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Show & Tell: MCP Memory Service — semantic memory plugin working with event hook #29022
Description
What is it?
MCP Memory Service is an open-source semantic memory layer for AI agents (vector embeddings, 12 REST API endpoints, MCP transport, 3 storage backends). It now ships a working OpenCode in-process plugin.
What the plugin does
- Auto-captures valuable content during conversations (decisions, errors, learnings — regex-based, configurable patterns + #skip/#remember overrides)
- Injects relevant memories into the system prompt via
experimental.chat.system.transform - Session-end write-back — full analysis + summary stored to memory on
session.deleted - Harvest integration — optional post-session batch analysis via POST /api/harvest
- Self-hosted — runs locally on HTTPS (self-signed cert supported)
Key implementation finding
The chat.message hook type exists in @opencode-ai/plugin but OpenCode never triggers plugin.trigger("chat.message", ...) anywhere in the server source. After a day of debugging a "loading plugin" that silently did nothing, we traced through the plugin loader (packages/opencode/src/plugin/index.ts) and confirmed the trigger call site does not exist.
Working approach: Use the event hook with bus subscription:
message.part.updated→ carries full text content inevent.properties.part.textforTextPartsession.created/session.deleted→ lifecycle managementmessage.updated→ carry only metadata, not content
This would be a great addition to the plugin docs.
Hooks used
| Hook | Purpose |
|---|---|
event |
Bus subscription — message.part.updated, session.created, session.deleted |
experimental.chat.system.transform |
Memory injection into system prompt |
experimental.session.compacting |
Memory preservation during compaction |
TLS tip
Bun's fetch() ignores the tls: { rejectUnauthorized: false } option. For self-signed certs, use new https.Agent({ rejectUnauthorized: false }) from node:https — it works reliably across Node.js and Bun.
Plugin file
https://github.com/doobidoo/mcp-memory-service/blob/main/opencode/memory-plugin.js (~820 lines, zero external deps)
Activity
github-actions commentedon May 23, 2026
This issue doesn't fully meet our contributing guidelines.
What needs to be fixed:
[FEATURE]: Add mcp-memory-service to ecosystem plugins) using the feature request template, with the verification checkbox checked and a description of the enhancement.Please edit this issue to address the above within 2 hours, or it will be automatically closed.
This issue might be a duplicate of existing issues. Please check:
chat.messageplugin hook (directly related to your finding aboutchat.messagenot being triggered)chat.messageplugin hook:SyncEvent.run: "sessionID" required but not foundwhen pushing tooutput.parts#23440: Bug report aboutchat.messageplugin hook failing withSyncEvent.run: "sessionID" requiredIf you believe this was flagged incorrectly, please let a maintainer know.
doobidoo commentedon May 23, 2026
@anomalyco/maintainers — this isn't a vanity post. It documents a gap in the plugin docs:
chat.messageis listed in@opencode-ai/pluginHooks interface but never triggered by the session processorpackages/opencode/src/plugin/index.tsto confirmeventhook (bus subscription) is the only way to capture message content — and this isn't documented eitherThis directly relates to #22831 (feature request to expose body to chat.message) and #23440 (chat.message crash). We've added our findings with concrete workarounds to both.
If this issue type isn't supported, that's fine — the information is already linked from the related issues. But it would be useful for other plugin developers who hit the same dead end.
github-actions commentedon May 23, 2026
This issue has been automatically closed because it was not updated to meet our contributing guidelines within the 2-hour window.
Feel free to open a new issue that follows our issue templates.