Fix Viewer server crash: serialise grid rendering, stop component echo cascade

[t0mdavid-m]

Summary

Fixes the "random white screen that needs a refresh" reported by users. It is the Streamlit server process dying with a native access violation (polars DataFrame.deserialize, called from st.cache_data) while two script threads render the FLASHDeconv Viewer at the same time. Reproduced three times with faulthandler; full analysis, timeline and measurements in docs/white-screen-root-cause.md (added in this PR).

Root cause chain:

1. Every grid cell of the Vue component sent setComponentValue on mount and on every echoed render; Streamlit turns each one into a full rerun request (no dedup), so one Viewer load produced 20 rerun requests and 8-12 script runs.
2. Streamlit's default runner.fastReruns stops the running ScriptRunner and starts a new script thread immediately, while the old thread keeps executing until its next Streamlit call (which never comes inside the polars/pyarrow work of initialize_data / filter_data).
3. Two to four concurrent executions of the same page share the session's polars/pyarrow objects and the st.cache_data pickles; polars' native deserializer crashes the whole process. Users see CONNECTING, then "Connection error", or an empty white page if the crash lands right after a sidebar click.

Changes

• src/render/render.py: per-session lock around render_grid (keyed by Streamlit session id). A runner that has been stopped releases the lock at its next Streamlit call, so the grid code can never run twice concurrently for one session. This alone removes the crash class.
• js-component/dist/: bundle rebuilt from Send selection state to Streamlit only on genuine user interaction t0mdavid-m/openms-streamlit-vue-component#30 (no setComponentValue on mount, no echo of Python-provided state, no duplicate payloads). CI clones FVdeploy fresh, so that PR must be merged for CI builds to include the Vue side; the committed bundle covers local runs and the Windows build meanwhile.
• docs/white-screen-root-cause.md: analysis, secondary findings, fix options and the before/after measurements.

Not included (separate follow-ups, documented in the analysis): the source watcher purging src.* modules because the packages have no __init__.py (add them or run production with --server.fileWatcherType none), the teleported table filter dialog leaving an overlay behind on navigation, and running production with PYTHONFAULTHANDLER=1.

Measurements (Edge via Playwright, 5 trials, median; default fastReruns, faulthandler on)

Metric	Before	After
Viewer load: rerun requests / script runs	20 / 11	4 / 5
Viewer load: last of 6 cells / settled	0.37 s / 2.47 s	0.26 s / 2.06 s
Row click: settled (runs / requests)	0.45 s (3 / 7)	0.27 s (2 / 1)
Row click updates Mass Table	5/5	5/5
Leave to Layout Manager: visible / settled	0.18 s / 0.16 s	0.18 s / 0.16 s
Return to Viewer: settled (runs / requests)	1.33 s (4 / 7)	0.19 s (1 / 1)
Stress runs, 60 navigation/row clicks each	crashed after 4 and 6 clicks	2 x 60 clicks, no crash

--runner.fastReruns false was also tried: no crash, but the Viewer stalls at one cell and ignores navigation, so the default stays.

Test plan

• npm run build and type check of the Vue component pass; bundle loads, grid renders, row click still updates the other cells
• 2 x 60-click stress runs on the fixed tree with faulthandler: no crash, no fatal exception in the server logs
• Merge Send selection state to Streamlit only on genuine user interaction t0mdavid-m/openms-streamlit-vue-component#30 so CI image builds include the Vue change

🤖 Generated with Claude Code

https://claude.ai/code/session_01Wda4mDs1DSWJuU1beJJKvL

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