fix(runtime-host): log transcript bootstrap failures

[jackeyfaker77]

Summary

When the initial subscription.open transcript bootstrap fails, the Host now logs the underlying cause before invoking the publication-failure hook. The diagnostic uses existing secret redaction and an 8 KiB limit; the hook still receives the original error, and the client still receives persistence_failed.

Refs #5572

Verification

• Regression test failed without the logging change, then passed with it.
• Session continuity coordinator suite: 46/46 passed, including log ordering, redaction, UTF-8 size limits, and the existing error response.
• Full-repository npm run build, npm run typecheck, npm run lint, and npm run format:check passed.
• Desktop and UI knip checks passed.
• Full-repository npm test was not run.

AI use

• No generative tool made a substantive contribution
• Generative tooling made a substantive contribution

Tool(s) and scope: Codex implemented the diagnostic logging and regression test, ran validation, and prepared this PR.

Checklist

• Tests cover the change and fail without it
• Lint, format, typecheck and the affected suites pass locally

Does this PR entail a change in behavior?

• Yes - described under Summary above
• No

[hqhq1025]

I reviewed current head e1a6161e5decd6fb9678e78c285e3482ac409adb and found no substantiated P0–P3 issue in the changed paths.

The subscription.open tail-transcript bootstrap catch now logs a bounded, redacted diagnostic before invoking the publication-failure hook, while the client still receives a generic persistence_failed response (packages/runtime-host/src/server/session-continuity-coordinator.ts:942-980). I checked failure ordering, log/client separation, the existing redaction and UTF-8 bound, and the added regression test. There is no database schema migration. Current-head test and label checks pass and the branch merges cleanly with current main.

I could not rerun tests locally (Node 18 and no dependencies), exhaustively audit arbitrary custom exception contents, or test multi-subscriber/restart log aggregation. This is not a merge approval.

Automated review notice: This comment was posted by an automated review agent operated by hqhq1025. It is not an independent human review and does not replace one.

[Astro-Han]

Approved at @Astro-Han's explicit request: a small, focused fix with no blocking findings in the automated review of this head and green CI.