Add system prompt options to extension commands

packages/coding-agent/docs/extensions.md

@@ -982,6 +982,19 @@ pi.on("before_agent_start", (event, ctx) => {
 
 Command handlers receive `ExtensionCommandContext`, which extends `ExtensionContext` with session control methods. These are only available in commands because they can deadlock if called from event handlers.
 
+### ctx.getSystemPromptOptions()
+
+Returns the base inputs Pi currently uses to build the system prompt.
+
+```typescript
+const options = ctx.getSystemPromptOptions();
+const contextPaths = options.contextFiles?.map((file) => file.path) ?? [];
+```
+
+This has the same shape and mutability as `before_agent_start` `event.systemPromptOptions`: custom prompt, active tools, tool snippets, prompt guidelines, appended system prompt text, cwd, loaded context files, and loaded skills. It may include full context file contents, so treat it as sensitive extension-local data and avoid exposing it through command lists, logs, or autocomplete metadata.
+
+This reports the current base prompt inputs. It does not include per-turn `before_agent_start` chained system-prompt changes, later `context` event message mutations, or `before_provider_request` payload rewrites.
+
 ### ctx.waitForIdle()
 
 Wait for the agent to finish streaming: