Add canonical event log and renderer skeleton (A10)

Build-order step 4, sequenced before the LLM client (step 3) because
the client interface consumes the canonical log.

- canonical.py: typed events for the full A10 table (user_message
  through compaction); canonical tool-call IDs minted locally,
  provider IDs never a join key; strict payload validation on load
- StateStore: canonical_events table via schema v2 — the first real
  migration, exercised in a test against a hand-built v1 database —
  with append_event/read_events on the same fsync-per-commit path
- render.py: request bodies rendered from the log at call time;
  first adapter targets the OpenAI-compatible shape of LiteLLM's
  normalized route; compaction events replace their id range at
  render time while staying in the durable log
- Crash integration test now also verifies transcript appends
  survive process death

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

nisse-dev/src/nisse_dev/canonical.py

@@ -0,0 +1,133 @@
+"""Canonical transcript schema (spec A10).
+
+The durable record is this event log, never a provider-shaped ``messages``
+array; provider request bodies are rendered from it at call time. Canonical
+tool-call IDs are minted locally — provider IDs are mapped at the boundary and
+never used as a join key.
+
+Transcript appends are the conversation record itself, not state-machine
+mutations, so they are deliberately outside the A9 state-change taxonomy.
+"""
+
+import uuid
+from dataclasses import asdict, dataclass, fields
+from typing import Any
+
+
+@dataclass(frozen=True)
+class UserMessage:
+    text: str
+    source: str  # e.g. a Matrix event ID
+
+
+@dataclass(frozen=True)
+class AssistantText:
+    text: str
+    model: str
+
+
+@dataclass(frozen=True)
+class ToolCall:
+    call_id: str  # canonical, minted locally via mint_call_id()
+    tool: str
+    arguments: dict[str, Any]
+
+
+@dataclass(frozen=True)
+class ToolResult:
+    call_id: str
+    result: str
+    success: bool
+
+
+@dataclass(frozen=True)
+class PlanSubmitted:
+    plan: str
+    model: str
+
+
+@dataclass(frozen=True)
+class GateOpened:
+    gate: str
+    reason: str
+
+
+@dataclass(frozen=True)
+class DelegationStarted:
+    brief: str
+    role: str
+    model: str
+    caps: dict[str, Any]  # turns / tokens / wall-clock limits
+
+
+@dataclass(frozen=True)
+class DelegationCompleted:
+    handback: str
+    artifacts: list[str]
+    tokens: int
+    duration_s: float
+    exit_status: str
+
+
+@dataclass(frozen=True)
+class Compaction:
+    summary: str
+    model: str
+    replaces: list[int]  # [first_id, last_id] inclusive range replaced
+
+
+CanonicalEvent = (
+    UserMessage
+    | AssistantText
+    | ToolCall
+    | ToolResult
+    | PlanSubmitted
+    | GateOpened
+    | DelegationStarted
+    | DelegationCompleted
+    | Compaction
+)
+
+EVENT_TYPES: dict[str, type] = {
+    "user_message": UserMessage,
+    "assistant_text": AssistantText,
+    "tool_call": ToolCall,
+    "tool_result": ToolResult,
+    "plan_submitted": PlanSubmitted,
+    "gate_opened": GateOpened,
+    "delegation_started": DelegationStarted,
+    "delegation_completed": DelegationCompleted,
+    "compaction": Compaction,
+}
+
+_TYPE_NAMES = {cls: name for name, cls in EVENT_TYPES.items()}
+
+
+@dataclass(frozen=True)
+class StoredEvent:
+    id: int
+    ts: str
+    event: CanonicalEvent
+
+
+def mint_call_id() -> str:
+    return f"call-{uuid.uuid4().hex}"
+
+
+def event_type(event: CanonicalEvent) -> str:
+    return _TYPE_NAMES[type(event)]
+
+
+def to_payload(event: CanonicalEvent) -> dict[str, Any]:
+    return asdict(event)
+
+
+def from_payload(type_name: str, payload: dict[str, Any]) -> CanonicalEvent:
+    cls = EVENT_TYPES.get(type_name)
+    if cls is None:
+        raise ValueError(f"unknown canonical event type: {type_name!r}")
+    known = {f.name for f in fields(cls)}
+    unknown = payload.keys() - known
+    if unknown:
+        raise ValueError(f"unknown fields for {type_name}: {sorted(unknown)}")
+    return cls(**payload)