[renkun-ken]

Repeated document scans, fragmented IPC input, long Interactive histories, and synchronous compiler probes can stall extension commands. Unresolved terminal PIDs and failed startup attempts can leave session operations waiting indefinitely. This change removes those stalls and fixes related editor and viewer failures.

• Cache chunk parsing by document version, avoid redundant decorations and hover lookups, and use indexed transcript and plot-history lookups.
• Process fragmented IPC input incrementally, cancel obsolete connections, and clean up failed or cancelled language-server startup.
• Discover terminal PIDs concurrently, return exact matches immediately, and bound unresolved attachment lookups to one second. Refresh other terminals' discovery files while one PID remains pending.
• Use the requested document's selection, report save failures, handle escaped strings and paths, run compiler probes asynchronously, and wait for completed CSV exports with reliable cleanup.
• Persist help favorites safely, deduplicate help-index loads, keep navigation usable without scroll acknowledgements, preserve httpgd HTTPS/authentication, and load initial standard plots without waiting for resize.

Validation on macOS with VS Code 1.144 and R 4.6.1:

• 405 Node tests, 733 VS Code tests across full and focused runs, and 1,298 sess checks passed.
• Build, lint, formatting, typecheck, and production VSIX packaging passed.
• A local parser microbenchmark of a 1.5 MB Unicode frame in 256-byte fragments improved from approximately 656 ms to 3.45 ms; this measures parsing rather than end-to-end editor latency.
• R integration used temporary libraries with matching sess, renv, and a committed languageserver snapshot. Browser fixtures disable background throttling and release their mocks and viewers after timeouts.

All six GitHub Actions checks passed for 345c781, including the macOS, Linux, and Windows test jobs. Remote SSH lifecycle checks have not been run.