fix(web): the roster shows recipients as a list, never comma-joined (CL-8585)

Author: TheGreatAxios

agents/myra/src/system-prompt.ts

@@ -39,6 +39,7 @@ export const ASSISTANT_SYSTEM_PROMPT =
   "message. Never construct an address from an agent's name or slug " +
   "to reach it — that address does not route.\n" +
   "\n" +
-  "When you hand a task to another participant, copy the person's " +
-  'address from that same "Participants:" block in `to` so they can ' +
-  "follow the conversation, and give every mail you send a short subject.";
+  "When you hand a task to another participant, pass `to` as a list " +
+  'holding their address and the person\'s from that same "Participants:" ' +
+  "block, never one comma-joined string, so the person can follow the " +
+  "conversation, and give every mail you send a short subject.";

apps/web/src/chat/room-roster.test.ts

@@ -29,7 +29,7 @@ describe("appendRoster / stripRoster", () => {
     expect(withRoster).toBe(
       "Please pass this to the scribe.\n\n" +
         "Participants:\nSawyer <usr_sawyer@room.example>\nScribe <run_abc@room.example>\n\n" +
-        "Copy usr_sawyer@room.example in `to` on any mail you send another participant, so they can follow along, and give every mail a short subject.",
+        'When you mail another participant, pass `to` as a list with them and the person, e.g. `to: ["<their address>", "usr_sawyer@room.example"]`, never one comma-joined string, and give every mail a short subject.',
     );
     expect(stripRoster(withRoster)).toBe(body);
   });
@@ -41,7 +41,7 @@ describe("appendRoster / stripRoster", () => {
       { name: "Scribe", address: "run_abc@room.example", kind: "agent" },
     ]);
     expect(withRoster).toContain(
-      "Copy usr_sawyer@room.example, usr_alex@room.example in `to` on any mail you send another participant, so they can follow along, and give every mail a short subject.",
+      '`to: ["<their address>", "usr_sawyer@room.example", "usr_alex@room.example"]`',
     );
   });
 });

apps/web/src/chat/room-roster.ts

@@ -30,10 +30,11 @@ function rosterBlock(entries: readonly RosterEntry[]): string {
 function ccInstruction(entries: readonly RosterEntry[]): string | undefined {
   const people = entries.filter((entry) => entry.kind === "person");
   if (people.length === 0) return undefined;
-  const addresses = people.map((entry) => entry.address).join(", ");
-  // The subject clause is load-bearing: a mail with an empty Subject ends
-  // the receiving agent's run today.
-  return `Copy ${addresses} in \`to\` on any mail you send another participant, so they can follow along, and give every mail a short subject.`;
+  const quoted = people.map((entry) => `"${entry.address}"`).join(", ");
+  // The list shape and the subject clause are both load-bearing: a
+  // comma-joined `to` string is dropped as one bad recipient, and a mail
+  // with an empty Subject ends the receiving agent's run today.
+  return `When you mail another participant, pass \`to\` as a list with them and the person, e.g. \`to: ["<their address>", ${quoted}]\`, never one comma-joined string, and give every mail a short subject.`;
 }
 
 /** Appends a `Participants:` block listing every entry's name and address,