Extend the browser download library beyond JSON so the Apps host's
ui/download-file support can download arbitrary embedded resources and
open http(s) links safely, with no UI wiring in this change:
- downloadBlob(): temp-anchor download core with a setTimeout(...,0)-
deferred revokeObjectURL so a synchronous revoke can't abort the
scheduled download (Firefox/Safari, intermittently Chrome).
- downloadJsonFile(): refactored on top of downloadBlob; callers unchanged.
- fileNameFromUri(): last path segment sanitized (control/format chars
stripped, disallowed filename chars -> _, capped at 255, "download"
fallback).
- isHttpUrl(): parse-and-allowlist http(s) only, else null.
Re-implementation of the downloadFile.ts slice of PR #1510 as Wave 1 of
the #1579 decomposition.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S3fTN8H3R8YV4yUGvZjYnX
26478159be