fix(tui): render inline diffs inside assistant completion

Follow-up for #13729: segment-level system artifacts still looked detached in real flow.\n\nInstead of appending inline_diff as a standalone segment/system row, queue sanitized diffs during tool.complete and append them as a fenced diff block to the assistant completion text on message.complete. This keeps the diff in the same message flow as the assistant response.

ui-tui/src/app/turnController.ts

@@ -39,6 +39,7 @@ class TurnController {
   bufRef = ''
   interrupted = false
   lastStatusNote = ''
+  pendingInlineDiffs: string[] = []
   persistedToolLabels = new Set<string>()
   protocolWarned = false
   reasoningText = ''
@@ -76,6 +77,7 @@ class TurnController {
     this.activeTools = []
     this.streamTimer = clear(this.streamTimer)
     this.bufRef = ''
+    this.pendingInlineDiffs = []
     this.pendingSegmentTools = []
     this.segmentMessages = []
 
@@ -182,26 +184,14 @@ class TurnController {
     }, REASONING_PULSE_MS)
   }
 
-  /**
-   * Append an inline artifact (e.g. tool-complete inline diff) to the active
-   * turn's segment stream. Routing through `historyItems` via `sys()` lands
-   * the artifact above the currently-streaming assistant bubble; adding it
-   * here keeps the paint order aligned with the order the gateway emitted.
-   */
-  appendSegmentMessage(msg: Msg) {
-    this.flushStreamingSegment()
+  queueInlineDiff(diffText: string) {
+    const text = diffText.trim()
 
-    if (this.pendingSegmentTools.length) {
-      this.segmentMessages = [
-        ...this.segmentMessages,
-        { kind: 'trail', role: 'system', text: '', tools: this.pendingSegmentTools }
-      ]
-      this.pendingSegmentTools = []
-      patchTurnState({ streamPendingTools: [] })
+    if (!text) {
+      return
     }
 
-    this.segmentMessages = [...this.segmentMessages, msg]
-    patchTurnState({ streamSegments: this.segmentMessages })
+    this.pendingInlineDiffs = [...this.pendingInlineDiffs, text]
   }
 
   pushActivity(text: string, tone: ActivityItem['tone'] = 'info', replaceLabel?: string) {
@@ -238,6 +228,7 @@ class TurnController {
     this.idle()
     this.clearReasoning()
     this.clearStatusTimer()
+    this.pendingInlineDiffs = []
     this.pendingSegmentTools = []
     this.segmentMessages = []
     this.turnTools = []
@@ -248,6 +239,10 @@ class TurnController {
     const rawText = (payload.rendered ?? payload.text ?? this.bufRef).trimStart()
     const split = splitReasoning(rawText)
     const finalText = split.text
+    const inlineDiffBlock = this.pendingInlineDiffs.length
+      ? `\`\`\`diff\n${this.pendingInlineDiffs.join('\n\n')}\n\`\`\``
+      : ''
+    const mergedText = [finalText, inlineDiffBlock].filter(Boolean).join('\n\n')
     const existingReasoning = this.reasoningText.trim() || String(payload.reasoning ?? '').trim()
     const savedReasoning = [existingReasoning, existingReasoning ? '' : split.reasoning].filter(Boolean).join('\n\n')
     const savedReasoningTokens = savedReasoning ? estimateTokensRough(savedReasoning) : 0
@@ -255,10 +250,10 @@ class TurnController {
     const tools = this.pendingSegmentTools
     const finalMessages = [...this.segmentMessages]
 
-    if (finalText) {
+    if (mergedText) {
       finalMessages.push({
         role: 'assistant',
-        text: finalText,
+        text: mergedText,
         thinking: savedReasoning || undefined,
         thinkingTokens: savedReasoning ? savedReasoningTokens : undefined,
         toolTokens: savedToolTokens || undefined,
@@ -275,7 +270,7 @@ class TurnController {
     this.bufRef = ''
     patchTurnState({ activity: [], outcome: '' })
 
-    return { finalMessages, finalText, wasInterrupted }
+    return { finalMessages, finalText: mergedText, wasInterrupted }
   }
 
   recordMessageDelta({ rendered, text }: { rendered?: string; text?: string }) {
@@ -381,6 +376,7 @@ class TurnController {
     this.bufRef = ''
     this.interrupted = false
     this.lastStatusNote = ''
+    this.pendingInlineDiffs = []
     this.pendingSegmentTools = []
     this.protocolWarned = false
     this.segmentMessages = []
@@ -426,6 +422,7 @@ class TurnController {
     this.endReasoningPhase()
     this.clearReasoning()
     this.activeTools = []
+    this.pendingInlineDiffs = []
     this.turnTools = []
     this.toolTokenAcc = 0
     this.persistedToolLabels.clear()