Add OpenStock agent CLI skill

skills/openstock-agent-cli/references/commands/cache/guide.md

@@ -0,0 +1,39 @@
+# `openstock cache`
+
+## Purpose
+
+Inspect and prune local cache under `~/.config/openstock/cache`.
+
+## Subcommands
+
+| Command | Purpose |
+| --- | --- |
+| `openstock cache status` | Show cache size and namespace summary. |
+| `openstock cache prune [--dry-run]` | Apply cache retention policy. |
+
+## IO
+
+| Direction | Data |
+| --- | --- |
+| File read | Cache directories. |
+| File delete | Old cache files unless `--dry-run` is used. |
+| External IO | none |
+| Side effect | `prune` deletes files unless dry-run. |
+
+## Output Fields
+
+| Field | Meaning |
+| --- | --- |
+| `root` | Cache root path. |
+| `exists` | Whether cache root exists. |
+| `total_files` | Number of cache files. |
+| `total_bytes` | Total cache size. |
+| `namespaces` | Cache namespace summaries. |
+| `dry_run` | Whether prune only reported actions. |
+| `deleted_files` | Number of deleted files. |
+| `deleted_bytes` | Bytes removed. |
+| `reports` | Prune reports by namespace. |
+
+## Agent Notes
+
+Run `cache prune --dry-run` before destructive pruning unless the user clearly asks to clean cache.