fix(workspace-server): tolerate not-ready DB in agent file activity path

[posthog]

Problem

An unhandled rejection — Database not initialized — call initialize() first — was firing in the workspace-server agent file-activity path (6 occurrences across 4 users, first seen 2026-06-28).

When the agent edits a file, AgentService.emitAgentFileActivityForCurrentBranch fires a fire-and-forget emit. The listener, WorkspaceService.handleAgentFileActivity, is async and its first statement does a synchronous DB read (workspaceRepo.findByTaskId), which throws from the DatabaseService.db getter during the startup/teardown window when the DB is closed (@preDestroy) or not yet initialized. Because the listener is async and TypedEventEmitter.emit discarded the returned promise, that synchronous throw became a rejected promise that escaped into error tracking as noise — it never broke a user-facing flow (branch association is best-effort observability).

Changes

• Add DatabaseService.isInitialized() and have handleAgentFileActivity bail gracefully when the DB isn't ready, so the best-effort branch-association read no longer throws during start/shutdown.
• Harden TypedEventEmitter.emit to swallow rejections from async listeners, so a throwing async listener can never become an unhandled rejection again (defense in depth).

How did you test this?

• Added a unit test asserting handleAgentFileActivity returns without touching the repo when the DB is not initialized.
• Added a unit test asserting emit does not surface a rejecting async listener as an unhandled rejection (and that later listeners still run).
• Ran pnpm --filter @posthog/workspace-server exec vitest run workspace (57 passed) and the shared emitter suite (14 passed).
• Typechecked @posthog/shared and @posthog/workspace-server; Biome clean on changed files.

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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Created with PostHog Code from an inbox report.

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 35af854.}