diff --git a/scripts/sx-primitives-up.sh b/scripts/sx-primitives-up.sh
new file mode 100755
index 00000000..756264d7
--- /dev/null
+++ b/scripts/sx-primitives-up.sh
@@ -0,0 +1,121 @@
+#!/usr/bin/env bash
+# Spawn a single claude session to implement SX primitives in sequence.
+# Runs in its own git worktree on branch sx-primitives from architecture.
+#
+# Usage: ./scripts/sx-primitives-up.sh [interval]
+#   interval defaults to self-paced (omit to let model decide)
+#
+# After the script prints done:
+#   tmux a -t sx-primitives
+#   Ctrl-B + d to detach
+#
+# Stop: ./scripts/sx-primitives-down.sh
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+cd "$ROOT"
+SESSION="sx-primitives"
+WORKTREE="$ROOT"          # runs in the main worktree — architecture branch
+BRANCH="architecture"
+INTERVAL="${1:-}"
+BOOT_WAIT=20
+
+if tmux has-session -t "$SESSION" 2>/dev/null; then
+  echo "Session '$SESSION' already exists."
+  echo "  Attach:  tmux a -t $SESSION"
+  echo "  Kill:    ./scripts/sx-primitives-down.sh"
+  exit 1
+fi
+
+# Write settings into the main worktree .claude dir
+SETTINGS_DIR="$ROOT/.claude"
+mkdir -p "$SETTINGS_DIR"
+cat > "$SETTINGS_DIR/settings.local.json" <<'SETTINGS'
+{
+  "permissions": {
+    "allow": [
+      "mcp__sx-tree__sx_summarise",
+      "mcp__sx-tree__sx_read_tree",
+      "mcp__sx-tree__sx_read_subtree",
+      "mcp__sx-tree__sx_get_context",
+      "mcp__sx-tree__sx_find_all",
+      "mcp__sx-tree__sx_find_across",
+      "mcp__sx-tree__sx_get_siblings",
+      "mcp__sx-tree__sx_validate",
+      "mcp__sx-tree__sx_replace_node",
+      "mcp__sx-tree__sx_insert_child",
+      "mcp__sx-tree__sx_insert_near",
+      "mcp__sx-tree__sx_delete_node",
+      "mcp__sx-tree__sx_wrap_node",
+      "mcp__sx-tree__sx_rename_symbol",
+      "mcp__sx-tree__sx_replace_by_pattern",
+      "mcp__sx-tree__sx_rename_across",
+      "mcp__sx-tree__sx_write_file",
+      "mcp__sx-tree__sx_pretty_print",
+      "mcp__sx-tree__sx_eval",
+      "mcp__sx-tree__sx_harness_eval",
+      "mcp__sx-tree__sx_macroexpand",
+      "mcp__sx-tree__sx_trace",
+      "mcp__sx-tree__sx_deps",
+      "mcp__sx-tree__sx_diff",
+      "mcp__sx-tree__sx_diff_branch",
+      "mcp__sx-tree__sx_changed",
+      "mcp__sx-tree__sx_blame",
+      "mcp__sx-tree__sx_build",
+      "mcp__sx-tree__sx_build_manifest",
+      "mcp__sx-tree__sx_build_bytecode",
+      "mcp__sx-tree__sx_test",
+      "mcp__sx-tree__sx_format_check",
+      "mcp__sx-tree__sx_comp_list",
+      "mcp__sx-tree__sx_comp_usage",
+      "mcp__sx-tree__sx_nav",
+      "mcp__sx-tree__sx_env",
+      "mcp__sx-tree__sx_playwright",
+      "mcp__hs-test__hs_test_run",
+      "mcp__hs-test__hs_test_regen",
+      "mcp__hs-test__hs_test_kill",
+      "mcp__hs-test__hs_test_status",
+      "Bash(node *)",
+      "Bash(python3 *)",
+      "Bash(bash *)",
+      "Bash(cp *)",
+      "Bash(git *)",
+      "Bash(tmux *)"
+    ]
+  },
+  "enabledMcpjsonServers": [
+    "sx-tree",
+    "rose-ash-services",
+    "hs-test"
+  ]
+}
+SETTINGS
+
+echo "Creating tmux session '$SESSION' in $ROOT ..."
+tmux new-session -d -s "$SESSION" -n "primitives" -c "$ROOT"
+
+echo "Starting claude..."
+tmux send-keys -t "$SESSION:primitives" "claude" C-m
+
+echo "Waiting ${BOOT_WAIT}s for claude to boot..."
+sleep "$BOOT_WAIT"
+
+if [ -n "$INTERVAL" ]; then
+  preamble="/loop $INTERVAL "
+else
+  preamble="/loop "
+fi
+
+cmd="${preamble}Read plans/agent-briefings/primitives-loop.md and do ONE step per fire: find the first unchecked [ ] task, implement it fully, run the relevant tests to verify, commit with a short factual message, push to origin/architecture, tick the box [x] in the plan, append one dated line to the Progress log (newest first), then stop. You are on branch architecture in /root/rose-ash. Use sx-tree MCP for all .sx edits. Never push to main."
+
+tmux send-keys -t "$SESSION:primitives" "$cmd"
+sleep 0.5
+tmux send-keys -t "$SESSION:primitives" Enter
+
+echo ""
+echo "Done. SX primitives loop started in tmux session '$SESSION'."
+echo ""
+echo "  Attach:    tmux a -t $SESSION"
+echo "  Detach:    Ctrl-B d"
+echo "  Stop:      ./scripts/sx-primitives-down.sh"
+echo ""