fix: guarantee text response when agent loop produces only thinking blocks

Remove MAX_TOOL_ROUNDS cap so the model decides when to stop calling
tools. Add a safety net that makes a final tool-free API call if the
loop ends without emitting any visible text, fixing empty assistant
bubbles. Clean up redundant comments.

js/cf-webapp/src/app/api/observability/chat/route.ts

@@ -14,7 +14,6 @@ interface ChatMessage {
   content: string
 }
 
-const MAX_TOOL_ROUNDS = 15
 const KEEPALIVE_INTERVAL_MS = 15_000
 const ROUND_TIMEOUT_MS = 3 * 60_000 // 3 minutes per API round
 
@@ -76,7 +75,6 @@ async function processToolCalls(
   )
   if (toolUseBlocks.length === 0) return []
 
-  // Emit tool_start events for all tools
   for (const block of toolUseBlocks) {
     enqueue(
       `data: ${JSON.stringify({
@@ -87,7 +85,6 @@ async function processToolCalls(
     )
   }
 
-  // Execute all tool calls in parallel
   const results = await Promise.all(
     toolUseBlocks.map(async (block) => {
       const result = await resolveToolCall(
@@ -116,10 +113,6 @@ async function processToolCalls(
   return results
 }
 
-// Shared base params for both streaming and non-streaming calls.
-// Adaptive thinking lets Claude decide how much reasoning is needed per request.
-// On Opus 4.6, this automatically enables interleaved thinking (thinking between
-// tool calls) without needing a beta header.
 function baseParams(
   systemPrompt: string,
   conversationMessages: Anthropic.MessageParam[],
@@ -181,19 +174,13 @@ export async function POST(request: NextRequest): Promise<Response> {
       const keepalive = setInterval(() => enqueue(": keepalive\n\n"), KEEPALIVE_INTERVAL_MS)
 
       try {
-        // Unified agent loop — each iteration either processes tool calls or
-        // extracts the final text. Uses stream()+finalMessage() to avoid the
-        // SDK's non-streaming timeout (max_tokens 32k estimates >10min).
-        // Each round has a timeout to catch silent connection drops from the
-        // Azure AI Foundry proxy. Thinking blocks from older rounds are
-        // redacted (emptied) before each call to keep context size manageable.
         let toolRounds = 0
-        while (toolRounds <= MAX_TOOL_ROUNDS) {
+        let emittedText = false
+        // eslint-disable-next-line no-constant-condition
+        while (true) {
           enqueue(`data: ${JSON.stringify({ type: "status", message: toolRounds === 0 ? "Thinking…" : "Analyzing…" })}\n\n`)
 
-          // Redact thinking content from previous assistant messages to prevent
-          // context blowup. The API requires the block structure but allows
-          // empty content. Each round's thinking can be 10-50KB.
+          // Redact thinking blocks from prior rounds (each can be 10-50KB)
           for (const msg of conversationMessages) {
             if (msg.role !== "assistant" || !Array.isArray(msg.content)) continue
             for (const block of msg.content) {
@@ -214,8 +201,9 @@ export async function POST(request: NextRequest): Promise<Response> {
 
           if (response.stop_reason !== "tool_use") {
             for (const block of response.content) {
-              if (block.type === "text") {
+              if (block.type === "text" && block.text) {
                 enqueue(`data: ${JSON.stringify({ type: "text", text: block.text })}\n\n`)
+                emittedText = true
               }
             }
             break
@@ -227,6 +215,34 @@ export async function POST(request: NextRequest): Promise<Response> {
           toolRounds++
         }
 
+        // Force a text response if the model only produced thinking blocks
+        if (!emittedText) {
+          enqueue(`data: ${JSON.stringify({ type: "status", message: "Summarizing…" })}\n\n`)
+
+          for (const msg of conversationMessages) {
+            if (msg.role !== "assistant" || !Array.isArray(msg.content)) continue
+            for (const block of msg.content) {
+              if ((block as { type: string }).type === "thinking") {
+                (block as { thinking: string }).thinking = ""
+              }
+            }
+          }
+
+          const { tools: _, ...noToolsParams } = baseParams(systemPrompt, conversationMessages)
+          const finalStream = client.messages.stream(noToolsParams)
+          const timeout = setTimeout(() => finalStream.abort(), ROUND_TIMEOUT_MS)
+          try {
+            const finalResponse = await finalStream.finalMessage()
+            for (const block of finalResponse.content) {
+              if (block.type === "text") {
+                enqueue(`data: ${JSON.stringify({ type: "text", text: block.text })}\n\n`)
+              }
+            }
+          } finally {
+            clearTimeout(timeout)
+          }
+        }
+
         enqueue("data: [DONE]\n\n")
       } catch (err) {
         const message = err instanceof Anthropic.APIError