feat(completion): annotate the file-basename pickers with size and date

Eight completing-read pickers listed bare file basenames, so marginalia had no directory to resolve and couldn't annotate them. Add cj/completion-file-annotator to system-lib — an annotation-function factory that takes a candidate->path resolver and yields a size + modification-date suffix (or "dir" for directories, nil for missing files). Wire each picker through cj/completion-table-annotated with a per-site category and resolver: timer sounds, drill flashcards, Info files, the test-runner focus add/remove, vc clone dirs, hugo drafts, and agenda projects (the project's todo.org mtime). music-config's existing completion table gains the category and annotator inline, keeping its sort metadata.

The candidate strings and every return value are unchanged — this only adds completion metadata — so all downstream logic is untouched. The six modules that didn't already pull in system-lib now require it.

Tests: cj/completion-file-annotator gets Normal/Boundary/Error coverage (file, directory, nil path, missing file). Full suite green at 5394.

Claude-Session: https://claude.ai/code/session_014fyKMTTqLrZpL3rDF3dYc3

1 files changed, 18 insertions, 8 deletions

diff --git a/modules/music-config.el b/modules/music-config.el
index c627d799..d16e2bb2 100644
--- a/modules/music-config.el
+++ b/modules/music-config.el
@@ -219,14 +219,24 @@ Directories are suffixed with /; files are plain. Hidden dirs/files skipped."
     (sort acc #'string-lessp)))
 
 (defun cj/music--completion-table (candidates)
-  "Completion table for CANDIDATES preserving order and case-insensitive match."
-  (lambda (string pred action)
-    (if (eq action 'metadata)
-        '(metadata
-          (display-sort-function . identity)
-          (cycle-sort-function . identity)
-          (completion-ignore-case . t))
-      (complete-with-action action candidates string pred))))
+  "Completion table for CANDIDATES preserving order and case-insensitive match.
+Tags the `cj-music-file' category and annotates each candidate (a path relative
+to `cj/music-root', with a trailing slash for directories) with its size and
+modification date so marginalia can show them."
+  (let ((annotate (cj/completion-file-annotator
+                   (lambda (c)
+                     (expand-file-name
+                      (if (string-suffix-p "/" c) (substring c 0 -1) c)
+                      cj/music-root)))))
+    (lambda (string pred action)
+      (if (eq action 'metadata)
+          `(metadata
+            (category . cj-music-file)
+            (annotation-function . ,annotate)
+            (display-sort-function . identity)
+            (cycle-sort-function . identity)
+            (completion-ignore-case . t))
+        (complete-with-action action candidates string pred)))))
 
 (defun cj/music--ensure-playlist-buffer ()
   "Ensure EMMS playlist buffer exists and is in playlist mode. Return buffer."