Early workspace read and a deferred raw editor chunk

Context

Desktop startup measured on a 582-note workspace spends its time in the web view, not in Rust: the shell's setup takes about 7 ms. The renderer asked for the bootstrap snapshot only after the bundle had loaded and evaluated and its startup listeners were registered.

The snapshot request could not simply move earlier. The renderer subscribes to history and sync events before it reads the snapshot so a change published during startup is not lost (see app/history-startup.ts and app/sync-startup.ts). A snapshot read before those listeners exist would miss any change published between the read and the subscription.

The main chunk also carried CodeMirror, its vim layer and the Lezer parsers, which only the raw Markdown editor uses.

Decision

index.html starts the snapshot, sidebar-expansion and pane-layout reads in an inline script, before the bundle is fetched. The snapshot comes from bootstrap_workspace_at_epoch, which returns [epoch, snapshot] JSON by wrapping the snapshot text the storage worker already encoded. The shell counts every history header and synced workspace change it publishes in a WorkspaceEventEpoch, and reads the epoch before it reads the snapshot. Once the renderer is listening it calls workspace_event_epoch. Equal epochs mean no change was published between the read and the subscription, so the early snapshot is used. Different epochs, or a failed early read, fall back to an ordinary bootstrap_workspace call made after subscribing, which is the previous behaviour. The early reads are handed over once; a retried startup reads again.

The raw Markdown editor moves into its own chunk behind features/editor/raw-markdown-editor-loader.tsx. When the first screen shows a raw note (the editor's default mode is raw, or a pane's active note renders raw), startup loads it before the first render. Otherwise warmEditorRenderers starts the load right after the first commit, beside KaTeX and Mermaid.

Consequences

• The performance contract's rule against editor chunk loading after startup gains one exception. The raw editor's load always starts during startup, never on demand, but a raw note opened between the first commit and the end of that load renders nothing until the load finishes.
• Startup issues one extra small IPC call (workspace_event_epoch). A change published during startup costs a second snapshot read, which is what every startup cost before.
• The browser runtime is unchanged: the inline script does nothing without the Tauri bridge, and the browser reads the workspace through its worker as before.
• On top of the startup work in #572 the snapshot is ready earlier, but the time to first paint is unchanged, because a main-thread task of about 250 ms on the WebKit side now fills the gap. See the measurement.
• The early read changes when data arrives, not how much. Sending note bodies after first paint would conflict with the rule that navigation never waits on IPC, and is not part of this decision.