Adds wasm-unsafe-eval to the plugin sandbox CSP, without which no plugin can execute WebAssembly at all. Unlocking that alone would let a plugin ship an inscrutable compiled blob with no way for a user (or a plugin reviewer) to know where it came from, so a manifest "executables" table (name, sourceUrl, sha256) is required and enforced by a prelude injected into the worker that hashes any bytes handed to WebAssembly.instantiate/ compile/Module and refuses anything undeclared - deliberately a provenance pointer, not an openness/license check. Also adds app.binaryCache, a host-mediated persistent store (Cache API backed, namespaced per plugin) for large downloads like a WASM engine or model file, since the plugin sandbox's own worker/iframe has an opaque origin and can't reliably cache such things itself. Builds on the binary-safe fetch() fix (separate PR/commit), since the binary cache moves bytes across the same base64-over-postMessage boundary that fix introduced. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>