feat(release): v2.9.1 - auto-save research to ~/Documents/Last30Days/

Sync from public repo. Every run now saves the complete briefing as a
topic-named .md file to ~/Documents/Last30Days/. Credit @devin_explores.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: last30days
-version: "2.9"
+version: "2.9.1"
 description: "Research a topic from the last 30 days. Also triggered by 'last30'. Sources: Reddit, X, YouTube, TikTok, Instagram, Hacker News, Polymarket, web. Become an expert and write copy-paste-ready prompts."
 argument-hint: 'last30 AI video tools, last30 best project management tools'
 allowed-tools: Bash, Read, Write, AskUserQuestion, WebSearch
@@ -30,7 +30,7 @@ metadata:
       - prompts
 ---
 
-# last30days v2.9: Research Any Topic from the Last 30 Days
+# last30days v2.9.1: Research Any Topic from the Last 30 Days
 
 Research ANY topic across Reddit, X, YouTube, TikTok, Hacker News, Polymarket, and the web. Surface what people are actually discussing, recommending, betting on, and debating right now.
 
@@ -123,6 +123,8 @@ If `--agent` appears in ARGUMENTS (e.g., `/last30days plaud granola --agent`):
 5. **Skip** the follow-up invitation ("I'm now an expert on X...")
 6. **Output** the complete research report and stop - do not wait for further input
 
+Agent mode still saves the research briefing to `~/Documents/Last30Days/` using the same logic as interactive mode (see "Save Research to Documents" section).
+
 Agent mode report format:
 
 ```
@@ -496,6 +498,51 @@ For `/last30days war in Iran` (NEWS):
 
 ---
 
+## Save Research to Documents
+
+After displaying the invitation, save the complete research briefing to the user's Documents folder. This happens automatically on every run.
+
+1. **Create the directory** (if it doesn't exist):
+   ```bash
+   mkdir -p ~/Documents/Last30Days
+   ```
+
+2. **Generate the filename** from TOPIC:
+   - Lowercase the topic
+   - Replace spaces and special characters with hyphens
+   - Remove consecutive hyphens
+   - Trim to 60 characters max
+   - Example: "Claude Code Best Practices" -> `claude-code-best-practices`
+
+3. **Check for duplicates**: If `~/Documents/Last30Days/{slug}.md` already exists, append today's date: `{slug}-YYYY-MM-DD.md`
+
+4. **Use the Write tool** to save to `~/Documents/Last30Days/{slug}.md` with this exact structure:
+
+```markdown
+# {TOPIC}
+
+> Researched {date} | Query type: {QUERY_TYPE} | Target tool: {TARGET_TOOL or "general"}
+
+## What I learned
+
+{The full synthesis section you just displayed - all topics, patterns, and citations}
+
+## Stats
+
+{The full stats box with source counts and engagement - copy exactly as displayed}
+
+## Follow-up suggestions
+
+{The 2-3 specific suggestions from the invitation block}
+
+---
+*Generated by [last30days](https://github.com/mvanhorn/last30days-skill) v2.9.1*
+```
+
+5. **Confirm briefly** after saving: `Saved to ~/Documents/Last30Days/{slug}.md`
+
+---
+
 ## WAIT FOR USER'S RESPONSE
 
 After showing the stats summary with your invitation, **STOP and wait** for the user to respond.
@@ -607,6 +654,7 @@ Want another prompt? Just tell me what you're creating next.
 - Optionally sends search queries to Brave Search API, Parallel AI API, or OpenRouter API for web search
 - Fetches public Reddit thread data from `reddit.com` for engagement metrics
 - Stores research findings in local SQLite database (watchlist mode only)
+- Saves research briefings as .md files to ~/Documents/Last30Days/
 
 **What this skill does NOT do:**
 - Does not post, like, or modify content on any platform