feat: vendor permission system source

pi-permission-system/src/active-agent.ts

@@ -0,0 +1,72 @@
+/**
+ * Minimal session-entry view: the only fields {@link getActiveAgentName}
+ * reads off each entry. Narrowing to this structural slice (rather than the
+ * SDK `SessionEntry` discriminated union) keeps callers and test fixtures free
+ * of the union's nine unrelated variants.
+ */
+export interface SessionEntryView {
+  type: string;
+  customType?: string;
+  data?: unknown;
+}
+
+/**
+ * Narrow context for {@link getActiveAgentName} — it reads only the session
+ * entries. A full `ExtensionContext` satisfies this structurally.
+ */
+export interface ActiveAgentContext {
+  sessionManager: { getEntries(): readonly SessionEntryView[] };
+}
+
+/**
+ * Matches the `<active_agent name="...">` tag injected by pi-agent-router
+ * into the system prompt to identify which agent definition is active.
+ */
+export const ACTIVE_AGENT_TAG_REGEX =
+  /<active_agent\s+name=["']([^"']+)["'][^>]*>/i;
+
+export function normalizeAgentName(value: unknown): string | null {
+  if (typeof value !== "string") {
+    return null;
+  }
+
+  const trimmed = value.trim();
+  return trimmed ? trimmed : null;
+}
+
+export function getActiveAgentName(ctx: ActiveAgentContext): string | null {
+  const entries = ctx.sessionManager.getEntries();
+  for (let i = entries.length - 1; i >= 0; i--) {
+    const entry = entries[i];
+    if (entry.type !== "custom" || entry.customType !== "active_agent") {
+      continue;
+    }
+
+    const data = entry.data as { name?: unknown } | undefined;
+    const normalizedName = normalizeAgentName(data?.name);
+    if (normalizedName) {
+      return normalizedName;
+    }
+
+    if (data?.name === null) {
+      return null;
+    }
+  }
+
+  return null;
+}
+
+export function getActiveAgentNameFromSystemPrompt(
+  systemPrompt: string | undefined,
+): string | null {
+  if (!systemPrompt) {
+    return null;
+  }
+
+  const match = ACTIVE_AGENT_TAG_REGEX.exec(systemPrompt);
+  if (!match?.[1]) {
+    return null;
+  }
+
+  return normalizeAgentName(match[1]);
+}