fix: reduce redundant work during chat and note startup

Avoid hidden activity renders, no-op message saves and attachment scans when pinning conversations. Reuse note body inspection and skip unchanged attachment reference writes while preserving recovery and cleanup behavior.

Skip unnecessary Markdown normalization and memoize subagent lookups without delaying live rich text. Add storage operation counts and real Electron rendering equivalence benchmarks; full-render speedup remains unproven.

Validation: 5397 tests passed, 84 skipped; typecheck passed. Lint passed excluding two existing untracked sidebar probe files.

Release note: Reduce repeated rendering and disk work during chat, conversation pinning and note startup while preserving existing content and interactions.

docs/features/magic-notes/technical-design.md

@@ -173,7 +173,12 @@ empty content. Failed creates leave no accepted database membership; their
 unaccepted files are removed on the next access or reopen.
 
 After commit, reconciliation derives `note.json` from database membership and
-scans all retained entry files before removing unreferenced assets. Manifest or
+inspects all retained entry files before removing unreferenced assets. Startup
+repair reads each current body once to inspect its revision and collect asset
+references, then passes the complete per-note reference set to reconciliation.
+If media inspection fails, cleanup uses its existing deferred retry path rather
+than trusting a partial set. Revision mismatch recovery still hydrates the body;
+legacy conversion still verifies its written content. Manifest or
 GC failures log `console.warn` with the note ID and error and remain in an
 in-memory retry set. Later database access retries; reopening derives cleanup
 again from membership. These cleanup failures do not turn a committed save,