feat(prompt): say which Chrome browser_* drives

The prompt told the model it drives "the user's running instance". With this
fork's default that is wrong: it is castle's shared Chrome, signed out of every
account. It now matters which is which, because pi-chrome's chrome_* tools
drive the user's signed-in Brave, and the model has to route between the two.

getBrowserSystemPrompt() takes the resolved target and describes it: castle's
shared browser for the built-in default, the user's own Chrome for local, the
endpoint otherwise.

2 files changed, 21 insertions, 3 deletions

diff --git a/src/index.ts b/src/index.ts
index 152c94d..e4d23f8 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -261,8 +261,9 @@ export default function browserHarnessExtension(pi: ExtensionAPI): void {
   });
 
   pi.on("before_agent_start", async (event) => {
+    const target = resolveCdpTarget(process.env, await readTarget());
     return {
-      systemPrompt: event.systemPrompt + getBrowserSystemPrompt(client?.status().alive ?? false),
+      systemPrompt: event.systemPrompt + getBrowserSystemPrompt(client?.status().alive ?? false, target),
     };
   });
 }
diff --git a/src/prompt.ts b/src/prompt.ts
index 4fb78a7..db0e6a4 100644
--- a/src/prompt.ts
+++ b/src/prompt.ts
@@ -1,11 +1,28 @@
-export function getBrowserSystemPrompt(connected = true): string {
+import { type CdpTarget, DEFAULT_REMOTE_CDP } from "./cdp/endpoint";
+
+/**
+ * FORK: which Chrome browser_* drives. Upstream always means "the user's own
+ * Chrome"; here the default is castle's shared one, signed out of everything,
+ * and pi-chrome's chrome_* tools drive a signed-in Brave - so the model has to
+ * be told which is which to route between them.
+ */
+const describeChrome = (target?: CdpTarget): string => {
+  if (!target || target.kind === "invalid") return "a real Chrome (not headless)";
+  if (target.kind === "local") return "a real Chrome (the user's own, on this machine)";
+  if (`${target.host}:${target.port}` === DEFAULT_REMOTE_CDP) {
+    return "a real Chrome (castle's shared browser on the wire network, signed out of every account — not the user's own browser)";
+  }
+  return `a real Chrome (the one at ${target.host}:${target.port})`;
+};
+
+export function getBrowserSystemPrompt(connected = true, target?: CdpTarget): string {
   const connectionNotice = connected
     ? ""
     : "Browser is not connected. Run browser_setup or /browser-setup to connect.\n\n";
   return `
 ## Browser Control
 
-${connectionNotice}You control the user's running Chrome through \`browser_*\` tools alongside the
+${connectionNotice}You control ${describeChrome(target)} through \`browser_*\` tools alongside the
 standard pi tools. Per-tool usage lives in tool descriptions, parameter schemas,
 and tool-specific guidelines.