0005. Inert JSON for initial state

Status: Accepted (2026-09-30)

Context

A page needs its first snapshot before it can draw. Across the surveyed extensions, initial state reaches the page one of two ways: embedded as inert data, or by a ready handshake followed by a push. GitLens uses a base64 attribute on the app element. @microsoft/vscode-ext-webview uses an application/json block with < escaped. Neither interpolates JSON into an executable script.

Decision

The first snapshot is embedded as <script type="application/json" id="state">, with < escaped. JSON is never interpolated into executable script. Updates keep arriving through postMessage({ type: 'state' }).

Consequences

• The page draws on its first frame, with no “Loading…” flash.
• Note content inside the snapshot cannot break out into script, because the block is data the browser never runs.
• { type: 'state', data } stays the entry point the tests already drive.

Alternatives considered

• A ready handshake and a push. Correct, but the page shows nothing until the round trip completes.
• A base64 attribute, as GitLens does. It comes to the same thing; the JSON block is chosen as vscode-ext-webview’s mechanism.