Update with fixes

[OisinKyne]

Summary

Verifier crashloop fix (the blocker)

• internal/x402/config.go: LoadConfig
  now treats os.ErrNotExist as a soft
  success — returns a defaulted
  PricingConfig (chain base, default
  facilitator, zero routes) and logs a
  friendly explanation. Other read errors
  (permission denied, IO failures) still
  surface so genuinely broken deployments
  fail loudly. defaultPricingConfig()
  helper introduced.
• Two tests pinning the new contract:
  TestLoadConfig_FileNotFound_ReturnsDefau
  ltsWithoutError (the rc10 reproducer)
  and TestLoadConfig_UnreadableFile_StillE
  rrors (permission-denied path still
  rejects). Skips the latter under root.
• End-to-end smoke: x402-verifier
  --config /tmp/does-not-exist.yaml
  --listen :18402 --watch=false boots
  cleanly, logs the friendly message,
  /healthz → 200, /verify → 200 for an
  unmatched URI. The new HTML 402 path is
  unblocked once the new image rolls.

setMetadata revert decoder (the partial
fix)

• internal/erc8004/revert.go: new
  decodeRevertReason(err) and
  wrapTransactError(prefix, err). Decodes
  the three Solidity revert shapes the
  node returns on the JSON-RPC data field:
  • Error(string) (selector 0x08c379a0)
    → the literal Solidity message.
  • Panic(uint256) (selector 0x4e487b71)
    → mapped to a human label via
    panicReason() (overflow, div-by-zero,
    OOB, etc.).
  • Any other 4-byte selector → surfaced
    as custom error 0x so an
    operator can grep the contract source.
• internal/erc8004/client.go:
  SetMetadata, SetMetadataWithOpts,
  SetAgentURI now wrap their Transact
  error with the decoder. The original
  error chain stays intact for
  errors.Is/As.
• internal/erc8004/revert_test.go: 4
  unit tests covering Error(string),
  Panic(uint256), unknown selector, and
  the no-data fast-paths.
• internal/erc8004/client_test.go:
  extended the mock RPC to attach data on
  JSON-RPC error envelopes via a new
  rpcMockDataError type. Two new
  SetMetadata tests assert the decoded
  reason / selector show up in the wrapped
  CLI error.

What this means for the rc10 reproducer:
next time someone runs obol sell
register twice in a row and hits the
revert, the CLI message will contain
either the Solidity revert("…") text or
custom error 0x — enough for
engineering to grep the registry
contract and identify the actual
rejection condition (probably
MetadataAlreadySet or a wallet-policy
check, per the report). Doesn't fix the
root cause, but turns the opaque error
into something diagnosable in one rerun
rather than a chain-trace expedition.