zylon-ai/private-gpt · error · ValueError

User block {i} does not end with an assistant message: {bloc

Error message

User block {i} does not end with an assistant message: {block[-1]}

What it means

Strict-mode user-block validation: every block with more than one message must end with an assistant message, enforcing the (user, (assistant, tool)*, assistant) shape. A block ending in a user message (consecutive user turns) or a tool message (unanswered tool call) fails this check in strict mode.

Source

Thrown at private_gpt/components/chat/processors/chat_history/memory/utils/repairs.py:145

    matrix = get_user_blocks(chat_history)
    for i, block in enumerate(matrix):
        if not block:
            raise ValueError(f"User block {i} is empty.")

        # Validate the first and last messages in the block
        if block[0].role != "user":
            raise ValueError(
                f"User block {i} does not start with a user message: {block[0]}"
            )

        if len(block) == 1:
            # No more validation needed for a single user message block
            continue

        # Validate the last message in the block
        if strict and block[-1].role != "assistant":
            raise ValueError(
                f"User block {i} does not end with an assistant message: {block[-1]}"
            )
        elif not strict and block[-1].role not in ["assistant", "tool"]:
            raise ValueError(
                f"User block {i} does not end with an assistant or tool message: {block[-1]}"
            )

        # Validate the tool messages
        for j, message in enumerate(block[1:-1]):
            if message.role == "tool":
                if j == 0 or block[j].role != "assistant":
                    raise ValueError(
                        f"Tool message {j} in user block {i} does not follow an assistant message: {message}"
                    )
            elif message.role != "assistant":
                raise ValueError(
                    f"Message {j} in user block {i} is neither an assistant nor a tool: {message}"
                )

View on GitHub (pinned to 4a030776a3)

Solutions

1. Pass strict=False to allow blocks ending with assistant OR tool messages
2. Repair the history first: merge adjacent user messages or append a placeholder assistant reply
3. Fix persistence so interrupted tool flows are not saved half-complete

Example fix

# before
repaired = repair_with_tools(chat_history, strict=True)

# after
repaired = repair_with_tools(chat_history, strict=False)

def blocks_end_with_assistant(history: list[ChatMessage]) -> bool:
    return all(b[-1].role == "assistant" for b in get_user_blocks(history) if len(b) > 1)

def is_strict_repairable(history: list[ChatMessage]) -> bool:
    for b in get_user_blocks(history):
        if not b or b[0].role != "user":
            return False
        if len(b) > 1 and b[-1].role != "assistant":
            return False
    return True

try:
    repaired = repair_with_tools(chat_history, strict=True)
except ValueError as e:
    if "does not end with an assistant message" in str(e):
        repaired = repair_with_tools(chat_history, strict=False)  # tolerate tool-ending blocks
    else:
        raise

When it happens

Trigger: Calling repair_without_tools(strict=True) or repair_with_tools(strict=True) on history where a user block ends with a user message (two user turns in a row) or with a tool message (assistant issued tool_call but no tool result / final assistant reply recorded).

Common situations: User sent follow-up messages before the assistant responded (multi-turn spamming); tool-call flows interrupted mid-execution and persisted; histories replayed from logs missing the final assistant answer.

Related errors

• User block {i} does not start with a user message: {block[0]
• User block {i} does not end with an assistant or tool messag
• Tool message {j} in user block {i} does not follow an assist
• Message {j} in user block {i} is neither an assistant nor a
• User block {i} is empty.

AI-assisted analysis of zylon-ai/private-gpt@4a030776a3 (2026-08-15). Data as JSON: /api/errors/d215cba02157e59b. Report an issue: GitHub.