fix(automation): enforce durable alert closure

Restore D037 durable incident readback without weakening database failure semantics.

Fence Agent99 dispatch and terminal learning to canonical identities, durable leases, verifier receipts, and reconciler-owned checkpoints.

Drain backup and restore legacy receipts in bounded cohorts with strict transport, claim, projection, and no-false-green controls.

Keep SSH service refusal visible while separating it from broker network-policy reachability.

apps/api/src/models/incident.py

@@ -22,7 +22,7 @@ C-Suite 戰略會議決議 (2026-03-22):
 
 from datetime import datetime, timezone
 from enum import Enum
-from typing import Literal
+from typing import Literal, cast, get_args
 from uuid import UUID, uuid4
 
 from pydantic import BaseModel, Field, field_validator
@@ -70,6 +70,33 @@ class IncidentStatus(str, Enum):
     ESCALATED = "escalated"  # 已升級 - 需要人工介入
 
 
+# Signal sources are a durable contract: values written by the host sensor and
+# the public signal ingress can remain in PostgreSQL long after a producer is
+# upgraded.  Keep this list bounded, but include every repo-owned producer
+# vocabulary instead of silently rewriting provenance during readback.
+SignalSource = Literal[
+    "prometheus",
+    "signoz",
+    "alertmanager",
+    "manual",
+    "telegram",
+    "journal",
+    "node-exporter",
+    "sensor-probe",
+    "sensor-agent",
+]
+SIGNAL_SOURCE_VALUES: frozenset[str] = frozenset(get_args(SignalSource))
+
+
+def parse_signal_source(value: object) -> SignalSource:
+    """Return a canonical known source or reject an unowned durable value."""
+
+    normalized = str(value or "").strip().lower()
+    if normalized not in SIGNAL_SOURCE_VALUES:
+        raise ValueError("unsupported_signal_source")
+    return cast(SignalSource, normalized)
+
+
 # =============================================================================
 # Signal (原始告警)
 # =============================================================================
@@ -89,9 +116,7 @@ class Signal(BaseModel):
     )
     alert_name: str = Field(..., description="告警名稱 (如 HighCPUUsage)")
     severity: Severity = Field(..., description="告警嚴重度")
-    source: Literal["prometheus", "signoz", "alertmanager", "manual", "telegram"] = (
-        Field(..., description="告警來源")
-    )
+    source: SignalSource = Field(..., description="告警來源")
     fired_at: datetime = Field(..., description="告警觸發時間")
     resolved_at: datetime | None = Field(None, description="告警解除時間")
     labels: dict[str, str] = Field(
@@ -107,9 +132,26 @@ class Signal(BaseModel):
         description="告警指紋 Hash，用於去重與聚合",
     )
 
+    @field_validator("source", mode="before")
+    @classmethod
+    def validate_source(cls, value: object) -> SignalSource:
+        return parse_signal_source(value)
+
     # [首席架構師] 移除 json_encoders (Pydantic v2 已 deprecated)，原生序列化輸出格式與 .isoformat() 一致 v1.1 2026-04-01 Asia/Taipei
 
 
+class IncidentReadDegradation(BaseModel):
+    """Public-safe metadata for one durable row excluded from a response."""
+
+    incident_id: str
+    reason_code: Literal[
+        "incident_signal_source_unsupported",
+        "incident_signal_schema_invalid",
+        "incident_record_schema_invalid",
+    ]
+    quarantined_from_response: bool = True
+
+
 # =============================================================================
 # AI Decision Chain (CISO 要求：可稽核性)
 # =============================================================================