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

packages/mosaic/src/commands/fleet.spec.ts

@@ -10,6 +10,7 @@ import {
   getDefaultOperatorSourceLabel,
   getRosterAgent,
   loadFleetRoster,
+  mergeAgentEnv,
   registerFleetCommand,
   resolveFleetPaths,
   type CommandRunner,
@@ -121,6 +122,37 @@ describe('fleet roster parsing', () => {
     );
   });
 
+  it('preserves site-owned agent EnvironmentFile overrides while refreshing roster keys', () => {
+    const generated = [
+      'MOSAIC_AGENT_NAME=coder0',
+      'MOSAIC_AGENT_RUNTIME=codex',
+      'MOSAIC_AGENT_WORKDIR=/srv/new',
+      'MOSAIC_TMUX_SOCKET=mosaic-factory',
+      '',
+    ].join('\n');
+    const existing = [
+      'MOSAIC_AGENT_NAME=old-name',
+      'MOSAIC_AGENT_RUNTIME=old-runtime',
+      'MOSAIC_AGENT_WORKDIR=/srv/old',
+      'MOSAIC_TMUX_SOCKET=old-socket',
+      'MOSAIC_AGENT_COMMAND=/home/jarvis/.config/mosaic/fleet/canary.sh',
+      '# site note',
+      '',
+    ].join('\n');
+
+    expect(mergeAgentEnv(generated, existing)).toBe(
+      [
+        'MOSAIC_AGENT_NAME=coder0',
+        'MOSAIC_AGENT_RUNTIME=codex',
+        'MOSAIC_AGENT_WORKDIR=/srv/new',
+        'MOSAIC_TMUX_SOCKET=mosaic-factory',
+        'MOSAIC_AGENT_COMMAND=/home/jarvis/.config/mosaic/fleet/canary.sh',
+        '# site note',
+        '',
+      ].join('\n'),
+    );
+  });
+
   it('rejects unknown roster fields instead of silently defaulting', async () => {
     cleanup = await tempDir();
     const rosterPath = join(cleanup, 'roster.yaml');