().map_or_else(
-            || {
-                observation
-                    .provider_accounts
-                    .normal
-                    .saturating_mul(max_concurrent_per_account)
-            },
-            |slots| {
-                slots
-                    .inherited_accounts
-                    .saturating_mul(max_concurrent_per_account)
-                    .saturating_add(slots.overridden_slots)
-            },
-        );
+        let (inherited_accounts, overridden_slots) = runtime_slots
+            .as_ref()
+            .map_or((observation.provider_accounts.normal, 0), |slots| {
+                (slots.inherited_accounts, slots.overridden_slots)
+            });
+        let total_slots = (max_concurrent_per_account > 0 || inherited_accounts == 0).then(|| {
+            inherited_accounts
+                .saturating_mul(max_concurrent_per_account)
+                .saturating_add(overridden_slots)
+        });
         let used_slots = runtime_slots.and_then(|slots| slots.used_slots);
         Ok(DashboardResult {
             capacity: DashboardCapacity {
                 max_concurrent_per_account,
                 total_slots,
                 used_slots,
-                available_slots: used_slots.map(|used| total_slots.saturating_sub(used)),
+                available_slots: used_slots
+                    .zip(total_slots)
+                    .map(|(used, total)| total.saturating_sub(used)),
             },
             rotation_strategy: settings.rotation_strategy,
             observation,
diff --git a/backend/crates/gateway-admin/src/use_case/settings.rs b/backend/crates/gateway-admin/src/use_case/settings.rs
index a91c72d25..c0cf52588 100644
--- a/backend/crates/gateway-admin/src/use_case/settings.rs
+++ b/backend/crates/gateway-admin/src/use_case/settings.rs
@@ -381,7 +381,6 @@ fn validate_settings(command: &ReplaceRuntimeSettings) -> Result<(), AdminError>
         && isize::try_from(command.responses_max_decompressed_body_bytes).is_ok()
         && command.refresh_margin_seconds > 0
         && command.refresh_concurrency > 0
-        && command.max_concurrent_per_account > 0
         && command.max_waiting_per_key <= 1_000
         && command.max_waiting_per_account <= 1_000
         && (1..=120).contains(&command.concurrency_wait_timeout_seconds)
diff --git a/backend/crates/gateway-admin/tests/use_case/account_groups.rs b/backend/crates/gateway-admin/tests/use_case/account_groups.rs
index 70fb3a6b6..b534ee213 100644
--- a/backend/crates/gateway-admin/tests/use_case/account_groups.rs
+++ b/backend/crates/gateway-admin/tests/use_case/account_groups.rs
@@ -82,7 +82,7 @@ async fn group_query_service_enriches_only_current_page_members_with_runtime_fac
         group.capacity,
         AccountGroupCapacity {
             used_slots: Some(2),
-            total_slots: 4,
+            total_slots: Some(4),
         }
     );
 }
@@ -90,6 +90,40 @@ async fn group_query_service_enriches_only_current_page_members_with_runtime_fac
 #[derive(Default)]
 struct FakeGroupStore {
     requested_groups: Mutex<Vec<String>>,
+    members: Option<Vec<AccountGroupMemberFact>>,
+}
+
+#[tokio::test]
+async fn group_capacity_only_becomes_unlimited_for_available_unlimited_members() {
+    for (available_slots, unavailable_slots, expected) in
+        [(None, Some(3), None), (Some(4), None, Some(4))]
+    {
+        let mut available = member("acct_available", 4);
+        available.total_slots = available_slots;
+        let mut unavailable = member("acct_limited", 3);
+        unavailable.total_slots = unavailable_slots;
+        let groups = Arc::new(FakeGroupStore {
+            members: Some(vec![available, unavailable]),
+            ..Default::default()
+        });
+        let service = AdminHarness::new()
+            .account_groups(groups)
+            .account_runtime(Arc::new(FakeRuntimeStore::default()))
+            .build()
+            .await;
+        let page = service
+            .account_groups()
+            .list(AccountGroupListQuery {
+                page: 1,
+                page_size: PageSize::new(20).expect("page size"),
+                search: None,
+                enabled: None,
+            })
+            .await
+            .expect("group capacity");
+        assert_eq!(page.items[0].capacity.total_slots, expected);
+        assert_eq!(page.items[0].capacity.used_slots, Some(2));
+    }
 }
 
 #[async_trait]
@@ -115,7 +149,10 @@ impl AccountGroupStore for FakeGroupStore {
             .iter()
             .map(|group_id| group_id.as_str().to_owned())
             .collect();
-        Ok(vec![member("acct_available", 4), member("acct_limited", 3)])
+        Ok(self
+            .members
+            .clone()
+            .unwrap_or_else(|| vec![member("acct_available", 4), member("acct_limited", 3)]))
     }
 
     async fn create_account_group(
@@ -218,7 +255,7 @@ fn group_record() -> AccountGroupRecord {
         },
         capacity: AccountGroupCapacity {
             used_slots: None,
-            total_slots: 0,
+            total_slots: Some(0),
         },
         usage: AccountGroupUsage {
             today_usd: DecimalAmount::from_str("1").expect("today usage"),
@@ -242,7 +279,7 @@ fn member(account_id: &str, total_slots: u64) -> AccountGroupMemberFact {
             last_error_reason: None,
             last_error_message: None,
         },
-        total_slots,
+        total_slots: Some(total_slots),
     }
 }
 
diff --git a/backend/crates/gateway-admin/tests/use_case/observability.rs b/backend/crates/gateway-admin/tests/use_case/observability.rs
index 961d981e4..37a3fe4d7 100644
--- a/backend/crates/gateway-admin/tests/use_case/observability.rs
+++ b/backend/crates/gateway-admin/tests/use_case/observability.rs
@@ -237,11 +237,45 @@ async fn dashboard_summary_should_project_rebuildable_runtime_slots() {
         .expect("dashboard summary")
         .capacity;
 
-    assert_eq!(capacity.total_slots, 7);
+    assert_eq!(capacity.total_slots, Some(7));
     assert_eq!(capacity.used_slots, Some(2));
     assert_eq!(capacity.available_slots, Some(5));
 }
 
+#[tokio::test]
+async fn dashboard_capacity_distinguishes_unlimited_inheritance_finite_overrides_and_empty_pool() {
+    for (inherited_accounts, overridden_slots, expected_total, expected_available) in [
+        (2, 5, None, None),
+        (0, 5, Some(5), Some(3)),
+        (0, 0, Some(0), Some(0)),
+    ] {
+        let now = Utc::now();
+        let store = Arc::new(FixtureObservabilityStore::new(observation_range(now)));
+        store.replace_runtime_slots(Some(DashboardRuntimeSlots {
+            inherited_accounts,
+            overridden_slots,
+            used_slots: Some(2),
+        }));
+        let services = super::AdminHarness::new()
+            .observability(store)
+            .settings(Arc::new(FixtureSettingsStore {
+                max_concurrent_per_account: 0,
+            }))
+            .provider(super::dashboard_profile_provider())
+            .build()
+            .await;
+        let capacity = services
+            .observability()
+            .dashboard_summary(observation_range(now), TrendKind::Usage)
+            .await
+            .expect("dashboard")
+            .capacity;
+        assert_eq!(capacity.total_slots, expected_total);
+        assert_eq!(capacity.available_slots, expected_available);
+        assert_eq!(capacity.used_slots, Some(2));
+    }
+}
+
 #[tokio::test]
 async fn dashboard_summary_should_share_one_current_observation_time_across_runtime_facts() {
     let historical_end = Utc::now() - Duration::hours(1);
@@ -749,7 +783,9 @@ impl ObservabilityStore for FixtureObservabilityStore {
     }
 }
 
-struct FixtureSettingsStore;
+struct FixtureSettingsStore {
+    max_concurrent_per_account: u32,
+}
 
 #[async_trait]
 impl SettingsStore for FixtureSettingsStore {
@@ -780,7 +816,7 @@ impl SettingsStore for FixtureSettingsStore {
             model_mappings: Default::default(),
             refresh_margin_seconds: 300,
             refresh_concurrency: 2,
-            max_concurrent_per_account: 1,
+            max_concurrent_per_account: self.max_concurrent_per_account,
             request_interval_ms: 0,
             max_waiting_per_key: 0,
             max_waiting_per_account: 0,
@@ -834,7 +870,9 @@ impl SettingsStore for FixtureSettingsStore {
 async fn observability_services(store: Arc<FixtureObservabilityStore>) -> AdminServices {
     super::AdminHarness::new()
         .observability(store)
-        .settings(Arc::new(FixtureSettingsStore))
+        .settings(Arc::new(FixtureSettingsStore {
+            max_concurrent_per_account: 1,
+        }))
         .provider(super::dashboard_profile_provider())
         .build()
         .await
@@ -845,7 +883,9 @@ async fn observability_services_with_calculated_billing(
 ) -> AdminServices {
     super::AdminHarness::new()
         .observability(store)
-        .settings(Arc::new(FixtureSettingsStore))
+        .settings(Arc::new(FixtureSettingsStore {
+            max_concurrent_per_account: 1,
+        }))
         .provider(super::calculated_billing_provider())
         .build()
         .await
diff --git a/backend/crates/gateway-api/src/admin/account_groups.rs b/backend/crates/gateway-api/src/admin/account_groups.rs
index 4c0c981d3..2bd6cb2d2 100644
--- a/backend/crates/gateway-api/src/admin/account_groups.rs
+++ b/backend/crates/gateway-api/src/admin/account_groups.rs
@@ -126,7 +126,7 @@ struct AccountGroupAccountSummaryView {
 #[serde(rename_all = "camelCase")]
 struct AccountGroupCapacityView {
     used_slots: Option<u64>,
-    total_slots: u64,
+    total_slots: Option<u64>,
 }
 
 #[derive(Debug, Clone, Serialize)]
diff --git a/backend/crates/gateway-api/src/admin/observability/wire.rs b/backend/crates/gateway-api/src/admin/observability/wire.rs
index 7f956f4be..26e5a0f13 100644
--- a/backend/crates/gateway-api/src/admin/observability/wire.rs
+++ b/backend/crates/gateway-api/src/admin/observability/wire.rs
@@ -425,7 +425,7 @@ pub struct DashboardPoolSummaryView {
 #[serde(rename_all = "camelCase")]
 pub struct DashboardCapacityInfoView {
     pub max_concurrent_per_account: u64,
-    pub total_slots: u64,
+    pub total_slots: Option<u64>,
     pub used_slots: Option<u64>,
     pub available_slots: Option<u64>,
 }
diff --git a/backend/crates/gateway-api/src/admin/settings.rs b/backend/crates/gateway-api/src/admin/settings.rs
index da7071bdf..abd8c734d 100644
--- a/backend/crates/gateway-api/src/admin/settings.rs
+++ b/backend/crates/gateway-api/src/admin/settings.rs
@@ -125,7 +125,6 @@ impl UpdateRuntimeSettingsRequest {
         for (value, field) in [
             (self.refresh_margin_seconds, "refreshMarginSeconds"),
             (self.refresh_concurrency, "refreshConcurrency"),
-            (self.max_concurrent_per_account, "maxConcurrentPerAccount"),
             (self.usage_retention_days, "usageRetentionDays"),
             (self.ops_event_retention_days, "opsEventRetentionDays"),
             (self.audit_retention_days, "auditRetentionDays"),
diff --git a/backend/crates/gateway-api/tests/admin/mod.rs b/backend/crates/gateway-api/tests/admin/mod.rs
index 01e800fe5..e7475c8cf 100644
--- a/backend/crates/gateway-api/tests/admin/mod.rs
+++ b/backend/crates/gateway-api/tests/admin/mod.rs
@@ -723,7 +723,7 @@ impl AccountGroupStore for MemoryAccountGroupStore {
                     last_error_reason: None,
                     last_error_message: None,
                 },
-                total_slots: 1,
+                total_slots: Some(1),
             },
             AccountGroupMemberFact {
                 group_id: group_id(PRIMARY_GROUP_ID),
@@ -737,7 +737,7 @@ impl AccountGroupStore for MemoryAccountGroupStore {
                     last_error_reason: None,
                     last_error_message: None,
                 },
-                total_slots: 1,
+                total_slots: Some(1),
             },
         ])
     }
@@ -1490,7 +1490,7 @@ fn group_color(value: &str) -> AccountGroupColor {
 fn capacity(used_slots: Option<u64>, total_slots: u64) -> AccountGroupCapacity {
     AccountGroupCapacity {
         used_slots,
-        total_slots,
+        total_slots: Some(total_slots),
     }
 }
 
diff --git a/backend/crates/gateway-api/tests/admin/settings.rs b/backend/crates/gateway-api/tests/admin/settings.rs
index b392d73a8..72a4b8762 100644
--- a/backend/crates/gateway-api/tests/admin/settings.rs
+++ b/backend/crates/gateway-api/tests/admin/settings.rs
@@ -77,6 +77,15 @@ fn settings_request_should_reject_unknown_rotation_strategy() {
     assert_eq!(request.validate().unwrap_err().field(), "rotationStrategy");
 }
 
+#[test]
+fn settings_request_accepts_unlimited_default_account_concurrency() {
+    let mut body = update_body();
+    body["maxConcurrentPerAccount"] = json!(0);
+    let request: UpdateRuntimeSettingsRequest =
+        serde_json::from_value(body).expect("decode settings");
+    request.validate().expect("zero means unlimited");
+}
+
 #[test]
 fn settings_request_should_reject_non_semver_client_min() {
     let mut body = update_body();
diff --git a/backend/crates/gateway-core/src/account/model.rs b/backend/crates/gateway-core/src/account/model.rs
index 5b484c371..e230426cd 100644
--- a/backend/crates/gateway-core/src/account/model.rs
+++ b/backend/crates/gateway-core/src/account/model.rs
@@ -58,6 +58,46 @@ impl AccountConcurrencyLimit {
     }
 }
 
+/// 账号继承默认值或应用独立覆盖后的实际并发约束。
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum AccountConcurrency {
+    Unlimited,
+    Limited(NonZeroU32),
+}
+
+impl AccountConcurrency {
+    /// 配置值零表示不限制；账号独立覆盖仍只接受正数。
+    #[must_use]
+    pub const fn new(value: u32) -> Self {
+        match NonZeroU32::new(value) {
+            Some(limit) => Self::Limited(limit),
+            None => Self::Unlimited,
+        }
+    }
+
+    #[must_use]
+    pub const fn get(self) -> u32 {
+        match self {
+            Self::Unlimited => 0,
+            Self::Limited(limit) => limit.get(),
+        }
+    }
+
+    #[must_use]
+    pub const fn limit(self) -> Option<NonZeroU32> {
+        match self {
+            Self::Unlimited => None,
+            Self::Limited(limit) => Some(limit),
+        }
+    }
+}
+
+impl From<NonZeroU32> for AccountConcurrency {
+    fn from(limit: NonZeroU32) -> Self {
+        Self::Limited(limit)
+    }
+}
+
 /// Relative scheduling priority for an account.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct AccountWeight(NonZeroU16);
@@ -958,9 +998,9 @@ impl ProviderAccount {
     }
 
     #[must_use]
-    pub const fn effective_concurrency(&self, default: NonZeroU32) -> NonZeroU32 {
+    pub const fn effective_concurrency(&self, default: AccountConcurrency) -> AccountConcurrency {
         match self.concurrency_limit {
-            Some(limit) => limit.into_non_zero(),
+            Some(limit) => AccountConcurrency::Limited(limit.into_non_zero()),
             None => default,
         }
     }
diff --git a/backend/crates/gateway-core/src/account/selection.rs b/backend/crates/gateway-core/src/account/selection.rs
index 884945161..2169a4d18 100644
--- a/backend/crates/gateway-core/src/account/selection.rs
+++ b/backend/crates/gateway-core/src/account/selection.rs
@@ -2,7 +2,6 @@
 
 use std::cmp::Reverse;
 use std::collections::{BTreeSet, HashMap};
-use std::num::NonZeroU32;
 use std::sync::atomic::{AtomicU64, Ordering};
 use std::sync::{Mutex, RwLock};
 use std::time::{Duration, Instant, SystemTime};
@@ -10,7 +9,7 @@ use std::time::{Duration, Instant, SystemTime};
 use crate::concurrency::ConcurrencyQueuePolicy;
 use crate::identity::ProviderKind;
 
-use super::{AccountStatus, ProviderAccount, ProviderAccountId};
+use super::{AccountConcurrency, AccountStatus, ProviderAccount, ProviderAccountId};
 
 /// `runtime_settings.rotation_strategy` 的稳定值。
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
@@ -48,21 +47,21 @@ impl RotationStrategy {
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct AccountSelectionPolicy {
     strategy: RotationStrategy,
-    max_concurrent_per_account: NonZeroU32,
+    max_concurrent_per_account: AccountConcurrency,
     request_interval: Duration,
     queue_policy: ConcurrencyQueuePolicy,
 }
 
 impl AccountSelectionPolicy {
     #[must_use]
-    pub const fn new(
+    pub fn new(
         strategy: RotationStrategy,
-        max_concurrent_per_account: NonZeroU32,
+        max_concurrent_per_account: impl Into<AccountConcurrency>,
         request_interval: Duration,
     ) -> Self {
         Self {
             strategy,
-            max_concurrent_per_account,
+            max_concurrent_per_account: max_concurrent_per_account.into(),
             request_interval,
             queue_policy: ConcurrencyQueuePolicy {
                 max_waiting: 0,
@@ -88,7 +87,7 @@ impl AccountSelectionPolicy {
     }
 
     #[must_use]
-    pub const fn max_concurrent_per_account(self) -> NonZeroU32 {
+    pub const fn max_concurrent_per_account(self) -> AccountConcurrency {
         self.max_concurrent_per_account
     }
 
@@ -502,18 +501,19 @@ impl AccountSelector {
                     )
                 )
             })
-            .fold((0_u64, 0_u64), |(used, total), candidate| {
+            .try_fold((0_u64, 0_u64), |(used, total), candidate| {
                 let capacity = u64::from(
                     candidate
                         .account
                         .effective_concurrency(context.policy.max_concurrent_per_account())
+                        .limit()?
                         .get(),
                 );
-                (
+                Some((
                     used.saturating_add(u64::from(candidate.signals.in_flight)),
                     total.saturating_add(capacity),
-                )
-            });
+                ))
+            })?;
         (total_slots > 0).then_some(AccountCapacitySnapshot {
             used_slots: used_slots.min(total_slots),
             total_slots,
@@ -671,11 +671,11 @@ impl AccountSelector {
         if context.excluded_accounts.contains(candidate.account.id()) {
             return Some(AccountSchedulingBlocker::Excluded);
         }
-        if candidate.signals.in_flight
-            >= candidate
-                .account
-                .effective_concurrency(context.policy.max_concurrent_per_account())
-                .get()
+        if candidate
+            .account
+            .effective_concurrency(context.policy.max_concurrent_per_account())
+            .limit()
+            .is_some_and(|limit| candidate.signals.in_flight >= limit.get())
         {
             return Some(AccountSchedulingBlocker::ConcurrencyLimit);
         }
@@ -704,19 +704,22 @@ pub(crate) const SMART_SCORE_TOLERANCE: f64 = 0.05;
 // 首输出 10 秒时延迟得分减半；固定尺度不随其他候选账号变化。
 const SMART_LATENCY_HALF_SCORE_MS: f64 = 10_000.0;
 
-fn capacity_utilization(candidate: &AccountCandidate, default_concurrency: NonZeroU32) -> f64 {
-    f64::from(candidate.signals.in_flight)
-        / f64::from(
-            candidate
-                .account
-                .effective_concurrency(default_concurrency)
-                .get(),
-        )
+fn capacity_utilization(
+    candidate: &AccountCandidate,
+    default_concurrency: AccountConcurrency,
+) -> f64 {
+    candidate
+        .account
+        .effective_concurrency(default_concurrency)
+        .limit()
+        .map_or(0.0, |limit| {
+            f64::from(candidate.signals.in_flight) / f64::from(limit.get())
+        })
 }
 
 fn select_smart_candidate<'a>(
     candidates: &[&'a AccountCandidate],
-    default_concurrency: NonZeroU32,
+    default_concurrency: AccountConcurrency,
     cursor: u64,
 ) -> Option<&'a AccountCandidate> {
     let mut ranked = candidates
@@ -734,7 +737,10 @@ fn select_smart_candidate<'a>(
     Some(ranked[index].0)
 }
 
-pub(crate) fn smart_score(candidate: &AccountCandidate, default_concurrency: NonZeroU32) -> f64 {
+pub(crate) fn smart_score(
+    candidate: &AccountCandidate,
+    default_concurrency: AccountConcurrency,
+) -> f64 {
     let load = 1.0 - capacity_utilization(candidate, default_concurrency).clamp(0.0, 1.0);
     let quota = candidate
         .signals
diff --git a/backend/crates/gateway-core/src/provider_ports/mod.rs b/backend/crates/gateway-core/src/provider_ports/mod.rs
index c1ddb34c0..1a35c3301 100644
--- a/backend/crates/gateway-core/src/provider_ports/mod.rs
+++ b/backend/crates/gateway-core/src/provider_ports/mod.rs
@@ -9,8 +9,8 @@ use std::time::{Duration, SystemTime};
 use futures::future::BoxFuture;
 
 use crate::account::{
-    AccountFeedbackStats, AccountRuntimeSignals, CredentialRevision, CredentialState,
-    OpaqueProviderData, ProviderAccountId, ProviderAccountStore,
+    AccountConcurrency, AccountFeedbackStats, AccountRuntimeSignals, CredentialRevision,
+    CredentialState, OpaqueProviderData, ProviderAccountId, ProviderAccountStore,
 };
 use crate::identity::ProviderKind;
 use crate::policy::ClientApiKeyId;
@@ -83,18 +83,18 @@ pub struct ProviderSchedulingLeaseRequest {
     provider_kind: ProviderKind,
     account_id: ProviderAccountId,
     credential_revision: CredentialRevision,
-    max_concurrent: NonZeroU32,
+    max_concurrent: AccountConcurrency,
     request_interval: Duration,
     deadline: SystemTime,
 }
 
 impl ProviderSchedulingLeaseRequest {
     #[must_use]
-    pub const fn new(
+    pub fn new(
         provider_kind: ProviderKind,
         account_id: ProviderAccountId,
         credential_revision: CredentialRevision,
-        max_concurrent: NonZeroU32,
+        max_concurrent: impl Into<AccountConcurrency>,
         request_interval: Duration,
         deadline: SystemTime,
     ) -> Self {
@@ -102,7 +102,7 @@ impl ProviderSchedulingLeaseRequest {
             provider_kind,
             account_id,
             credential_revision,
-            max_concurrent,
+            max_concurrent: max_concurrent.into(),
             request_interval,
             deadline,
         }
@@ -124,7 +124,7 @@ impl ProviderSchedulingLeaseRequest {
     }
 
     #[must_use]
-    pub const fn max_concurrent(&self) -> NonZeroU32 {
+    pub const fn max_concurrent(&self) -> AccountConcurrency {
         self.max_concurrent
     }
 
diff --git a/backend/crates/gateway-core/src/routing/snapshot.rs b/backend/crates/gateway-core/src/routing/snapshot.rs
index 037b15a54..6b132b65e 100644
--- a/backend/crates/gateway-core/src/routing/snapshot.rs
+++ b/backend/crates/gateway-core/src/routing/snapshot.rs
@@ -7,7 +7,9 @@ use std::time::Duration;
 
 use futures::future::BoxFuture;
 
-use crate::account::{AccountSelectionPolicy, ProviderAccountId, RotationStrategy};
+use crate::account::{
+    AccountConcurrency, AccountSelectionPolicy, ProviderAccountId, RotationStrategy,
+};
 use crate::concurrency::ConcurrencyQueuePolicy;
 use crate::operation::Operation;
 use crate::policy::{
@@ -474,8 +476,7 @@ async fn compile_runtime_snapshot(
         .ok_or(RuntimeSnapshotCompileError::InvalidData)?;
     let selection_policy = AccountSelectionPolicy::new(
         rotation_strategy,
-        NonZeroU32::new(facts.settings.max_concurrent_per_account)
-            .ok_or(RuntimeSnapshotCompileError::InvalidData)?,
+        AccountConcurrency::new(facts.settings.max_concurrent_per_account),
         Duration::from_millis(facts.settings.request_interval_ms),
     )
     .with_queue(ConcurrencyQueuePolicy {
diff --git a/backend/crates/gateway-core/tests/account/mod.rs b/backend/crates/gateway-core/tests/account/mod.rs
index 048671b0c..edf98bcc2 100644
--- a/backend/crates/gateway-core/tests/account/mod.rs
+++ b/backend/crates/gateway-core/tests/account/mod.rs
@@ -77,7 +77,7 @@ fn weighted_candidate(id: &str, weight: u16, in_flight: u32) -> AccountCandidate
 
 #[test]
 fn account_scheduling_should_default_and_resolve_concurrency_override() {
-    let default = NonZeroU32::new(12).expect("default concurrency");
+    let default = gateway_core::account::AccountConcurrency::new(12);
     let account = account("acct_scheduling_default");
     assert_eq!(account.concurrency_limit(), None);
     assert_eq!(account.weight(), AccountWeight::DEFAULT);
diff --git a/backend/crates/gateway-core/tests/account/selection.rs b/backend/crates/gateway-core/tests/account/selection.rs
index 085cb8393..e9fa3cfd1 100644
--- a/backend/crates/gateway-core/tests/account/selection.rs
+++ b/backend/crates/gateway-core/tests/account/selection.rs
@@ -10,6 +10,91 @@ use super::{candidate, candidate_with_concurrency, context};
 
 const FAILURE_RATE_HALF_LIFE: Duration = Duration::from_secs(15 * 60);
 
+#[test]
+fn unlimited_account_concurrency_preserves_overrides_intervals_and_finite_scores() {
+    use gateway_core::account::{AccountConcurrency, AccountSelectionPolicy};
+
+    for strategy in [
+        RotationStrategy::Smart,
+        RotationStrategy::RoundRobin,
+        RotationStrategy::Sticky,
+        RotationStrategy::QuotaResetPriority,
+    ] {
+        let mut context = context(strategy);
+        context.policy =
+            AccountSelectionPolicy::new(strategy, AccountConcurrency::Unlimited, Duration::ZERO);
+        let candidates = [
+            candidate("acct_unlimited", u32::MAX, None),
+            candidate_with_concurrency("acct_limited", 2, 2),
+        ];
+        assert_eq!(
+            AccountSelector
+                .select(&candidates, &context)
+                .expect("unlimited remains eligible")
+                .candidate()
+                .account
+                .id()
+                .as_str(),
+            "acct_unlimited"
+        );
+        assert!(AccountSelector.select(&candidates[1..], &context).is_none());
+        assert!(
+            AccountSelector
+                .capacity_snapshot(&candidates, &context)
+                .is_none()
+        );
+        let trace = gateway_core::diagnostics::TraceContext::new("req_unlimited_concurrency");
+        trace.account_selection(
+            &candidates,
+            &context,
+            AccountSelector.select(&candidates, &context).as_ref(),
+        );
+        if strategy == RotationStrategy::Smart {
+            let snapshot = trace.snapshot().expect("trace");
+            assert!(
+                snapshot["events"][0]["data"]["candidates"][0]["smartScore"]
+                    .as_f64()
+                    .expect("finite score")
+                    .is_finite()
+            );
+        }
+        context.policy = AccountSelectionPolicy::new(
+            strategy,
+            AccountConcurrency::Unlimited,
+            Duration::from_secs(1),
+        );
+        let mut recent = candidate("acct_unlimited", u32::MAX, None);
+        recent.signals.last_started_at = Some(context.now);
+        assert!(AccountSelector.select(&[recent], &context).is_none());
+    }
+}
+
+#[test]
+fn unavailable_unlimited_account_does_not_hide_the_finite_pool_capacity() {
+    use gateway_core::account::{
+        AccountConcurrency, AccountSelectionPolicy, CredentialState, QuotaState,
+    };
+    let mut context = context(RotationStrategy::Smart);
+    context.policy = AccountSelectionPolicy::new(
+        RotationStrategy::Smart,
+        AccountConcurrency::Unlimited,
+        Duration::ZERO,
+    );
+    let mut unavailable = candidate("acct_disabled", 0, None);
+    unavailable.account = unavailable.account.with_account_facts(
+        false,
+        CredentialState::Ready,
+        QuotaState::unknown(),
+        None,
+        None,
+    );
+    let finite = candidate_with_concurrency("acct_limited", 1, 2);
+    let capacity = AccountSelector
+        .capacity_snapshot(&[unavailable, finite], &context)
+        .expect("finite available pool");
+    assert_eq!((capacity.used_slots(), capacity.total_slots()), (1, 2));
+}
+
 fn feedback_subject() -> (AccountFeedbackStats, ProviderKind, ProviderAccountId) {
     (
         AccountFeedbackStats::default(),
diff --git a/backend/crates/gateway-core/tests/routing/snapshot.rs b/backend/crates/gateway-core/tests/routing/snapshot.rs
index 809bc7796..330076c80 100644
--- a/backend/crates/gateway-core/tests/routing/snapshot.rs
+++ b/backend/crates/gateway-core/tests/routing/snapshot.rs
@@ -135,6 +135,43 @@ fn compiler_should_reject_revision_changed_during_consistent_read() {
     assert_eq!(error, RuntimeSnapshotCompileError::RevisionChanged);
 }
 
+#[test]
+fn compiler_accepts_unlimited_default_account_concurrency() {
+    let facts = SnapshotFacts::new(
+        revision(1),
+        revision(1),
+        SnapshotSettingsFacts::new(0, 50, "smart", BTreeMap::new(), None, None),
+        Vec::new(),
+        Vec::new(),
+        vec![SnapshotProviderAccountFacts::new(
+            gateway_core::account::ProviderAccountId::new("acct_unlimited").expect("account"),
+            "alpha",
+        )],
+        Vec::new(),
+    );
+    let compiler = RuntimeSnapshotCompiler::new(
+        Arc::new(TestSnapshotStore::new(Ok(facts))),
+        Arc::new(TestCatalog::Unavailable),
+    );
+    let snapshot = block_on(compiler.compile()).expect("compile unlimited default");
+    let plan = snapshot
+        .plan(
+            &PublicModelId::new("any-model").expect("model"),
+            &super::operation(),
+            snapshot.all_account_scope(),
+            &Default::default(),
+        )
+        .expect("plan request");
+    assert_eq!(
+        plan.account_selection_policy().max_concurrent_per_account(),
+        gateway_core::account::AccountConcurrency::Unlimited
+    );
+    assert_eq!(
+        plan.account_selection_policy().request_interval(),
+        std::time::Duration::from_millis(50)
+    );
+}
+
 #[test]
 fn routing_plans_share_frozen_pricing_after_a_new_snapshot_is_published() {
     use gateway_core::{metering::PricingOverrides, runtime::RuntimeSnapshotHandle};
diff --git a/backend/crates/gateway-store/src/postgres/account_groups.rs b/backend/crates/gateway-store/src/postgres/account_groups.rs
index 394ff76d1..6d6874e58 100644
--- a/backend/crates/gateway-store/src/postgres/account_groups.rs
+++ b/backend/crates/gateway-store/src/postgres/account_groups.rs
@@ -213,9 +213,10 @@ impl AccountGroupStore for PgAccountGroupRepository {
                         last_error_reason: account.last_error_reason,
                         last_error_message: account.last_error_message,
                     },
-                    total_slots: account
-                        .concurrency_limit
-                        .map_or(default_slots, |limit| u64::from(limit.get())),
+                    total_slots: account.concurrency_limit.map_or_else(
+                        || (default_slots > 0).then_some(default_slots),
+                        |limit| Some(u64::from(limit.get())),
+                    ),
                 })
             })
             .collect::<StoreResult<Vec<_>>>()
@@ -504,7 +505,7 @@ fn group_record(row: &sqlx::postgres::PgRow) -> StoreResult<AccountGroupRecord>
         },
         capacity: AccountGroupCapacity {
             used_slots: None,
-            total_slots: 0,
+            total_slots: Some(0),
         },
         usage: AccountGroupUsage {
             today_usd: DecimalAmount::from_str("0").map_err(|_| invalid("invalid zero cost"))?,
diff --git a/backend/crates/gateway-store/src/postgres/provider_accounts/admin_adapter.rs b/backend/crates/gateway-store/src/postgres/provider_accounts/admin_adapter.rs
index ac7b695a8..461d7bc24 100644
--- a/backend/crates/gateway-store/src/postgres/provider_accounts/admin_adapter.rs
+++ b/backend/crates/gateway-store/src/postgres/provider_accounts/admin_adapter.rs
@@ -755,7 +755,8 @@ impl AccountStore for PgAdminAccountStore {
                 .map_err(|_| postgres_unavailable("lock default concurrency"))?;
                 let changed = sqlx::query_scalar::<_, String>(
                     "update provider_accounts set concurrency_limit = $2, updated_at = greatest(now(), updated_at)
-                 where id = $1 and enabled = true and coalesce(concurrency_limit, $3) > $2
+                 where id = $1 and enabled = true
+                   and (coalesce(concurrency_limit, $3) = 0 or coalesce(concurrency_limit, $3) > $2)
                  returning id",
                 )
                 .bind(account_id.as_str())
diff --git a/backend/crates/gateway-store/src/postgres/runtime_settings.rs b/backend/crates/gateway-store/src/postgres/runtime_settings.rs
index 1fbcd4f45..8bc3f18f0 100644
--- a/backend/crates/gateway-store/src/postgres/runtime_settings.rs
+++ b/backend/crates/gateway-store/src/postgres/runtime_settings.rs
@@ -162,7 +162,6 @@ impl RuntimeSettingsUpdate {
             || isize::try_from(self.responses_max_decompressed_body_bytes).is_err()
             || self.refresh_margin_seconds == 0
             || self.refresh_concurrency == 0
-            || self.max_concurrent_per_account == 0
             || self.max_waiting_per_key > 1_000
             || self.max_waiting_per_account > 1_000
             || !(1..=120).contains(&self.concurrency_wait_timeout_seconds)
diff --git a/backend/crates/gateway-store/src/redis/credential_leases.rs b/backend/crates/gateway-store/src/redis/credential_leases.rs
index ed9fa8e0f..86e217ef9 100644
--- a/backend/crates/gateway-store/src/redis/credential_leases.rs
+++ b/backend/crates/gateway-store/src/redis/credential_leases.rs
@@ -38,7 +38,7 @@ local max_concurrent = tonumber(ARGV[4])
 local interval_ms = tonumber(ARGV[5])
 local retry_ms = 0
 
-if in_flight >= max_concurrent then
+if max_concurrent > 0 and in_flight >= max_concurrent then
   local earliest = redis.call('ZRANGE', KEYS[1], 0, 0, 'WITHSCORES')
   if #earliest == 2 then
     retry_ms = math.max(retry_ms, math.ceil(tonumber(earliest[2]) - now_ms))
@@ -177,7 +177,7 @@ impl CredentialBoundedLeaseRequest {
     pub fn validate(&self) -> StoreResult<()> {
         require_nonempty("credential bounded lease", "resource_id", &self.resource_id)?;
         require_nonempty("credential bounded lease", "owner_id", &self.owner_id)?;
-        if self.max_concurrent == 0 {
+        if self.max_concurrent == 0 && self.scope != CredentialLeaseScope::ProviderAccount {
             return Err(invalid("max_concurrent must be positive"));
         }
         supported_duration(self.request_interval, true, "request interval")?;
@@ -395,7 +395,7 @@ impl RedisCredentialLeaseRepository {
         request_interval: Duration,
     ) -> StoreResult<LeaseAttempt> {
         request.validate()?;
-        if max_concurrent == 0 {
+        if max_concurrent == 0 && request.scope != CredentialLeaseScope::ProviderAccount {
             return Err(invalid("max_concurrent must be positive"));
         }
         let keys = self.keys(request)?;
diff --git a/backend/crates/gateway-store/tests/postgres/account_groups.rs b/backend/crates/gateway-store/tests/postgres/account_groups.rs
index fa2c75b4f..87cfaceba 100644
--- a/backend/crates/gateway-store/tests/postgres/account_groups.rs
+++ b/backend/crates/gateway-store/tests/postgres/account_groups.rs
@@ -113,8 +113,11 @@ async fn groups_aggregate_cross_provider_members_and_key_bindings_without_multip
         .expect("load current-page group members");
     assert_eq!(members.len(), 2);
     assert_eq!(
-        members.iter().map(|member| member.total_slots).sum::<u64>(),
-        7
+        members
+            .iter()
+            .map(|member| member.total_slots)
+            .sum::<Option<u64>>(),
+        Some(7)
     );
     assert_eq!(page.total, 2);
     let by_id = page
@@ -134,7 +137,7 @@ async fn groups_aggregate_cross_provider_members_and_key_bindings_without_multip
     assert_eq!(mixed.account_summary.limited, 0);
     assert_eq!(mixed.account_summary.total, 0);
     assert_eq!(mixed.capacity.used_slots, None);
-    assert_eq!(mixed.capacity.total_slots, 0);
+    assert_eq!(mixed.capacity.total_slots, Some(0));
     assert_eq!(mixed.usage.today_usd.as_str(), "0");
     assert_eq!(mixed.usage.retained_total_usd.as_str(), "0");
     let empty = by_id.get(EMPTY_GROUP).expect("empty group");
diff --git a/backend/crates/gateway-store/tests/postgres/provider_accounts/mod.rs b/backend/crates/gateway-store/tests/postgres/provider_accounts/mod.rs
index 4f7b90804..ea19dba85 100644
--- a/backend/crates/gateway-store/tests/postgres/provider_accounts/mod.rs
+++ b/backend/crates/gateway-store/tests/postgres/provider_accounts/mod.rs
@@ -3445,7 +3445,8 @@ async fn model_access_only_batch_update_preserves_other_settings_and_survives_re
 }
 
 #[tokio::test]
-async fn adaptive_concurrency_uses_latest_locked_settings_without_overwriting_admin_fields() {
+async fn adaptive_concurrency_handles_unlimited_and_latest_locked_settings_without_overwriting_admin_fields()
+ {
     let Some(database) = TestDatabase::create("adaptive_concurrency").await else {
         return;
     };
@@ -3466,6 +3467,9 @@ async fn adaptive_concurrency_uses_latest_locked_settings_without_overwriting_ad
         (true, Some(2), 10, Some(2), false),
         (true, None, 2, None, false),
         (true, None, 10, Some(3), true),
+        (true, None, 0, Some(3), true),
+        (true, Some(2), 0, Some(2), false),
+        (false, None, 0, None, false),
     ] {
         let mut admin = database.pool.begin().await.expect("admin transaction");
         sqlx::query("update runtime_settings set max_concurrent_per_account = $1 where id = 1")
@@ -3520,6 +3524,9 @@ async fn adaptive_concurrency_uses_latest_locked_settings_without_overwriting_ad
     .fetch_all(&database.pool)
     .await
     .expect("audit");
-    assert_eq!(audited_fields, vec![vec!["concurrency_limit".to_owned()]]);
+    assert_eq!(
+        audited_fields,
+        vec![vec!["concurrency_limit".to_owned()]; 2]
+    );
     database.close().await;
 }
diff --git a/backend/crates/gateway-store/tests/postgres/runtime_settings.rs b/backend/crates/gateway-store/tests/postgres/runtime_settings.rs
index 8ad2a09b4..e11693bfb 100644
--- a/backend/crates/gateway-store/tests/postgres/runtime_settings.rs
+++ b/backend/crates/gateway-store/tests/postgres/runtime_settings.rs
@@ -48,6 +48,45 @@ fn runtime_settings_keep_account_rotation_global() {
     assert!(settings.validate().is_ok());
 }
 
+#[tokio::test]
+async fn unlimited_default_account_concurrency_round_trips_without_relaxing_other_limits() {
+    let Some(database) = TestDatabase::create("unlimited_default_concurrency").await else {
+        return;
+    };
+    let repository = PgRuntimeSettingsRepository::new(database.pool.clone());
+    let mut update = settings_with_margin(3_600);
+    update.max_concurrent_per_account = 0;
+    repository
+        .update_runtime_settings(update)
+        .await
+        .expect("persist unlimited default");
+    let settings = repository
+        .load_runtime_settings()
+        .await
+        .expect("read unlimited default");
+    assert_eq!(settings.max_concurrent_per_account, 0);
+    for statement in [
+        "update runtime_settings set max_concurrent_per_account = -1 where id = 1",
+        "update runtime_settings set refresh_concurrency = 0 where id = 1",
+        "update runtime_settings set refresh_margin_seconds = 0 where id = 1",
+        "update runtime_settings set request_interval_ms = -1 where id = 1",
+    ] {
+        let error = sqlx::query(statement)
+            .execute(&database.pool)
+            .await
+            .expect_err("constraint must reject invalid setting");
+        assert_eq!(
+            error
+                .as_database_error()
+                .and_then(|error| error.code())
+                .as_deref(),
+            Some("23514"),
+            "{statement}"
+        );
+    }
+    database.close().await;
+}
+
 #[test]
 fn runtime_settings_reject_invalid_model_mapping() {
     let settings = RuntimeSettingsUpdate {
diff --git a/backend/crates/gateway-store/tests/redis/credential_leases.rs b/backend/crates/gateway-store/tests/redis/credential_leases.rs
index 675258acf..2e2c0283d 100644
--- a/backend/crates/gateway-store/tests/redis/credential_leases.rs
+++ b/backend/crates/gateway-store/tests/redis/credential_leases.rs
@@ -19,9 +19,101 @@ fn credential_lease_rejects_zero_ttl() {
 }
 
 #[test]
-fn scheduling_lease_rejects_zero_concurrency() {
-    let request = scheduling_request("acct_invalid", "worker-invalid", 0, Duration::ZERO);
-    assert!(request.validate().is_err());
+fn only_account_scheduling_leases_allow_unlimited_concurrency() {
+    let mut request = scheduling_request("acct_unlimited", "worker-unlimited", 0, Duration::ZERO);
+    request.validate().expect("unlimited account concurrency");
+    for scope in [
+        CredentialLeaseScope::OAuthRefresh,
+        CredentialLeaseScope::OAuthRefreshCapacity,
+    ] {
+        request.scope = scope;
+        assert!(request.validate().is_err());
+    }
+}
+
+#[tokio::test]
+async fn unlimited_scheduling_leases_still_count_release_and_enforce_request_interval() {
+    let Some((repository, mut connection, namespace)) = repository().await else {
+        return;
+    };
+    let request = scheduling_request("acct_unlimited", "worker-unlimited", 0, Duration::ZERO);
+    let mut leases = Vec::new();
+    for _ in 0..5 {
+        leases.push(acquired(
+            repository
+                .try_acquire_bounded_lease(&request)
+                .await
+                .expect("unlimited slot"),
+        ));
+    }
+    assert_eq!(
+        repository
+            .credential_runtime_signals(std::slice::from_ref(&request.resource_id))
+            .await
+            .expect("signals")[0]
+            .in_flight,
+        5
+    );
+    let limited = CredentialBoundedLeaseRequest {
+        max_concurrent: 3,
+        ..request.clone()
+    };
+    assert!(matches!(
+        repository
+            .try_acquire_bounded_lease(&limited)
+            .await
+            .expect("positive limit still applies"),
+        CredentialBoundedLeaseAcquisition::Busy { .. }
+    ));
+    for lease in leases {
+        assert!(lease.release().await.expect("release unlimited slot"));
+    }
+    assert_eq!(
+        repository
+            .credential_runtime_signals(std::slice::from_ref(&request.resource_id))
+            .await
+            .expect("released signals")[0]
+            .in_flight,
+        0
+    );
+    let interval = scheduling_request(
+        "acct_unlimited_interval",
+        "worker-interval",
+        0,
+        Duration::from_secs(30),
+    );
+    acquired(
+        repository
+            .try_acquire_bounded_lease(&interval)
+            .await
+            .expect("first start"),
+    )
+    .release()
+    .await
+    .expect("release interval slot");
+    assert!(
+        matches!(repository.try_acquire_bounded_lease(&interval).await.expect("interval decision"), CredentialBoundedLeaseAcquisition::Busy { retry_after: Some(value) } if value > Duration::ZERO)
+    );
+    let keys = redis::cmd("KEYS")
+        .arg(format!("{namespace}:*"))
+        .query_async::<Vec<String>>(&mut connection)
+        .await
+        .expect("isolated keys");
+    for key in &keys {
+        assert!(
+            redis::cmd("PTTL")
+                .arg(key)
+                .query_async::<i64>(&mut connection)
+                .await
+                .expect("TTL")
+                > 0
+        );
+    }
+    redis::cmd("DEL")
+        .arg(keys)
+        .query_async::<i64>(&mut connection)
+        .await
+        .expect("cleanup isolated keys");
 }
 
 #[tokio::test]
diff --git a/backend/crates/providers/openai/src/credential/selector.rs b/backend/crates/providers/openai/src/credential/selector.rs
index 29418af90..0b11637dc 100644
--- a/backend/crates/providers/openai/src/credential/selector.rs
+++ b/backend/crates/providers/openai/src/credential/selector.rs
@@ -43,6 +43,7 @@ const CLOUDFLARE_CHALLENGE_BACKOFF: [Duration; 4] = [
 const CLOUDFLARE_PATH_BLOCK_THRESHOLD: u32 = 3;
 const SESSION_AFFINITY_TIMEOUT: Duration = Duration::from_millis(100);
 const CYBER_POLICY_SESSION_TTL: Duration = Duration::from_secs(60 * 60);
+const MAX_ACCOUNT_SNAPSHOT_RETRIES: u32 = 3;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum CodexAccountFailure {
@@ -351,6 +352,7 @@ impl CodexCredentialSelector {
             request.attempt.deadline(),
             request.attempt.concurrency_wait_budget(),
         );
+        let mut snapshot_retries = 0;
         'capacity: loop {
             let diagnostic = request.attempt.is_diagnostic_required_account();
             let mut accounts = self.repository.list_for_provider().await?;
@@ -396,7 +398,18 @@ impl CodexCredentialSelector {
                 if request.requires_websocket
                     && account.authentication_kind() == super::CODEX_AUTHENTICATION_KIND_API_KEY
                 {
-                    let runtime = self.repository.load_runtime_credential(&account).await?;
+                    let runtime = match self.repository.load_runtime_credential(&account).await {
+                        Ok(runtime) => runtime,
+                        Err(CredentialRepositoryError::RevisionConflict) => {
+                            retry_account_snapshot(
+                                request.attempt,
+                                &account,
+                                &mut snapshot_retries,
+                            )?;
+                            continue 'capacity;
+                        }
+                        Err(error) => return Err(error.into()),
+                    };
                     if !matches!(runtime.authentication, CodexRuntimeAuthentication::ApiKey(ref auth)
                         if auth.configuration.transport == super::ApiKeyTransport::PreferWebsocket)
                     {
@@ -609,6 +622,16 @@ impl CodexCredentialSelector {
                     .find(|candidate| candidate.account.id() == selected.account.id())
                     .map(|candidate| candidate.account.clone())
                     .ok_or(CredentialSelectionError::InvalidCredential)?;
+                // 额度观测等并发更新会使整个账号快照失效，必须重新选号并校验资格。
+                // 在占用租约和请求间隔前完成校验，避免重读被自己的异步释放挡住。
+                let runtime = match self.repository.load_runtime_credential(&account).await {
+                    Ok(runtime) => runtime,
+                    Err(CredentialRepositoryError::RevisionConflict) => {
+                        retry_account_snapshot(request.attempt, &account, &mut snapshot_retries)?;
+                        continue 'capacity;
+                    }
+                    Err(error) => return Err(error.into()),
+                };
                 let allows_account_state_mutation = !diagnostic || account.enabled();
                 match self
                     .leases
@@ -690,7 +713,6 @@ impl CodexCredentialSelector {
                                 .is_some_and(CodexSessionAffinity::session_id_present),
                             "OpenAI account selected"
                         );
-                        let runtime = self.repository.load_runtime_credential(&account).await?;
                         let cookies = runtime
                             .cookies
                             .into_iter()
@@ -1459,6 +1481,32 @@ impl fmt::Debug for CodexCredentialLease {
     }
 }
 
+fn retry_account_snapshot(
+    attempt: &AttemptContext,
+    account: &ProviderAccount,
+    retries: &mut u32,
+) -> Result<(), CredentialSelectionError> {
+    let retry = *retries < MAX_ACCOUNT_SNAPSHOT_RETRIES;
+    if retry {
+        *retries += 1;
+    }
+    attempt.trace().record(
+        "account.snapshot_conflict",
+        serde_json::json!({
+            "accountId": account.id().as_str(),
+            "credentialRevision": account.revision().get(),
+            "retry": retry,
+            "retryCount": *retries,
+            "maxRetries": MAX_ACCOUNT_SNAPSHOT_RETRIES,
+        }),
+    );
+    if retry {
+        Ok(())
+    } else {
+        Err(CredentialSelectionError::AccountSnapshotChanged)
+    }
+}
+
 #[derive(Debug, Error)]
 pub enum CredentialSelectionError {
     #[error(transparent)]
@@ -1471,6 +1519,8 @@ pub enum CredentialSelectionError {
     CapacityUnavailable { retry_after: Option<Duration> },
     #[error("Codex account data is invalid")]
     InvalidCredential,
+    #[error("Codex account changed repeatedly during selection")]
+    AccountSnapshotChanged,
     #[error("Codex account store is unavailable")]
     Store,
     #[error("Codex account lease runtime is unavailable")]
diff --git a/backend/crates/providers/openai/src/provider/observation.rs b/backend/crates/providers/openai/src/provider/observation.rs
index 620f56420..7040ab50c 100644
--- a/backend/crates/providers/openai/src/provider/observation.rs
+++ b/backend/crates/providers/openai/src/provider/observation.rs
@@ -797,6 +797,14 @@ pub(super) fn map_selection_error(error: CredentialSelectionError) -> ProviderEr
             Some("usage_limit_reached".to_owned()),
             Some("usage_limit_reached".to_owned()),
         )),
+        CredentialSelectionError::AccountSnapshotChanged => provider_error(
+            ProviderErrorKind::ProviderInfrastructureUnavailable,
+            UpstreamSendState::NotSent,
+        )
+        .with_diagnostic(
+            ProviderDiagnostic::new("OpenAI account changed repeatedly during selection")
+                .with_classification("account_selection", "account_snapshot_conflict"),
+        ),
         CredentialSelectionError::InvalidCredential
         | CredentialSelectionError::Store
         | CredentialSelectionError::Coordinator
diff --git a/backend/crates/providers/openai/tests/credential/contract.rs b/backend/crates/providers/openai/tests/credential/contract.rs
index 102d75774..694784985 100644
--- a/backend/crates/providers/openai/tests/credential/contract.rs
+++ b/backend/crates/providers/openai/tests/credential/contract.rs
@@ -411,6 +411,226 @@ fn selector_uses_the_account_concurrency_override_for_the_redis_lease() {
     assert_eq!(requests[0].max_concurrent().get(), 7);
 }
 
+#[test]
+fn selector_reloads_quota_snapshot_before_acquiring_the_only_lease() {
+    let store = Arc::new(MemoryAccountStore::default());
+    create_account(&store, "acct_primary", "at-primary");
+    store.set_scheduling(
+        "acct_primary",
+        Some(AccountConcurrencyLimit::new(1).expect("single slot")),
+        AccountWeight::DEFAULT,
+    );
+    let original = store.account("acct_primary").expect("account");
+    let observed_at = SystemTime::now();
+    block_on(store.apply_quota_access(QuotaAccessChange {
+        account_id: original.id().clone(),
+        expected_revision: original.revision(),
+        state: QuotaState::allowed(observed_at),
+    }))
+    .expect("initial quota observation");
+    store.on_credential_load(Arc::new(move |store, id, count| {
+        Box::pin(async move {
+            if count == 1 {
+                let account = store.account(id.as_str()).expect("account");
+                store
+                    .apply_quota_access(QuotaAccessChange {
+                        account_id: id.clone(),
+                        expected_revision: account.revision(),
+                        state: QuotaState::allowed(observed_at + Duration::from_millis(1)),
+                    })
+                    .await?;
+            }
+            Ok(())
+        })
+    }));
+    let leases = Arc::new(TestLeaseCoordinator::default());
+    let selector = selector(&store, Arc::clone(&leases));
+    let attempt = attempt(BTreeSet::new());
+    let selected = block_on(selector.select(&SelectCodexCredential {
+        upstream_model: "gpt-5.4",
+        request_url: &Url::parse("https://chatgpt.com/backend-api/codex/responses").expect("URL"),
+        attempt: &attempt,
+        session_affinity_key: None,
+    }))
+    .expect("a newer allowed observation must not fail selection");
+
+    assert_eq!(selected.account().revision(), original.revision());
+    assert_eq!(
+        selected.account(),
+        &store.account("acct_primary").expect("current account")
+    );
+    assert_eq!(store.credential_loads(), 2);
+    let requests = leases.requests.lock().expect("lease requests");
+    assert_eq!(
+        requests.len(),
+        1,
+        "conflicted snapshots must never consume capacity or request interval"
+    );
+    assert_eq!(requests[0].max_concurrent().get(), 1);
+    assert_eq!(requests[0].request_interval(), Duration::from_millis(10));
+}
+
+#[test]
+fn selector_uses_rotated_credentials_after_a_snapshot_conflict() {
+    use gateway_core::account::{CredentialCasOutcome, CredentialCasUpdate, ProviderAccountUpdate};
+
+    let store = Arc::new(MemoryAccountStore::default());
+    create_account(&store, "acct_primary", "at-old");
+    let old_revision = store.account("acct_primary").expect("account").revision();
+    store.on_credential_load(Arc::new(|store, id, count| {
+        Box::pin(async move {
+            if count == 1 {
+                let account = store.account(id.as_str()).expect("account");
+                let update = CredentialCasUpdate::new(
+                    id.clone(),
+                    account.revision(),
+                    ProviderAccountUpdate {
+                        account_id: id.clone(),
+                        name: account.name().to_owned(),
+                        email: account.email().map(str::to_owned),
+                        plan_type: account.plan_type().map(str::to_owned),
+                    },
+                    CodexCredentialCodec::encode_new(
+                        &secret("at-rotated"),
+                        &profile("chatgpt-acct_primary"),
+                        Vec::new(),
+                    )
+                    .expect("rotated credential"),
+                    account.has_refresh_token(),
+                    account.access_token_expires_at(),
+                    account.next_refresh_at(),
+                )
+                .expect("credential update")
+                .preserving_profile();
+                assert!(matches!(
+                    store.compare_and_swap_credential(update).await?,
+                    CredentialCasOutcome::Updated(_)
+                ));
+            }
+            Ok(())
+        })
+    }));
+    let leases = Arc::new(TestLeaseCoordinator::default());
+    let selector = selector(&store, Arc::clone(&leases));
+    let attempt = attempt(BTreeSet::new());
+    let selected = block_on(selector.select(&SelectCodexCredential {
+        upstream_model: "gpt-5.4",
+        request_url: &Url::parse("https://chatgpt.com/backend-api/codex/responses").expect("URL"),
+        attempt: &attempt,
+        session_affinity_key: None,
+    }))
+    .expect("reload rotated credentials");
+
+    assert_eq!(
+        selected.account().revision(),
+        old_revision.next().expect("next revision")
+    );
+    assert_eq!(
+        selected
+            .authentication()
+            .oauth()
+            .expect("OAuth")
+            .access_token
+            .expose_secret(),
+        "at-rotated"
+    );
+    assert_eq!(store.credential_loads(), 2);
+    let requests = leases.requests.lock().expect("lease requests");
+    assert_eq!(requests.len(), 1);
+    assert_eq!(
+        requests[0].credential_revision(),
+        selected.account().revision()
+    );
+}
+
+#[test]
+fn selector_snapshot_retry_preserves_frozen_account_scope_and_model_permissions() {
+    let store = Arc::new(MemoryAccountStore::default());
+    for id in ["acct_primary", "acct_other", "acct_outside_scope"] {
+        create_account(&store, id, "at-test");
+    }
+    store.on_credential_load(Arc::new(|store, id, count| {
+        Box::pin(async move {
+            assert_eq!(id.as_str(), "acct_primary");
+            assert_eq!(count, 1);
+            store.set_enabled(id, false).await
+        })
+    }));
+    let leases = Arc::new(TestLeaseCoordinator::default());
+    let selector = selector(&store, Arc::clone(&leases));
+    let attempt = model_restricted_attempt(None, BTreeSet::new());
+    let error = block_on(selector.select(&SelectCodexCredential {
+        upstream_model: "test-luna",
+        request_url: &Url::parse("https://chatgpt.com/backend-api/codex/responses").expect("URL"),
+        attempt: &attempt,
+        session_affinity_key: None,
+    }))
+    .expect_err("retry cannot escape the frozen scope or use a denied model");
+
+    assert!(matches!(
+        error,
+        CredentialSelectionError::NoEligibleCredential
+    ));
+    assert!(leases.requests.lock().expect("lease requests").is_empty());
+}
+
+#[test]
+fn selector_does_not_retry_credential_store_unavailability() {
+    let store = Arc::new(MemoryAccountStore::default());
+    create_account(&store, "acct_primary", "at-primary");
+    store.on_credential_load(Arc::new(|_, _, _| {
+        Box::pin(async {
+            Err(gateway_core::error::StoreError::new(
+                gateway_core::error::StoreErrorKind::Unavailable,
+            ))
+        })
+    }));
+    let leases = Arc::new(TestLeaseCoordinator::default());
+    let selector = selector(&store, Arc::clone(&leases));
+    let attempt = attempt(BTreeSet::new());
+    let error = block_on(selector.select(&SelectCodexCredential {
+        upstream_model: "gpt-5.4",
+        request_url: &Url::parse("https://chatgpt.com/backend-api/codex/responses").expect("URL"),
+        attempt: &attempt,
+        session_affinity_key: None,
+    }))
+    .expect_err("unavailability is not an account snapshot conflict");
+
+    assert!(matches!(error, CredentialSelectionError::Store));
+    assert_eq!(store.credential_loads(), 1);
+    assert!(leases.requests.lock().expect("lease requests").is_empty());
+}
+
+#[test]
+fn selector_does_not_retry_invalid_credential_data() {
+    use gateway_core::account::{NewProviderAccount, PlaintextCredential};
+
+    let store = Arc::new(MemoryAccountStore::default());
+    create_account(&store, "acct_primary", "at-primary");
+    let account = store.account("acct_primary").expect("account");
+    block_on(store.delete_account(account.id())).expect("replace stored credential");
+    block_on(store.create_account(NewProviderAccount {
+        account,
+        credential: PlaintextCredential::new(serde_json::Map::new()),
+        model_access: None,
+    }))
+    .expect("persist invalid provider data");
+    let leases = Arc::new(TestLeaseCoordinator::default());
+    let selector = selector(&store, Arc::clone(&leases));
+    let attempt = attempt(BTreeSet::new());
+    let error = block_on(selector.select(&SelectCodexCredential {
+        upstream_model: "gpt-5.4",
+        request_url: &Url::parse("https://chatgpt.com/backend-api/codex/responses").expect("URL"),
+        attempt: &attempt,
+        session_affinity_key: None,
+    }))
+    .expect_err("invalid data is not an account snapshot conflict");
+
+    assert!(matches!(error, CredentialSelectionError::InvalidCredential));
+    assert_eq!(store.credential_loads(), 1);
+    assert!(leases.requests.lock().expect("lease requests").is_empty());
+}
+
 #[test]
 fn selector_round_robin_cursor_advances_across_requests() {
     let store = Arc::new(MemoryAccountStore::default());
diff --git a/backend/crates/providers/openai/tests/provider/contract.rs b/backend/crates/providers/openai/tests/provider/contract.rs
index 203471675..d17792a37 100644
--- a/backend/crates/providers/openai/tests/provider/contract.rs
+++ b/backend/crates/providers/openai/tests/provider/contract.rs
@@ -1504,6 +1504,340 @@ async fn generate_without_an_eligible_openai_account_fails_before_network_io() {
     assert_eq!(error.send_state(), UpstreamSendState::NotSent);
 }
 
+#[tokio::test]
+async fn quota_snapshot_race_reloads_and_sends_the_request_once() {
+    let store = Arc::new(MemoryAccountStore::default());
+    create_account(&store, "acct_provider_contract").await;
+    let original = store.account("acct_provider_contract").expect("account");
+    let observed_at = SystemTime::now();
+    store
+        .apply_quota_access(QuotaAccessChange {
+            account_id: original.id().clone(),
+            expected_revision: original.revision(),
+            state: QuotaState::allowed(observed_at),
+        })
+        .await
+        .expect("initial quota");
+    store.on_credential_load(Arc::new(move |store, id, count| {
+        Box::pin(async move {
+            if count == 1 {
+                let account = store.account(id.as_str()).expect("account");
+                store
+                    .apply_quota_access(QuotaAccessChange {
+                        account_id: id.clone(),
+                        expected_revision: account.revision(),
+                        state: QuotaState::allowed(observed_at + Duration::from_millis(1)),
+                    })
+                    .await?;
+            }
+            Ok(())
+        })
+    }));
+    let upstream = MockServer::start().await;
+    Mock::given(method("POST"))
+        .and(path("/codex/responses"))
+        .and(header("authorization", "Bearer at-acct_provider_contract"))
+        .respond_with(
+            ResponseTemplate::new(200).set_body_raw(CAPTURE_COMPLETED_SSE, "text/event-stream"),
+        )
+        .expect(1)
+        .mount(&upstream)
+        .await;
+    let leases = Arc::new(TestLeaseCoordinator::default());
+    let provider = provider_with_affinity_and_base_url_and_leases(
+        &store,
+        Arc::new(MemorySessionAffinity::default()),
+        upstream.uri(),
+        Arc::clone(&leases),
+    );
+    let mut stream = provider
+        .execute(
+            planned_request("openai", http_generate_operation()),
+            context("req_quota_snapshot_race", CancellationToken::new()),
+        )
+        .await
+        .expect("concurrent quota observation must not fail prepare");
+    assert_eq!(stream.metadata().provider_account_id(), original.id());
+    assert_eq!(store.credential_loads(), 2);
+    assert_eq!(leases.requests.lock().expect("leases").len(), 1);
+    let mut completed = false;
+    while let Some(event) = stream.next().await {
+        let event = event.expect("upstream event");
+        completed |= event
+            .wire_event()
+            .is_some_and(|wire| wire.data()["type"] == "response.completed");
+    }
+    assert!(
+        completed,
+        "the successful upstream response must reach the client stream"
+    );
+    upstream.verify().await;
+}
+
+#[tokio::test]
+async fn snapshot_retry_rechecks_account_availability_without_sending() {
+    for change in ["disabled", "revoked", "exhausted"] {
+        let store = Arc::new(MemoryAccountStore::default());
+        create_account(&store, "acct_provider_contract").await;
+        store.on_credential_load(Arc::new(move |store, id, count| {
+            Box::pin(async move {
+                assert_eq!(count, 1, "an unavailable account cannot be selected again");
+                let account = store.account(id.as_str()).expect("account");
+                match change {
+                    "disabled" => store.set_enabled(id, false).await?,
+                    "revoked" => {
+                        store
+                            .apply_state_change(gateway_core::account::AccountStateChange {
+                                account_id: id.clone(),
+                                expected_revision: account.revision(),
+                                credential_state: CredentialState::Invalid,
+                                observed_at: SystemTime::now(),
+                                error_reason: None,
+                                message: None,
+                            })
+                            .await?
+                    }
+                    "exhausted" => {
+                        store
+                            .apply_quota_access(QuotaAccessChange {
+                                account_id: id.clone(),
+                                expected_revision: account.revision(),
+                                state: QuotaState::exhausted(
+                                    QuotaEvidence::UsageLimitReached,
+                                    SystemTime::now(),
+                                    None,
+                                ),
+                            })
+                            .await?;
+                    }
+                    _ => unreachable!("test case"),
+                }
+                Ok(())
+            })
+        }));
+        let upstream = MockServer::start().await;
+        let leases = Arc::new(TestLeaseCoordinator::default());
+        let provider = provider_with_affinity_and_base_url_and_leases(
+            &store,
+            Arc::new(MemorySessionAffinity::default()),
+            upstream.uri(),
+            Arc::clone(&leases),
+        );
+        let Err(error) = provider
+            .execute(
+                planned_request("openai", http_generate_operation()),
+                context("req_snapshot_unavailable", CancellationToken::new()),
+            )
+            .await
+        else {
+            panic!("{change} account must not produce an upstream stream");
+        };
+        let expected = if change == "exhausted" {
+            ProviderErrorKind::QuotaExhausted
+        } else {
+            ProviderErrorKind::NoEligibleAccount
+        };
+        assert_eq!(error.kind(), expected, "{change}");
+        assert_eq!(error.send_state(), UpstreamSendState::NotSent);
+        assert!(leases.requests.lock().expect("leases").is_empty());
+        assert!(
+            upstream
+                .received_requests()
+                .await
+                .expect("requests")
+                .is_empty()
+        );
+    }
+}
+
+#[tokio::test]
+async fn snapshot_retry_cannot_switch_a_disabled_native_continuation_account() {
+    let store = Arc::new(MemoryAccountStore::default());
+    create_account(&store, "acct_provider_contract").await;
+    create_account(&store, "acct_scope_new").await;
+    store.on_credential_load(Arc::new(|store, id, count| {
+        Box::pin(async move {
+            assert_eq!(id.as_str(), "acct_provider_contract");
+            assert_eq!(count, 1);
+            store.set_enabled(id, false).await
+        })
+    }));
+    let upstream = MockServer::start().await;
+    let leases = Arc::new(TestLeaseCoordinator::default());
+    let provider = provider_with_affinity_and_base_url_and_leases(
+        &store,
+        Arc::new(MemorySessionAffinity::default()),
+        upstream.uri(),
+        Arc::clone(&leases),
+    );
+    let Err(error) = provider
+        .execute(
+            planned_request("openai", http_generate_operation()),
+            pinned_continuation_context(
+                "req_snapshot_pinned",
+                "acct_provider_contract",
+                "client-previous",
+                "upstream-previous",
+                1,
+                ContinuationAttempt::Native,
+            ),
+        )
+        .await
+    else {
+        panic!("native continuation cannot move to the healthy second account");
+    };
+    assert_eq!(error.kind(), ProviderErrorKind::NoEligibleAccount);
+    assert_eq!(error.send_state(), UpstreamSendState::NotSent);
+    assert!(leases.requests.lock().expect("leases").is_empty());
+    assert!(
+        upstream
+            .received_requests()
+            .await
+            .expect("requests")
+            .is_empty()
+    );
+}
+
+#[tokio::test]
+async fn repeated_snapshot_conflicts_are_bounded_and_report_the_selection_stage() {
+    let store = Arc::new(MemoryAccountStore::default());
+    create_account(&store, "acct_provider_contract").await;
+    store.on_credential_load(Arc::new(|store, id, count| {
+        Box::pin(async move {
+            assert!(count <= 4, "snapshot conflict retries must be bounded");
+            let account = store.account(id.as_str()).expect("account");
+            let observed_at = account
+                .quota()
+                .observed_at()
+                .unwrap_or_else(SystemTime::now)
+                + Duration::from_millis(1);
+            store
+                .apply_quota_access(QuotaAccessChange {
+                    account_id: id.clone(),
+                    expected_revision: account.revision(),
+                    state: QuotaState::allowed(observed_at),
+                })
+                .await?;
+            Ok(())
+        })
+    }));
+    let upstream = MockServer::start().await;
+    let leases = Arc::new(TestLeaseCoordinator::default());
+    let provider = provider_with_affinity_and_base_url_and_leases(
+        &store,
+        Arc::new(MemorySessionAffinity::default()),
+        upstream.uri(),
+        Arc::clone(&leases),
+    );
+    let Err(error) = provider
+        .execute(
+            planned_request("openai", http_generate_operation()),
+            context("req_snapshot_conflicts", CancellationToken::new()),
+        )
+        .await
+    else {
+        panic!("continuously changing snapshots must not be sent");
+    };
+    assert_eq!(
+        error.kind(),
+        ProviderErrorKind::ProviderInfrastructureUnavailable
+    );
+    assert_eq!(error.send_state(), UpstreamSendState::NotSent);
+    let diagnostic = error.diagnostic().expect("selection diagnostic");
+    assert_eq!(diagnostic.stage(), Some("account_selection"));
+    assert_eq!(diagnostic.code(), Some("account_snapshot_conflict"));
+    assert_eq!(store.credential_loads(), 4);
+    assert!(leases.requests.lock().expect("leases").is_empty());
+    assert!(
+        upstream
+            .received_requests()
+            .await
+            .expect("requests")
+            .is_empty()
+    );
+}
+
+#[tokio::test]
+async fn api_websocket_precheck_and_selection_share_the_snapshot_retry_budget() {
+    let upstream = MockServer::start().await;
+    let store = Arc::new(MemoryAccountStore::default());
+    store
+        .seed_api_key(
+            "acct_provider_contract",
+            upstream.uri(),
+            provider_openai::credential::ApiKeyTransport::PreferWebsocket,
+        )
+        .await;
+    store.on_credential_load(Arc::new(|store, id, count| {
+        Box::pin(async move {
+            assert!(
+                count <= 6,
+                "both credential checks must share one retry budget"
+            );
+            // 第 1、4 次在传输预检冲突，第 3、6 次在最终候选校验冲突。
+            if matches!(count, 1 | 3 | 4 | 6) {
+                let account = store.account(id.as_str()).expect("account");
+                let observed_at = account
+                    .quota()
+                    .observed_at()
+                    .unwrap_or_else(SystemTime::now)
+                    + Duration::from_millis(1);
+                store
+                    .apply_quota_access(QuotaAccessChange {
+                        account_id: id.clone(),
+                        expected_revision: account.revision(),
+                        state: QuotaState::allowed(observed_at),
+                    })
+                    .await?;
+            }
+            Ok(())
+        })
+    }));
+    let leases = Arc::new(TestLeaseCoordinator::default());
+    let provider = provider_with_affinity_and_base_url_and_leases(
+        &store,
+        Arc::new(MemorySessionAffinity::default()),
+        upstream.uri(),
+        Arc::clone(&leases),
+    );
+    let warmup = Operation::Generate(GenerateRequest::from_protocol_payload(
+        ProtocolPayload::json_object(
+            "openai",
+            json!({"model":"gpt-5.4","input":[],"store":false,"generate":false})
+                .as_object()
+                .expect("object")
+                .clone(),
+        )
+        .expect("warmup"),
+    ));
+    let Err(error) = provider
+        .execute(
+            planned_request("openai", warmup),
+            context("req_api_snapshot_conflicts", CancellationToken::new()),
+        )
+        .await
+    else {
+        panic!("mixed snapshot conflicts must stop before WebSocket connection");
+    };
+    assert_eq!(
+        error.kind(),
+        ProviderErrorKind::ProviderInfrastructureUnavailable
+    );
+    assert_eq!(
+        error.diagnostic().and_then(|diagnostic| diagnostic.code()),
+        Some("account_snapshot_conflict")
+    );
+    assert_eq!(store.credential_loads(), 6);
+    assert!(leases.requests.lock().expect("leases").is_empty());
+    assert!(
+        upstream
+            .received_requests()
+            .await
+            .expect("requests")
+            .is_empty()
+    );
+}
+
 async fn exhaust_account_quota(store: &Arc<MemoryAccountStore>, account_id: &str) {
     let account = store.account(account_id).expect("test account");
     store
diff --git a/backend/crates/providers/openai/tests/support.rs b/backend/crates/providers/openai/tests/support.rs
index 0b09601a8..07ec6454f 100644
--- a/backend/crates/providers/openai/tests/support.rs
+++ b/backend/crates/providers/openai/tests/support.rs
@@ -41,11 +41,21 @@ struct StoredAccount {
     state_observed_at: Option<SystemTime>,
 }
 
+type CredentialLoadHook = dyn for<'a> Fn(
+        &'a MemoryAccountStore,
+        &'a ProviderAccountId,
+        usize,
+    ) -> BoxFuture<'a, Result<(), StoreError>>
+    + Send
+    + Sync;
+
 #[derive(Default)]
 pub(crate) struct MemoryAccountStore {
     accounts: Mutex<BTreeMap<ProviderAccountId, StoredAccount>>,
     quota_reads: AtomicUsize,
     fail_provider_listing: AtomicBool,
+    credential_load_hook: Mutex<Option<Arc<CredentialLoadHook>>>,
+    credential_loads: AtomicUsize,
 }
 
 impl MemoryAccountStore {
@@ -175,6 +185,17 @@ impl MemoryAccountStore {
     pub(crate) fn fail_provider_listing(&self) {
         self.fail_provider_listing.store(true, Ordering::SeqCst);
     }
+
+    pub(crate) fn on_credential_load(&self, hook: Arc<CredentialLoadHook>) {
+        *self
+            .credential_load_hook
+            .lock()
+            .expect("credential hook lock") = Some(hook);
+    }
+
+    pub(crate) fn credential_loads(&self) -> usize {
+        self.credential_loads.load(Ordering::SeqCst)
+    }
 }
 
 #[async_trait]
@@ -266,6 +287,16 @@ impl ProviderAccountStore for MemoryAccountStore {
         account: &ProviderAccountId,
         expected_revision: CredentialRevision,
     ) -> Result<LoadedCredential, StoreError> {
+        let count = self.credential_loads.fetch_add(1, Ordering::SeqCst) + 1;
+        let hook = self
+            .credential_load_hook
+            .lock()
+            .expect("credential hook lock")
+            .clone();
+        // 在列表快照与凭据读取之间确定性提交并发变更，不依赖线程调度或延时。
+        if let Some(hook) = hook {
+            hook(self, account, count).await?;
+        }
         let loaded = self.load_current_credential(account).await?;
         if loaded.account.revision() != expected_revision {
             return Err(store_error(StoreErrorKind::Conflict));
diff --git a/backend/migrations/.frozen-sha256 b/backend/migrations/.frozen-sha256
index b9df0bc09..8d360df6e 100644
--- a/backend/migrations/.frozen-sha256
+++ b/backend/migrations/.frozen-sha256
@@ -14,3 +14,4 @@ b20e425c0b062b72d35fdebe294e023eb17ceb44ac93083ff3d48400715bf430  0012_upstream_
 12a540be31d65c4925cbe63dab42ea2d4ec2864fecf71a6dd4ee942e71726857  0014_disable_fast.sql
 9bd37bd314b6864816c43cb4fd1869fb415920d4f10f766976e344334a1f60fc  0015_proxy_dual_stack_exit.sql
 a1e23b8535ed41de27861833cd2d5ee7498a9bb0e523156ba3f011f9c6b3966b  0016_client_profiles_and_model_pricing.sql
+fcfae912ddefd54551ebf8e7e733442519d2862d2977134d548ebc1e75c1dc34  0017_unlimited_default_account_concurrency.sql
diff --git a/backend/migrations/0017_unlimited_default_account_concurrency.sql b/backend/migrations/0017_unlimited_default_account_concurrency.sql
new file mode 100644
index 000000000..c488242fa
--- /dev/null
+++ b/backend/migrations/0017_unlimited_default_account_concurrency.sql
@@ -0,0 +1,8 @@
+alter table runtime_settings
+  drop constraint runtime_settings_refresh_ck,
+  add constraint runtime_settings_refresh_ck check (
+    refresh_margin_seconds > 0
+    and refresh_concurrency > 0
+    and max_concurrent_per_account >= 0
+    and request_interval_ms >= 0
+  );
diff --git a/docs/api.md b/docs/api.md
index c42d69a93..50293a7c0 100644
--- a/docs/api.md
+++ b/docs/api.md
@@ -934,6 +934,8 @@ HTTP 请求头及新建 WS 的握手提示按当时的最终出站档位构造
 列表数据为 `{ items, page, configRevision }`，其中 item 返回 `memberCount`、按 Provider 聚合的
 `providerCounts` 和 `clientKeyCount`。查询分组成员使用账号列表的 `groupId` 筛选，
 不提供独立的分组成员路由；账号的 Provider 不代表整个分组的 Provider。
+`capacity.totalSlots` 为 `number | null`：`null` 表示可用成员中存在继承无限并发的账号，`0` 表示没有可用槽位。
+`capacity.usedSlots` 继续返回实际在途数；Redis 不可用时为 `null`。
 
 ## 7. Client Key
 
@@ -1071,6 +1073,10 @@ accountAutoFreezeAdaptiveConcurrency
 关联代理配置了自定义位置时优先使用代理值。保存后通过现有配置发布机制对新请求生效，
 已开始请求及其重试保持同一份全局值；普通文本、绝对时间戳和数据驻留要求不受影响。
 
+`maxConcurrentPerAccount` 是默认账号并发上限，取值 0～4294967295；`0` 表示不限制。
+账号的 `concurrencyLimit: null` 继承该默认值，单独设置的正数上限仍优先生效。
+无限并发仍统计在途请求，并遵守最小请求间隔、账号可用性与 Client Key 限制。
+
 `maxWaitingPerKey` 与 `maxWaitingPerAccount` 是全局统一的排队容量，取值 0～1,000，默认 0（关闭）；
 每个 Key、每个账号各自独立计数，没有单对象覆盖字段。执行并发为 5、最大排队数为 5 时，
 该对象最多容纳 5 个执行请求与 5 个等待请求。Key 并发为 0（不限）时跳过 Key 排队。
@@ -1325,6 +1331,10 @@ errorCode, errorMessage, startedAt, completedAt, expiresAt, createdAt, updatedAt
 | `GET` | `/api/admin/usage/insights/diagnostics` | 按维度聚合诊断 |
 | `GET` | `/api/admin/operations/errors` | 运维错误分页列表 |
 
+Dashboard 的 `capacityInfo.maxConcurrentPerAccount` 为默认账号并发上限，`0` 表示不限制。
+`capacityInfo.totalSlots` 为 `number | null`；可用账号池含无限并发账号时为 `null`，此时 `availableSlots` 也为 `null`。
+`usedSlots` 仍表示实际在途数，Redis 不可用时为 `null`；没有可用账号时 `totalSlots` 为 `0`。
+
 用量查询可组合页码/游标、时间范围、Provider、Client Key、账号、模型、route、transport、状态码、
 request/response/upstream ID、outcome 与搜索文本。诊断 `dimension` 可取 `model`、`account`、
 `apiKey`、`provider`、`transport`、`failureClass`、`status`。
diff --git a/docs/architecture.md b/docs/architecture.md
index 964c77384..628468fdb 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -355,6 +355,8 @@ Client Key 与账号分组形成授权范围：
 - 分组可以包含多个 Provider，账号也可以属于多个分组。
 
 账号选择综合启停状态、credential/quota 事实、Redis cooldown、并发上限、权重、请求间隔和会话亲和。
+默认账号并发上限为 `0` 时表示无限；账号独立正数上限仍优先，未设置则继承默认值。
+无限并发只跳过并发上限判断，保留在途租约计数、请求间隔及其他准入约束；含无限账号的容量不投影有限占用比例。
 `account::AccountModelAccess` 拥有管理员模型政策的校验与精确匹配语义，存入账号行的 `model_access_json`，
 由 `RuntimeAccountDirectory` / `FrozenAccountScope` 随配置快照冻结。Provider 在额度、亲和与租约之前
 按映射后的上游模型筛选账号；重试和 fallback 使用同一冻结政策。上游目录和凭据不承载或改写该政策。
diff --git a/frontend/src/api/modules/account-groups.ts b/frontend/src/api/modules/account-groups.ts
index 3bee61f24..005cff5d3 100644
--- a/frontend/src/api/modules/account-groups.ts
+++ b/frontend/src/api/modules/account-groups.ts
@@ -16,7 +16,7 @@ export interface AccountGroupAccountSummary {
 
 export interface AccountGroupCapacity {
   usedSlots: number | null
-  totalSlots: number
+  totalSlots: number | null
 }
 
 export interface AccountGroupUsage {
diff --git a/frontend/src/api/modules/dashboard.ts b/frontend/src/api/modules/dashboard.ts
index 978cd6b97..3f7176e1f 100644
--- a/frontend/src/api/modules/dashboard.ts
+++ b/frontend/src/api/modules/dashboard.ts
@@ -165,7 +165,7 @@ export interface DashboardPoolSummary {
 
 export interface DashboardCapacityInfo {
   maxConcurrentPerAccount: number
-  totalSlots: number
+  totalSlots: number | null
   usedSlots: number | null
   availableSlots: number | null
 }
diff --git a/frontend/src/views/accounts/components/AccountConnectionTestModal.vue b/frontend/src/views/accounts/components/AccountConnectionTestModal.vue
index 5519aba47..660c82fbe 100644
--- a/frontend/src/views/accounts/components/AccountConnectionTestModal.vue
+++ b/frontend/src/views/accounts/components/AccountConnectionTestModal.vue
@@ -5,7 +5,6 @@ import { RefreshCw } from '@lucide/vue'
 import BaseButton from '@/components/base/BaseButton.vue'
 import BaseIconButton from '@/components/base/BaseIconButton.vue'
 import BaseModal from '@/components/base/BaseModal/index.vue'
-import BaseScrollbar from '@/components/base/BaseScrollbar.vue'
 import BaseSelect from '@/components/base/BaseSelect.vue'
 import AccountIdentityCell from './AccountIdentityCell.vue'
 import AccountStatusBadge from './AccountStatusBadge/index.vue'
@@ -176,46 +175,40 @@ function connectionLogClass(tone: string) {
           <p class="m-0 text-cp-xs font-heavy text-cp-text-quaternary">
             事件轨迹
           </p>
-          <BaseScrollbar max-height="260px">
-            <div class="pt-2">
-              <div v-if="logs.length === 0" class="text-cp-sm font-emphasis text-cp-text-quaternary">
-                -
-              </div>
-              <div v-else class="flex flex-col gap-1.5">
-                <div
-                  v-for="item in logs"
-                  :key="item.key"
-                  class="grid grid-cols-[54px_minmax(0,1fr)] gap-2 text-cp-sm leading-[1.45] font-emphasis"
-                >
-                  <span class="font-mono text-cp-text-quaternary">{{ item.time }}</span>
-                  <div class="min-w-0">
+          <div class="pt-2">
+            <div v-if="logs.length === 0" class="text-cp-sm font-emphasis text-cp-text-quaternary">
+              -
+            </div>
+            <div v-else class="flex flex-col gap-1.5">
+              <div
+                v-for="item in logs"
+                :key="item.key"
+                class="grid grid-cols-[54px_minmax(0,1fr)] gap-2 text-cp-sm leading-[1.45] font-emphasis"
+              >
+                <span class="font-mono text-cp-text-quaternary">{{ item.time }}</span>
+                <div class="min-w-0">
+                  <p
+                    class="m-0 wrap-break-word"
+                    :class="connectionLogClass(item.tone)"
+                  >
+                    {{ item.text }}
+                  </p>
+                  <div v-if="item.detail" class="mt-2 rounded-lg bg-cp-fill-quaternary px-3 py-2">
                     <p
-                      class="m-0 wrap-break-word"
-                      :class="connectionLogClass(item.tone)"
+                      v-if="item.tone === 'danger'"
+                      class="mt-0 mb-2 text-cp-xs font-heavy text-cp-text-quaternary"
                     >
-                      {{ item.text }}
+                      原始诊断
                     </p>
-                    <div v-if="item.detail" class="mt-2 rounded-lg bg-cp-fill-quaternary px-3 py-2">
-                      <p
-                        v-if="item.tone === 'danger'"
-                        class="mt-0 mb-2 text-cp-xs font-heavy text-cp-text-quaternary"
-                      >
-                        原始诊断
-                      </p>
-                      <BaseScrollbar max-height="138px">
-                        <div>
-                          <pre
-                            class="m-0 whitespace-pre-wrap wrap-break-word font-mono text-cp-xs leading-[1.6] font-emphasis text-cp-text"
-                            v-text="item.detail"
-                          />
-                        </div>
-                      </BaseScrollbar>
-                    </div>
+                    <pre
+                      class="m-0 whitespace-pre-wrap wrap-break-word font-mono text-cp-xs leading-[1.6] font-emphasis text-cp-text"
+                      v-text="item.detail"
+                    />
                   </div>
                 </div>
               </div>
             </div>
-          </BaseScrollbar>
+          </div>
         </div>
       </section>
     </div>
diff --git a/frontend/src/views/dashboard/components/AccountOverviewCard.vue b/frontend/src/views/dashboard/components/AccountOverviewCard.vue
index a13d4cd38..01135803c 100644
--- a/frontend/src/views/dashboard/components/AccountOverviewCard.vue
+++ b/frontend/src/views/dashboard/components/AccountOverviewCard.vue
@@ -19,15 +19,17 @@ const props = defineProps<{
   rotationStrategy?: string | null
 }>()
 
+const unlimitedCapacity = computed(() => props.capacity?.maxConcurrentPerAccount === 0 && props.capacity.totalSlots === null)
+
 const scheduleStats = computed(() => {
   const cap = props.capacity
   const display = (value: number | null | undefined) => value === null || value === undefined
     ? '—'
     : formatCompactNumber(value)
   return [
-    { label: '默认并发', value: display(cap?.maxConcurrentPerAccount) },
-    { label: '总槽位', value: display(cap?.totalSlots) },
-    { label: '空闲槽位', value: display(cap?.availableSlots) },
+    { label: '默认并发', value: cap?.maxConcurrentPerAccount === 0 ? '不限制' : display(cap?.maxConcurrentPerAccount) },
+    { label: '总槽位', value: unlimitedCapacity.value ? '不限制' : display(cap?.totalSlots) },
+    { label: '空闲槽位', value: unlimitedCapacity.value ? '不限制' : display(cap?.availableSlots) },
   ]
 })
 
@@ -44,6 +46,8 @@ const usedProgressStyle = computed(() => {
 
 const usedRatio = computed(() => {
   const cap = props.capacity
+  if (unlimitedCapacity.value)
+    return `${cap?.usedSlots === null || cap?.usedSlots === undefined ? '—' : formatCompactNumber(cap.usedSlots)} / ∞`
   if (!cap || cap.totalSlots === null || cap.totalSlots === undefined)
     return '— / —'
   if (cap.usedSlots === null || cap.usedSlots === undefined)
@@ -180,7 +184,7 @@ const statusBars = computed(() => {
                   {{ usedRatio }}
                 </strong>
               </div>
-              <div class="mt-4 h-2.5 w-full overflow-hidden rounded-full bg-cp-progress-remaining">
+              <div v-if="!unlimitedCapacity" class="mt-4 h-2.5 w-full overflow-hidden rounded-full bg-cp-progress-remaining">
                 <i
                   class="block h-2.5 rounded-full bg-cp-success"
                   :style="usedProgressStyle"
diff --git a/frontend/src/views/groups/components/AccountGroupMetricsCell.vue b/frontend/src/views/groups/components/AccountGroupMetricsCell.vue
index 05271c071..7c30ac7d7 100644
--- a/frontend/src/views/groups/components/AccountGroupMetricsCell.vue
+++ b/frontend/src/views/groups/components/AccountGroupMetricsCell.vue
@@ -57,7 +57,7 @@ const metrics = computed<MetricItem[]>(() => {
     return [
       {
         label: '并发',
-        value: `${props.group.capacity.usedSlots ?? '—'} / ${props.group.capacity.totalSlots}`,
+        value: `${props.group.capacity.usedSlots ?? '—'} / ${props.group.capacity.totalSlots ?? '∞'}`,
         tone: (props.group.capacity.usedSlots ?? 0) > 0 ? 'active' : 'primary',
         icon: Grid2X2,
       },
diff --git a/frontend/src/views/settings/components/RuntimeSettingsCard.vue b/frontend/src/views/settings/components/RuntimeSettingsCard.vue
index fc4d04581..bc397dd19 100644
--- a/frontend/src/views/settings/components/RuntimeSettingsCard.vue
+++ b/frontend/src/views/settings/components/RuntimeSettingsCard.vue
@@ -15,12 +15,15 @@ const requestIntervalMs = defineModel<string>('requestIntervalMs', { required: t
     <BaseForm class="max-w-6xl sm:grid-cols-2">
       <BaseFormItem
         label="默认账号并发上限"
-        description="账号未单独设置时使用的并发上限"
+        description="账号未单独设置时使用的并发上限，0 表示不限制"
       >
         <BaseInput
           v-model="maxConcurrentPerAccount"
           aria-label="默认账号并发上限"
           type="number"
+          min="0"
+          max="4294967295"
+          step="1"
         >
           <template #prefix>
             <Gauge class="size-4" />
diff --git a/frontend/src/views/settings/composables/useSettingsForm.ts b/frontend/src/views/settings/composables/useSettingsForm.ts
index eb3f43a83..4d76e1a33 100644
--- a/frontend/src/views/settings/composables/useSettingsForm.ts
+++ b/frontend/src/views/settings/composables/useSettingsForm.ts
@@ -192,6 +192,10 @@ export function useSettingsForm() {
       toast.warning('请完整填写并发、队列、凭据刷新参数和调度策略')
       return
     }
+    if (!Number.isInteger(maxConcurrentPerAccount) || maxConcurrentPerAccount < 0 || maxConcurrentPerAccount > 4294967295) {
+      toast.warning('默认账号并发上限应为 0～4294967295 的整数，0 表示不限制')
+      return
+    }
     if (responsesMaxDecompressedBodyMiB === null || !Number.isInteger(responsesMaxDecompressedBodyMiB) || responsesMaxDecompressedBodyMiB < 1
       || !Number.isSafeInteger(responsesMaxDecompressedBodyMiB * MIB)) {
       toast.warning('Responses 解压上限应为有效的正整数（MiB）')