Fix SSE relay backlog during delta storms - #17979

Hey! Your PR title Fix SSE relay backlog during delta storms 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

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Deployment/update note:

• rebased the PR branch cleanly onto anomaly/dev and force-updated fix/17977-event-relay so the PR is no longer DIRTY
• cherry-picked the same patch onto origin/dev and pushed it there as commit 802a6fd3abcf1d8df01494923fd853a5c4b82479
• ran on the clean origin/dev worktree:
  • bun test test/server/relay.test.ts test/acp/event-subscription.test.ts --timeout 30000
  • bun typecheck
• ran the same two checks on the clean anomaly/dev PR worktree
• built and installed the local binary from origin/dev with bun run install:local
• restarted opencode serve on 100.68.120.26:4096 using the newly installed binary
• verified live endpoints after restart:
  • /global/health => {"healthy":true,"version":"0.0.0-local-202603171756"}
  • the previously hanging session URL now returns the OpenCode HTML document again

The earlier push hook failure was environmental (No space left on device in .turbo cache inside the temp worktree), not a code failure; the manual checks above completed successfully on both rebased branches.

This pull request has been automatically closed because it was not updated to meet our contributing guidelines within the 2-hour window.

Feel free to open a new pull request that follows our guidelines.