prompt: instruct agent to make parallel tool calls

Agents now know to batch independent reads and writes in a single
turn rather than serializing them across multiple turns.

cmd/olliesrv/internal/prompts/system_prompt.md

@@ -30,6 +30,15 @@ Tools are loaded at startup. Additional tools can be loaded at runtime via the `
 
 To see all available tools (loaded and unloaded): `ollie-9p read tools`
 
+## Parallel Calls
+
+Make independent tool calls in the same turn whenever possible. Non-conflicting calls execute in parallel automatically:
+- Multiple reads (file_read, file_grep, file_glob) — always parallel.
+- Multiple writes to different files (file_write, file_edit) — parallel.
+- Shell is always sequential (one at a time).
+
+Do NOT serialize calls that could be parallel. If you need to read 3 files, call file_read 3 times in one turn, not across 3 turns.
+
 ## Skills
 
 Use `skill_list` to discover available skills. Use `skill_load` to inject one into context. When you encounter a task that maps to an available skill, load it immediately without asking.