Implement authenticated resource bootstrap and bounded client cache ownership

[zoeyrose]

Outcome

Fetch only authorized resource releases from the connected server, verify them atomically, and expose them to renderer through a trust-scoped provider.

Scope and invariants

• Negotiate manifest/version/digests/capabilities through Game Protocol 1; distinguish code-bundled assets, server-authenticated resources, and user/editor-local files.
• Prioritize gameplay messages over bulk transfers; bound concurrent requests, bytes, retries, bandwidth, memory, disk, filenames, and decompression.
• Scope caches by authenticated server identity and release digest; never allow one server to satisfy another server's trust namespace accidentally.
• Download to temporary files, verify length/hash/type/license manifest as applicable, then atomically publish; corrupt/partial files remain invisible.
• Define eviction, offline/reconnect, manifest change, cache reset, diagnostics, and privacy behavior.

Acceptance criteria

• Tests cover missing/corrupt/truncated/oversized/compression-bomb data, identity/certificate change, stale manifests, interrupted writes, disk full, eviction races, reconnect, and slow delivery.
• Renderer receives only verified immutable IDs/digests/revisions and never owns network/disk policy.
• No path traversal, executable shader/code delivery, or unauthenticated cache poisoning is possible.
• A clean M3 client bootstraps the selected content/resources without source checkout access.
• Metrics are bounded and distinguish download/verify/cache/provider stages.

Dependencies and parallelization

Depends on #12 and renderer resource-provider issue. Server/protocol resource work and client cache work can proceed in parallel against shared fixtures.

Licensing

Client code/tests are MIT. Legacy reuse requires an audited approved-grantor grant; all other implementation is independent. Content, sound, and graphics retain their exact asset licenses and notices.