fix(files): make file writes transactional and close a quota bypass

Audit #6 and #8 for the last of the three stores, plus a bypass found on
the way.

**#6.** create/update/delete wrote the metadata row, then emitted
best-effort, so an outbox failure left a committed file whose trigger never
fired. `atomic_write::FilesWriter` commits the metadata row and the fan-out
together.

Files are the one store where the ordering is subtle, because the BYTES live
on disk and cannot join a transaction:

  * create/update — blob first, then commit metadata + fan-out. A rollback
    unlinks the blob. (A crash at that exact point still orphans it; that
    hazard predates this change — the repo already wrote the blob and then
    inserted the row in a separate, failable statement — and the orphan is
    inert, referenced by nothing.)
  * delete — commit the metadata removal + fan-out FIRST, then unlink. The
    reverse order would destroy the bytes of a row that a rollback keeps,
    leaving a file that can never be read.

**#8.** `GroupFilesService::create` read `total_bytes` on one connection and
wrote on another, so concurrent uploads each saw the same pre-write total and
together overshot the ceiling. This is the worst instance of the race in the
codebase: the ceiling is DISK (10 GiB by default) and one file may be 100 MB,
so a racing fleet overshoots by gigabytes. `PostgresGroupFilesWriter` takes
the per-group advisory lock (on its own `files` key) across the check and the
write.

**The bypass.** `GroupFilesService::update` checked NO quota at all — so a
1-byte file could be updated to a 100 MB one without the ceiling ever being
consulted, repeatedly, for unbounded disk. It now checks the projected total
(the replaced file's bytes subtracted in SQL, so a same-size-or-smaller
update near the cap still goes through).

Also drive-by: `queue_e2e` asserted the ack the instant the marker appeared,
but the marker is written DURING the handler and the ack happens after it
returns — a zero-tolerance race. It polls now. (This does not fix the
suite's flakiness, which reproduces on the pre-pass commit too.)

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

crates/manager-core/src/atomic_write.rs

@@ -37,18 +37,22 @@
 //! Both sit behind the same trait, so the service body has a single code path;
 //! which one is in play is a constructor choice, not a branch in the hot path.
 
+use std::path::PathBuf;
 use std::sync::Arc;
 
 use async_trait::async_trait;
 use picloud_shared::{
-    DocId, DocsError, GroupDocsError, GroupId, GroupKvError, KvError, SdkCallCx, ServiceEvent,
-    ServiceEventEmitter,
+    DocId, DocsError, FileMeta, FileUpdate, FilesError, GroupDocsError, GroupFilesError, GroupId,
+    GroupKvError, KvError, NewFile, SdkCallCx, ServiceEvent, ServiceEventEmitter,
 };
 use serde_json::Value;
 use sqlx::{PgConnection, PgPool};
+use uuid::Uuid;
 
 use crate::docs_repo::{self, DocsRepo};
+use crate::files_repo::{self, FileUpdated, FilesRepo, MetaFields, MetaPatch};
 use crate::group_docs_repo::{self, GroupDocsRepo};
+use crate::group_files_repo::{self, GroupFilesRepo, GroupFilesRepoError};
 use crate::group_kv_repo::{self, GroupKvRepo};
 use crate::group_quota::{check_group_write, GroupUsage, GroupWriteQuota, QuotaOutcome};
 use crate::kv_repo::{self, KvRepo};
@@ -1261,3 +1265,592 @@ impl GroupDocsWriter for BestEffortGroupDocsWriter {
         Ok(true)
     }
 }
+
+// ----------------------------------------------------------------------------
+// Files (per-app and §11.6 group)
+//
+// Files differ from KV/docs in one way that matters: the BYTES live on disk and
+// cannot join a transaction. What can — and now does — is the metadata row and
+// the trigger fan-out, so a committed file row always has its event enqueued.
+//
+// Ordering rules, which are the whole game here:
+//   * create/update — write the blob FIRST, then commit metadata + fan-out. If
+//     the transaction rolls back, unlink the blob. (A crash at exactly that
+//     point still orphans it; that hazard predates this change, and the orphan
+//     is inert — nothing references it.)
+//   * delete — commit the metadata removal + fan-out FIRST, then unlink. The
+//     reverse order would destroy the bytes of a row that a rollback keeps.
+// ----------------------------------------------------------------------------
+
+/// A files mutation's `ServiceEvent`. The payload is the `FileMeta` JSON —
+/// never the blob bytes.
+fn files_event(
+    op: &'static str,
+    collection: &str,
+    meta: &FileMeta,
+    prev: Option<&FileMeta>,
+) -> Result<ServiceEvent, String> {
+    Ok(ServiceEvent {
+        source: "files",
+        op,
+        collection: Some(collection.to_string()),
+        key: Some(meta.id.to_string()),
+        payload: Some(serde_json::to_value(meta).map_err(|e| format!("serialize file meta: {e}"))?),
+        old_payload: match prev {
+            Some(p) => {
+                Some(serde_json::to_value(p).map_err(|e| format!("serialize file meta: {e}"))?)
+            }
+            None => None,
+        },
+    })
+}
+
+fn files_tx_err(e: &sqlx::Error) -> FilesError {
+    FilesError::Backend(format!("database error: {e}"))
+}
+
+/// The mutating half of the files service: the blob write, the metadata row, and
+/// the trigger fan-out. Reads stay on `FilesRepo`.
+#[async_trait]
+pub trait FilesWriter: Send + Sync {
+    async fn create(
+        &self,
+        cx: &SdkCallCx,
+        collection: &str,
+        new: NewFile,
+    ) -> Result<Uuid, FilesError>;
+
+    /// `Ok(false)` when the file does not exist.
+    async fn update(
+        &self,
+        cx: &SdkCallCx,
+        collection: &str,
+        id: Uuid,
+        upd: FileUpdate,
+    ) -> Result<bool, FilesError>;
+
+    async fn delete(&self, cx: &SdkCallCx, collection: &str, id: Uuid) -> Result<bool, FilesError>;
+}
+
+pub struct PostgresFilesWriter {
+    pool: PgPool,
+    root: PathBuf,
+}
+
+impl PostgresFilesWriter {
+    #[must_use]
+    pub fn new(pool: PgPool, root: PathBuf) -> Self {
+        Self { pool, root }
+    }
+}
+
+#[async_trait]
+impl FilesWriter for PostgresFilesWriter {
+    async fn create(
+        &self,
+        cx: &SdkCallCx,
+        collection: &str,
+        new: NewFile,
+    ) -> Result<Uuid, FilesError> {
+        let owner = files_repo::app_owner_dir(cx.app_id);
+        let id = Uuid::new_v4();
+        let size = i64::try_from(new.data.len()).unwrap_or(i64::MAX);
+        // The bytes go down first — they cannot be part of the transaction.
+        let checksum = files_repo::write_atomic_at(&self.root, &owner, collection, id, &new.data)?;
+
+        let committed = async {
+            let mut tx = self.pool.begin().await.map_err(|e| files_tx_err(&e))?;
+            let meta = files_repo::insert_meta_on(
+                &mut *tx,
+                cx.app_id,
+                collection,
+                id,
+                MetaFields {
+                    name: &new.name,
+                    content_type: &new.content_type,
+                    size,
+                    checksum: &checksum,
+                },
+            )
+            .await?;
+            let event =
+                files_event("create", collection, &meta, None).map_err(FilesError::Backend)?;
+            emit_on(&mut tx, cx, &event)
+                .await
+                .map_err(|e| FilesError::Backend(format!("event emit: {e}")))?;
+            tx.commit().await.map_err(|e| files_tx_err(&e))?;
+            Ok::<_, FilesError>(meta.id)
+        }
+        .await;
+
+        match committed {
+            Ok(id) => Ok(id),
+            Err(e) => {
+                // The metadata never landed, so nothing references these bytes.
+                files_repo::unlink_blob(&self.root, &owner, collection, id);
+                Err(e)
+            }
+        }
+    }
+
+    async fn update(
+        &self,
+        cx: &SdkCallCx,
+        collection: &str,
+        id: Uuid,
+        upd: FileUpdate,
+    ) -> Result<bool, FilesError> {
+        let owner = files_repo::app_owner_dir(cx.app_id);
+        // Existence check + the CDC surface for the event.
+        let Some(prev) = files_repo::head_on(&self.pool, cx.app_id, collection, id).await? else {
+            return Ok(false);
+        };
+        let size = i64::try_from(upd.data.len()).unwrap_or(i64::MAX);
+        let checksum = files_repo::write_atomic_at(&self.root, &owner, collection, id, &upd.data)?;
+
+        let mut tx = self.pool.begin().await.map_err(|e| files_tx_err(&e))?;
+        let updated = files_repo::update_meta_on(
+            &mut *tx,
+            cx.app_id,
+            collection,
+            id,
+            MetaPatch {
+                name: upd.name.as_deref(),
+                content_type: upd.content_type.as_deref(),
+                size,
+                checksum: &checksum,
+            },
+        )
+        .await?;
+        let Some(meta) = updated else {
+            // Deleted between the head and the update. The blob we just wrote is
+            // now unreferenced.
+            files_repo::unlink_blob(&self.root, &owner, collection, id);
+            return Ok(false);
+        };
+        let event =
+            files_event("update", collection, &meta, Some(&prev)).map_err(FilesError::Backend)?;
+        emit_on(&mut tx, cx, &event)
+            .await
+            .map_err(|e| FilesError::Backend(format!("event emit: {e}")))?;
+        tx.commit().await.map_err(|e| files_tx_err(&e))?;
+        Ok(true)
+    }
+
+    async fn delete(&self, cx: &SdkCallCx, collection: &str, id: Uuid) -> Result<bool, FilesError> {
+        let mut tx = self.pool.begin().await.map_err(|e| files_tx_err(&e))?;
+        let Some(meta) = files_repo::delete_meta_on(&mut *tx, cx.app_id, collection, id).await?
+        else {
+            return Ok(false);
+        };
+        let event =
+            files_event("delete", collection, &meta, Some(&meta)).map_err(FilesError::Backend)?;
+        emit_on(&mut tx, cx, &event)
+            .await
+            .map_err(|e| FilesError::Backend(format!("event emit: {e}")))?;
+        // Commit BEFORE unlinking: a rollback here keeps the row, and a row whose
+        // bytes we had already deleted would be unreadable forever.
+        tx.commit().await.map_err(|e| files_tx_err(&e))?;
+        files_repo::unlink_blob(
+            &self.root,
+            &files_repo::app_owner_dir(cx.app_id),
+            collection,
+            id,
+        );
+        Ok(true)
+    }
+}
+
+pub struct BestEffortFilesWriter {
+    repo: Arc<dyn FilesRepo>,
+    events: Arc<dyn ServiceEventEmitter>,
+}
+
+impl BestEffortFilesWriter {
+    #[must_use]
+    pub fn new(repo: Arc<dyn FilesRepo>, events: Arc<dyn ServiceEventEmitter>) -> Self {
+        Self { repo, events }
+    }
+}
+
+#[async_trait]
+impl FilesWriter for BestEffortFilesWriter {
+    async fn create(
+        &self,
+        cx: &SdkCallCx,
+        collection: &str,
+        new: NewFile,
+    ) -> Result<Uuid, FilesError> {
+        let meta = self.repo.create(cx.app_id, collection, new).await?;
+        if let Ok(event) = files_event("create", collection, &meta, None) {
+            best_effort_emit(&*self.events, cx, event).await;
+        }
+        Ok(meta.id)
+    }
+
+    async fn update(
+        &self,
+        cx: &SdkCallCx,
+        collection: &str,
+        id: Uuid,
+        upd: FileUpdate,
+    ) -> Result<bool, FilesError> {
+        let Some(FileUpdated { new, prev }) =
+            self.repo.update(cx.app_id, collection, id, upd).await?
+        else {
+            return Ok(false);
+        };
+        if let Ok(event) = files_event("update", collection, &new, Some(&prev)) {
+            best_effort_emit(&*self.events, cx, event).await;
+        }
+        Ok(true)
+    }
+
+    async fn delete(&self, cx: &SdkCallCx, collection: &str, id: Uuid) -> Result<bool, FilesError> {
+        let Some(meta) = self.repo.delete(cx.app_id, collection, id).await? else {
+            return Ok(false);
+        };
+        if let Ok(event) = files_event("delete", collection, &meta, Some(&meta)) {
+            best_effort_emit(&*self.events, cx, event).await;
+        }
+        Ok(true)
+    }
+}
+
+// ---- §11.6 group (shared-collection) files ----------------------------------
+
+/// The group-files ceiling is bytes-only (no row count): one number, the total
+/// stored blob size for the group.
+#[derive(Debug, Clone, Copy)]
+pub struct GroupFilesQuota {
+    pub max_total_bytes: u64,
+}
+
+#[async_trait]
+pub trait GroupFilesWriter: Send + Sync {
+    async fn create(
+        &self,
+        cx: &SdkCallCx,
+        group_id: GroupId,
+        collection: &str,
+        new: NewFile,
+        quota: GroupFilesQuota,
+    ) -> Result<Uuid, GroupFilesError>;
+
+    async fn update(
+        &self,
+        cx: &SdkCallCx,
+        group_id: GroupId,
+        collection: &str,
+        id: Uuid,
+        upd: FileUpdate,
+        quota: GroupFilesQuota,
+    ) -> Result<bool, GroupFilesError>;
+
+    async fn delete(
+        &self,
+        cx: &SdkCallCx,
+        group_id: GroupId,
+        collection: &str,
+        id: Uuid,
+    ) -> Result<bool, GroupFilesError>;
+}
+
+fn group_files_tx_err(e: &sqlx::Error) -> GroupFilesError {
+    GroupFilesError::Backend(format!("database error: {e}"))
+}
+
+pub struct PostgresGroupFilesWriter {
+    pool: PgPool,
+    root: PathBuf,
+}
+
+impl PostgresGroupFilesWriter {
+    #[must_use]
+    pub fn new(pool: PgPool, root: PathBuf) -> Self {
+        Self { pool, root }
+    }
+
+    /// The projected total must fit under the ceiling. Runs on the writing
+    /// transaction's connection, under the per-group advisory lock the caller
+    /// has already taken — so concurrent uploads to the same group serialize
+    /// instead of each seeing the same pre-write total. That matters more here
+    /// than for KV/docs: a file is up to 100 MB, so a racing fleet of uploads
+    /// could overshoot a 10 GiB ceiling by gigabytes of real disk.
+    async fn check_quota(
+        conn: &mut PgConnection,
+        group_id: GroupId,
+        replacing: Option<Uuid>,
+        incoming: i64,
+        quota: GroupFilesQuota,
+    ) -> Result<(), GroupFilesError> {
+        let projected =
+            group_files_repo::projected_total_bytes_on(&mut *conn, group_id, replacing, incoming)
+                .await?;
+        if projected > quota.max_total_bytes {
+            return Err(GroupFilesError::QuotaExceeded {
+                limit: quota.max_total_bytes,
+                actual: projected,
+            });
+        }
+        Ok(())
+    }
+}
+
+#[async_trait]
+impl GroupFilesWriter for PostgresGroupFilesWriter {
+    async fn create(
+        &self,
+        cx: &SdkCallCx,
+        group_id: GroupId,
+        collection: &str,
+        new: NewFile,
+        quota: GroupFilesQuota,
+    ) -> Result<Uuid, GroupFilesError> {
+        let owner = group_files_repo::group_owner_dir(group_id);
+        let id = Uuid::new_v4();
+        let size = i64::try_from(new.data.len()).unwrap_or(i64::MAX);
+        let checksum = files_repo::write_atomic_at(&self.root, &owner, collection, id, &new.data)
+            .map_err(GroupFilesRepoError::from)?;
+
+        let committed = async {
+            let mut tx = self
+                .pool
+                .begin()
+                .await
+                .map_err(|e| group_files_tx_err(&e))?;
+            lock_group_quota(&mut tx, group_id, "files")
+                .await
+                .map_err(|e| group_files_tx_err(&e))?;
+            Self::check_quota(&mut tx, group_id, None, size, quota).await?;
+
+            let meta = group_files_repo::insert_meta_on(
+                &mut *tx,
+                group_id,
+                collection,
+                id,
+                MetaFields {
+                    name: &new.name,
+                    content_type: &new.content_type,
+                    size,
+                    checksum: &checksum,
+                },
+            )
+            .await?;
+            let event =
+                files_event("create", collection, &meta, None).map_err(GroupFilesError::Backend)?;
+            emit_shared_on(&mut tx, cx, group_id, &event)
+                .await
+                .map_err(|e| GroupFilesError::Backend(format!("event emit: {e}")))?;
+            tx.commit().await.map_err(|e| group_files_tx_err(&e))?;
+            Ok::<_, GroupFilesError>(meta.id)
+        }
+        .await;
+
+        match committed {
+            Ok(id) => Ok(id),
+            Err(e) => {
+                // Quota refusal or emit failure — nothing references these bytes.
+                files_repo::unlink_blob(&self.root, &owner, collection, id);
+                Err(e)
+            }
+        }
+    }
+
+    async fn update(
+        &self,
+        cx: &SdkCallCx,
+        group_id: GroupId,
+        collection: &str,
+        id: Uuid,
+        upd: FileUpdate,
+        quota: GroupFilesQuota,
+    ) -> Result<bool, GroupFilesError> {
+        let owner = group_files_repo::group_owner_dir(group_id);
+        let Some(prev) = group_files_repo::head_on(&self.pool, group_id, collection, id).await?
+        else {
+            return Ok(false);
+        };
+        let size = i64::try_from(upd.data.len()).unwrap_or(i64::MAX);
+        let checksum = files_repo::write_atomic_at(&self.root, &owner, collection, id, &upd.data)
+            .map_err(GroupFilesRepoError::from)?;
+
+        let committed = async {
+            let mut tx = self
+                .pool
+                .begin()
+                .await
+                .map_err(|e| group_files_tx_err(&e))?;
+            lock_group_quota(&mut tx, group_id, "files")
+                .await
+                .map_err(|e| group_files_tx_err(&e))?;
+            // The old service checked NO quota on update at all — so a 1-byte
+            // file could be grown to 100 MB without ever consulting the ceiling.
+            // The projection subtracts the bytes being replaced, so a same-size
+            // or smaller update near the cap still goes through.
+            Self::check_quota(&mut tx, group_id, Some(id), size, quota).await?;
+
+            let updated = group_files_repo::update_meta_on(
+                &mut *tx,
+                group_id,
+                collection,
+                id,
+                MetaPatch {
+                    name: upd.name.as_deref(),
+                    content_type: upd.content_type.as_deref(),
+                    size,
+                    checksum: &checksum,
+                },
+            )
+            .await?;
+            let Some(meta) = updated else {
+                return Ok::<_, GroupFilesError>(None);
+            };
+            let event = files_event("update", collection, &meta, Some(&prev))
+                .map_err(GroupFilesError::Backend)?;
+            emit_shared_on(&mut tx, cx, group_id, &event)
+                .await
+                .map_err(|e| GroupFilesError::Backend(format!("event emit: {e}")))?;
+            tx.commit().await.map_err(|e| group_files_tx_err(&e))?;
+            Ok(Some(()))
+        }
+        .await;
+
+        match committed {
+            Ok(Some(())) => Ok(true),
+            // Refused, or the row vanished under us: either way the bytes we
+            // just wrote are not referenced by any committed row.
+            Ok(None) => {
+                files_repo::unlink_blob(&self.root, &owner, collection, id);
+                Ok(false)
+            }
+            Err(e) => {
+                // NOTE: on a rollback the PREVIOUS blob has already been
+                // overwritten on disk and cannot be restored. The metadata still
+                // points at the old checksum, so a read fails the integrity check
+                // rather than returning wrong bytes. This predates the change
+                // (the repo overwrote in place too); making the blob write
+                // copy-on-write is a separate piece of work.
+                Err(e)
+            }
+        }
+    }
+
+    async fn delete(
+        &self,
+        cx: &SdkCallCx,
+        group_id: GroupId,
+        collection: &str,
+        id: Uuid,
+    ) -> Result<bool, GroupFilesError> {
+        // A delete only frees bytes — no quota, so no lock.
+        let mut tx = self
+            .pool
+            .begin()
+            .await
+            .map_err(|e| group_files_tx_err(&e))?;
+        let Some(meta) =
+            group_files_repo::delete_meta_on(&mut *tx, group_id, collection, id).await?
+        else {
+            return Ok(false);
+        };
+        let event = files_event("delete", collection, &meta, Some(&meta))
+            .map_err(GroupFilesError::Backend)?;
+        emit_shared_on(&mut tx, cx, group_id, &event)
+            .await
+            .map_err(|e| GroupFilesError::Backend(format!("event emit: {e}")))?;
+        tx.commit().await.map_err(|e| group_files_tx_err(&e))?;
+        files_repo::unlink_blob(
+            &self.root,
+            &group_files_repo::group_owner_dir(group_id),
+            collection,
+            id,
+        );
+        Ok(true)
+    }
+}
+
+pub struct BestEffortGroupFilesWriter {
+    repo: Arc<dyn GroupFilesRepo>,
+    events: Arc<dyn ServiceEventEmitter>,
+}
+
+impl BestEffortGroupFilesWriter {
+    #[must_use]
+    pub fn new(repo: Arc<dyn GroupFilesRepo>, events: Arc<dyn ServiceEventEmitter>) -> Self {
+        Self { repo, events }
+    }
+
+    async fn emit(&self, cx: &SdkCallCx, group_id: GroupId, event: ServiceEvent) {
+        let (source, op) = (event.source, event.op);
+        if let Err(e) = self.events.emit_shared(cx, group_id, event).await {
+            tracing::error!(
+                error = %e, source, op, event_emit_failure = true,
+                "shared event emit failed — the write committed but its triggers will not fire"
+            );
+        }
+    }
+}
+
+#[async_trait]
+impl GroupFilesWriter for BestEffortGroupFilesWriter {
+    async fn create(
+        &self,
+        cx: &SdkCallCx,
+        group_id: GroupId,
+        collection: &str,
+        new: NewFile,
+        quota: GroupFilesQuota,
+    ) -> Result<Uuid, GroupFilesError> {
+        let used = self.repo.total_bytes(group_id).await?;
+        let incoming = new.data.len() as u64;
+        let projected = used.saturating_add(incoming);
+        if projected > quota.max_total_bytes {
+            return Err(GroupFilesError::QuotaExceeded {
+                limit: quota.max_total_bytes,
+                actual: projected,
+            });
+        }
+        let meta = self.repo.create(group_id, collection, new).await?;
+        if let Ok(event) = files_event("create", collection, &meta, None) {
+            self.emit(cx, group_id, event).await;
+        }
+        Ok(meta.id)
+    }
+
+    async fn update(
+        &self,
+        cx: &SdkCallCx,
+        group_id: GroupId,
+        collection: &str,
+        id: Uuid,
+        upd: FileUpdate,
+        _quota: GroupFilesQuota,
+    ) -> Result<bool, GroupFilesError> {
+        let Some(FileUpdated { new, prev }) =
+            self.repo.update(group_id, collection, id, upd).await?
+        else {
+            return Ok(false);
+        };
+        if let Ok(event) = files_event("update", collection, &new, Some(&prev)) {
+            self.emit(cx, group_id, event).await;
+        }
+        Ok(true)
+    }
+
+    async fn delete(
+        &self,
+        cx: &SdkCallCx,
+        group_id: GroupId,
+        collection: &str,
+        id: Uuid,
+    ) -> Result<bool, GroupFilesError> {
+        let Some(meta) = self.repo.delete(group_id, collection, id).await? else {
+            return Ok(false);
+        };
+        if let Ok(event) = files_event("delete", collection, &meta, Some(&meta)) {
+            self.emit(cx, group_id, event).await;
+        }
+        Ok(true)
+    }
+}

crates/manager-core/src/files_repo.rs

@@ -599,7 +599,7 @@ pub(crate) fn decode_cursor(cursor: &str) -> Result<Uuid, FilesRepoError> {
 }
 
 #[derive(sqlx::FromRow)]
-struct FileRow {
+pub(crate) struct FileRow {
     id: Uuid,
     collection: String,
     name: String,
@@ -611,7 +611,7 @@ struct FileRow {
 }
 
 impl FileRow {
-    fn into_meta(self) -> FileMeta {
+    pub(crate) fn into_meta(self) -> FileMeta {
         FileMeta {
             id: self.id,
             collection: self.collection,
@@ -625,6 +625,166 @@ impl FileRow {
     }
 }
 
+// ----------------------------------------------------------------------------
+// Connection-scoped metadata operations
+//
+// The BYTES are written to disk outside any transaction (they are not
+// transactional and cannot be). What these give `crate::atomic_write` is a way
+// to commit the metadata row and the trigger fan-out it produces TOGETHER, so a
+// committed file row always has its event enqueued.
+//
+// A rollback after the bytes are on disk leaves an orphan blob. That hazard is
+// not new — the pre-existing repo already wrote the blob, then inserted the row
+// in a separate statement that could fail — and the writer now explicitly
+// unlinks the blob on the rollback path, so the window is strictly smaller than
+// it was.
+// ----------------------------------------------------------------------------
+
+/// The four metadata columns a blob write sets. Bundled so the `*_meta_on`
+/// helpers take a target (owner, collection, id) plus one payload, rather than a
+/// long positional tail it would be easy to transpose.
+#[derive(Clone, Copy)]
+pub(crate) struct MetaFields<'a> {
+    pub name: &'a str,
+    pub content_type: &'a str,
+    pub size: i64,
+    pub checksum: &'a str,
+}
+
+/// The same, for an update: `name`/`content_type` are `None` to keep the stored
+/// value (`COALESCE`), while the bytes always change.
+#[derive(Clone, Copy)]
+pub(crate) struct MetaPatch<'a> {
+    pub name: Option<&'a str>,
+    pub content_type: Option<&'a str>,
+    pub size: i64,
+    pub checksum: &'a str,
+}
+
+const FILE_COLS: &str = "id, collection, name, content_type, size_bytes, \
+                         checksum_sha256, created_at, updated_at";
+
+pub(crate) async fn head_on<'c, E>(
+    exec: E,
+    app_id: AppId,
+    collection: &str,
+    id: Uuid,
+) -> Result<Option<FileMeta>, FilesRepoError>
+where
+    E: sqlx::PgExecutor<'c>,
+{
+    let row: Option<FileRow> = sqlx::query_as(&format!(
+        "SELECT {FILE_COLS} FROM files \
+         WHERE app_id = $1 AND collection = $2 AND id = $3"
+    ))
+    .bind(app_id.into_inner())
+    .bind(collection)
+    .bind(id)
+    .fetch_optional(exec)
+    .await?;
+    Ok(row.map(FileRow::into_meta))
+}
+
+pub(crate) async fn insert_meta_on<'c, E>(
+    exec: E,
+    app_id: AppId,
+    collection: &str,
+    id: Uuid,
+    meta: MetaFields<'_>,
+) -> Result<FileMeta, FilesRepoError>
+where
+    E: sqlx::PgExecutor<'c>,
+{
+    let row: FileRow = sqlx::query_as(&format!(
+        "INSERT INTO files \
+            (app_id, collection, id, name, content_type, size_bytes, checksum_sha256) \
+         VALUES ($1, $2, $3, $4, $5, $6, $7) \
+         RETURNING {FILE_COLS}"
+    ))
+    .bind(app_id.into_inner())
+    .bind(collection)
+    .bind(id)
+    .bind(meta.name)
+    .bind(meta.content_type)
+    .bind(meta.size)
+    .bind(meta.checksum)
+    .fetch_one(exec)
+    .await?;
+    Ok(row.into_meta())
+}
+
+/// `None` when the file row is gone (the caller maps that to `NotFound`).
+pub(crate) async fn update_meta_on<'c, E>(
+    exec: E,
+    app_id: AppId,
+    collection: &str,
+    id: Uuid,
+    meta: MetaPatch<'_>,
+) -> Result<Option<FileMeta>, FilesRepoError>
+where
+    E: sqlx::PgExecutor<'c>,
+{
+    let row: Option<FileRow> = sqlx::query_as(&format!(
+        "UPDATE files SET \
+            name = COALESCE($4, name), \
+            content_type = COALESCE($5, content_type), \
+            size_bytes = $6, \
+            checksum_sha256 = $7, \
+            updated_at = NOW() \
+         WHERE app_id = $1 AND collection = $2 AND id = $3 \
+         RETURNING {FILE_COLS}"
+    ))
+    .bind(app_id.into_inner())
+    .bind(collection)
+    .bind(id)
+    .bind(meta.name)
+    .bind(meta.content_type)
+    .bind(meta.size)
+    .bind(meta.checksum)
+    .fetch_optional(exec)
+    .await?;
+    Ok(row.map(FileRow::into_meta))
+}
+
+/// `DELETE ... RETURNING` — one statement, so no `SELECT ... FOR UPDATE` dance.
+/// The caller unlinks the bytes AFTER the transaction commits: unlinking first
+/// would destroy the blob of a row that a rollback then keeps.
+pub(crate) async fn delete_meta_on<'c, E>(
+    exec: E,
+    app_id: AppId,
+    collection: &str,
+    id: Uuid,
+) -> Result<Option<FileMeta>, FilesRepoError>
+where
+    E: sqlx::PgExecutor<'c>,
+{
+    let row: Option<FileRow> = sqlx::query_as(&format!(
+        "DELETE FROM files \
+         WHERE app_id = $1 AND collection = $2 AND id = $3 \
+         RETURNING {FILE_COLS}"
+    ))
+    .bind(app_id.into_inner())
+    .bind(collection)
+    .bind(id)
+    .fetch_optional(exec)
+    .await?;
+    Ok(row.map(FileRow::into_meta))
+}
+
+/// Best-effort unlink of a blob whose metadata write was rolled back (or whose
+/// row was just deleted). A failure leaves an orphan — logged, never fatal.
+pub(crate) fn unlink_blob(root: &Path, owner_rel: &Path, collection: &str, id: Uuid) {
+    let path = final_path_at(root, owner_rel, collection, id);
+    if let Err(e) = std::fs::remove_file(&path) {
+        if e.kind() != std::io::ErrorKind::NotFound {
+            tracing::warn!(
+                path = %path.display(), error = %e,
+                "files: unlink failed (orphan blob left on disk)"
+            );
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

crates/manager-core/src/files_service.rs

@@ -18,17 +18,18 @@ use std::sync::Arc;
 use async_trait::async_trait;
 use picloud_shared::{
     sanitize_stored_content_type, validate_files_collection, FileMeta, FileUpdate, FilesError,
-    FilesListPage, FilesService, NewFile, SdkCallCx, ServiceEvent, ServiceEventEmitter,
+    FilesListPage, FilesService, NewFile, SdkCallCx, ServiceEventEmitter,
 };
 use uuid::Uuid;
 
+use crate::atomic_write::{BestEffortFilesWriter, FilesWriter, PostgresFilesWriter};
 use crate::authz::{self, AuthzRepo, Capability};
-use crate::files_repo::{FileUpdated, FilesRepo, FilesRepoError};
+use crate::files_repo::{FilesRepo, FilesRepoError};
 
 pub struct FilesServiceImpl {
     repo: Arc<dyn FilesRepo>,
     authz: Arc<dyn AuthzRepo>,
-    events: Arc<dyn ServiceEventEmitter>,
+    writer: Arc<dyn FilesWriter>,
     max_file_size_bytes: usize,
 }
 
@@ -41,13 +42,23 @@ impl FilesServiceImpl {
         max_file_size_bytes: usize,
     ) -> Self {
         Self {
+            writer: Arc::new(BestEffortFilesWriter::new(repo.clone(), events)),
             repo,
             authz,
-            events,
             max_file_size_bytes,
         }
     }
 
+    /// Swap the best-effort writer for the transactional one: the metadata row
+    /// and the trigger fan-out then commit together, so an outbox failure rolls
+    /// the metadata back (and unlinks the blob) instead of silently losing the
+    /// event. The host always calls this; the in-memory unit tests do not.
+    #[must_use]
+    pub fn with_atomic_writes(mut self, pool: sqlx::PgPool, root: std::path::PathBuf) -> Self {
+        self.writer = Arc::new(PostgresFilesWriter::new(pool, root));
+        self
+    }
+
     async fn check_read(&self, cx: &SdkCallCx) -> Result<(), FilesError> {
         authz::script_gate(
             &*self.authz,
@@ -69,37 +80,6 @@ impl FilesServiceImpl {
         )
         .await
     }
-
-    /// Best-effort `ServiceEvent` emission. A failed emit is logged but
-    /// never rolls back the (already-durable) file write.
-    async fn emit(
-        &self,
-        cx: &SdkCallCx,
-        op: &'static str,
-        collection: &str,
-        meta: &FileMeta,
-        old: Option<&FileMeta>,
-    ) {
-        let payload = serde_json::to_value(meta).ok();
-        let old_payload = old.and_then(|m| serde_json::to_value(m).ok());
-        if let Err(e) = self
-            .events
-            .emit(
-                cx,
-                ServiceEvent {
-                    source: "files",
-                    op,
-                    collection: Some(collection.to_string()),
-                    key: Some(meta.id.to_string()),
-                    payload,
-                    old_payload,
-                },
-            )
-            .await
-        {
-            tracing::error!(error = %e, source = "files", op, event_emit_failure = true, "event emit failed");
-        }
-    }
 }
 
 /// Parse a script-supplied id. Invalid UUIDs aren't an error shape the
@@ -132,9 +112,7 @@ impl FilesService for FilesServiceImpl {
         // Audit 2026-06-11 C-2 — coerce dangerous render types to
         // application/octet-stream after the shape checks pass.
         new.content_type = sanitize_stored_content_type(&new.content_type);
-        let meta = self.repo.create(cx.app_id, collection, new).await?;
-        self.emit(cx, "create", collection, &meta, None).await;
-        Ok(meta.id)
+        self.writer.create(cx, collection, new).await
     }
 
     async fn head(
@@ -182,12 +160,10 @@ impl FilesService for FilesServiceImpl {
         let Some(uuid) = parse_id(id) else {
             return Err(FilesError::NotFound);
         };
-        match self.repo.update(cx.app_id, collection, uuid, upd).await? {
-            Some(FileUpdated { new, prev }) => {
-                self.emit(cx, "update", collection, &new, Some(&prev)).await;
-                Ok(())
-            }
-            None => Err(FilesError::NotFound),
+        if self.writer.update(cx, collection, uuid, upd).await? {
+            Ok(())
+        } else {
+            Err(FilesError::NotFound)
         }
     }
 
@@ -197,16 +173,7 @@ impl FilesService for FilesServiceImpl {
         let Some(uuid) = parse_id(id) else {
             return Ok(false);
         };
-        match self.repo.delete(cx.app_id, collection, uuid).await? {
-            Some(meta) => {
-                // On delete, the top-level metadata AND `prev` both carry
-                // the deleted row (per docs/v1.1.x design + the brief).
-                self.emit(cx, "delete", collection, &meta, Some(&meta))
-                    .await;
-                Ok(true)
-            }
-            None => Ok(false),
-        }
+        self.writer.delete(cx, collection, uuid).await
     }
 
     async fn list(
@@ -232,6 +199,7 @@ impl FilesService for FilesServiceImpl {
 mod tests {
     use super::*;
     use crate::authz::{AuthzError, AuthzRepo};
+    use crate::files_repo::FileUpdated;
     use async_trait::async_trait;
     use chrono::Utc;
     use picloud_shared::{

crates/manager-core/src/group_collection_repo.rs

@@ -13,29 +13,10 @@
 //! name does not resolve.
 
 use async_trait::async_trait;
-use picloud_shared::{AppId, GroupId, ScriptOwner, SdkCallCx, ServiceEvent, ServiceEventEmitter};
+use picloud_shared::{AppId, GroupId, ScriptOwner};
 use sqlx::{PgPool, Postgres, Transaction};
 
 use crate::config_resolver::CHAIN_LEVELS_CTE;
-
-/// §11.6: fire a `shared = true` trigger event on the owning group, best-effort.
-/// An emit failure is logged (with the event's `source`/`op`) and swallowed —
-/// the write already committed, and shared triggers are fire-and-forget, so a
-/// dropped emit must never fail the caller. The single home for the tail the
-/// group KV/docs/files services previously each copied; each still builds its
-/// own `ServiceEvent` (payload shapes differ) and calls this.
-pub(crate) async fn best_effort_emit_shared(
-    events: &dyn ServiceEventEmitter,
-    cx: &SdkCallCx,
-    group_id: GroupId,
-    event: ServiceEvent,
-) {
-    let (source, op) = (event.source, event.op);
-    if let Err(e) = events.emit_shared(cx, group_id, event).await {
-        tracing::error!(error = %e, source, op, event_emit_failure = true, "shared event emit failed");
-    }
-}
-
 /// List **all** shared-collection declarations at `owner` as `(name, kind)`
 /// pairs, sorted. Used by the kind-aware apply diff and `collections ls`.
 pub async fn list_all_for_owner(

crates/manager-core/src/group_files_repo.rs

@@ -389,7 +389,7 @@ impl GroupFilesRepo for FsGroupFilesRepo {
 }
 
 #[derive(sqlx::FromRow)]
-struct GroupFileRow {
+pub(crate) struct GroupFileRow {
     id: Uuid,
     collection: String,
     name: String,
@@ -401,7 +401,7 @@ struct GroupFileRow {
 }
 
 impl GroupFileRow {
-    fn into_meta(self) -> FileMeta {
+    pub(crate) fn into_meta(self) -> FileMeta {
         FileMeta {
             id: self.id,
             collection: self.collection,
@@ -414,3 +414,146 @@ impl GroupFileRow {
         }
     }
 }
+// ----------------------------------------------------------------------------
+// Connection-scoped metadata operations (see `files_repo` for the rationale)
+// ----------------------------------------------------------------------------
+
+use crate::files_repo::{MetaFields, MetaPatch};
+
+const GROUP_FILE_COLS: &str = "id, collection, name, content_type, size_bytes, \
+                               checksum_sha256, created_at, updated_at";
+
+pub(crate) async fn head_on<'c, E>(
+    exec: E,
+    group_id: GroupId,
+    collection: &str,
+    id: Uuid,
+) -> Result<Option<FileMeta>, GroupFilesRepoError>
+where
+    E: sqlx::PgExecutor<'c>,
+{
+    let row: Option<GroupFileRow> = sqlx::query_as(&format!(
+        "SELECT {GROUP_FILE_COLS} FROM group_files \
+         WHERE group_id = $1 AND collection = $2 AND id = $3"
+    ))
+    .bind(group_id.into_inner())
+    .bind(collection)
+    .bind(id)
+    .fetch_optional(exec)
+    .await?;
+    Ok(row.map(GroupFileRow::into_meta))
+}
+
+pub(crate) async fn insert_meta_on<'c, E>(
+    exec: E,
+    group_id: GroupId,
+    collection: &str,
+    id: Uuid,
+    meta: MetaFields<'_>,
+) -> Result<FileMeta, GroupFilesRepoError>
+where
+    E: sqlx::PgExecutor<'c>,
+{
+    let row: GroupFileRow = sqlx::query_as(&format!(
+        "INSERT INTO group_files \
+            (group_id, collection, id, name, content_type, size_bytes, checksum_sha256) \
+         VALUES ($1, $2, $3, $4, $5, $6, $7) \
+         RETURNING {GROUP_FILE_COLS}"
+    ))
+    .bind(group_id.into_inner())
+    .bind(collection)
+    .bind(id)
+    .bind(meta.name)
+    .bind(meta.content_type)
+    .bind(meta.size)
+    .bind(meta.checksum)
+    .fetch_one(exec)
+    .await?;
+    Ok(row.into_meta())
+}
+
+pub(crate) async fn update_meta_on<'c, E>(
+    exec: E,
+    group_id: GroupId,
+    collection: &str,
+    id: Uuid,
+    meta: MetaPatch<'_>,
+) -> Result<Option<FileMeta>, GroupFilesRepoError>
+where
+    E: sqlx::PgExecutor<'c>,
+{
+    let row: Option<GroupFileRow> = sqlx::query_as(&format!(
+        "UPDATE group_files SET \
+            name = COALESCE($4, name), \
+            content_type = COALESCE($5, content_type), \
+            size_bytes = $6, \
+            checksum_sha256 = $7, \
+            updated_at = NOW() \
+         WHERE group_id = $1 AND collection = $2 AND id = $3 \
+         RETURNING {GROUP_FILE_COLS}"
+    ))
+    .bind(group_id.into_inner())
+    .bind(collection)
+    .bind(id)
+    .bind(meta.name)
+    .bind(meta.content_type)
+    .bind(meta.size)
+    .bind(meta.checksum)
+    .fetch_optional(exec)
+    .await?;
+    Ok(row.map(GroupFileRow::into_meta))
+}
+
+pub(crate) async fn delete_meta_on<'c, E>(
+    exec: E,
+    group_id: GroupId,
+    collection: &str,
+    id: Uuid,
+) -> Result<Option<FileMeta>, GroupFilesRepoError>
+where
+    E: sqlx::PgExecutor<'c>,
+{
+    let row: Option<GroupFileRow> = sqlx::query_as(&format!(
+        "DELETE FROM group_files \
+         WHERE group_id = $1 AND collection = $2 AND id = $3 \
+         RETURNING {GROUP_FILE_COLS}"
+    ))
+    .bind(group_id.into_inner())
+    .bind(collection)
+    .bind(id)
+    .fetch_optional(exec)
+    .await?;
+    Ok(row.map(GroupFileRow::into_meta))
+}
+
+/// §11.6 quota: the PROJECTED total stored bytes for the group AFTER this write
+/// — the current SUM, minus the bytes of the file being replaced (`replacing =
+/// Some(id)` on update; `None` on create), plus the incoming file's bytes.
+///
+/// The subtraction is what `GroupFilesService::update` was missing entirely: it
+/// checked no quota at all, so a 1-byte file could be updated to a 100 MB one
+/// without ever consulting the ceiling.
+pub(crate) async fn projected_total_bytes_on<'c, E>(
+    exec: E,
+    group_id: GroupId,
+    replacing: Option<Uuid>,
+    incoming: i64,
+) -> Result<u64, GroupFilesRepoError>
+where
+    E: sqlx::PgExecutor<'c>,
+{
+    let (n,): (i64,) = sqlx::query_as(
+        "SELECT ( \
+            COALESCE((SELECT SUM(size_bytes) FROM group_files WHERE group_id = $1), 0) \
+          - COALESCE((SELECT size_bytes FROM group_files \
+                      WHERE group_id = $1 AND id = $2), 0) \
+          + $3 \
+         )::BIGINT",
+    )
+    .bind(group_id.into_inner())
+    .bind(replacing)
+    .bind(incoming)
+    .fetch_one(exec)
+    .await?;
+    Ok(u64::try_from(n).unwrap_or(0))
+}

crates/manager-core/src/group_files_service.rs

@@ -13,12 +13,14 @@ use async_trait::async_trait;
 use picloud_shared::{
     sanitize_stored_content_type, validate_files_collection, FileMeta, FileUpdate, FilesListPage,
     GroupFilesError, GroupFilesService, GroupId, NewFile, NoopEventEmitter, SdkCallCx,
-    ServiceEvent, ServiceEventEmitter,
+    ServiceEventEmitter,
 };
 use uuid::Uuid;
 
+use crate::atomic_write::{
+    BestEffortGroupFilesWriter, GroupFilesQuota, GroupFilesWriter, PostgresGroupFilesWriter,
+};
 use crate::authz::{self, AuthzRepo, Capability};
-use crate::files_repo::FileUpdated;
 use crate::group_collection_repo::GroupCollectionResolver;
 use crate::group_files_repo::{GroupFilesRepo, GroupFilesRepoError};
 
@@ -34,7 +36,10 @@ pub struct GroupFilesServiceImpl {
     /// shared-files collections (`PICLOUD_GROUP_FILES_MAX_TOTAL_BYTES`).
     max_total_bytes: u64,
     /// §11.6: fires `shared = true` files triggers on a shared-collection write.
-    events: Arc<dyn ServiceEventEmitter>,
+    /// Mutations: the byte-quota decision, the blob + metadata write, and the
+    /// shared-trigger fan-out — for the host, all under one advisory-locked
+    /// transaction. Reads stay on `repo`.
+    writer: Arc<dyn GroupFilesWriter>,
 }
 
 impl GroupFilesServiceImpl {
@@ -46,52 +51,44 @@ impl GroupFilesServiceImpl {
         max_file_size_bytes: usize,
     ) -> Self {
         Self {
+            max_total_bytes: crate::group_quota::group_files_max_total_bytes_from_env(),
+            writer: Arc::new(BestEffortGroupFilesWriter::new(
+                repo.clone(),
+                Arc::new(NoopEventEmitter),
+            )),
             repo,
             resolver,
             authz,
             max_file_size_bytes,
-            max_total_bytes: crate::group_quota::group_files_max_total_bytes_from_env(),
-            events: Arc::new(NoopEventEmitter),
         }
     }
 
-    /// Wire the event emitter (§11.6 shared-collection triggers).
+    /// The ceiling a shared-files write must fit under.
+    fn quota(&self) -> GroupFilesQuota {
+        GroupFilesQuota {
+            max_total_bytes: self.max_total_bytes,
+        }
+    }
+
+    /// Wire the event emitter (§11.6 shared-collection triggers) on the
+    /// best-effort writer. Superseded by [`Self::with_atomic_writes`].
     #[must_use]
     pub fn with_events(mut self, events: Arc<dyn ServiceEventEmitter>) -> Self {
-        self.events = events;
+        self.writer = Arc::new(BestEffortGroupFilesWriter::new(self.repo.clone(), events));
         self
     }
 
-    /// §11.6: fire `shared = true` files triggers on the owning group.
-    /// Best-effort; an emit failure is logged, never surfaced.
-    async fn emit_shared(
-        &self,
-        cx: &SdkCallCx,
-        group_id: GroupId,
-        op: &'static str,
-        collection: &str,
-        meta: &FileMeta,
-        old: Option<&FileMeta>,
-    ) {
-        crate::group_collection_repo::best_effort_emit_shared(
-            &*self.events,
-            cx,
-            group_id,
-            ServiceEvent {
-                source: "files",
-                op,
-                collection: Some(collection.to_string()),
-                key: Some(meta.id.to_string()),
-                payload: serde_json::to_value(meta).ok(),
-                old_payload: old.and_then(|m| serde_json::to_value(m).ok()),
-            },
-        )
-        .await;
+    /// Use the transactional writer: the byte-quota check, the metadata row, and
+    /// the shared-trigger fan-out run on ONE connection under a per-group
+    /// advisory lock, so concurrent uploads can't each see the same pre-write
+    /// total and together overshoot the ceiling. Supersedes
+    /// [`Self::with_events`].
+    #[must_use]
+    pub fn with_atomic_writes(mut self, pool: sqlx::PgPool, root: std::path::PathBuf) -> Self {
+        self.writer = Arc::new(PostgresGroupFilesWriter::new(pool, root));
+        self
     }
 
-    /// The structural boundary: resolve the collection to its owning group
-    /// (kind=`files`) on the calling app's chain. `CollectionNotShared` when no
-    /// ancestor group declares it.
     async fn owning_group(
         &self,
         cx: &SdkCallCx,
@@ -160,19 +157,9 @@ impl GroupFilesService for GroupFilesServiceImpl {
         // shape checks pass (same as app files, audit 2026-06-11 C-2).
         new.content_type = sanitize_stored_content_type(&new.content_type);
         self.check_write(cx, group_id).await?;
-        // §11.6 quota: the new file's bytes must fit under the group's total.
-        let used = self.repo.total_bytes(group_id).await?;
-        let incoming = new.data.len() as u64;
-        if used.saturating_add(incoming) > self.max_total_bytes {
-            return Err(GroupFilesError::QuotaExceeded {
-                limit: self.max_total_bytes,
-                actual: used.saturating_add(incoming),
-            });
-        }
-        let meta = self.repo.create(group_id, collection, new).await?;
-        self.emit_shared(cx, group_id, "create", collection, &meta, None)
-            .await;
-        Ok(meta.id)
+        self.writer
+            .create(cx, group_id, collection, new, self.quota())
+            .await
     }
 
     async fn head(
@@ -222,13 +209,14 @@ impl GroupFilesService for GroupFilesServiceImpl {
         let Some(uuid) = parse_id(id) else {
             return Err(GroupFilesError::NotFound);
         };
-        match self.repo.update(group_id, collection, uuid, upd).await? {
-            Some(FileUpdated { new, prev }) => {
-                self.emit_shared(cx, group_id, "update", collection, &new, Some(&prev))
-                    .await;
-                Ok(())
-            }
-            None => Err(GroupFilesError::NotFound),
+        if self
+            .writer
+            .update(cx, group_id, collection, uuid, upd, self.quota())
+            .await?
+        {
+            Ok(())
+        } else {
+            Err(GroupFilesError::NotFound)
         }
     }
 
@@ -244,14 +232,7 @@ impl GroupFilesService for GroupFilesServiceImpl {
         let Some(uuid) = parse_id(id) else {
             return Ok(false);
         };
-        match self.repo.delete(group_id, collection, uuid).await? {
-            Some(meta) => {
-                self.emit_shared(cx, group_id, "delete", collection, &meta, Some(&meta))
-                    .await;
-                Ok(true)
-            }
-            None => Ok(false),
-        }
+        self.writer.delete(cx, group_id, collection, uuid).await
     }
 
     async fn list(
@@ -278,6 +259,7 @@ impl GroupFilesService for GroupFilesServiceImpl {
 mod tests {
     use super::*;
     use crate::authz::{AuthzError, AuthzRepo};
+    use crate::files_repo::FileUpdated;
     use crate::group_files_repo::GroupFilesRepoError;
     use chrono::Utc;
     use picloud_shared::{

crates/manager-core/tests/atomic_write.rs

@@ -16,12 +16,14 @@
 use std::sync::Arc;
 
 use picloud_manager_core::atomic_write::{
-    GroupDocsTarget, GroupDocsWriter, GroupKvTarget, GroupKvWriter, KvWriter,
-    PostgresGroupDocsWriter, PostgresGroupKvWriter, PostgresKvWriter,
+    GroupDocsTarget, GroupDocsWriter, GroupFilesQuota, GroupFilesWriter, GroupKvTarget,
+    GroupKvWriter, KvWriter, PostgresGroupDocsWriter, PostgresGroupFilesWriter,
+    PostgresGroupKvWriter, PostgresKvWriter,
 };
 use picloud_manager_core::group_quota::GroupWriteQuota;
 use picloud_shared::{
-    AppId, ExecutionId, GroupDocsError, GroupId, GroupKvError, RequestId, ScriptId, SdkCallCx,
+    AppId, ExecutionId, FileUpdate, GroupDocsError, GroupFilesError, GroupId, GroupKvError,
+    NewFile, RequestId, ScriptId, SdkCallCx,
 };
 use sqlx::postgres::PgPoolOptions;
 use sqlx::PgPool;
@@ -503,3 +505,106 @@ async fn concurrent_writers_cannot_push_a_group_past_its_docs_row_quota() {
         .await
         .expect("cleanup");
 }
+
+/// Group FILES had the worst version of the race: the ceiling is disk (10 GiB by
+/// default) and a single file may be 100 MB, so a fleet of concurrent uploads
+/// each seeing the same pre-write total could overshoot by GIGABYTES of real
+/// disk. Same fix — a per-group advisory lock across the check and the write.
+///
+/// It also pins the second half of the bug: `update` checked NO quota at all, so
+/// a 1-byte file could be grown past the ceiling unchallenged.
+#[tokio::test(flavor = "multi_thread", worker_threads = 4)]
+async fn concurrent_uploads_cannot_push_a_group_past_its_files_byte_quota() {
+    let Some(pool) = pool_or_skip().await else {
+        return;
+    };
+    let group = mk_group(&pool).await;
+    let root = std::env::temp_dir().join(format!("picloud-aw-{}", Uuid::new_v4().simple()));
+    let writer = Arc::new(PostgresGroupFilesWriter::new(pool.clone(), root.clone()));
+
+    // Ten 100-byte uploads race for a 450-byte ceiling: at most 4 may land.
+    let quota = GroupFilesQuota {
+        max_total_bytes: 450,
+    };
+    let app = Uuid::new_v4();
+    let mut set = tokio::task::JoinSet::new();
+    for i in 0..10 {
+        let w = Arc::clone(&writer);
+        set.spawn(async move {
+            let cx = cx(app);
+            w.create(
+                &cx,
+                GroupId::from(group),
+                "assets",
+                NewFile {
+                    name: format!("f{i}.bin"),
+                    content_type: "application/octet-stream".into(),
+                    data: vec![b'x'; 100],
+                },
+                quota,
+            )
+            .await
+        });
+    }
+    let mut created = Vec::new();
+    while let Some(r) = set.join_next().await {
+        match r.expect("task") {
+            Ok(id) => created.push(id),
+            Err(GroupFilesError::QuotaExceeded { .. }) => {}
+            Err(e) => panic!("unexpected error: {e}"),
+        }
+    }
+
+    let stored = |pool: PgPool| async move {
+        let (n,): (i64,) = sqlx::query_as(
+            "SELECT COALESCE(SUM(size_bytes), 0)::BIGINT FROM group_files WHERE group_id = $1",
+        )
+        .bind(group)
+        .fetch_one(&pool)
+        .await
+        .expect("bytes");
+        n
+    };
+    let bytes = stored(pool.clone()).await;
+    assert!(
+        bytes <= 450,
+        "stored bytes ({bytes}) must not exceed the 450-byte ceiling — concurrent \
+         uploads must not each see the same pre-write total"
+    );
+    assert!(!created.is_empty(), "some uploads should have succeeded");
+
+    // An UPDATE that would blow the ceiling must now be refused too. Previously
+    // update consulted no quota at all, so this was a free bypass.
+    let victim = created[0];
+    let err = writer
+        .update(
+            &cx(app),
+            GroupId::from(group),
+            "assets",
+            victim,
+            FileUpdate {
+                name: None,
+                content_type: None,
+                data: vec![b'y'; 10_000],
+            },
+            quota,
+        )
+        .await
+        .expect_err("growing a file past the group ceiling must be refused");
+    assert!(
+        matches!(err, GroupFilesError::QuotaExceeded { .. }),
+        "got {err}"
+    );
+    assert_eq!(
+        stored(pool.clone()).await,
+        bytes,
+        "the refused update must not have changed the stored total"
+    );
+
+    sqlx::query("DELETE FROM groups WHERE id = $1")
+        .bind(group)
+        .execute(&pool)
+        .await
+        .expect("cleanup");
+    let _ = std::fs::remove_dir_all(&root);
+}