From 7c864e9588e8950c5d5ccf138d7f63d7de5d83ef Mon Sep 17 00:00:00 2001
From: Jamie Pine <ijamespine@me.com>
Date: Fri, 28 Nov 2025 08:37:27 -0800
Subject: [PATCH] Buffer shared changes when FK dep missing

---
 core/src/service/sync/backfill.rs | 121 +++++++++++++++++++++++-------
 1 file changed, 94 insertions(+), 27 deletions(-)

diff --git a/core/src/service/sync/backfill.rs b/core/src/service/sync/backfill.rs
index 0c61acb53..cc5a0837d 100644
--- a/core/src/service/sync/backfill.rs
+++ b/core/src/service/sync/backfill.rs
@@ -667,7 +667,52 @@ impl BackfillManager {
 
 				// Apply entries in HLC order (already sorted from peer)
 				for entry in &entries {
-					self.log_handler.handle_shared_change(entry.clone()).await?;
+					// Attempt to apply the shared change
+					// If it fails due to missing FK dependency, buffer it for retry
+					match self.log_handler.handle_shared_change(entry.clone()).await {
+						Ok(()) => {
+							// Success - resolve any waiting dependencies
+						}
+						Err(e) => {
+							let error_str = e.to_string();
+
+							// Check if this is a FK dependency error
+							if error_str.contains("Sync dependency missing") {
+								// Extract the missing UUID and buffer this entry
+								if let Some(missing_uuid) = super::dependency::extract_missing_dependency_uuid(&error_str) {
+									tracing::debug!(
+										record_uuid = %entry.record_uuid,
+										model_type = %entry.model_type,
+										missing_uuid = %missing_uuid,
+										"Shared resource has missing FK dependency, buffering for retry"
+									);
+
+									// Buffer this shared change for retry when dependency arrives
+									self.peer_sync
+										.dependency_tracker()
+										.add_dependency(
+											missing_uuid,
+											super::state::BufferedUpdate::SharedChange(entry.clone()),
+										)
+										.await;
+
+									continue; // Skip to next entry
+								} else {
+									tracing::warn!(
+										error = %e,
+										record_uuid = %entry.record_uuid,
+										"Sync dependency missing but couldn't extract UUID, buffering: {}",
+										error_str
+									);
+									// TODO: Consider buffering blind or failing
+									continue;
+								}
+							}
+
+							// Non-dependency error - fail backfill
+							return Err(e);
+						}
+					}
 
 					// Resolve any state changes waiting for this shared resource
 					// This handles cross-type dependencies (e.g., entries waiting for content_identities)
@@ -686,18 +731,29 @@ impl BackfillManager {
 						);
 
 						for update in waiting_updates {
-							if let super::state::BufferedUpdate::StateChange(dependent_change) = update
-							{
-								if let Err(e) = self
-									.peer_sync
-									.apply_state_change(dependent_change.clone())
-									.await
-								{
-									tracing::warn!(
-										error = %e,
-										record_uuid = %dependent_change.record_uuid,
-										"Failed to apply dependent state change after shared resource backfill"
-									);
+							match update {
+								super::state::BufferedUpdate::StateChange(dependent_change) => {
+									if let Err(e) = self
+										.peer_sync
+										.apply_state_change(dependent_change.clone())
+										.await
+									{
+										tracing::warn!(
+											error = %e,
+											record_uuid = %dependent_change.record_uuid,
+											"Failed to apply dependent state change after shared resource backfill"
+										);
+									}
+								}
+								super::state::BufferedUpdate::SharedChange(dependent_entry) => {
+									// Retry the shared change now that its dependency exists
+									if let Err(e) = self.log_handler.handle_shared_change(dependent_entry.clone()).await {
+										tracing::warn!(
+											error = %e,
+											record_uuid = %dependent_entry.record_uuid,
+											"Failed to apply dependent shared change after parent resolved"
+										);
+									}
 								}
 							}
 						}
@@ -858,20 +914,31 @@ impl BackfillManager {
 															);
 
 															for update in waiting_updates {
-																if let super::state::BufferedUpdate::StateChange(
-																	dependent_change,
-																) = update
-																{
-																	if let Err(e) = self
-																		.peer_sync
-																		.apply_state_change(dependent_change.clone())
-																		.await
-																	{
-																		tracing::warn!(
-																			error = %e,
-																			record_uuid = %dependent_change.record_uuid,
-																			"Failed to apply dependent state change after current_state snapshot"
-																		);
+																match update {
+																	super::state::BufferedUpdate::StateChange(dependent_change) => {
+																		if let Err(e) = self
+																			.peer_sync
+																			.apply_state_change(dependent_change.clone())
+																			.await
+																		{
+																			tracing::warn!(
+																				error = %e,
+																				record_uuid = %dependent_change.record_uuid,
+																				"Failed to apply dependent state change after current_state snapshot"
+																			);
+																		}
+																	}
+																	super::state::BufferedUpdate::SharedChange(dependent_entry) => {
+																		// Retry the shared change now that its dependency exists
+																		let entry_clone = dependent_entry.clone();
+																		let db = self.peer_sync.db().clone();
+																		if let Err(e) = crate::infra::sync::registry::apply_shared_change(entry_clone, db).await {
+																			tracing::warn!(
+																				error = %e,
+																				record_uuid = %dependent_entry.record_uuid,
+																				"Failed to apply dependent shared change after current_state snapshot"
+																			);
+																		}
 																	}
 																}
 															}