Keep deployment logs findable after the container is recreated (closes #214)

Deployment log files were stored under a directory named after the
container's hostname, which Docker changes whenever the container is
recreated, so every older log download returned 404. Logs now live under
logs/<appname>/. The download handler still finds logs written by older
versions under any hostname directory.

Model: opus-5-5

internal/handlers/app.go

@@ -6,9 +6,11 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io/fs"
 	"net/http"
 	"net/url"
 	"os"
+	"path"
 	"path/filepath"
 	"strconv"
 	"strings"
@@ -640,7 +642,7 @@ func (h *Handlers) HandleDeploymentLogDownload() http.HandlerFunc {
 		}
 		defer func() { _ = root.Close() }()
 
-		file, openErr := root.Open(relPath)
+		file, openErr := openDeploymentLog(root, relPath)
 		if openErr != nil {
 			http.NotFound(writer, request)
 
@@ -665,6 +667,24 @@ func (h *Handlers) HandleDeploymentLogDownload() http.HandlerFunc {
 	}
 }
 
+// openDeploymentLog opens a deployment log file inside the log root.
+// Logs written by older versions sit one directory deeper, under the
+// hostname of the container that wrote them, so when the file is not at
+// relPath it is looked for under any directory directly below the root.
+func openDeploymentLog(root *os.Root, relPath string) (*os.File, error) {
+	file, err := root.Open(relPath)
+	if err == nil {
+		return file, nil
+	}
+
+	matches, globErr := fs.Glob(root.FS(), path.Join("*", filepath.ToSlash(relPath)))
+	if globErr != nil || len(matches) == 0 {
+		return nil, err
+	}
+
+	return root.Open(matches[0])
+}
+
 // containerLogsAPITail is the default number of log lines for the container logs API.
 const containerLogsAPITail = "100"