refactor: deepen Google sync domain modules

CONTEXT.md

@@ -126,9 +126,25 @@ A Google Calendar import into Compass.
 A Google sync recovery path that refreshes or restarts Google data when metadata
 says the existing sync needs repair.
 
+**Google Watch repair**:
+A repair path that recreates missing, expired, stale, or incomplete **Google
+Watches** for a **Google-connected user**. Repair should happen only when watch
+state is broken; regular health checks should not repeatedly call Google when
+watches are already healthy. When sync tokens are usable, watch repair should
+also catch up missed Google-side changes through incremental import; when sync
+tokens are missing or invalid, fall back to full **Repair**.
+
 **Public watch notifications**:
 Google-to-Compass webhook posts at `/api/sync/gcal/notifications`.
 
+**Compass-to-Google event propagation**:
+The backend flow that applies Compass Event writes and mirrors eligible Google
+side effects.
+
+**Google-to-Compass event propagation**:
+The backend flow that applies Google Calendar event changes to Compass data
+during Import or Public watch notification handling.
+
 ## Relationships
 
 - An **Anonymous user** stores **Events** and **Tasks** in browser IndexedDB.

docs/architecture/event-and-task-domain-model.md

@@ -59,7 +59,7 @@ If you change recurring edit behavior, check:
 
 - `packages/core/src/types/event.types.ts`
 - `packages/backend/src/event/controllers/event.controller.ts`
-- `packages/backend/src/sync/services/sync/compass/compass.sync.processor.ts`
+- `packages/backend/src/sync/services/event-propagation/compass-to-google/compass-to-google.event-propagation.ts`
 
 ## Backend Event Shape Semantics
 

docs/backend/README.md

@@ -49,24 +49,26 @@ Important runtime behavior:
 
 ## Event Writes
 
-- Event writes route through the Compass sync processor and can apply Google side effects.
+- Event writes route through Compass-to-Google event propagation and can apply Google side effects.
 - Missing Google refresh token does not block Compass-local event writes; Google side effects are skipped.
 - Controllers use the shared `res.promise(...)` response helper and centralized
   error handling.
 
 Key files:
 
 - `packages/backend/src/event/controllers/event.controller.ts`
-- `packages/backend/src/sync/services/sync/compass/compass.sync.processor.ts`
-- `packages/backend/src/sync/services/outbound/compass-google-mirror.service.ts`
+- `packages/backend/src/sync/services/event-propagation/compass-to-google/compass-to-google.event-propagation.ts`
+- `packages/backend/src/sync/services/event-propagation/compass-to-google/compass-to-google-backfill.ts`
 
 ## Google Notification Ingress
 
 - endpoint: `POST /api/sync/gcal/notifications`
 - source: `packages/backend/src/sync/controllers/sync.controller.ts`
-- middleware: `authMiddleware.verifyIsFromGoogle`
+- middleware: `publicWatchNotificationIngress.verify`
+- ingress owner: `packages/backend/src/sync/services/public-watch-notifications/public-watch-notification.ingress.ts`
 - notification owner: `packages/backend/src/sync/services/watch/google-watch.service.ts`
-- import/repair owner: `packages/backend/src/sync/services/google-calendar-sync/google-calendar-sync.service.ts`
+- repair/setup owner: `packages/backend/src/sync/services/google-sync/google-sync.service.ts`
+- import owner: `packages/backend/src/sync/services/import/google-import.service.ts`
 - maintenance owner: `packages/backend/src/sync/services/watch/google-watch-maintenance.service.ts`
 
 Observed outcomes include:

docs/backend/backend-request-flow.md

@@ -92,9 +92,9 @@ For `POST /api/event`:
 1. route requires `verifySession()`
 2. controller adds the authenticated user id
 3. controller normalizes single vs array payloads
-4. controller forwards the change set to `CompassSyncProcessor`
+4. controller forwards the change set to `CompassToGoogleEventPropagation`
 5. controller returns a status-only payload (`{ statusCode: 204 }`) through `res.promise(...)`
-6. processor:
+6. Compass-to-Google event propagation:
    - loads current Compass DB state
    - analyzes the transition into a persistence plan
    - applies Compass DB mutations first
@@ -118,7 +118,8 @@ Frequently used middleware:
 - `requireGoogleConnectionSession`: active Google connection required for routes that call Google directly (for example `/api/sync/import-gcal`)
 - `authMiddleware.verifyIsDev`: development-only route
 - `authMiddleware.verifyIsFromCompass`: trusted internal caller
-- `authMiddleware.verifyIsFromGoogle`: trusted Google notification source
+- `publicWatchNotificationIngress.verify`: trusted Google notification source
+- `packages/backend/src/sync/services/public-watch-notifications/public-watch-notification.ingress.ts`: Public watch notification header validation and payload parsing
 
 Intentional unauthenticated route:
 

docs/development/common-change-recipes.md

@@ -28,7 +28,7 @@ Rule: never treat event shape as web-only unless the field is strictly presentat
 3. Read `packages/backend/src/event/classes/compass.event.generator.ts`.
 4. Read `packages/backend/src/event/classes/compass.event.parser.ts`.
 5. Read `packages/backend/src/event/classes/compass.event.executor.ts`.
-6. Read `packages/backend/src/sync/services/sync/compass/compass.sync.processor.ts`.
+6. Read `packages/backend/src/sync/services/event-propagation/compass-to-google/compass-to-google.event-propagation.ts`.
 7. Update the planner, executor, or scope-expansion path that actually owns the behavior.
 8. Add focused tests for the exact recurrence transition you changed.
 
@@ -43,13 +43,13 @@ Do not edit recurring behavior from one layer only.
 ## Triage A Recurrence Sync Regression
 
 1. Reproduce with one event and one expected transition outcome.
-2. Capture processor logs for the transition key:
+2. Capture Compass-to-Google event propagation logs for the transition key:
    - `Handle Compass event(<id>): <transitionKey>`
 3. Find the key in `PLAN_BUILDERS` in `packages/backend/src/event/classes/compass.event.parser.ts`.
 4. Confirm planned `steps` and `googleEffect` match expected behavior.
 5. Confirm executor step mapping in `packages/backend/src/event/classes/compass.event.executor.ts`.
 6. Run focused tests:
-   - `bun run test:backend --runTestsByPath packages/backend/src/event/classes/compass.event.parser.test.ts packages/backend/src/event/classes/compass.event.executor.test.ts packages/backend/src/sync/services/sync/__tests__/compass.sync.processor.test.ts --runInBand`
+   - `bun run test:backend --runTestsByPath packages/backend/src/event/classes/compass.event.parser.test.ts packages/backend/src/event/classes/compass.event.executor.test.ts packages/backend/src/sync/services/event-propagation/__tests__/compass-to-google.event-propagation.test.ts --runInBand`
 
 ## Add An SSE Event
 

docs/development/feature-file-map.md

@@ -82,12 +82,14 @@ Use this document to find the first files to inspect for common Compass changes.
 - Backend SSE server: `packages/backend/src/servers/sse/sse.server.ts`
 - Events stream route: `packages/backend/src/events/events.routes.config.ts`
 - Backend sync routes: `packages/backend/src/sync/sync.routes.config.ts`
+- Public watch notification ingress: `packages/backend/src/sync/services/public-watch-notifications/public-watch-notification.ingress.ts`
 - Google Watch lifecycle and notifications: `packages/backend/src/sync/services/watch`
-- Google Calendar sync import and repair: `packages/backend/src/sync/services/google-calendar-sync/google-calendar-sync.service.ts`
-- Compass-to-Google repair mirroring: `packages/backend/src/sync/services/outbound/compass-google-mirror.service.ts`
-- Sync record persistence: `packages/backend/src/sync/services/records/sync.records.ts`
+- Google Calendar sync import and repair: `packages/backend/src/sync/services/google-sync/google-sync.service.ts`
+- Google sync health diagnosis: `packages/backend/src/sync/services/google-sync/google-sync.health.ts`
+- Compass-to-Google repair mirroring: `packages/backend/src/sync/services/event-propagation/compass-to-google/compass-to-google-backfill.ts`
+- Sync record persistence: `packages/backend/src/sync/services/records/sync-records.repository.ts`
 - Google import internals: `packages/backend/src/sync/services/import`
-- Google/Compass event processors: `packages/backend/src/sync/services/sync`
+- Google/Compass event propagation: `packages/backend/src/sync/services/event-propagation`
 
 ## Users / Metadata / Priority
 

docs/development/testing-playbook.md

@@ -236,7 +236,7 @@ Preferred style:
 - realistic request flows when possible
 - mock only external services, not internal business logic
 
-**Do not import `mongoService` (or other persistence implementations) directly in tests.** Use test drivers instead (e.g. `UserDriver`, `WatchDriver` in `packages/backend/src/__tests__/drivers/`). Drivers encapsulate persistence so that switching away from Mongo (or another store) in the future does not require changing test code.
+**Do not import `mongoService` (or other persistence implementations) directly in tests.** Use test drivers instead (e.g. `UserDriver`, `GoogleWatchDriver` in `packages/backend/src/__tests__/drivers/`). Drivers encapsulate persistence so that switching away from Mongo (or another store) in the future does not require changing test code.
 
 Useful anchors:
 

docs/development/types-and-validation.md

@@ -58,7 +58,7 @@ Use the generic base schema with `parseApiError(error, ApiErrorResponseSchema)`
 
 - `packages/backend/src/common/constants/env.constants.ts`
 - `packages/backend/src/common/validators`
-- feature-specific query validators such as `packages/backend/src/sync/util/sync.queries.ts`
+- feature-specific query validators such as `packages/backend/src/sync/services/records/sync-records.repository.ts`
 
 ### Web form/client validation
 

docs/features/google-sync-and-sse-flow.md

@@ -1,6 +1,6 @@
 # Google Sync And Server-Sent Events (SSE)
 
-Compass sync is bidirectional:
+Compass Google Calendar integration is bidirectional:
 
 - Compass-originated event changes can propagate to Google and then notify web clients.
 - Google-originated changes can flow back into Compass and then notify web clients.
@@ -78,7 +78,7 @@ Source:
 
 - `packages/core/src/types/sse.types.ts`
 - `packages/backend/src/user/services/user.service.ts`
-- `packages/backend/src/sync/services/google-calendar-sync/google-calendar-sync.service.ts`
+- `packages/backend/src/sync/services/google-sync/google-sync.service.ts`
 
 `IMPORT_GCAL_END` carries an explicit `operation` so the client can distinguish repair completion from incremental completion.
 
@@ -114,41 +114,42 @@ High-level path:
 3. The selected repository writes locally or remotely.
 4. Remote event writes hit backend event routes.
 5. `EventController` packages the change as a `CompassEvent`.
-6. `CompassSyncProcessor.processEvents()` loads the DB event, plans work, applies persistence, and runs Google side effects.
+6. `CompassToGoogleEventPropagation.processEvents()` loads the DB event, plans work, applies persistence, and runs Google side effects.
 7. After commit, the backend calls `sseServer` to publish notifications based on whether the change affected normal or someday events (`EVENT_CHANGED` vs `SOMEDAY_EVENT_CHANGED`).
 
 Primary files:
 
 - `packages/web/src/ducks/events/sagas/event.sagas.ts`
 - `packages/web/src/common/repositories/event`
 - `packages/backend/src/event/controllers/event.controller.ts`
-- `packages/backend/src/sync/services/sync/compass/compass.sync.processor.ts`
+- `packages/backend/src/sync/services/event-propagation/compass-to-google/compass-to-google.event-propagation.ts`
 
 ## Inbound Flow: Google Notifies Compass About Changes
 
 High-level path:
 
 1. Google posts to the notification endpoint in sync routes.
-2. Backend verifies the request origin.
+2. `publicWatchNotificationIngress` validates and parses the Google headers.
 3. `googleWatchService.handleGoogleWatchNotification()` locates the watch and sync record.
 4. The service builds a Google Calendar client for the user.
 5. `GCalNotificationHandler` fetches incremental changes using the stored sync token.
-6. `GcalSyncProcessor` applies those changes to Compass data.
+6. `GoogleToCompassEventPropagation` applies those changes to Compass data.
 7. The backend publishes `EVENT_CHANGED` (or someday equivalent) so clients refetch.
 
 Primary files:
 
 - `packages/backend/src/sync/sync.routes.config.ts`
+- `packages/backend/src/sync/services/public-watch-notifications/public-watch-notification.ingress.ts`
 - `packages/backend/src/sync/services/watch/google-watch.service.ts`
-- `packages/backend/src/sync/services/google-calendar-sync/google-calendar-sync.service.ts`
-- `packages/backend/src/sync/services/records/sync.records.ts`
+- `packages/backend/src/sync/services/google-sync/google-sync.service.ts`
+- `packages/backend/src/sync/services/records/sync-records.repository.ts`
 - `packages/backend/src/sync/services/notify/handler/gcal.notification.handler.ts`
-- `packages/backend/src/sync/services/sync/google/gcal.sync.processor.ts`
+- `packages/backend/src/sync/services/event-propagation/google-to-compass/google-to-compass.event-propagation.ts`
 
 Lifecycle and outbound repair paths live in:
 
-- `packages/backend/src/sync/services/google-calendar-sync/google-calendar-sync.service.ts`
-- `packages/backend/src/sync/services/outbound/compass-google-mirror.service.ts`
+- `packages/backend/src/sync/services/google-sync/google-sync.service.ts`
+- `packages/backend/src/sync/services/event-propagation/compass-to-google/compass-to-google-backfill.ts`
 - `packages/backend/src/sync/services/watch/google-watch-maintenance.service.ts`
 
 ### Notification Outcomes And Error Semantics
@@ -206,9 +207,15 @@ Redux reasons for refetch (`Sync_AsyncStateContextReason`) reuse the same string
 Source files:
 
 - `packages/backend/src/user/services/user-metadata.service.ts`
+- `packages/backend/src/sync/services/google-sync/google-sync.health.ts`
 - `packages/core/src/types/user.types.ts`
 - `packages/web/src/sse/hooks/useGcalSSE.ts`
 
+The sidebar Google connection state is derived from user metadata. The backend
+metadata service delegates HEALTHY vs ATTENTION diagnosis to Google sync health,
+which checks stored sync tokens and, when public HTTPS watch notifications are
+enabled, active Google watches.
+
 Auto-import guardrail:
 
 - client auto-starts import only when `sync.importGCal === "RESTART"` **and** `google.connectionState` is not `NOT_CONNECTED` or `RECONNECT_REQUIRED`

docs/features/password-auth-flow.md

@@ -378,8 +378,8 @@ Password-only users can now mutate Compass events without a Google connection at
 Relevant changes:
 
 - `event.routes.config.ts` no longer requires route-level Google connection middleware for create/update/delete
-- `CompassSyncProcessor` applies the Compass mutation first
-- if the Google side effect fails only because the user has no Google refresh token, the processor keeps the Compass mutation and skips the Google effect
+- `CompassToGoogleEventPropagation` applies the Compass mutation first
+- if the Google side effect fails only because the user has no Google refresh token, Compass-to-Google event propagation keeps the Compass mutation and skips the Google effect
 
 That lets password-auth users use Compass without blocking on Google connectivity.
 

docs/features/recurring-events-handling.md

@@ -19,7 +19,7 @@ Primary files:
 
 ## Recurrence Categories
 
-Compass sync logic classifies event shape using `Categories_Recurrence`:
+Compass-to-Google event propagation classifies event shape using `Categories_Recurrence`:
 
 - `STANDALONE`
 - `RECURRENCE_BASE`
@@ -28,7 +28,7 @@ Compass sync logic classifies event shape using `Categories_Recurrence`:
 - `RECURRENCE_BASE_SOMEDAY`
 - `RECURRENCE_INSTANCE_SOMEDAY`
 
-The Compass sync path treats recurrence handling as a transition problem:
+The Compass-to-Google path treats recurrence handling as a transition problem:
 
 1. build a transition context from the incoming Compass payload plus the current DB event
 2. analyze that transition into a plain `CompassOperationPlan`
@@ -39,7 +39,7 @@ Primary files:
 
 - `packages/backend/src/event/classes/compass.event.parser.ts`
 - `packages/backend/src/event/classes/compass.event.executor.ts`
-- `packages/backend/src/sync/services/sync/compass/compass.sync.processor.ts`
+- `packages/backend/src/sync/services/event-propagation/compass-to-google/compass-to-google.event-propagation.ts`
 
 ## Update Scopes
 
@@ -95,7 +95,7 @@ Useful heuristics during Google sync:
 - cancelled instances should be handled as instance-level deletions
 - payload ordering is not reliable enough to infer user intent by itself
 
-This is why Compass sync logic keys off persisted state plus event properties instead of trying to reconstruct a single high-level Google UI action.
+This is why Compass-to-Google event propagation keys off persisted state plus event properties instead of trying to reconstruct a single high-level Google UI action.
 
 ## Someday And Provider Semantics
 
@@ -114,7 +114,7 @@ Instead:
 
 - `analyzeCompassTransition(...)` describes the implied Google effect
 - `applyCompassPlan(...)` performs only Compass DB mutations
-- `CompassSyncProcessor` executes Google create/update/delete after Compass persistence succeeds
+- `CompassToGoogleEventPropagation` executes Google create/update/delete after Compass persistence succeeds
 
 Delete-oriented Google effects should prefer the persisted DB `gEventId` when available, then fall back to the incoming payload `gEventId`.
 
@@ -143,7 +143,7 @@ Concrete examples from current tests:
 - last persisted Compass event when a step returns one
 - `googleDeleteEventId` resolved from persisted event first, otherwise planner fallback
 
-The processor executes Google effects only after Compass persistence succeeds.
+Compass-to-Google event propagation executes Google effects only after Compass persistence succeeds.
 
 ## Recurrence Sync Triage Runbook
 
@@ -155,7 +155,7 @@ Use this sequence when recurring edits behave unexpectedly:
 3. Verify the planned `steps` order and `googleEffect` in unit tests:
    - `compass.event.parser.test.ts`
    - `compass.event.executor.test.ts`
-   - `compass.sync.processor.test.ts`
+   - `compass-to-google.event-propagation.test.ts`
 4. Map each step to persistence calls in `executeStep(...)`:
    - `create` -> `_createCompassEvent`
    - `update` -> `_updateCompassEvent`
@@ -183,5 +183,5 @@ Good test anchors:
 
 - `packages/backend/src/event/classes/compass.event.parser.test.ts`
 - `packages/backend/src/event/classes/compass.event.executor.test.ts`
-- `packages/backend/src/sync/services/sync/__tests__/compass.sync.processor.all-event.test.ts`
-- `packages/backend/src/sync/services/sync/__tests__/compass-sync-processor-this-event/*.test.ts`
+- `packages/backend/src/sync/services/event-propagation/__tests__/compass-to-google.all-event.test.ts`
+- `packages/backend/src/sync/services/event-propagation/__tests__/compass-to-google-this-event/*.test.ts`

packages/backend/src/__tests__/drivers/event.driver.ts

@@ -6,7 +6,7 @@ import { UserDriver } from "@backend/__tests__/drivers/user.driver";
 import { mockGcalEvents } from "@backend/__tests__/mocks.gcal/factories/gcal.event.factory";
 import calendarService from "@backend/calendar/services/calendar.service";
 import mongoService from "@backend/common/services/mongo.service";
-import { getGcalClient } from "@backend/sync/services/google-calendar-sync/google.calendar.client";
+import { getGcalClient } from "@backend/sync/services/google-sync/gcal.client";
 
 export class EventDriver {
   static async generateV0Data(count = 3) {

packages/backend/src/__tests__/drivers/sync.driver.ts → packages/backend/src/__tests__/drivers/google-sync.driver.ts

@@ -5,12 +5,12 @@ import { type Schema_User } from "@core/types/user.types";
 import dayjs from "@core/util/date/dayjs";
 import { UserDriver } from "@backend/__tests__/drivers/user.driver";
 import mongoService from "@backend/common/services/mongo.service";
-import { getGcalClient } from "@backend/sync/services/google-calendar-sync/google.calendar.client";
+import { getGcalClient } from "@backend/sync/services/google-sync/gcal.client";
+import { updateSync } from "@backend/sync/services/records/sync-records.repository";
 import { googleWatchService } from "@backend/sync/services/watch/google-watch.service";
-import { updateSync } from "@backend/sync/util/sync.queries";
 
-export class SyncDriver {
-  static async createSync(
+export class GoogleSyncDriver {
+  static async createHealthyGoogleSync(
     user: Pick<WithId<Schema_User>, "_id">,
     defaultUser = false,
   ): Promise<void> {
@@ -31,7 +31,7 @@ export class SyncDriver {
     );
   }
 
-  static async generateV0Data(
+  static async generateLegacySyncWatchData(
     numUsers = 3,
     generateExpiredWatches = false,
   ): Promise<Array<WithId<Omit<Schema_Sync, "_id">>>> {