[nightly-regression] Lock runtime diagnostics context keys

[r3dbars]

Summary

• add exact key-shape coverage for unclean-shutdown runtime diagnostics context
• assert previous_clean_shutdown stays current-session-only and raw marker fields stay out of analytics context

Nightly review findings

1. Recent runtime diagnostics refactor was intentional, but unclean-shutdown context lacked an exact regression guard after sharing the common context builder.
2. PostHog still shows unclean shutdown detections in the last week, so this signal should stay stable and privacy-safe.
3. Open issue Mic audio recording is a lot quiter #500 remains the main product watch item, but recent meeting transcript failures are low after 1.1.33 and did not justify a same-night behavior patch.

Live evidence

• Recent merged PRs reviewed: [nightly-simplify] Simplify runtime diagnostics context #697, [nightly-docs] Refresh docs drift counts #696, Publish Transcripted 1.1.33 metadata #695, Reduce idle audio recovery noise #694, plus current origin/main.
• Open GitHub issue reviewed: Mic audio recording is a lot quiter #500.
• Latest release checked: v1.1.33, published 2026-05-08, release asset live.
• PostHog 7-day spot check: 1.1.33 launch traffic is current; meeting transcript failures were 0 on 2026-05-09 and 2026-05-10 UTC at check time.
• Sentry MCP and local env-token paths were unavailable in this run, so Sentry was not used as evidence.

Verification

• bash run-tests.sh
• bash build-deps.sh --force
• bash build.sh

Note: the first build.sh attempt correctly failed before dependency rebuild because local deps were missing/stale.