store: give ecosystem traces their own table

Traces were written as facts. A single Praxis action wrote several of
them, so machine-rate rows crowded out the bounded fact readers that
humans and evaluation consume. The habit profile window of 2000 facts
and the memeval snapshot both filled with call records instead of what
Maven learned about the owner. Traces now go to ecosystem_traces, with
correlation, causation, duration and HTTP status as columns, pruned to
the most recent 5000. The new reader is exposed over IPC and rendered
as the Calls card on the ecosystem page, so it is a table someone
actually looks at.

Found in review of #84.

internal/ipc/api.go

@@ -24,6 +24,23 @@ type Fact struct {
 	VoidsID    *int64    `json:"voids_id,omitempty"`
 }
 
+// EcosystemTrace — one hop of a cross-service ecosystem call, read by the
+// monitoring surfaces. Traces live in their own store table, not in facts:
+// they are written at machine rate and would otherwise crowd every bounded
+// reader of facts.
+type EcosystemTrace struct {
+	ID            int64          `json:"id"`
+	Ts            time.Time      `json:"ts"`
+	Service       string         `json:"service"`
+	Operation     string         `json:"operation"`
+	Status        string         `json:"status"`
+	DurationMs    int64          `json:"duration_ms"`
+	CorrelationID string         `json:"correlation_id"`
+	CausationID   string         `json:"causation_id"`
+	HTTPStatus    int            `json:"http_status"`
+	Fields        map[string]any `json:"fields,omitempty"`
+}
+
 // Bucket — presence hysteresis state: "present" | "away".
 type Bucket string
 
@@ -588,6 +605,10 @@ type CoreAPI interface {
 	RecentFacts(ctx context.Context, n int) ([]Fact, error)
 	CalendarEvents(ctx context.Context, from, to time.Time) ([]Fact, error)
 	RecentNudges(ctx context.Context, n int) ([]Nudge, error)
+
+	// RecentEcosystemTraces reads the ecosystem call log, which lives in its
+	// own table so machine-rate traces never crowd out human-rate facts.
+	RecentEcosystemTraces(ctx context.Context, n int) ([]EcosystemTrace, error)
 	WriteNote(ctx context.Context, ts time.Time, text string, embedding []float32, source string) (int64, error)
 	QueryNotes(ctx context.Context, embedding []float32, k int) ([]Note, error)
 	RecentNotes(ctx context.Context, n int) ([]Note, error)