feat(v2): persist execution event revisions

backend/src/backup_tool/execution.py

@@ -7,7 +7,7 @@ from sqlalchemy import select, update
 from sqlalchemy.exc import IntegrityError
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from backup_tool.db.models import Execution, Job
+from backup_tool.db.models import Execution, ExecutionEvent, Job
 from backup_tool.security.redaction import redact
 
 ACTIVE_STATES = frozenset({"queued", "preparing", "running", "verifying", "cancelling"})
@@ -67,6 +67,8 @@ async def enqueue(db: AsyncSession, job_id: str, trigger: str = "manual") -> Exe
             "execution_active", "Job already has an active execution.", existing
         ) from error
     await db.refresh(execution)
+    await record_event(db, execution)
+    await db.commit()
     return execution
 
 
@@ -89,7 +91,11 @@ async def claim(
         await db.rollback()
         return None
     await db.commit()
-    return await db.get(Execution, execution_id)
+    execution = await db.get(Execution, execution_id)
+    if execution is not None:
+        await record_event(db, execution)
+        await db.commit()
+    return execution
 
 
 async def heartbeat(
@@ -128,7 +134,11 @@ async def request_cancellation(db: AsyncSession, execution_id: str) -> Execution
         await db.rollback()
         return None
     await db.commit()
-    return await db.get(Execution, execution_id)
+    execution = await db.get(Execution, execution_id)
+    if execution is not None:
+        await record_event(db, execution)
+        await db.commit()
+    return execution
 
 
 async def complete_cancellation(db: AsyncSession, execution_id: str, owner: str) -> bool:
@@ -177,6 +187,8 @@ async def retry(db: AsyncSession, execution_id: str) -> Execution | None:
             "execution_active", "Job already has an active execution.", active_id
         ) from error
     await db.refresh(execution)
+    await record_event(db, execution)
+    await db.commit()
     return execution
 
 
@@ -196,6 +208,19 @@ def _redact_progress(value: object) -> object:
     return redact(value)
 
 
+async def record_event(db: AsyncSession, execution: Execution) -> ExecutionEvent:
+    """Append the public representation as the next durable event revision."""
+    execution.revision += 1
+    event = ExecutionEvent(
+        execution_id=execution.id,
+        revision=execution.revision,
+        payload=public_event(execution),
+    )
+    db.add(event)
+    await db.flush()
+    return event
+
+
 def public_event(execution: Execution) -> dict[str, object]:
     """Return redacted progress suitable for polling or SSE."""
     progress = _redact_progress(execution.progress)
@@ -203,6 +228,7 @@ def public_event(execution: Execution) -> dict[str, object]:
         "id": execution.id,
         "state": execution.state,
         "attempt": execution.attempt,
+        "revision": execution.revision,
         "reason_code": execution.reason_code,
         "progress": progress,
     }