feat(quota): per-group total-byte quotas for shared KV + docs (Track A M4)

M3 quotas capped a group's shared KV/docs by ROW count only; a group could still
blow past storage with few-but-huge values. Add the symmetric total-bytes ceiling
(files already had one).

- group_quota: PICLOUD_GROUP_{KV,DOCS}_MAX_TOTAL_BYTES env vars (default 256 MiB)
  + accessors.
- GroupKvRepo/GroupDocsRepo: total_bytes(group) = SUM(octet_length(value::text))
  (default Ok(0) so non-Postgres impls skip the check).
- GroupKv/DocsServiceImpl: check the PROJECTED total (old value's bytes
  subtracted, new added) on every set/create/update, so a same-or-smaller update
  near the cap is still allowed (unlike a naive used+new check). New
  TotalBytesQuotaExceeded errors; +with_max_total_bytes for tests.
- KV set switched has->get to obtain the old value's size for the delta.

Pinned by group_kv_service + group_docs_service per_group_byte_quota_uses_the_
projected_total unit tests (reject over-cap, allow same/smaller update near cap).
No migration. CLAUDE.md env-var table updated.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -134,6 +134,8 @@ Environment variables consumed by the `picloud` binary:
 | `PICLOUD_QUEUE_MAX_PAYLOAD_BYTES` | `262144` (256 KB) | Per-message JSON-encoded payload cap for `queue::enqueue`. |
 | `PICLOUD_GROUP_KV_MAX_ROWS` | `100000` | §11.6 M3 per-group quota: max total keys across a group's shared-KV collections. Checked only on a NEW key (`kv::shared_collection().set`); an update is exempt. |
 | `PICLOUD_GROUP_DOCS_MAX_ROWS` | `100000` | §11.6 M3 per-group quota: max total docs across a group's shared-docs collections (`docs::shared_collection().create`). |
+| `PICLOUD_GROUP_KV_MAX_TOTAL_BYTES` | `268435456` (256 MiB) | §11.6 M4 per-group quota: max total stored JSON bytes across a group's shared-KV collections. Checked on the projected total (old value subtracted, new added), so a same/smaller update near the cap is still allowed. |
+| `PICLOUD_GROUP_DOCS_MAX_TOTAL_BYTES` | `268435456` (256 MiB) | §11.6 M4 per-group quota: max total stored JSON bytes across a group's shared-docs collections (projected-total check, as KV). |
 | `PICLOUD_GROUP_FILES_MAX_TOTAL_BYTES` | `10737418240` (10 GiB) | §11.6 M3 per-group quota: max total stored bytes across a group's shared-files collections (`files::shared_collection().create`). |
 
 ## Out of MVP

crates/manager-core/src/group_docs_repo.rs

@@ -88,6 +88,13 @@ pub trait GroupDocsRepo: Send + Sync {
         let _ = group_id;
         Ok(0)
     }
+
+    /// §11.6 M4 quota: total stored JSON bytes across the group's shared-docs
+    /// collections (`octet_length(data::text)`). Default `Ok(0)`.
+    async fn total_bytes(&self, group_id: GroupId) -> Result<u64, GroupDocsRepoError> {
+        let _ = group_id;
+        Ok(0)
+    }
 }
 
 pub struct PostgresGroupDocsRepo {
@@ -281,6 +288,17 @@ impl GroupDocsRepo for PostgresGroupDocsRepo {
             .await?;
         Ok(u64::try_from(n).unwrap_or(0))
     }
+
+    async fn total_bytes(&self, group_id: GroupId) -> Result<u64, GroupDocsRepoError> {
+        let (n,): (i64,) = sqlx::query_as(
+            "SELECT COALESCE(SUM(octet_length(data::text)), 0)::BIGINT \
+             FROM group_docs WHERE group_id = $1",
+        )
+        .bind(group_id.into_inner())
+        .fetch_one(&self.pool)
+        .await?;
+        Ok(u64::try_from(n).unwrap_or(0))
+    }
 }
 
 fn encode_cursor(last_id: &Uuid) -> String {

crates/manager-core/src/group_docs_service.rs

@@ -32,6 +32,10 @@ pub struct GroupDocsServiceImpl {
     /// §11.6 per-group quota: max total docs across the group's shared-docs
     /// collections (`PICLOUD_GROUP_DOCS_MAX_ROWS`).
     max_rows: u64,
+    /// §11.6 M4 per-group quota: max total stored bytes across the group's
+    /// shared-docs collections (`PICLOUD_GROUP_DOCS_MAX_TOTAL_BYTES`). Checked on
+    /// the projected total so a same/smaller update near the cap is still allowed.
+    max_total_bytes: u64,
     /// §11.6: fires `shared = true` docs triggers on a shared-collection write.
     events: Arc<dyn ServiceEventEmitter>,
 }
@@ -63,6 +67,7 @@ impl GroupDocsServiceImpl {
         Self {
             events: Arc::new(NoopEventEmitter),
             max_rows: crate::group_quota::group_docs_max_rows_from_env(),
+            max_total_bytes: crate::group_quota::group_docs_max_total_bytes_from_env(),
             repo,
             resolver,
             authz,
@@ -70,6 +75,34 @@ impl GroupDocsServiceImpl {
         }
     }
 
+    /// Override the per-group total-bytes quota (§11.6 M4). Mainly for tests.
+    #[must_use]
+    pub fn with_max_total_bytes(mut self, max_total_bytes: u64) -> Self {
+        self.max_total_bytes = max_total_bytes;
+        self
+    }
+
+    /// §11.6 M4: reject a write whose PROJECTED total (old doc's bytes subtracted,
+    /// new doc's added — `old_len = 0` for a create) would exceed the group's
+    /// total-bytes ceiling. `new_len` is the JSON-encoded size of the incoming
+    /// data (already validated ≤ per-doc cap).
+    async fn check_total_bytes(
+        &self,
+        group_id: GroupId,
+        new_len: u64,
+        old_len: u64,
+    ) -> Result<(), GroupDocsError> {
+        let used = self.repo.total_bytes(group_id).await?;
+        let projected = used.saturating_sub(old_len) + new_len;
+        if projected > self.max_total_bytes {
+            return Err(GroupDocsError::TotalBytesQuotaExceeded {
+                limit: self.max_total_bytes,
+                actual: projected,
+            });
+        }
+        Ok(())
+    }
+
     /// §11.6: fire `shared = true` docs triggers on the owning group.
     /// Best-effort; an emit failure is logged, never surfaced.
     #[allow(clippy::too_many_arguments)] // op/collection/id + new + old payloads
@@ -201,6 +234,9 @@ impl GroupDocsService for GroupDocsServiceImpl {
                 actual: usize::try_from(count).unwrap_or(usize::MAX),
             });
         }
+        // §11.6 M4 byte quota: a create only adds bytes (old_len = 0).
+        let new_len = serde_json::to_vec(&data).map_or(0u64, |b| b.len() as u64);
+        self.check_total_bytes(group_id, new_len, 0).await?;
         let created = self.repo.create(group_id, collection, data.clone()).await?;
         self.emit_shared(
             cx,
@@ -265,6 +301,17 @@ impl GroupDocsService for GroupDocsServiceImpl {
         validate_data(&data)?;
         self.check_data_size(&data)?;
         self.check_write(cx, group_id).await?;
+        // §11.6 M4 byte quota: check the projected total before writing. Fetch the
+        // current doc for its old byte size (a missing doc → old_len 0, and the
+        // update below no-ops to `None`).
+        let old_len = self
+            .repo
+            .get(group_id, collection, id)
+            .await?
+            .and_then(|d| serde_json::to_vec(&d.data).ok())
+            .map_or(0u64, |b| b.len() as u64);
+        let new_len = serde_json::to_vec(&data).map_or(0u64, |b| b.len() as u64);
+        self.check_total_bytes(group_id, new_len, old_len).await?;
         match self
             .repo
             .update(group_id, collection, id, data.clone())
@@ -447,6 +494,16 @@ mod tests {
                 next_cursor: None,
             })
         }
+
+        async fn total_bytes(&self, group_id: GroupId) -> Result<u64, GroupDocsRepoError> {
+            let data = self.data.lock().await;
+            Ok(data
+                .iter()
+                .filter(|((g, _), _)| *g == group_id)
+                .flat_map(|(_, docs)| docs.values())
+                .map(|v| serde_json::to_vec(v).map_or(0, |b| b.len() as u64))
+                .sum())
+        }
     }
 
     #[derive(Default)]
@@ -578,4 +635,51 @@ mod tests {
             .unwrap_err();
         assert!(matches!(err, GroupDocsError::InvalidData));
     }
+
+    #[tokio::test]
+    async fn per_group_byte_quota_uses_the_projected_total() {
+        // §11.6 M4: the shared-docs byte ceiling is checked on the PROJECTED
+        // total — a create over the cap is rejected, and a shrinking update near
+        // the cap is allowed (the delta rule).
+        let app = AppId::new();
+        let group = GroupId::new();
+        let mut resolver = FakeResolver::default();
+        resolver.map.insert((app, "articles".into()), group);
+        let docs = GroupDocsServiceImpl::new(
+            Arc::new(InMemoryGroupDocsRepo::default()),
+            Arc::new(resolver),
+            Arc::new(DenyingAuthzRepo),
+        )
+        .with_max_total_bytes(40);
+        let cx = cx_with(app, Some(owner()));
+
+        // {"t":"xxxxx"} encodes to 13 bytes.
+        let id = docs
+            .create(&cx, "articles", serde_json::json!({"t": "xxxxx"}))
+            .await
+            .unwrap(); // used = 13
+        docs.create(&cx, "articles", serde_json::json!({"t": "xxxxx"}))
+            .await
+            .unwrap(); // used = 26
+                       // A third 13-byte doc → projected 39 ≤ 40 → ok.
+        docs.create(&cx, "articles", serde_json::json!({"t": "xxxxx"}))
+            .await
+            .unwrap(); // used = 39
+                       // A fourth → projected 52 > 40 → rejected.
+        let err = docs
+            .create(&cx, "articles", serde_json::json!({"t": "xxxxx"}))
+            .await
+            .unwrap_err();
+        assert!(
+            matches!(
+                err,
+                GroupDocsError::TotalBytesQuotaExceeded { limit: 40, .. }
+            ),
+            "got {err:?}"
+        );
+        // Shrinking an existing doc frees budget (projected 39 - 13 + 9 = 35).
+        docs.update(&cx, "articles", id, serde_json::json!({"t": "y"}))
+            .await
+            .expect("a shrinking update near the cap must be allowed");
+    }
 }

crates/manager-core/src/group_kv_repo.rs

@@ -68,6 +68,14 @@ pub trait GroupKvRepo: Send + Sync {
         let _ = group_id;
         Ok(0)
     }
+
+    /// §11.6 M4 quota: total stored JSON bytes across all of the group's shared-KV
+    /// collections (`octet_length(value::text)`). Default `Ok(0)` so non-Postgres
+    /// impls skip the byte-quota check.
+    async fn total_bytes(&self, group_id: GroupId) -> Result<u64, GroupKvRepoError> {
+        let _ = group_id;
+        Ok(0)
+    }
 }
 
 pub struct PostgresGroupKvRepo {
@@ -224,6 +232,17 @@ impl GroupKvRepo for PostgresGroupKvRepo {
                 .await?;
         Ok(u64::try_from(n).unwrap_or(0))
     }
+
+    async fn total_bytes(&self, group_id: GroupId) -> Result<u64, GroupKvRepoError> {
+        let (n,): (i64,) = sqlx::query_as(
+            "SELECT COALESCE(SUM(octet_length(value::text)), 0)::BIGINT \
+             FROM group_kv_entries WHERE group_id = $1",
+        )
+        .bind(group_id.into_inner())
+        .fetch_one(&self.pool)
+        .await?;
+        Ok(u64::try_from(n).unwrap_or(0))
+    }
 }
 
 fn encode_cursor(last_key: &str) -> String {

crates/manager-core/src/group_kv_service.rs

@@ -43,6 +43,11 @@ pub struct GroupKvServiceImpl {
     /// collections (`PICLOUD_GROUP_KV_MAX_ROWS`). Checked only when inserting a
     /// NEW key.
     max_rows: u64,
+    /// §11.6 M4 per-group quota: max total stored bytes across the group's
+    /// shared-KV collections (`PICLOUD_GROUP_KV_MAX_TOTAL_BYTES`). Checked on the
+    /// projected total (old value subtracted, new added) so a same/smaller update
+    /// near the cap is still allowed.
+    max_total_bytes: u64,
     /// §11.6: fires `shared = true` triggers on a shared-collection write.
     /// Defaults to the noop emitter; the host wires the outbox emitter via
     /// [`Self::with_events`].
@@ -85,6 +90,7 @@ impl GroupKvServiceImpl {
         Self {
             events: Arc::new(NoopEventEmitter),
             max_rows: crate::group_quota::group_kv_max_rows_from_env(),
+            max_total_bytes: crate::group_quota::group_kv_max_total_bytes_from_env(),
             repo,
             resolver,
             authz,
@@ -92,6 +98,13 @@ impl GroupKvServiceImpl {
         }
     }
 
+    /// Override the per-group total-bytes quota (§11.6 M4). Mainly for tests.
+    #[must_use]
+    pub fn with_max_total_bytes(mut self, max_total_bytes: u64) -> Self {
+        self.max_total_bytes = max_total_bytes;
+        self
+    }
+
     /// The structural boundary: resolve the collection to its owning group on
     /// the calling app's chain. `CollectionNotShared` when no ancestor group
     /// declares it — the same outcome a foreign app gets, by construction.
@@ -204,11 +217,12 @@ impl GroupKvService for GroupKvServiceImpl {
             });
         }
         self.check_write(cx, group_id).await?;
-        // Determine insert vs update for the event op (best-effort, like the
-        // per-app path — the has+set is non-transactional but triggers are
-        // fire-and-forget).
-        let existed = self.repo.has(group_id, collection, key).await?;
-        // §11.6 quota: a NEW key must fit under the group's row ceiling; an
+        // Determine insert vs update for the event op + quota deltas (best-effort,
+        // like the per-app path — the get+set is non-transactional but triggers
+        // are fire-and-forget and quotas are safety rails, not exact accounting).
+        let existing = self.repo.get(group_id, collection, key).await?;
+        let existed = existing.is_some();
+        // §11.6 row quota: a NEW key must fit under the group's row ceiling; an
         // update of an existing key is net-zero and exempt.
         if !existed {
             let count = self.repo.count_rows(group_id).await?;
@@ -219,6 +233,21 @@ impl GroupKvService for GroupKvServiceImpl {
                 });
             }
         }
+        // §11.6 M4 byte quota: the PROJECTED total (old value's bytes subtracted,
+        // new value's added) must fit under the group's total-bytes ceiling, so a
+        // same-or-smaller update near the cap is still allowed.
+        let old_len = existing
+            .as_ref()
+            .and_then(|v| serde_json::to_vec(v).ok())
+            .map_or(0u64, |b| b.len() as u64);
+        let used = self.repo.total_bytes(group_id).await?;
+        let projected = used.saturating_sub(old_len) + encoded_len as u64;
+        if projected > self.max_total_bytes {
+            return Err(GroupKvError::TotalBytesQuotaExceeded {
+                limit: self.max_total_bytes,
+                actual: projected,
+            });
+        }
         self.repo
             .set(group_id, collection, key, value.clone())
             .await?;
@@ -370,6 +399,15 @@ mod tests {
             let data = self.data.lock().await;
             Ok(data.keys().filter(|(g, _, _)| *g == group_id).count() as u64)
         }
+
+        async fn total_bytes(&self, group_id: GroupId) -> Result<u64, GroupKvRepoError> {
+            let data = self.data.lock().await;
+            Ok(data
+                .iter()
+                .filter(|((g, _, _), _)| *g == group_id)
+                .map(|(_, v)| serde_json::to_vec(v).map_or(0, |b| b.len() as u64))
+                .sum())
+        }
     }
 
     /// Maps `(app_id, lowercased name) -> owning group`. Anything absent is
@@ -488,6 +526,56 @@ mod tests {
             .expect("update of an existing key must be allowed at the cap");
     }
 
+    #[tokio::test]
+    async fn per_group_byte_quota_uses_the_projected_total() {
+        // §11.6 M4: the byte ceiling is checked on the PROJECTED total, so a
+        // write that would push the group over is rejected, but a same/smaller
+        // update near the cap is still allowed (unlike a naive used+new check).
+        let app = AppId::new();
+        let group = GroupId::new();
+        let mut resolver = FakeResolver::default();
+        resolver.map.insert((app, "catalog".into()), group);
+        // A 20-byte ceiling; each `"xxxxx"` value encodes to 7 bytes ("\"xxxxx\"").
+        let kv = GroupKvServiceImpl::new(
+            Arc::new(InMemoryGroupKvRepo::default()),
+            Arc::new(resolver),
+            Arc::new(DenyingAuthzRepo),
+        )
+        .with_max_rows(1000)
+        .with_max_total_bytes(20);
+        let cx = cx_with(app, Some(owner()));
+
+        kv.set(&cx, "catalog", "a", serde_json::json!("xxxxx"))
+            .await
+            .unwrap(); // used = 7
+        kv.set(&cx, "catalog", "b", serde_json::json!("xxxxx"))
+            .await
+            .unwrap(); // used = 14
+                       // A third 7-byte value → projected 21 > 20 → rejected.
+        let err = kv
+            .set(&cx, "catalog", "c", serde_json::json!("xxxxx"))
+            .await
+            .unwrap_err();
+        assert!(
+            matches!(err, GroupKvError::TotalBytesQuotaExceeded { limit: 20, .. }),
+            "got {err:?}"
+        );
+        // A same-size update of an existing key stays within budget (projected
+        // = 14 - 7 + 7 = 14 ≤ 20) — the delta rule, not used+new.
+        kv.set(&cx, "catalog", "a", serde_json::json!("yyyyy"))
+            .await
+            .expect("a same-size update near the cap must be allowed");
+        // Growing an existing value past the cap is still rejected.
+        let err = kv
+            .set(&cx, "catalog", "a", serde_json::json!("zzzzzzzzzzzzzzz"))
+            .await
+            .unwrap_err();
+        assert!(
+            matches!(err, GroupKvError::TotalBytesQuotaExceeded { .. }),
+            "got {err:?}"
+        );
+    }
+
     #[tokio::test]
     async fn unrelated_app_gets_collection_not_shared() {
         // app_a's chain declares "catalog"; app_b's does not.

crates/manager-core/src/group_quota.rs

@@ -3,14 +3,23 @@
 //! `PICLOUD_*_MAX_*_BYTES` caps). One default applies to every group; per-group
 //! configurable limits are deferred.
 //!
-//! - KV / docs: a per-group ROW-count ceiling (across the group's collections of
-//!   that kind). An update of an existing key/doc is net-zero and exempt.
+//! - KV / docs: a per-group ROW-count ceiling AND a per-group TOTAL-BYTES ceiling
+//!   (across the group's collections of that kind). Row count exempts an update
+//!   of an existing key/doc (net-zero rows); the byte ceiling is checked on the
+//!   projected total (old value's bytes subtracted, new value's added) so a
+//!   same-or-smaller update near the cap is still allowed.
 //! - files: a per-group TOTAL-BYTES ceiling (sum of stored blob sizes).
 
 /// Default per-group shared-KV row ceiling. Override `PICLOUD_GROUP_KV_MAX_ROWS`.
 pub const DEFAULT_GROUP_KV_MAX_ROWS: u64 = 100_000;
 /// Default per-group shared-docs row ceiling. Override `PICLOUD_GROUP_DOCS_MAX_ROWS`.
 pub const DEFAULT_GROUP_DOCS_MAX_ROWS: u64 = 100_000;
+/// Default per-group shared-KV total-bytes ceiling (256 MiB). Override
+/// `PICLOUD_GROUP_KV_MAX_TOTAL_BYTES`.
+pub const DEFAULT_GROUP_KV_MAX_TOTAL_BYTES: u64 = 256 * 1024 * 1024;
+/// Default per-group shared-docs total-bytes ceiling (256 MiB). Override
+/// `PICLOUD_GROUP_DOCS_MAX_TOTAL_BYTES`.
+pub const DEFAULT_GROUP_DOCS_MAX_TOTAL_BYTES: u64 = 256 * 1024 * 1024;
 /// Default per-group shared-files total-bytes ceiling (10 GiB). Override
 /// `PICLOUD_GROUP_FILES_MAX_TOTAL_BYTES`.
 pub const DEFAULT_GROUP_FILES_MAX_TOTAL_BYTES: u64 = 10 * 1024 * 1024 * 1024;
@@ -35,6 +44,22 @@ pub fn group_docs_max_rows_from_env() -> u64 {
     u64_from_env("PICLOUD_GROUP_DOCS_MAX_ROWS", DEFAULT_GROUP_DOCS_MAX_ROWS)
 }
 
+#[must_use]
+pub fn group_kv_max_total_bytes_from_env() -> u64 {
+    u64_from_env(
+        "PICLOUD_GROUP_KV_MAX_TOTAL_BYTES",
+        DEFAULT_GROUP_KV_MAX_TOTAL_BYTES,
+    )
+}
+
+#[must_use]
+pub fn group_docs_max_total_bytes_from_env() -> u64 {
+    u64_from_env(
+        "PICLOUD_GROUP_DOCS_MAX_TOTAL_BYTES",
+        DEFAULT_GROUP_DOCS_MAX_TOTAL_BYTES,
+    )
+}
+
 #[must_use]
 pub fn group_files_max_total_bytes_from_env() -> u64 {
     u64_from_env(

crates/shared/src/group_docs.rs

@@ -181,6 +181,11 @@ pub enum GroupDocsError {
     #[error("group docs: quota exceeded ({actual} rows; limit {limit})")]
     QuotaExceeded { limit: usize, actual: usize },
 
+    /// The owning group's shared-docs store would exceed its total-bytes quota
+    /// (`PICLOUD_GROUP_DOCS_MAX_TOTAL_BYTES`). `actual` is the projected total.
+    #[error("group docs: total-bytes quota exceeded ({actual} bytes; limit {limit})")]
+    TotalBytesQuotaExceeded { limit: u64, actual: u64 },
+
     #[error("group docs backend error: {0}")]
     Backend(String),
 }

crates/shared/src/group_kv.rs

@@ -141,6 +141,12 @@ pub enum GroupKvError {
     #[error("group kv: quota exceeded ({actual} rows; limit {limit})")]
     QuotaExceeded { limit: usize, actual: usize },
 
+    /// The owning group's shared-KV store would exceed its total-bytes quota
+    /// (`PICLOUD_GROUP_KV_MAX_TOTAL_BYTES`). `actual` is the projected total
+    /// (old value's bytes subtracted, new value's added).
+    #[error("group kv: total-bytes quota exceeded ({actual} bytes; limit {limit})")]
+    TotalBytesQuotaExceeded { limit: u64, actual: u64 },
+
     /// Anything else — Postgres unavailable, serialization failure, etc.
     #[error("group kv backend error: {0}")]
     Backend(String),