feat: ACT/ECT strategy, package restructure, draft -01/-02 prep

Strategic work for IETF submission of draft-nennemann-act-01 and
draft-nennemann-wimse-ect-02:

Package restructure:
- move ACT and ECT refimpls to workspace/packages/{act,ect}/
- ietf-act and ietf-ect distribution names (sibling packages)
- cross-spec interop test plan (INTEROP-TEST-PLAN.md)

ACT draft -01 revisions:
- rename 'par' claim to 'pred' (align with ECT)
- rename 'Agent Compact Token' to 'Agent Context Token' (semantic
  alignment with ECT family)
- add Applicability section (MCP, OpenAI, LangGraph, A2A, CrewAI)
- add DAG vs Linear Delegation Chains section (differentiator vs
  txn-tokens-for-agents actchain, Agentic JWT, AIP/IBCTs)
- add Related Work: AIP, SentinelAgent, Agentic JWT, txn-tokens-for-agents,
  HDP, SCITT-AI-agent-execution
- pin SCITT arch to -22, note AUTH48 status

Outreach drafts:
- Emirdag liaison email (SCITT-AI coordination)
- OAuth ML response on txn-tokens-for-agents-06

Strategy document:
- STRATEGY.md with phased action plan, risk register, timeline

Submodule:
- update workspace/drafts/ietf-wimse-ect pointer to -02 commit

workspace/packages/ect/README.md

@@ -0,0 +1,111 @@
+# WIMSE ECT — Python Reference Implementation
+
+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
+
+```
+python/
+├── pyproject.toml
+├── ect/                 # library
+│   ├── __init__.py
+│   ├── types.py         # Payload, constants
+│   ├── create.py        # create(), generate_key()
+│   ├── verify.py        # parse(), verify(), VerifyOptions
+│   ├── dag.py           # validate_dag(), ECTStore, DAGConfig
+│   ├── ledger.py        # Ledger, MemoryLedger
+│   ├── config.py        # Config, load_config_from_env()
+│   ├── jti_cache.py     # JTICache for replay protection
+│   └── validate.py      # validate_ext, valid_uuid, validate_hash_format
+├── tests/
+│   ├── test_create.py
+│   └── test_dag.py
+├── testdata/
+│   └── valid_root_ect_payload.json
+└── demo.py              # two-agent workflow demo
+```
+
+## Install
+
+```bash
+cd refimpl/python && pip install -e .
+```
+
+## Usage
+
+```python
+from ect import (
+    Payload,
+    create,
+    generate_key,
+    CreateOptions,
+    verify,
+    VerifyOptions,
+    MemoryLedger,
+)
+
+cfg = load_config_from_env()
+key = generate_key()
+payload = Payload(
+    iss="spiffe://example.com/agent/a",
+    aud=["spiffe://example.com/agent/b"],
+    iat=int(time.time()),
+    exp=int(time.time()) + 600,
+    jti="550e8400-e29b-41d4-a716-446655440000",
+    exec_act="review_spec",
+    pred=[],
+    ext={
+        "pol": "policy_v1",
+        "pol_decision": "approved",
+    },
+)
+compact = create(payload, key, cfg.create_options("agent-a-key"))
+
+store = MemoryLedger()
+opts = cfg.verify_options()
+opts.verifier_id = "spiffe://example.com/agent/b"
+opts.resolve_key = lambda kid: key.public_key() if kid == "agent-a-key" else None
+opts.store = store
+parsed = verify(compact, opts)
+store.append(compact, parsed.payload)
+```
+
+## Demo
+
+```bash
+cd refimpl/python && python3 demo.py
+```
+
+## Tests
+
+```bash
+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`.
+
+### Replay cache (multi-instance)
+
+The provided JTI cache is in-memory only. For multiple verifier instances, use a shared store (Redis, DB) and pass a `jti_seen` callable that checks/records JTIs there. See refimpl/README for an overview.
+
+## Dependencies
+
+- PyJWT, cryptography (ES256).
+
+## License
+
+Same as the Internet-Draft (IETF Trust). Code under Revised BSD per BCP 78/79.