test(spec-conformance): AdcpError codes against canonical error-code enum (#429)

* feat(testing): spec-conformance test for AdcpError codes against canonical enum

Issue #375 / PR #393 demonstrated that four error codes
(AGENT_SUSPENDED, AGENT_BLOCKED, REQUEST_AUTH_UNRECOGNIZED_AGENT,
INVALID_BILLING_MODEL) shipped for months as non-spec-conformant
before being caught and migrated to PERMISSION_DENIED /
BILLING_NOT_PERMITTED_FOR_AGENT. Add an automated CI guard so the
next drift is caught at commit time.

The test AST-walks every .py file under src/adcp/ for AdcpError(...)
calls, extracts the literal first positional (or `code=` kwarg)
argument, and asserts each code is either:

* in the canonical enum bundled at
  src/adcp/types/generated_poc/enums/error_code.py (generated from
  schemas/cache/enums/error-code.json);
* prefixed with X_ per the AdCP vendor-extension convention; or
* in a small documented allowlist (KNOWN_NON_SPEC_CODES) covering
  INTERNAL_ERROR (universal exception wrap), AUTH_INVALID
  (pre-canonical 3.1 split of AUTH_REQUIRED), and
  BILLING_NOT_PERMITTED_FOR_AGENT (pinned by tier2_spec_conformance).

Walks 22 AdcpError raise sites today; all literal, all conformant.
The companion test_allowlist_entries_are_actually_used keeps the
allowlist from accumulating dead entries that would silently mask
future drift.

Runs as part of the existing pytest matrix — no new CI job needed.

The local pre-commit mypy hook reports 96 unrelated errors against
the a2a-sdk / protobuf surface (env drift in the uv-managed
pre-commit venv); they are present on clean main and not caused by
this commit. Skipped with SKIP=mypy; CI mypy via the locked
project venv is unaffected.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix(testing): refresh stale error-code.json cache + drop unneeded allowlist (PR #429 fix-pack)

The bundled schemas/cache/enums/error-code.json was stale at 45 entries
while the canonical upstream enum has 60. The generated ErrorCode enum
was regenerated from that stale cache, so the allowlist entry for
BILLING_NOT_PERMITTED_FOR_AGENT was masking a resync gap rather than a
real spec discrepancy.

Changes:
- schemas/cache/enums/error-code.json: refreshed from upstream (60 entries)
- src/adcp/types/generated_poc/enums/error_code.py: regenerated
- tests/test_error_code_conformance.py:
  - Drop BILLING_NOT_PERMITTED_FOR_AGENT from KNOWN_NON_SPEC_CODES
    (now in canonical enum)
  - Update sanity-check assertions: AGENT_SUSPENDED is now in spec, so
    swap the spot-check for REQUEST_AUTH_UNRECOGNIZED_AGENT (still non-spec)
  - Add length-guard: assert CANONICAL_CODES has 60 entries so a silent
    schema cache change surfaces here
  - Add TODO refs to remaining INTERNAL_ERROR + AUTH_INVALID allowlist entries

Pre-commit mypy hook is bypassed because the 96 errors it reports
(in src/adcp/{webhooks,server,protocols,client}.py) are preexisting
environmental issues with a2a-sdk version mismatch on this branch —
verified to predate this commit and unrelated to the changes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: bokelley