fix: resolve intermittent reasoning content not displayed for Claude Code provider (#5111)

- Modified fallback logic in stream parsing to handle all message types, not just assistant messages
- Added proper parsing attempts for partial data before yielding
- Improved error logging to help debug streaming issues
- Added debug logging (controlled by DEBUG_CLAUDE_CODE env var) to trace message types

This ensures reasoning/thinking content from Claude 3.5 Sonnet 4.0 is properly displayed in all cases.

Author: hannesrudolph

src/integrations/claude-code/run.ts

@@ -63,10 +63,21 @@ export async function* runClaudeCode(options: ClaudeCodeOptions): AsyncGenerator
 			}
 		}
 
-		// We rely on the assistant message. If the output was truncated, it's better having a poorly formatted message
-		// from which to extract something, than throwing an error/showing the model didn't return any messages.
-		if (processState.partialData && processState.partialData.startsWith(`{"type":"assistant"`)) {
-			yield processState.partialData
+		// Handle any remaining partial data that could be a valid message
+		// This helps recover from truncated output and ensures we don't lose reasoning/thinking content
+		if (processState.partialData) {
+			// Try to parse the partial data as it might be a complete message
+			const partialChunk = attemptParseChunk(processState.partialData)
+			if (partialChunk) {
+				yield partialChunk
+			} else {
+				// If it's not parseable but looks like it could be a message, yield it as raw string
+				// The provider will handle string messages appropriately
+				const partialTrimmed = processState.partialData.trim()
+				if (partialTrimmed.startsWith('{"type":') && partialTrimmed.includes('"message"')) {
+					yield processState.partialData
+				}
+			}
 		}
 
 		const { exitCode } = await process
@@ -169,9 +180,24 @@ function parseChunk(data: string, processState: ProcessState) {
 
 function attemptParseChunk(data: string): ClaudeCodeMessage | null {
 	try {
-		return JSON.parse(data)
+		const parsed = JSON.parse(data)
+		// Log message types for debugging streaming issues
+		if (parsed?.type && process.env.DEBUG_CLAUDE_CODE) {
+			console.debug(`Claude Code message type: ${parsed.type}`, {
+				hasMessage: !!parsed.message,
+				contentTypes: parsed.message?.content?.map((c: any) => c.type) || [],
+			})
+		}
+		return parsed
 	} catch (error) {
-		console.error("Error parsing chunk:", error, data.length)
+		// Only log errors for non-empty data
+		if (data.trim()) {
+			console.error(
+				"Error parsing chunk:",
+				error,
+				`Length: ${data.length}, Preview: ${data.substring(0, 100)}...`,
+			)
+		}
 		return null
 	}
 }