* fix(app): stabilize streamed chat rendering
Use deterministic Markdown AST keys and preserve unique row identities when an assistant message resumes after a tool. Keep native gesture and plan-card children correctly keyed to avoid unsupported Fabric reconciliation paths.
* fix(app): stabilize retained native panels
Keep retained workspace roots in a stable native order and make active
panels present in the selection commit. Hidden panels now stop expensive
subscriptions and animations without losing mounted state.
* fix(app): harden retained panel activity
* perf(app): keep large sidebars responsive
Sidebar rows rescanned every agent for each session update, multiplying work with both workspace and agent count. Build workspace activity once and share the derived sidebar model so updates scale with the underlying collections.
* test(app): use valid agent fixture for workspace restore
* refactor(app): keep sidebar model surface focused