fix: improve Claude Code provider JSON handling and test reliability

- Remove unnecessary type assertion for better type safety
- Add isLikelyValidJSON helper to validate JSON structure before processing
- Implement getContentText helper for cleaner error message extraction
- Standardize buffer trimming logic across the codebase
- Enhance error logging with data preview for better debugging
- Replace setTimeout with setImmediate for more reliable test timing
- Add test case for incomplete JSON handling on process close

These changes address all review feedback and improve the robustness
of JSON parsing in the Claude Code provider.

Author: daniel-lxs

src/api/providers/__tests__/claude-code.spec.ts

@@ -206,4 +206,25 @@ describe("ClaudeCodeHandler", () => {
 		// Should throw error with thinking content
 		await expect(streamGenerator.next()).rejects.toThrow("This is an error scenario")
 	})
+
+	test("should handle incomplete JSON in buffer on process close", async () => {
+		const systemPrompt = "You are a helpful assistant"
+		const messages = [{ role: "user" as const, content: "Hello" }]
+
+		const stream = handler.createMessage(systemPrompt, messages)
+		const streamGenerator = stream[Symbol.asyncIterator]()
+
+		// Simulate incomplete JSON data followed by process close
+		setImmediate(() => {
+			// Send incomplete JSON (missing closing brace)
+			mockProcess.stdout.emit("data", '{"type":"assistant","message":{"id":"msg_123"')
+			setImmediate(() => {
+				mockProcess.emit("close", 0)
+			})
+		})
+
+		// Should complete without throwing, incomplete JSON should be discarded
+		const result = await streamGenerator.next()
+		expect(result.done).toBe(true)
+	})
 })

src/api/providers/claude-code.ts

@@ -55,7 +55,15 @@ export class ClaudeCodeHandler extends BaseProvider implements ApiHandler {
 			// Process any remaining data in buffer
 			const trimmedBuffer = buffer.trim()
 			if (trimmedBuffer) {
-				dataQueue.push(trimmedBuffer)
+				// Validate that the remaining buffer looks like valid JSON before processing
+				if (this.isLikelyValidJSON(trimmedBuffer)) {
+					dataQueue.push(trimmedBuffer)
+				} else {
+					console.warn(
+						"Discarding incomplete JSON data on process close:",
+						trimmedBuffer.substring(0, 100) + (trimmedBuffer.length > 100 ? "..." : ""),
+					)
+				}
 				buffer = ""
 			}
 		})
@@ -191,6 +199,30 @@ export class ClaudeCodeHandler extends BaseProvider implements ApiHandler {
 		}
 	}
 
+	private isLikelyValidJSON(data: string): boolean {
+		// Basic validation to check if the data looks like it could be valid JSON
+		const trimmed = data.trim()
+		if (!trimmed) return false
+
+		// Must start and end with appropriate JSON delimiters
+		const startsCorrectly = trimmed.startsWith("{") || trimmed.startsWith("[")
+		const endsCorrectly = trimmed.endsWith("}") || trimmed.endsWith("]")
+
+		if (!startsCorrectly || !endsCorrectly) return false
+
+		// Check for balanced braces/brackets (simple heuristic)
+		let braceCount = 0
+		let bracketCount = 0
+		for (const char of trimmed) {
+			if (char === "{") braceCount++
+			else if (char === "}") braceCount--
+			else if (char === "[") bracketCount++
+			else if (char === "]") bracketCount--
+		}
+
+		return braceCount === 0 && bracketCount === 0
+	}
+
 	// TODO: Validate instead of parsing
 	private attemptParseChunk(data: string): ClaudeCodeMessage | null {
 		try {