feat(build): render client customizations

scripts/commands/build.sh

@@ -153,11 +153,17 @@ ${claude_rule_loading_list%$'\n'}"
 
 shared_template=$(<"$shared/global-instructions.md")
 general_content=$(<"$shared/rules/general.md")
+credential_helper_extension=sh
+[ "$shell" != powershell ] || credential_helper_extension=ps1
 
 agents_content=${shared_template//__RULE_LOADING__/$codex_rule_loading}
+agents_content=${agents_content//__CLIENT__/codex}
+agents_content=${agents_content//__SHELL__/$credential_helper_extension}
 printf '%s\n\n---\n\n%s\n' "${agents_content%$'\n'}" "$general_content" > "$output/codex-$shell/AGENTS.md"
 
 claude_content=${shared_template//__RULE_LOADING__/$claude_rule_loading}
+claude_content=${claude_content//__CLIENT__/claude}
+claude_content=${claude_content//__SHELL__/$credential_helper_extension}
 printf '%s\n\n---\n\n%s\n' "${claude_content%$'\n'}" "$general_content" > "$output/claude-$shell/CLAUDE.md"
 
 cp "$root/adapters/codex/config/config.toml" "$output/codex-$shell/config.toml"