ticket: finish observation replay removal

.yoi/tickets/00001KX7645ZS/item.md

@@ -1,8 +1,8 @@
 ---
 title: 'Remove backend worker observation replay'
-state: 'inprogress'
+state: 'done'
 created_at: '2026-07-10T23:34:39Z'
-updated_at: '2026-07-10T23:35:04Z'
+updated_at: '2026-07-10T23:50:50Z'
 assignee: null
 queued_by: 'yoi ticket'
 queued_at: '2026-07-10T23:35:04Z'

.yoi/tickets/00001KX7645ZS/thread.md

@@ -39,4 +39,33 @@ Ticket を `yoi ticket` が queued にしました。
 State changed to `inprogress`.
 
 
+---
+
+<!-- event: implementation_report author: hare at: 2026-07-10T23:50:49Z -->
+
+## Implementation report
+
+Removed backend-local worker observation replay.
+
+- BackendObservationProxy no longer stores/replays event history.
+- Browser worker observation WS connects upstream directly after validating cursor syntax; any cursor is no longer matched against backend replay history.
+- Runtime Snapshot remains the connection bootstrap, and subsequent frames are live upstream events only.
+- Updated proxy tests to assert fresh connections receive Snapshot and not previously stored live events.
+
+Validation:
+- cargo test -q -p yoi-workspace-server
+- cargo test -q
+- git diff --check
+- nix build .#yoi --no-link
+
+
+---
+
+<!-- event: state_changed author: "yoi ticket" at: 2026-07-10T23:50:50Z from: inprogress to: done reason: cli_state field: state -->
+
+## State changed
+
+State changed to `done`.
+
+
 ---