fix(scheduler): derive entity health from all its checks, not the last one

host:strong logged 226 health.changed events in one hour, oscillating
down/healthy while the host was fine throughout. host:hubris did it 126 times.

runCheck wrote entity_status.health on every check completion, so an entity's
health was simply whichever of its checks finished most recently. A host with
six checks reported whichever facet happened to be sampled last, and one
failing probe alternating with five passing ones flapped forever. resolveSignal
forced "healthy" too, a second path by which one passing probe erased another
probe's genuine failure.

On this fleet the trigger is a known false positive: the scheduler's network
vantage point cannot ICMP host:strong, so its ping check fails while every
ssh-script check succeeds. Under last-writer-wins that single probe declared
the whole host down, twice a minute.

Each check now records its own verdict (check_defs.last_health, migration 027)
and the entity's health is the worst across its enabled checks. A failing probe
now degrades the entity honestly and *stably*, without erasing what the other
five report, and health.changed fires only when that aggregate actually moves.
Checks that have never run are ignored rather than counted as unknown, so
adding a check cannot drag a known-good entity down before it has a verdict.

Also declares service:oikos in the seed. The previous commit re-pointed the mcp
ingress at it, but the entity only ever existed in the production database — so
a fresh seed (a new install, or a DR restore) failed on an unresolvable edge.
Caught by seeding an empty database rather than a copy of prod, which is the
only way that class of bug shows up.

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

internal/db/queries/operations.sql

@@ -68,7 +68,21 @@ WHERE cd.enabled = true
        OR cd.last_run_at <= now() - make_interval(secs => cd.interval_s));
 
 -- name: MarkCheckRun :exec
-UPDATE check_defs SET last_run_at = now() WHERE entity_id = $1;
+UPDATE check_defs SET last_run_at = now(), last_health = $2 WHERE entity_id = $1;
+
+-- name: WorstHealthForTarget :one
+-- An entity is as healthy as its unhealthiest check. Checks that have not run
+-- yet (last_health IS NULL) are ignored rather than counted as unknown, so a
+-- newly added check does not drag a known-good entity down before it has
+-- produced a verdict.
+SELECT COALESCE(
+  (SELECT last_health FROM check_defs
+   WHERE enabled AND target_id = $1 AND last_health IS NOT NULL
+   ORDER BY CASE last_health
+     WHEN 'down' THEN 0 WHEN 'degraded' THEN 1 WHEN 'stale' THEN 2
+     WHEN 'unknown' THEN 3 ELSE 4 END
+   LIMIT 1),
+  'unknown')::text AS health;
 
 -- name: GetCheckDef :one
 SELECT * FROM check_defs WHERE entity_id = $1;

internal/db/sqlcgen/models.go

@@ -114,6 +114,8 @@ type CheckDef struct {
 	UpdatedAt  time.Time
 	// When this check last executed. NULL = never, due immediately. Compared against interval_s to decide due-ness.
 	LastRunAt *time.Time
+	// This check's own most recent verdict (healthy/degraded/down/unknown). entity_status.health is the worst of these across the target's enabled checks.
+	LastHealth *string
 }
 
 type Classification struct {
@@ -255,6 +257,20 @@ type KnowledgeEntity struct {
 	UpdatedAt   time.Time
 	ContentHash *string
 	Search      interface{}
+	EditedBy    string
+	DeletedAt   *time.Time
+}
+
+type KnowledgeRevision struct {
+	ID        int64
+	EntityID  uuid.UUID
+	Title     string
+	Content   string
+	Source    *string
+	Tags      []string
+	EditedBy  string
+	VersionAt time.Time
+	RevisedAt time.Time
 }
 
 type Ledger struct {

internal/db/sqlcgen/operations.sql.go

@@ -51,7 +51,7 @@ func (q *Queries) GetAutonomySetting(ctx context.Context, key string) (string, e
 }
 
 const getCheckDef = `-- name: GetCheckDef :one
-SELECT entity_id, target_id, target_type, kind, config, interval_s, timeout_s, zone, enabled, updated_at, last_run_at FROM check_defs WHERE entity_id = $1
+SELECT entity_id, target_id, target_type, kind, config, interval_s, timeout_s, zone, enabled, updated_at, last_run_at, last_health FROM check_defs WHERE entity_id = $1
 `
 
 func (q *Queries) GetCheckDef(ctx context.Context, entityID uuid.UUID) (CheckDef, error) {
@@ -69,6 +69,7 @@ func (q *Queries) GetCheckDef(ctx context.Context, entityID uuid.UUID) (CheckDef
 		&i.Enabled,
 		&i.UpdatedAt,
 		&i.LastRunAt,
+		&i.LastHealth,
 	)
 	return i, err
 }
@@ -1133,11 +1134,16 @@ func (q *Queries) ListSkills(ctx context.Context, status *string) ([]Skill, erro
 }
 
 const markCheckRun = `-- name: MarkCheckRun :exec
-UPDATE check_defs SET last_run_at = now() WHERE entity_id = $1
+UPDATE check_defs SET last_run_at = now(), last_health = $2 WHERE entity_id = $1
 `
 
-func (q *Queries) MarkCheckRun(ctx context.Context, entityID uuid.UUID) error {
-	_, err := q.db.Exec(ctx, markCheckRun, entityID)
+type MarkCheckRunParams struct {
+	EntityID   uuid.UUID
+	LastHealth *string
+}
+
+func (q *Queries) MarkCheckRun(ctx context.Context, arg MarkCheckRunParams) error {
+	_, err := q.db.Exec(ctx, markCheckRun, arg.EntityID, arg.LastHealth)
 	return err
 }
 
@@ -1462,3 +1468,25 @@ func (q *Queries) UpsertSignal(ctx context.Context, arg UpsertSignalParams) (Sig
 	)
 	return i, err
 }
+
+const worstHealthForTarget = `-- name: WorstHealthForTarget :one
+SELECT COALESCE(
+  (SELECT last_health FROM check_defs
+   WHERE enabled AND target_id = $1 AND last_health IS NOT NULL
+   ORDER BY CASE last_health
+     WHEN 'down' THEN 0 WHEN 'degraded' THEN 1 WHEN 'stale' THEN 2
+     WHEN 'unknown' THEN 3 ELSE 4 END
+   LIMIT 1),
+  'unknown')::text AS health
+`
+
+// An entity is as healthy as its unhealthiest check. Checks that have not run
+// yet (last_health IS NULL) are ignored rather than counted as unknown, so a
+// newly added check does not drag a known-good entity down before it has
+// produced a verdict.
+func (q *Queries) WorstHealthForTarget(ctx context.Context, targetID *uuid.UUID) (string, error) {
+	row := q.db.QueryRow(ctx, worstHealthForTarget, targetID)
+	var health string
+	err := row.Scan(&health)
+	return health, err
+}