perf: speed up app initialization and add startup timing telemetry (THU-595)

[ital0]

Note

Medium Risk
Touches core boot path (DB init, sync gate, defaults reconciliation) and changes how PowerSync is imported at startup; failures are mostly telemetry or best-effort sync, but regressions could affect time-to-interactive or sync readiness.

Overview
Adds startup performance telemetry (app_init_timing after init completes, app_chat_ready on first chat hydration) via a lightweight init-timing module that records bundle eval, first mount, per-step durations, sync gate outcome, and total time.

Init pipeline changes overlap config fetch with later steps, add a first select 1 step to absorb PowerSync’s deferred DB ready work, time data migrations, run tray and PostHog init in parallel, and report initial_sync_outcome (disabled / synced / timed_out / failed) from waitForInitialSync.

Bundle-size work moves sync helpers into SDK-free sync-state.ts (entry code imports that path instead of the PowerSync barrel), plus Vite treeshake/alias tweaks so more @powersync/common stays in the lazy PowerSync chunk.

Boot DB work batches default reconciliation lookups and reduces redundant queries in removed-default cleanup.

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Preview environment destroyed 🧹

Stack preview-pr-984 and its Cloudflare subdomain have been cleaned up.

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PR Metrics

Metric	Value
Lines changed (prod code)	+431 / -187
JS bundle size (gzipped)	🟢 737.6 KB → 682.1 KB (-55.5 KB, -7.5%)
Test coverage	🟢 78.13% → 78.09% (+-0.0%)
Performance (preview)	Preview not ready — Render deploy may have timed out
Accessibility	—
Best Practices	—
SEO	—

Updated Mon, 15 Jun 2026 15:53:49 GMT · run #1885