fix(fleet): preserve agent env overrides on install (#567)

packages/mosaic/src/commands/fleet.ts

@@ -148,6 +148,29 @@ export function generateAgentEnv(roster: FleetRoster, agent: FleetAgent): string
   ].join('\n');
 }
 
+export function mergeAgentEnv(generatedEnv: string, existingEnv?: string): string {
+  if (!existingEnv?.trim()) {
+    return generatedEnv;
+  }
+  const generatedKeys = new Set(
+    generatedEnv
+      .split('\n')
+      .map((line) => line.match(/^([A-Za-z_][A-Za-z0-9_]*)=/)?.[1])
+      .filter((key): key is string => key !== undefined),
+  );
+  const preservedLines = existingEnv.split('\n').filter((line) => {
+    if (!line.trim()) {
+      return false;
+    }
+    const key = line.match(/^([A-Za-z_][A-Za-z0-9_]*)=/)?.[1];
+    return key === undefined || !generatedKeys.has(key);
+  });
+  if (preservedLines.length === 0) {
+    return generatedEnv;
+  }
+  return [generatedEnv.trimEnd(), ...preservedLines, ''].join('\n');
+}
+
 export function buildFleetServiceCommand(action: FleetServiceAction, agentName?: string): string[] {
   const service = agentName ? `mosaic-agent@${agentName}.service` : 'mosaic-tmux-holder.service';
   return ['systemctl', '--user', action, service];
@@ -477,10 +500,9 @@ async function installFleet(cmd: Command, frameworkRoot: string): Promise<void>
   );
 
   for (const agent of roster.agents) {
-    await writeFile(
-      join(activePaths.agentEnvDir, `${agent.name}.env`),
-      generateAgentEnv(roster, agent),
-    );
+    const envPath = join(activePaths.agentEnvDir, `${agent.name}.env`);
+    const existingEnv = (await canRead(envPath)) ? await readFile(envPath, 'utf8') : undefined;
+    await writeFile(envPath, mergeAgentEnv(generateAgentEnv(roster, agent), existingEnv));
   }
 
   console.log(`Installed fleet files for ${roster.agents.length} agent(s).`);