feat: Add NEAR key management with transaction signing and policy engine

Implements hybrid-custody NEAR key management where the agent holds scoped
function-call keys for routine operations while high-value operations require
explicit user approval through the existing channel approval flow.

Core infrastructure:
- Ed25519 key generation/import via ed25519-dalek (not near-crypto)
- AES-256-GCM encrypted storage via existing SecretsStore
- Hand-rolled borsh-serializable NEAR transaction types
- NEP-413 intent signing and MPC chain signature support
- Configurable policy engine with transaction analysis pipeline
- Daily spend tracking with automatic midnight UTC reset
- Encrypted backup/restore with Argon2id KDF
- CLI subcommands: generate, import, list, info, remove, export, policy, backup, restore
- NEAR ed25519 secret key leak detection (Critical/Block)
- WASM sign-payload host function (keys never enter WASM memory)
- KeyManager wired into AgentDeps for agent-wide access

Security invariants: private keys never reach the LLM or WASM boundary,
signing happens in host Rust code with Zeroize on drop, every transaction
is analyzed before signing, most-restrictive policy rule wins.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

Cargo.lock

@@ -170,6 +170,18 @@ version = "1.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c3d036a3c4ab069c7b410a2ce876bd74808d2d0888a82667669f8e783a898bf1"
 
+[[package]]
+name = "argon2"
+version = "0.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3c3610892ee6e0cbce8ae2700349fcf8f98adb0dbfbee85aec3c9179d29cc072"
+dependencies = [
+ "base64ct",
+ "blake2",
+ "cpufeatures",
+ "password-hash",
+]
+
 [[package]]
 name = "arrayref"
 version = "0.3.9"
@@ -403,6 +415,12 @@ version = "0.22.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "72b3254f16251a8381aa12e40e3c4d2f0199f8c6508fbecb9d91f575e0fbb8c6"
 
+[[package]]
+name = "base64ct"
+version = "1.8.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2af50177e190e07a26ab74f8b1efbfe2ef87da2116221318cb1c2e82baf7de06"
+
 [[package]]
 name = "bitflags"
 version = "1.3.2"
@@ -427,6 +445,15 @@ dependencies = [
  "wyz",
 ]
 
+[[package]]
+name = "blake2"
+version = "0.10.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "46502ad458c9a52b69d4d4d32775c788b7a1b85e8bc9d482d92250fc0e3f8efe"
+dependencies = [
+ "digest",
+]
+
 [[package]]
 name = "blake3"
 version = "1.8.3"
@@ -545,6 +572,15 @@ dependencies = [
  "syn 2.0.114",
 ]
 
+[[package]]
+name = "bs58"
+version = "0.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bf88ba1141d185c399bee5288d850d63b8369520c1eafc32a0430b5b6c287bf4"
+dependencies = [
+ "tinyvec",
+]
+
 [[package]]
 name = "bumpalo"
 version = "3.19.1"
@@ -796,6 +832,12 @@ dependencies = [
  "crossbeam-utils",
 ]
 
+[[package]]
+name = "const-oid"
+version = "0.9.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c2459377285ad874054d797f3ccebf984978aa39129f6eafde5cdc8315b612f8"
+
 [[package]]
 name = "constant_time_eq"
 version = "0.4.2"
@@ -1115,6 +1157,33 @@ dependencies = [
  "cipher",
 ]
 
+[[package]]
+name = "curve25519-dalek"
+version = "4.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "97fb8b7c4503de7d6ae7b42ab72a5a59857b4c937ec27a3d4539dba95b5ab2be"
+dependencies = [
+ "cfg-if",
+ "cpufeatures",
+ "curve25519-dalek-derive",
+ "digest",
+ "fiat-crypto",
+ "rustc_version",
+ "subtle",
+ "zeroize",
+]
+
+[[package]]
+name = "curve25519-dalek-derive"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f46882e17999c6cc590af592290432be3bce0428cb0d5f8b6715e4dc7b383eb3"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.114",
+]
+
 [[package]]
 name = "darling"
 version = "0.21.3"
@@ -1200,6 +1269,16 @@ dependencies = [
  "uuid",
 ]
 
+[[package]]
+name = "der"
+version = "0.7.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e7c1832837b905bbfb5101e07cc24c8deddf52f93225eee6ead5f4d63d53ddcb"
+dependencies = [
+ "const-oid",
+ "zeroize",
+]
+
 [[package]]
 name = "deranged"
 version = "0.5.5"
@@ -1354,6 +1433,31 @@ version = "1.0.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d0881ea181b1df73ff77ffaaf9c7544ecc11e82fba9b5f27b262a3c73a332555"
 
+[[package]]
+name = "ed25519"
+version = "2.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "115531babc129696a58c64a4fef0a8bf9e9698629fb97e9e40767d235cfbcd53"
+dependencies = [
+ "pkcs8",
+ "signature",
+]
+
+[[package]]
+name = "ed25519-dalek"
+version = "2.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "70e796c081cee67dc755e1a36a0a172b897fab85fc3f6bc48307991f64e4eca9"
+dependencies = [
+ "curve25519-dalek",
+ "ed25519",
+ "rand_core 0.6.4",
+ "serde",
+ "sha2",
+ "subtle",
+ "zeroize",
+]
+
 [[package]]
 name = "either"
 version = "1.15.0"
@@ -1497,6 +1601,12 @@ dependencies = [
  "windows-sys 0.59.0",
 ]
 
+[[package]]
+name = "fiat-crypto"
+version = "0.2.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "28dea519a9695b9977216879a3ebfddf92f1c08c05d984f8996aecd6ecdc811d"
+
 [[package]]
 name = "filetime"
 version = "0.2.27"
@@ -2181,11 +2291,14 @@ dependencies = [
  "aes-gcm",
  "aho-corasick",
  "anyhow",
+ "argon2",
  "async-trait",
  "axum",
  "base64 0.22.1",
  "blake3",
  "bollard",
+ "borsh",
+ "bs58",
  "bytes",
  "chrono",
  "clap",
@@ -2193,6 +2306,7 @@ dependencies = [
  "deadpool-postgres",
  "dirs 6.0.0",
  "dotenvy",
+ "ed25519-dalek",
  "futures",
  "hkdf",
  "http-body-util",
@@ -2234,6 +2348,7 @@ dependencies = [
  "wasmtime",
  "wasmtime-wasi",
  "zbus",
+ "zeroize",
 ]
 
 [[package]]
@@ -2774,6 +2889,17 @@ dependencies = [
  "syn 2.0.114",
 ]
 
+[[package]]
+name = "password-hash"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "346f04948ba92c43e8469c1ee6736c7563d71012b17d40745260fe106aac2166"
+dependencies = [
+ "base64ct",
+ "rand_core 0.6.4",
+ "subtle",
+]
+
 [[package]]
 name = "paste"
 version = "1.0.15"
@@ -2844,6 +2970,16 @@ dependencies = [
  "futures-io",
 ]
 
+[[package]]
+name = "pkcs8"
+version = "0.10.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f950b2377845cebe5cf8b5165cb3cc1a5e0fa5cfa3e1f7f55707d8fd82e0a7b7"
+dependencies = [
+ "der",
+ "spki",
+]
+
 [[package]]
 name = "pkg-config"
 version = "0.3.32"
@@ -3925,6 +4061,15 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "signature"
+version = "2.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "77549399552de45a898a580c1b41d445bf730df867cc44e6c0233bbc4b8329de"
+dependencies = [
+ "rand_core 0.6.4",
+]
+
 [[package]]
 name = "simdutf8"
 version = "0.1.5"
@@ -3962,6 +4107,16 @@ dependencies = [
  "windows-sys 0.60.2",
 ]
 
+[[package]]
+name = "spki"
+version = "0.7.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d91ed6c858b01f942cd56b37a94b3e0a1798290327d1236e4d9cf4eaca44d29d"
+dependencies = [
+ "base64ct",
+ "der",
+]
+
 [[package]]
 name = "sptr"
 version = "0.3.2"
@@ -5946,6 +6101,20 @@ name = "zeroize"
 version = "1.8.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b97154e67e32c85465826e8bcc1c59429aaaf107c1e4a9e53c8d8ccd5eff88d0"
+dependencies = [
+ "zeroize_derive",
+]
+
+[[package]]
+name = "zeroize_derive"
+version = "1.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "85a5b4158499876c763cb03bc4e49185d3cccbabb15b33c627f7884f43db852e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.114",
+]
 
 [[package]]
 name = "zerotrie"