NK-WP-0056-T15: receipt schema v0.1, validator and executor fixtures; audit sender exercise

- canon/schemas/execution-attribution-receipt_v0.1.schema.json: the bounded-executor profile
  of the PCC v0.2 receipt, both audit-core events (started, receipt), every object closed.
- tools/execution-attribution-receipt: EAR-1..EAR-10 validator, fixtures generated from the
  real executor (completed, reverted, completed-on-retry) with a drift check.
- executor: started carries receipt_version, digests, steps_planned and data.window.not_after
  (audit-core AUDIT-WP-0018-T03 request); receipt carries receipt_version and initiator.iss
  (configured approver_issuer, else unknown).
- bounded-executor/exercise_audit_sender.py: real executor and client against audit-core's
  real ingestion and the Git scope overlay: 202, duplicate 200, conflict 409 as a defect,
  wrong source/tenant/token refused and not stored, a receipt-less start flagged by its own
  window.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 523928@bnt-lap001
Assistant-Session: 6c737afb-9c14-4152-9f02-477214b9c350

bounded-executor/cli.py

@@ -128,7 +128,8 @@ def build(cfg: dict, logins: list):
                   alert=alert)
     config = X.Config(executor_identity=cfg["executor_identity"], runtime_principal=cfg["runtime_principal"],
                       tenant=cfg["tenant"], environment=cfg["environment"],
-                      approver_subjects=dict(cfg["approver_subjects"]))
+                      approver_subjects=dict(cfg["approver_subjects"]),
+                      approver_issuer=cfg.get("approver_issuer", "unknown"))
     return config, deps