feat: user-defined custom prompts for Moonbeam interactions by Copilot · Pull Request #203 · dev-chat/mocker

Copilot · 2026-03-24T02:41:21Z

Users can now define a custom system prompt that overrides Moonbeam's default instructions when interacting via /prompt and direct @mentions.

Schema

Added nullable customPrompt text column to SlackUser (TypeORM sync applies automatically)

Custom Prompt Persistence

CRUD methods (getCustomPrompt, setCustomPrompt, clearCustomPrompt) are added to SlackPersistenceService — no separate service needed. setCustomPrompt trims and normalizes the prompt before persisting (whitespace-only values are stored as null).

New: `/ai/set-prompt` endpoint

Subject to the standard suppressedMiddleware / textMiddleware / aiMiddleware stack. Prompts are trimmed on receipt; whitespace-only values and prompts exceeding 800 characters are rejected with user-friendly error messages.

Input	Behavior
`clear` (case-insensitive, whitespace-tolerant)	Resets to default
any text (≤ 800 chars)	Saves as custom prompt

`AIService` changes

Custom prompt CRUD is exposed via public setCustomPrompt / clearCustomPrompt methods on AIService, which delegates to SlackPersistenceService. The controller calls these service methods — no persistence service is instantiated directly in the controller.

Custom prompts apply to the participate and promptWithHistory code paths only. generateText always uses GENERAL_TEXT_INSTRUCTIONS unchanged. Both paths normalize the stored value (customPrompt?.trim() || null) before use to prevent blank overrides of the default system instructions.

Method	Behavior with custom prompt
`generateText()`	Always uses `GENERAL_TEXT_INSTRUCTIONS` (unaffected)
`promptWithHistory()`	Custom prompt prepended to history instructions when set
`participate(teamId, channelId, msg, userId?)`	Replaces `MOONBEAM_SYSTEM_INSTRUCTIONS` when set

handle() forwards request.event.user to participate() so tagging lookups resolve to the correct user's prompt.

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Co-authored-by: sfreeman422 <16405652+sfreeman422@users.noreply.github.com> Agent-Logs-Url: https://github.com/dev-chat/mocker/sessions/914ee584-2937-48f5-b6b1-9827d6d84224

sfreeman422 · 2026-03-24T02:58:20Z

@copilot actually can you make this only apply to the participate code path and the prompt with history? The text path should stay with its current instructions

…cipate and promptWithHistory Co-authored-by: sfreeman422 <16405652+sfreeman422@users.noreply.github.com> Agent-Logs-Url: https://github.com/dev-chat/mocker/sessions/e5dacb98-90b9-4ae4-9d41-7b25200e02e8

Copilot · 2026-03-24T03:00:23Z

@copilot actually can you make this only apply to the participate code path and the prompt with history? The text path should stay with its current instructions

Done in b6c8f8a. Custom prompts now only apply to participate (tagging) and promptWithHistory (/prompt). generateText (/text) always uses GENERAL_TEXT_INSTRUCTIONS unchanged.

Copilot

Pull request overview

Adds support for per-user custom system prompts (“custom prompts”) that override Moonbeam’s default instructions for /prompt and @mention participation, with persistence in the SlackUser table and a new endpoint to manage the prompt.

Changes:

Add nullable SlackUser.customPrompt column and CRUD persistence service for custom prompts.
Apply custom prompts in AIService.promptWithHistory() (prepend) and AIService.participate() (replace), and forward the triggering Slack user ID into participate().
Add /ai/set-prompt endpoint (registered before suppression/text/ai middleware) with controller + tests.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
packages/backend/src/shared/db/models/SlackUser.ts	Adds `customPrompt` column for per-user AI instructions.
packages/backend/src/ai/user-prompt.persistence.service.ts	Implements DB read/update/clear for `customPrompt`.
packages/backend/src/ai/user-prompt.persistence.service.spec.ts	Adds unit tests for custom prompt persistence behavior.
packages/backend/src/ai/ai.service.ts	Fetches and applies `customPrompt` in `promptWithHistory` and `participate`; passes event user ID into `participate`.
packages/backend/src/ai/ai.service.spec.ts	Adds tests asserting custom prompt is used/falls back correctly.
packages/backend/src/ai/ai.controller.ts	Adds `/set-prompt` management endpoint before existing middlewares.
packages/backend/src/ai/ai.controller.spec.ts	Adds endpoint tests for viewing/setting/clearing custom prompts.

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Copilot · 2026-03-24T03:06:13Z

packages/backend/src/ai/ai.controller.ts

+  const { user_id, team_id, text } = req.body;
+
+  if (!text) {
+    void userPromptPersistenceService.getCustomPrompt(user_id, team_id).then((prompt) => {
+      if (prompt) {
+        res.send(`Your current custom prompt: "${prompt}"`);
+      } else {
+        res.send(
+          'You have no custom prompt set. Use `/set-prompt [prompt]` to set one, or `/set-prompt clear` to remove it.',
+        );
+      }
+    });
+    return;
+  }
+
+  if (text.toLowerCase() === 'clear') {
+    void userPromptPersistenceService.clearCustomPrompt(user_id, team_id).then((success) => {


text is used without normalization. A whitespace-only value (e.g. " ") will be treated as a real prompt and saved, and clear with surrounding whitespace (" clear ") won’t match the clear branch. Consider trimming once (e.g. const normalized = (text ?? '').trim()), treating empty-after-trim as “show current prompt”, and using the normalized value for the clear check + save.

@copilot fix it

Fixed in d07dc43. text is now trimmed once up front ((text ?? '').trim()), whitespace-only values are rejected, and " CLEAR " correctly routes to the clear branch.

Copilot · 2026-03-24T03:06:14Z

packages/backend/src/ai/ai.controller.ts

+  void userPromptPersistenceService.setCustomPrompt(user_id, team_id, text).then((success) => {
+    if (success) {
+      res.send(`Your custom prompt has been set.`);
+    } else {
+      res.send('Failed to set your custom prompt. Please try again.');
+    }


Because /set-prompt bypasses textMiddleware’s 800-char guard, users can persist very large prompts. That can cause DB bloat and downstream OpenAI request failures (token/size limits) when the prompt is later used as instructions. Consider enforcing an explicit maximum length for customPrompt here (with a user-friendly error message) before calling setCustomPrompt.

@copilot fix it

Fixed in d07dc43. Added an explicit 800-character limit check in the handler with a user-friendly error message before any persistence call.

Copilot · 2026-03-24T03:06:14Z

packages/backend/src/ai/ai.service.ts

+    const baseInstructions = customPrompt ?? MOONBEAM_SYSTEM_INSTRUCTIONS;
+    const systemInstructions = this.appendMemoryContext(baseInstructions, memoryContext);


customPrompt ?? MOONBEAM_SYSTEM_INSTRUCTIONS treats an empty string as a valid override, which can effectively wipe Moonbeam’s system instructions if a blank/whitespace prompt is stored. Consider normalizing via const normalized = customPrompt?.trim(); and only overriding when normalized is non-empty (otherwise fall back to MOONBEAM_SYSTEM_INSTRUCTIONS).

@copilot fix it

Fixed in d07dc43. Both promptWithHistory and participate now do customPrompt?.trim() || null so blank/whitespace-stored values fall back to the default system instructions.

packages/backend/src/ai/user-prompt.persistence.service.ts

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

sfreeman422 · 2026-03-24T03:03:11Z

packages/backend/src/ai/ai.controller.ts

+import { UserPromptPersistenceService } from './user-prompt.persistence.service';

 export const aiController: Router = express.Router();
-aiController.use(suppressedMiddleware);


These should definitely still apply. Please add back.

Done in d07dc43. suppressedMiddleware, textMiddleware, and aiMiddleware are now registered before all routes, including /set-prompt.

sfreeman422 · 2026-03-24T03:03:39Z

packages/backend/src/ai/ai.controller.ts


 const webService = new WebService();
 const aiService = new AIService();
+const userPromptPersistenceService = new UserPromptPersistenceService();


I don't think we need a whole new service for this. Can these be moved into the user persistence service?

You are also breaking a pattern here by having the ai.controller hit a persistence service directly. The AIService should be leveraging any persistence services.

Done in d07dc43. getCustomPrompt, setCustomPrompt, and clearCustomPrompt are now methods on SlackPersistenceService. UserPromptPersistenceService has been deleted. The controller now calls aiService.setCustomPrompt/clearCustomPrompt — no persistence service is instantiated directly in the controller.

sfreeman422 · 2026-03-24T05:10:23Z

packages/backend/src/ai/ai.controller.ts

+const userPromptPersistenceService = new UserPromptPersistenceService();
 const aiLogger = logger.child({ module: 'AIController' });

+// /set-prompt does not require rate-limiting or text-length validation


Yes it does.

sfreeman422 · 2026-03-24T05:11:05Z

packages/backend/src/ai/ai.service.ts

+    const baseInstructions = customPrompt ?? MOONBEAM_SYSTEM_INSTRUCTIONS;
+    const systemInstructions = this.appendMemoryContext(baseInstructions, memoryContext);


@copilot fix it

sfreeman422 · 2026-03-24T05:11:12Z

packages/backend/src/ai/ai.controller.ts

+  void userPromptPersistenceService.setCustomPrompt(user_id, team_id, text).then((success) => {
+    if (success) {
+      res.send(`Your custom prompt has been set.`);
+    } else {
+      res.send('Failed to set your custom prompt. Please try again.');
+    }


@copilot fix it

sfreeman422 · 2026-03-24T05:11:19Z

packages/backend/src/ai/ai.controller.ts

+  const { user_id, team_id, text } = req.body;
+
+  if (!text) {
+    void userPromptPersistenceService.getCustomPrompt(user_id, team_id).then((prompt) => {
+      if (prompt) {
+        res.send(`Your current custom prompt: "${prompt}"`);
+      } else {
+        res.send(
+          'You have no custom prompt set. Use `/set-prompt [prompt]` to set one, or `/set-prompt clear` to remove it.',
+        );
+      }
+    });
+    return;
+  }
+
+  if (text.toLowerCase() === 'clear') {
+    void userPromptPersistenceService.clearCustomPrompt(user_id, team_id).then((success) => {


@copilot fix it

…hrough AIService, restore middleware order Co-authored-by: sfreeman422 <16405652+sfreeman422@users.noreply.github.com> Agent-Logs-Url: https://github.com/dev-chat/mocker/sessions/ef34bcb8-cd7e-474b-913e-339106bccdb1

Initial plan

8ec3e95

Copilot AI assigned Copilot and sfreeman422 Mar 24, 2026

Copilot started work on behalf of sfreeman422 March 24, 2026 02:41 View session

feat: add user-defined custom prompt for Moonbeam interactions

268c7df

Co-authored-by: sfreeman422 <16405652+sfreeman422@users.noreply.github.com> Agent-Logs-Url: https://github.com/dev-chat/mocker/sessions/914ee584-2937-48f5-b6b1-9827d6d84224

Copilot AI changed the title ~~[WIP] Add ability for users to create custom prompts for moonbeam~~ feat: user-defined custom prompts for Moonbeam interactions Mar 24, 2026

Copilot AI requested a review from sfreeman422 March 24, 2026 02:56

Copilot finished work on behalf of sfreeman422 March 24, 2026 02:56

Copilot started work on behalf of sfreeman422 March 24, 2026 02:58 View session

refactor: remove custom prompt from generateText, keep only for parti…

b6c8f8a

…cipate and promptWithHistory Co-authored-by: sfreeman422 <16405652+sfreeman422@users.noreply.github.com> Agent-Logs-Url: https://github.com/dev-chat/mocker/sessions/e5dacb98-90b9-4ae4-9d41-7b25200e02e8

Copilot finished work on behalf of sfreeman422 March 24, 2026 03:01

sfreeman422 marked this pull request as ready for review March 24, 2026 03:02

Copilot AI review requested due to automatic review settings March 24, 2026 03:02

Copilot started reviewing on behalf of sfreeman422 March 24, 2026 03:03 View session

Copilot AI reviewed Mar 24, 2026

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c799e62

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

sfreeman422 requested changes Mar 24, 2026

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Copilot started work on behalf of sfreeman422 March 24, 2026 05:11 View session

Copilot AI requested a review from sfreeman422 March 24, 2026 05:25

Copilot finished work on behalf of sfreeman422 March 24, 2026 05:25

		const baseInstructions = customPrompt ?? MOONBEAM_SYSTEM_INSTRUCTIONS;
		const systemInstructions = this.appendMemoryContext(baseInstructions, memoryContext);

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Copilot AI commented Mar 24, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Schema

Custom Prompt Persistence

New: /ai/set-prompt endpoint

AIService changes

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sfreeman422 commented Mar 24, 2026

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Copilot AI commented Mar 24, 2026 •

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New: `/ai/set-prompt` endpoint

`AIService` changes