claude-subagents skill: add concurrency guidance for container memory cap

claude-plugins/plugins/base/skills/claude-subagents/SKILL.md

@@ -96,6 +96,17 @@ running at once instead of handing the whole thing to one.
   same as the one-subagent case, just N background bash tasks instead of
   one. Check on them as a batch, not by polling each individually in a
   loop.
+- **Mind the container's memory cap before picking N.** Your whole
+  container shares one `MemoryMax` (a few GB by default) with every
+  subagent you spawn *and* your own process. A `claude` process plus its
+  MCP servers can hold several hundred MB to ~1GB depending on the task;
+  spawning a dozen at once on a small container doesn't just slow
+  things down, it can OOM the whole container — taking your own
+  in-flight turn down with it, not just the subagents. Rule of thumb:
+  **2-4 concurrent workers** on a default-sized container; check
+  `free -h` (or ask whoever owns the container's config for its
+  `MemoryMax`) before going higher, and chunk a bigger batch into
+  successive waves of that size rather than firing everything at once.
 - **You own the merge.** Once all N report done, review + verify each
   worker's slice (same "don't trust the self-report blind" rule as
   below), then combine — for a git-based split, that's you merging N