fix(core): bound event log compaction

[chubes4]

Issue for this PR

Closes #33356

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Adds read-only event-log status plus explicit, dry-run-by-default bounded compaction (--session or --all, --apply, maximum 10,000 rows). Apply verifies latest message/part projection contents, batches in one immediate transaction, and only writes checkpoints for aggregates with no workspace or sync owner. Sync has no marker version negotiation, so synced/owned aggregates are reported and rejected.

How did you verify your code works?

• bun test test/session-event-log-compaction.test.ts test/event.test.ts
• bun typecheck (30 packages)
• Prettier check

Screenshots / recordings

Not applicable; database maintenance CLI.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

AI assistance

• AI assistance: Yes
• Tool(s): GPT-5.6-terra via OpenCode
• Used for: Implementation, tests, and review-driven revision; Chris owns the change.

[github-actions]

Hey! Your PR title Compact superseded session event snapshots doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍

[chubes4]

Rebased onto current dev (323d687173) and reverified after the latest upstream changes.

Fresh production evidence from today: ~/.local/share/opencode/opencode.db is now 27.2 GiB (page_size=4096, page_count=7,124,817, freelist_count=0), so this remains live append-only event data rather than reclaimable SQLite slack.

Verification on the rebased branch:

• bun test test/session-event-log-compaction.test.ts test/event.test.ts — 45 passed
• bun typecheck — 30 tasks passed across the workspace
• bun prettier --check $(git diff --name-only origin/dev...HEAD) — passed

The branch is current, clean, mergeable, and CI is green. Maintainer review would be appreciated.