feat: migrate refimpls from draft-00 to draft-01 claim names

- Rename `par` to `pred` (predecessor) in types, serialization, tests
- Remove `pol`, `pol_decision` from core payload; move to `ect_ext`
- Remove `sub` from payload (not part of ECT spec)
- Update `typ` from `wimse-exec+jwt` to `exec+jwt` (accept both)
- Rename MaxParLength to MaxPredLength everywhere
- Update testdata, demos, READMEs with migration table
- All Go tests pass, all 56 Python tests pass (90% coverage)

refimpl/python/README.md

@@ -1,6 +1,6 @@
 # WIMSE ECT — Python Reference Implementation
 
-Python reference implementation of [Execution Context Tokens (ECTs)](../../draft-nennemann-wimse-execution-context-00.txt) for WIMSE. Implements ECT creation (ES256), verification (Section 7), DAG validation (Section 6), and an in-memory audit ledger (Section 9).
+Python reference implementation of [Execution Context Tokens (ECTs)](../../draft-nennemann-wimse-execution-context-01.txt) for WIMSE. Implements ECT creation (ES256), verification (Section 7), DAG validation (Section 6), and an in-memory audit ledger (Section 9).
 
 ## Layout
 
@@ -42,7 +42,6 @@ from ect import (
     verify,
     VerifyOptions,
     MemoryLedger,
-    POL_DECISION_APPROVED,
 )
 
 cfg = load_config_from_env()
@@ -54,9 +53,11 @@ payload = Payload(
     exp=int(time.time()) + 600,
     jti="550e8400-e29b-41d4-a716-446655440000",
     exec_act="review_spec",
-    par=[],
-    pol="policy_v1",
-    pol_decision=POL_DECISION_APPROVED,
+    pred=[],
+    ext={
+        "pol": "policy_v1",
+        "pol_decision": "approved",
+    },
 )
 compact = create(payload, key, cfg.create_options("agent-a-key"))
 
@@ -83,6 +84,16 @@ cd refimpl/python && python3 -m pytest tests/ -v
 
 Unit tests require **90% coverage** minimum (`pytest` is configured with `--cov-fail-under=90` in `pyproject.toml`). Install dev deps: `pip install -e ".[dev]"`. Uncovered lines are mainly abstract base methods and a few verify branches that need manually built tokens.
 
+## draft-01 claim changes
+
+| -00 (previous) | -01 (current) | Notes |
+|----------------|---------------|-------|
+| `par`          | `pred`        | Predecessor task IDs |
+| `pol`, `pol_decision` | removed (use `ect_ext`) | Policy claims moved to extension object |
+| `sub`          | not defined   | Standard JWT claim, not part of ECT spec |
+| `typ: wimse-exec+jwt` | `typ: exec+jwt` (preferred) | Both accepted for backward compat |
+| `max_par_length` | `max_pred_length` | Renamed to match `pred` claim |
+
 ## Production configuration (environment)
 
 Same env vars as the Go refimpl: `ECT_IAT_MAX_AGE_MINUTES`, `ECT_IAT_MAX_FUTURE_SEC`, `ECT_DEFAULT_EXPIRY_MIN`, `ECT_JTI_REPLAY_CACHE_SIZE`, `ECT_JTI_REPLAY_TTL_MIN`.