Problem

When LCM assembles context from the SQLite database, assistant messages can end up with an empty content array ([]). This causes provider APIs like Anthropic Claude to reject the request with:

The content field in the Message object at messages.0 is empty. Add a ContentBlock object to the content field and try again.

Root Cause

In src/assembler.ts, contentFromParts() returns [] when:

1. The message has no stored parts (parts.length === 0)
2. The fallback content is an empty string ("" is falsy)

// Before (bug):
return fallbackContent ? [{ type: "text", text: fallbackContent }] : [];

This can happen when:

• A stored assistant message has no message_parts rows and empty content text
• Tool-call-only assistant turns are stored without text content
• Session reset/compaction leaves orphaned empty assistant records

Additionally, filterNonFreshAssistantToolCalls() can strip all tool-call blocks from a non-fresh assistant message, leaving content: [], but the empty-check only skips messages where the filtering itself produced an empty array — messages that started empty pass through.

Fix

Two defensive layers:

1. contentFromParts(): Always return at least one text block for assistant messages instead of an empty array:

   return [{ type: "text", text: fallbackContent || "" }];

2. assemble() safety net: Filter out any assistant messages that still have empty content arrays before returning, catching edge cases from tool-call orphan filtering:

   const nonEmptyMessages = rawMessages.filter((msg) => {
     if (msg?.role === "assistant" && Array.isArray(msg.content) && msg.content.length === 0) {
       return false;
     }
     return true;
   });

Testing

• Verified the fix handles the exact error scenario from production logs
• Both Anthropic and OpenAI APIs require non-empty content arrays for assistant messages
• The changeset is included for version bumping