perf(runtime): quiet diagnostics and external history refresh

[Neonforge98]

Summary

• suspend Ctrl+5 diagnostics recomputation while the Tauri window is hidden or unfocused, with one immediate refresh on focus return
• skip production Timer/RAF wrappers when source maps are unavailable and instrumentation cannot produce actionable rows
• reuse the external-history signature already observed by the refresh scheduler, retain the required post-load race check, and remember stable empty transcripts
• stop the round selector from animating forever for a loaded external session with zero rounds
• preserve concrete Rust definition names in Kanban filters after the shared Session display pipeline standardized native provider labels as ORG2
• record the completed runtime evidence in the performance-guard report

Real Tauri / Computer Use validation

• Ctrl+5 foreground idle: ~2.89% before, 0.30% after; repeated open/close stabilized at 0.06% with working set -0.1 MiB over 20s
• final minimized large-session process tree: 0.31% single-core CPU over 20s; no external-history or cloud calls occurred while hidden
• empty external session: 30.2% CPU before; removing the lone animate-spin live dropped it to 7.08%; final implementation measured 1.89% over 20s at 661.1 MiB working set / 368.5 MiB private
• external-history refresh: normal stat probes remain at the configured 5-second cadence; a real transcript update caused one es_set and two metadata-index calls without the prior four-stat refresh chain
• external CLI session: first shell/skeleton 523-654ms, full cold content 895ms in the measured run, warm full reopen 120-321ms; older-turn page 282-450ms
• Work Item startup sync burst matched stored org/project cardinality and remained flat with no likely-polling classification

Verification

• rebased onto develop at fcf6cd88b; the later 2e00d8e06 audit-note/Rust-formatting-only commit is non-overlapping
• TypeScript typecheck
• ESLint, Prettier, and git diff --check
• 8 adjacent test files / 44 tests passed after the final rebase
• final Tauri Windows development build
• Computer Use validation against the built Windows binary, including WebView Inspector and Ctrl+5
• GitHub CI: Frontend and Rust checks green

Performance verdict

Pass for the remediated production paths in this PR. The product-wide load-scale monitors that still require dedicated stress rigs remain explicitly listed in docs/org2-performance-guard-2026-07-23/RepeatedPollingAndResourceIntensiveProcesses.md.