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/ect/dag.py

@@ -8,7 +8,7 @@ from typing import TYPE_CHECKING
 if TYPE_CHECKING:
     from ect.types import Payload
 
-from ect.validate import DEFAULT_MAX_PAR_LENGTH
+from ect.validate import DEFAULT_MAX_PRED_LENGTH
 
 DEFAULT_CLOCK_SKEW_TOLERANCE = 30
 DEFAULT_MAX_ANCESTOR_LIMIT = 10000
@@ -31,11 +31,11 @@ class DAGConfig:
         self,
         clock_skew_tolerance: int = DEFAULT_CLOCK_SKEW_TOLERANCE,
         max_ancestor_limit: int = DEFAULT_MAX_ANCESTOR_LIMIT,
-        max_par_length: int = 0,
+        max_pred_length: int = 0,
     ):
         self.clock_skew_tolerance = clock_skew_tolerance or DEFAULT_CLOCK_SKEW_TOLERANCE
         self.max_ancestor_limit = max_ancestor_limit or DEFAULT_MAX_ANCESTOR_LIMIT
-        self.max_par_length = max_par_length or 0
+        self.max_pred_length = max_pred_length or 0
 
 
 def default_dag_config() -> DAGConfig:
@@ -44,22 +44,22 @@ def default_dag_config() -> DAGConfig:
 
 def _has_cycle(
     target_tid: str,
-    parent_ids: list[str],
+    pred_ids: list[str],
     store: ECTStore,
     visited: set[str],
     max_depth: int,
 ) -> bool:
     if len(visited) >= max_depth:
         return True
-    for parent_id in parent_ids:
-        if parent_id == target_tid:
+    for pred_id in pred_ids:
+        if pred_id == target_tid:
             return True
-        if parent_id in visited:
+        if pred_id in visited:
             continue
-        visited.add(parent_id)
-        parent = store.get_by_tid(parent_id)
-        if parent is not None:
-            if _has_cycle(target_tid, parent.par, store, visited, max_depth):
+        visited.add(pred_id)
+        pred = store.get_by_tid(pred_id)
+        if pred is not None:
+            if _has_cycle(target_tid, pred.pred, store, visited, max_depth):
                 return True
     return False
 
@@ -69,29 +69,28 @@ def validate_dag(
     store: ECTStore,
     cfg: DAGConfig,
 ) -> None:
-    """Section 6.2: uniqueness (by jti), parent existence, temporal ordering, acyclicity, parent policy."""
-    if cfg.max_par_length > 0 and len(payload.par) > cfg.max_par_length:
-        raise ValueError("ect: par exceeds max length")
+    """Section 6.2: uniqueness (by jti), predecessor existence, temporal ordering, acyclicity, predecessor policy."""
+    if cfg.max_pred_length > 0 and len(payload.pred) > cfg.max_pred_length:
+        raise ValueError("ect: pred exceeds max length")
     if store.contains(payload.jti, payload.wid or ""):
         raise ValueError(f"ect: task ID (jti) already exists: {payload.jti}")
-    from ect.types import POL_DECISION_REJECTED, POL_DECISION_PENDING_HUMAN_REVIEW
 
-    for parent_id in payload.par:
-        parent = store.get_by_tid(parent_id)
-        if parent is None:
-            raise ValueError(f"ect: parent task not found: {parent_id}")
-        if parent.iat >= payload.iat + cfg.clock_skew_tolerance:
-            raise ValueError(f"ect: parent task not earlier than current: {parent_id}")
+    for pred_id in payload.pred:
+        pred = store.get_by_tid(pred_id)
+        if pred is None:
+            raise ValueError(f"ect: predecessor task not found: {pred_id}")
+        if pred.iat >= payload.iat + cfg.clock_skew_tolerance:
+            raise ValueError(f"ect: predecessor task not earlier than current: {pred_id}")
 
     visited: set[str] = set()
-    if _has_cycle(payload.jti, payload.par, store, visited, cfg.max_ancestor_limit):
+    if _has_cycle(payload.jti, payload.pred, store, visited, cfg.max_ancestor_limit):
         raise ValueError("ect: circular dependency or depth limit exceeded")
 
-    # Parent policy decision: only when parent has policy claims per spec
-    for parent_id in payload.par:
-        parent = store.get_by_tid(parent_id)
-        if parent and parent.has_policy_claims() and parent.pol_decision in (POL_DECISION_REJECTED, POL_DECISION_PENDING_HUMAN_REVIEW):
+    # Predecessor policy decision: only when predecessor has policy claims in ext per -01
+    for pred_id in payload.pred:
+        pred = store.get_by_tid(pred_id)
+        if pred and pred.has_policy_claims() and pred.pol_decision() in ("rejected", "pending_human_review"):
             if not payload.compensation_required():
                 raise ValueError(
-                    "ect: parent has non-approved pol_decision; current ECT must be compensation/remediation or have ext.compensation_required true"
+                    "ect: predecessor has non-approved pol_decision; current ECT must be compensation/remediation or have ext.compensation_required true"
                 )