F6 deeper half: poll agent /disks/format/status on the 15s client timeout (slow USB mkfs runs detached) — agentapi.FormatStatus + awaitAgentFormat; then mount+register. Found on the live leg.

controller/internal/agentapi/client.go

@@ -661,6 +661,30 @@ func (c *Client) FormatDisk(ctx context.Context, device, fstype string, confirme
 	return out, nil
 }
 
+// FormatStatusResult mirrors GET /disks/format/status (F20-BUG3): the most-recent / in-flight format
+// job on the host. Phase ∈ idle | running | done | failed. The drive-init flow polls this to follow a
+// mkfs that outran the 15 s client timeout — the agent runs the mkfs DETACHED and keeps the record, so
+// the client can learn the real outcome instead of assuming failure (F6).
+type FormatStatusResult struct {
+	Phase  string `json:"phase"`
+	Device string `json:"device"`
+	FSType string `json:"fstype"`
+	Error  string `json:"error"`
+}
+
+// FormatStatus fetches the agent's most-recent format-job record.
+func (c *Client) FormatStatus(ctx context.Context) (FormatStatusResult, error) {
+	var out FormatStatusResult
+	body, err := c.get(ctx, "/disks/format/status")
+	if err != nil {
+		return out, err
+	}
+	if err := json.Unmarshal(body, &out); err != nil {
+		return out, fmt.Errorf("agentapi: decode /disks/format/status: %w", err)
+	}
+	return out, nil
+}
+
 // ---- NAS network storage (Part A2 → agent A1 /netstorage/*) ------------------------------
 //
 // A NAS share is a DISTINCT storage class from a drive: the controller proxies add/list/remove to the