Add a pure, DOM-free CSP-builder library at
clients/web/src/lib/sandbox-csp.ts that validates app-supplied
`_meta.ui.csp` requests, filters them to safe sources, builds the
locked-down Content-Security-Policy string, and wraps untrusted widget
HTML in a fixed host shell whose first <head> child is the CSP meta.
- SAFE_CSP_SOURCE: strict regex that rejects directive/attribute
breakouts (`;`, `"`, `<`, `>`, whitespace).
- approveCspSources(): drops unsafe entries (with a warning) and omits
empty keys; echoes back only what the host will enforce.
- buildSandboxCspPolicy(): `default-src 'none'` catch-all, `form-action
'none'`, source-allowlist filtering, `'unsafe-inline'` for the app's
own inline script/style.
- escapeHtmlAttr() / wrapSandboxedHtml(): defense-in-depth so untrusted
bytes never precede the applied policy.
Re-implements the sandbox-csp portion of PR #1510 (Wave 1 of #1579) as a
standalone library; wiring into the app bridge is a follow-up issue.
Adds full unit tests (100% lines/statements/functions/branches) and
lists the file in the web coverage `include` so it is gated (the
untested legacy src/lib siblings stay out until they get tests).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S3fTN8H3R8YV4yUGvZjYnX
77e57e0d25