feat(flags): build-time client config overrides via Feature Flags

Inject homeserverList, experiments, and other client config fields from
GitHub environment variables at build time via a new inject-client-config
script. Adds typed experiment bucketing with rollout percentages, an
Experiments panel in developer tools, and CI job summary logging.
Includes tests for the bucketing helper and injector.

Author: Just-Insane

.changeset/add_shorts_support_to_fix_crash.md

@@ -0,0 +1,5 @@
+---
+default: minor
+---
+
+Add build-time client config overrides via environment variables, with typed deterministic experiment bucketing helpers for progressive feature rollout and A/B testing.

.changeset/feature-flag-env-vars.md

@@ -34,6 +34,36 @@ runs:
       env:
         INPUTS_INSTALL_COMMAND: ${{ inputs.install-command }}
 
+    - name: Inject runtime config overrides
+      if: ${{ env.CLIENT_CONFIG_OVERRIDES_JSON != '' }}
+      shell: bash
+      working-directory: ${{ github.workspace }}
+      run: node scripts/inject-client-config.js
+      env:
+        CLIENT_CONFIG_OVERRIDES_JSON: ${{ env.CLIENT_CONFIG_OVERRIDES_JSON }}
+        CLIENT_CONFIG_OVERRIDES_STRICT: ${{ env.CLIENT_CONFIG_OVERRIDES_STRICT }}
+
+    - name: Display injected config
+      if: ${{ env.CLIENT_CONFIG_OVERRIDES_JSON != '' }}
+      shell: bash
+      working-directory: ${{ github.workspace }}
+      run: |
+        summary_file="${GITHUB_STEP_SUMMARY:-}"
+        echo "::group::Injected Client Config"
+        experiments_json="$(jq -c '.experiments // "No experiments configured"' config.json 2>/dev/null || echo 'config.json not readable')"
+        echo "$experiments_json"
+        echo "::endgroup::"
+
+        if [[ -n "$summary_file" ]]; then
+          {
+            echo "### Injected client config"
+            echo
+            echo "\`\`\`json"
+            echo "$experiments_json"
+            echo "\`\`\`"
+          } >> "$summary_file"
+        fi
+
     - name: Build app
       if: ${{ inputs.build == 'true' }}
       shell: bash

.changeset/fix_pmp_id_handling.md

@@ -40,6 +40,10 @@ jobs:
   plan:
     if: github.event_name == 'pull_request' && github.event.pull_request.head.repo.full_name == github.repository
     runs-on: ubuntu-latest
+    environment: preview
+    env:
+      CLIENT_CONFIG_OVERRIDES_JSON: ${{ vars.CLIENT_CONFIG_OVERRIDES_JSON }}
+      CLIENT_CONFIG_OVERRIDES_STRICT: ${{ vars.CLIENT_CONFIG_OVERRIDES_STRICT || 'false' }}
     permissions:
       contents: read
       pull-requests: write
@@ -73,6 +77,10 @@ jobs:
   apply:
     if: (github.event_name == 'push' && startsWith(github.ref, 'refs/tags/v')) || github.event_name == 'workflow_dispatch'
     runs-on: ubuntu-latest
+    environment: production
+    env:
+      CLIENT_CONFIG_OVERRIDES_JSON: ${{ vars.CLIENT_CONFIG_OVERRIDES_JSON }}
+      CLIENT_CONFIG_OVERRIDES_STRICT: ${{ vars.CLIENT_CONFIG_OVERRIDES_STRICT || 'false' }}
     permissions:
       contents: read
     defaults:

.github/actions/setup/action.yml

@@ -32,9 +32,13 @@ jobs:
   deploy:
     if: github.event.pull_request.head.repo.full_name == github.repository || github.event_name == 'push'
     runs-on: ubuntu-latest
+    environment: preview
     permissions:
       contents: read
       pull-requests: write
+    env:
+      CLIENT_CONFIG_OVERRIDES_JSON: ${{ vars.CLIENT_CONFIG_OVERRIDES_JSON }}
+      CLIENT_CONFIG_OVERRIDES_STRICT: ${{ vars.CLIENT_CONFIG_OVERRIDES_STRICT || 'false' }}
     steps:
       - name: Checkout repository
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2

.github/workflows/cloudflare-web-deploy.yml

@@ -1,6 +1,6 @@
 {
   "$schema": "https://unpkg.com/knip@5/schema.json",
-  "entry": ["src/sw.ts", "scripts/normalize-imports.js"],
+  "entry": ["src/sw.ts", "scripts/normalize-imports.js", "scripts/inject-client-config.js"],
   "ignoreExportsUsedInFile": {
     "interface": true,
     "type": true

.github/workflows/cloudflare-web-preview.yml

@@ -0,0 +1,71 @@
+import { readFile, writeFile } from 'node:fs/promises';
+import process from 'node:process';
+import { PrefixedLogger } from './utils/console-style.js';
+
+const CONFIG_PATH = 'config.json';
+const OVERRIDES_ENV = 'CLIENT_CONFIG_OVERRIDES_JSON';
+const STRICT_ENV = 'CLIENT_CONFIG_OVERRIDES_STRICT';
+const logger = new PrefixedLogger('[config-inject]');
+
+const formatError = (error) => {
+  if (error instanceof Error) return error.stack ?? error.message;
+  return String(error);
+};
+
+const isPlainObject = (value) =>
+  typeof value === 'object' && value !== null && !Array.isArray(value);
+
+const deepMerge = (target, source) => {
+  if (!isPlainObject(target) || !isPlainObject(source)) return source;
+
+  const merged = { ...target };
+  Object.entries(source).forEach(([key, value]) => {
+    const targetValue = merged[key];
+    merged[key] =
+      isPlainObject(targetValue) && isPlainObject(value) ? deepMerge(targetValue, value) : value;
+  });
+  return merged;
+};
+
+const failOnError = process.env[STRICT_ENV] === 'true';
+const overridesRaw = process.env[OVERRIDES_ENV];
+
+if (!overridesRaw) {
+  logger.info(`No ${OVERRIDES_ENV} provided; leaving ${CONFIG_PATH} unchanged.`);
+  process.exit(0);
+}
+
+let fileConfig;
+let overrides;
+
+try {
+  const file = await readFile(CONFIG_PATH, 'utf8');
+  fileConfig = JSON.parse(file);
+} catch (error) {
+  logger.error(`Failed reading ${CONFIG_PATH}: ${formatError(error)}`);
+  process.exit(1);
+}
+
+try {
+  overrides = JSON.parse(overridesRaw);
+  if (!isPlainObject(overrides)) {
+    throw new Error(`${OVERRIDES_ENV} must be a JSON object.`);
+  }
+} catch (error) {
+  const message = `[config-inject] Invalid ${OVERRIDES_ENV}; ${
+    failOnError ? 'failing build' : 'skipping overrides'
+  }.`;
+  if (failOnError) {
+    logger.error(`${message} ${formatError(error)}`);
+    process.exit(1);
+  }
+  logger.info(`[warning] ${message} ${formatError(error)}`);
+  process.exit(0);
+}
+
+const mergedConfig = deepMerge(fileConfig, overrides);
+
+await writeFile(CONFIG_PATH, `${JSON.stringify(mergedConfig, null, 2)}\n`, 'utf8');
+logger.info(
+  `Applied overrides to ${CONFIG_PATH}. Top-level keys: ${Object.keys(overrides).join(', ')}`
+);

knip.json

@@ -167,14 +167,10 @@ function parseYoutubeLink(url: string): YoutubeLink | null {
     const split = path.split('?');
     [videoId] = split;
     params = split[1]?.split('&');
-  } else if (url.includes('/shorts/')) {
-    const split = path.split('/shorts/');
-    [videoId] = split;
-    params = split[1]?.split('shorts');
-  } else if (url.includes('youtube.com')) {
+  } else {
     params = path.split('?')[1].split('&');
     videoId = params.find((s) => s.startsWith('v='), params)?.split('v=')[1];
-  } else return null;
+  }
 
   if (!videoId) return null;
 

scripts/inject-client-config.js

@@ -6,7 +6,6 @@ import {
 } from '$hooks/usePerMessageProfile';
 import { useEffect, useState } from 'react';
 import { Box, Button, Text } from 'folds';
-import { generateShortId } from '$utils/shortIdGen';
 import { PerMessageProfileEditor } from './PerMessageProfileEditor';
 
 /**
@@ -37,7 +36,7 @@ export function PerMessageProfileOverview() {
         <Button
           onClick={() => {
             const newProfile: PerMessageProfile = {
-              id: generateShortId(5),
+              id: crypto.randomUUID(),
               name: 'New Profile',
             };
             addOrUpdatePerMessageProfile(mx, newProfile).then(() => {