feat: improve AI chat - system prompt, tool output, context window display (#17769)

⚠️ **AI-generated PR — not ready for review** ⚠️

cc @FelixMalfait

---

## Changes

### System prompt improvements
- Explicit skill-before-tools workflow to prevent the model from calling
tools without loading the matching skill first
- Data efficiency guidance (default small limits, use filters)
- Pluralized `load_skill` → `load_skills` for consistency with
`load_tools`

### Token usage reduction
- Output serialization layer: strips null/undefined/empty values from
tool results
- Lowered default `find_*` limit from 100 → 10, max from 1000 → 100

### System object tool generation
- System objects (calendar events, messages, etc.) now generate AI tools
- Only workflow-related and favorite-related objects are excluded

### Context window display fix
- **Bug**: UI compared cumulative tokens (sum of all turns) against
single-request context window → showed 100% after a few turns
- **Fix**: Track `conversationSize` (last step's `inputTokens`) which
represents the actual conversation history size sent to the model
- New `conversationSize` column on thread entity with migration

### Workspace AI instructions
- Support for custom workspace-level AI instructions

---------

Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>

packages/twenty-front/src/modules/ai/hooks/useAgentChat.ts

@@ -119,8 +119,10 @@ export const useAgentChat = (uiMessages: ExtendedUIMessage[]) => {
       type UsageMetadata = {
         inputTokens: number;
         outputTokens: number;
+        cachedInputTokens: number;
         inputCredits: number;
         outputCredits: number;
+        conversationSize: number;
       };
       type ModelMetadata = {
         contextWindowTokens: number;
@@ -133,11 +135,17 @@ export const useAgentChat = (uiMessages: ExtendedUIMessage[]) => {
 
       if (isDefined(usage) && isDefined(model)) {
         setAgentChatUsage((prev) => ({
+          lastMessage: {
+            inputTokens: usage.inputTokens,
+            outputTokens: usage.outputTokens,
+            cachedInputTokens: usage.cachedInputTokens,
+            inputCredits: usage.inputCredits,
+            outputCredits: usage.outputCredits,
+          },
+          conversationSize: usage.conversationSize,
+          contextWindowTokens: model.contextWindowTokens,
           inputTokens: (prev?.inputTokens ?? 0) + usage.inputTokens,
           outputTokens: (prev?.outputTokens ?? 0) + usage.outputTokens,
-          totalTokens:
-            (prev?.totalTokens ?? 0) + usage.inputTokens + usage.outputTokens,
-          contextWindowTokens: model.contextWindowTokens,
           inputCredits: (prev?.inputCredits ?? 0) + usage.inputCredits,
           outputCredits: (prev?.outputCredits ?? 0) + usage.outputCredits,
         }));

packages/twenty-front/src/modules/ai/hooks/useAgentChatData.ts

@@ -23,16 +23,17 @@ const setUsageFromThread = (
   thread: AgentChatThread,
   setAgentChatUsage: SetterOrUpdater<AgentChatUsageState | null>,
 ) => {
-  const totalTokens = thread.totalInputTokens + thread.totalOutputTokens;
-  const hasUsageData = totalTokens > 0 && isDefined(thread.contextWindowTokens);
+  const hasUsageData =
+    (thread.conversationSize ?? 0) > 0 && isDefined(thread.contextWindowTokens);
 
   setAgentChatUsage(
     hasUsageData
       ? {
+          lastMessage: null,
+          conversationSize: thread.conversationSize ?? 0,
+          contextWindowTokens: thread.contextWindowTokens ?? 0,
           inputTokens: thread.totalInputTokens,
           outputTokens: thread.totalOutputTokens,
-          totalTokens,
-          contextWindowTokens: thread.contextWindowTokens ?? 0,
           inputCredits: thread.totalInputCredits,
           outputCredits: thread.totalOutputCredits,
         }