feat(shopfloor): fpRpc skips tablet_tech_id injection in session_swap mode

When tablet_session_mode='session_swap', the server attributes every
write via request.env.user — there's no need to pass tablet_tech_id
in the RPC params. Caches the mode lookup at module level so we don't
round-trip on every RPC.

Legacy mode unchanged — fpRpc still injects tablet_tech_id from
techStore.currentTechId.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

fusion_plating/fusion_plating_shopfloor/static/src/js/services/fp_rpc.js

@@ -16,10 +16,37 @@
 //   import { fpRpc } from "../services/fp_rpc";
 //   await fpRpc("/fp/shopfloor/start_wo", { workorder_id: stepId });
 //
+// Phase D — in `session_swap` mode, the tablet operates on a REAL Odoo
+// session minted by /fp/tablet/unlock_session whose uid IS the tech.
+// In that mode tablet_tech_id is redundant; the server attributes the
+// write to request.env.user directly. We cache the mode at module
+// level (refresh on every page load, exactly when the session may
+// have flipped).
 // =============================================================================
 
 import { rpc as baseRpc } from "@web/core/network/rpc";
 
+let _sessionModeCache = null;  // 'legacy' | 'session_swap' | null (unknown)
+
+async function _getSessionMode() {
+    if (_sessionModeCache !== null) return _sessionModeCache;
+    try {
+        const res = await baseRpc("/web/dataset/call_kw", {
+            model: "ir.config_parameter",
+            method: "get_param",
+            args: ["fp.shopfloor.tablet_session_mode", "legacy"],
+            kwargs: {},
+        });
+        _sessionModeCache = res || "legacy";
+    } catch (e) {
+        // If the lookup fails (network blip, ACL change), fail SAFE
+        // to legacy — that keeps tablet_tech_id injection on so the
+        // server-side audit attribution still works.
+        _sessionModeCache = "legacy";
+    }
+    return _sessionModeCache;
+}
+
 function _getTechStore() {
     // Lazy-resolve via the global debug API — avoids circular service init
     try {
@@ -33,10 +60,13 @@ function _getTechStore() {
     return null;
 }
 
-export function fpRpc(url, params = {}) {
+export async function fpRpc(url, params = {}) {
-    const techStore = _getTechStore();
+    const mode = await _getSessionMode();
-    if (techStore && techStore.currentTechId) {
+    if (mode !== "session_swap") {
-        params = { ...params, tablet_tech_id: techStore.currentTechId };
+        const techStore = _getTechStore();
+        if (techStore && techStore.currentTechId) {
+            params = { ...params, tablet_tech_id: techStore.currentTechId };
+        }
     }
     return baseRpc(url, params);
 }