Initial Arka plugin registry: Official plugins mirror + Arka-signed index

11 plugins from github.com/librefang/librefang-registry plugins/.
index.json / index.json.sig are signed with Arka's Ed25519 key
(not upstream stats.librefang.ai). Private key is not in this repo.

plugins/auto-summarizer/README.md

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+# auto-summarizer
+
+Maintains a running conversation summary to help agents handle long conversations without losing context. Uses extractive summarization (no ML or external dependencies) to identify the most important parts of a conversation.
+
+## How it works
+
+After each conversation turn, the plugin scans all messages and extracts:
+
+- **Topic opener** -- the first user message that started the conversation
+- **Questions** -- any messages containing questions (detected via `?`)
+- **Decisions** -- messages with conclusion/decision language ("let's", "decided", "the plan is", etc.)
+- **Recent context** -- the last 2 exchanges to preserve immediate context
+
+These are combined into a compact summary (max 500 characters) and persisted to disk. On the next ingest, the summary is returned as a memory fragment so the agent retains awareness of the full conversation.
+
+Summarization only activates when the conversation exceeds 6 messages -- shorter conversations are passed through as-is.
+
+## Hooks
+
+| Hook | Script | Description |
+|------|--------|-------------|
+| ingest | `hooks/ingest.py` | Returns the stored conversation summary as a memory fragment |
+| after_turn | `hooks/after_turn.py` | Builds and persists an extractive summary of the conversation |
+
+## Storage
+
+Summaries are stored at `~/.librefang/plugins/auto-summarizer/{agent_id}.summary`.
+
+## Usage
+
+Installed automatically when enabled in agent configuration.