feat(versioning): snapshot corpus per spec version

A frozen spec is only meaningful if it's paired with the corpus that was current at release time — otherwise a v0.1.0 reader follows "see corpus/payloads/ack/" and lands on a file whose test vectors may have changed since v0.1.0 was cut. Three changes: 1. `cut-version` now copies BOTH src/ AND corpus/ into the snapshot directory. A release is the pair, not just the text. 2. The corpus URL rewriting in cut-version now retargets /tree/main/corpus -> /tree/main/versions/<v>/corpus (and the blob variant). This lets the link resolve on GitHub from main alone — no git tag required, since the frozen copy is a real path under main. Downgrades the "tag is REQUIRED" message from last commit back to "optionally tag the commit". 3. The frozen corpus's spec_ref fields get rewritten too: from `src/04-payload-ack.md` to `versions/<v>/04-payload-ack.md`, so a reader following a test vector lands on the spec text the vector was paired with at release time. versions/v0.1.0/ regenerated from scratch via `just cut-version v0.1.0` to pick up the corpus snapshot + the new sed patterns. The release is now self-consistent: v0.1.0 spec links go to v0.1.0 corpus, which links back to v0.1.0 spec. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
2026-05-12 10:38:02 -06:00
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+{
+  "$schema": "../../schema/test-vector.schema.json",
+  "name": "ECDH Shared Secret (X25519)",
+  "spec_ref": "versions/v0.1.0/15-identity.md",
+  "protocol_version": 0,
+  "description": "X25519 ECDH key exchange test vectors. MeshCore uses Ed25519 keys transposed to X25519 for key exchange. The resulting 32-byte shared secret is used as: AES key (bytes 0-15) and HMAC key (bytes 0-31).",
+  "vectors": [
+    {
+      "id": "ecdh-001",
+      "description": "RFC 7748 Test Vector: X25519 key exchange (Alice's perspective)",
+      "type": "encode_decode",
+      "structured": {
+        "header": {
+          "version": 0,
+          "payload_type": "raw_custom",
+          "route_type": "flood"
+        },
+        "path": {
+          "hash_size": 1,
+          "hash_count": 0,
+          "hashes": []
+        },
+        "payload": {
+          "data": "4A5D9D5BA4CE2DE1728E3BF480350F25E07E21C947D19E3376F09B3C1E161742"
+        }
+      },
+      "binary": "3D 00 4A5D9D5BA4CE2DE1728E3BF480350F25E07E21C947D19E3376F09B3C1E161742",
+      "crypto_context": {
+        "sender_private_key": "77076D0A7318A57D3C16C17251B26645DF4C2F87EBC0992AB177FBA51DB92C2A",
+        "recipient_public_key": "DE9EDB7D7B7DC1B4D35B61C2ECE435373F8343C85B78674DADFC7E146F882B4F"
+      },
+      "notes": "RFC 7748 Section 6.1. Alice's private key and Bob's public key produce the shared secret. Note: MeshCore transposes Ed25519 keys to X25519, so actual ECDH inputs differ from raw Ed25519 keys."
+    },
+    {
+      "id": "ecdh-002",
+      "description": "RFC 7748 Test Vector: X25519 key exchange (Bob's perspective)",
+      "type": "encode_decode",
+      "structured": {
+        "header": {
+          "version": 0,
+          "payload_type": "raw_custom",
+          "route_type": "flood"
+        },
+        "path": {
+          "hash_size": 1,
+          "hash_count": 0,
+          "hashes": []
+        },
+        "payload": {
+          "data": "4A5D9D5BA4CE2DE1728E3BF480350F25E07E21C947D19E3376F09B3C1E161742"
+        }
+      },
+      "binary": "3D 00 4A5D9D5BA4CE2DE1728E3BF480350F25E07E21C947D19E3376F09B3C1E161742",
+      "crypto_context": {
+        "sender_private_key": "5DAB087E624A8A4B79E17F8B83800EE66F3BB1292618B6FD1C2F8B27FF88E0EB",
+        "recipient_public_key": "8520F0098930A754748B7DDCB43EF75A0DBF3A0D26381AF4EBA4A98EAA9B4E6A"
+      },
+      "notes": "RFC 7748 Section 6.1. Bob's private key and Alice's public key produce the same shared secret as ecdh-001, verifying the commutative property of ECDH."
+    },
+    {
+      "id": "ecdh-003",
+      "description": "X25519 with all-zeros private key scalar (edge case)",
+      "type": "encode_decode",
+      "structured": {
+        "header": {
+          "version": 0,
+          "payload_type": "raw_custom",
+          "route_type": "flood"
+        },
+        "path": {
+          "hash_size": 1,
+          "hash_count": 0,
+          "hashes": []
+        },
+        "payload": {
+          "data": "0000000000000000000000000000000000000000000000000000000000000000"
+        }
+      },
+      "binary": "3D 00 0000000000000000000000000000000000000000000000000000000000000000",
+      "crypto_context": {
+        "sender_private_key": "0000000000000000000000000000000000000000000000000000000000000000",
+        "recipient_public_key": "DE9EDB7D7B7DC1B4D35B61C2ECE435373F8343C85B78674DADFC7E146F882B4F"
+      },
+      "notes": "Edge case: all-zero private key after clamping becomes a low-order scalar. X25519 with a clamped all-zero key (which becomes 0x40...00) against any public key. The all-zero shared secret indicates this is a degenerate key and implementations SHOULD reject it."
+    }
+  ]
+}