Plumbs the BlobStore from blobs.rs into ApiHandler. The HMAC capability
key is derived from the node's Ed25519 signing key via a domain-separated
SHA-256 — rotating the identity rotates every outstanding cap (intentional
so a replaced node cannot honour old tokens).
New routes (added to nginx config in both server blocks):
- POST /api/blob — session-authenticated raw upload, returns
{cid, size, mime, filename, self_test_url}. The self_test_url is a
pre-signed cap pointing at the local node so the UI can verify the
round-trip without needing a peer pubkey.
- GET /blob/<cid>?cap=<hex>&exp=<epoch>&peer=<pubkey> — peer-facing,
HMAC-verified in constant time, expiry-checked, then streams bytes.
Mesh.vue gets a minimal "Attachment test (blob store)" section: file
picker → upload → cid display → "Verify round-trip" and "Open in new
tab" buttons. This validates Phase 3a end-to-end before we layer the
ContentRef typed envelope variant on top.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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