converge everything into one data folder

server/src/services/mediaMtxService/supervisor.js

@@ -5,7 +5,7 @@ const fs = require('fs');
 const path = require('path');
 const { spawn } = require('child_process');
 const yaml = require('js-yaml');
-const { resolveDataPath } = require('../../helpers/dataPaths');
+const { resolveDataDir, resolveDataPath } = require('../../helpers/dataPaths');
 const { buildMediaMtxConfig } = require('./config');
 
 function createMediaMtxSupervisor(deps) {
@@ -52,6 +52,16 @@ function createMediaMtxSupervisor(deps) {
     logger.info(`Starting MediaMTX with generated config ${configPath}`);
     child = spawnProcess(mediaMtxBin, [configPath], {
       stdio: ['ignore', 'pipe', 'pipe'],
+      /*
+        MediaMTX passes its environment to runOnReady hooks. Supplying the
+        resolved value here also covers development starts where
+        SERVER_DATA_DIR was omitted, so the installed snapshot writer and every
+        Node snapshot reader still converge on the same canonical data root.
+      */
+      env: {
+        ...process.env,
+        SERVER_DATA_DIR: resolveDataDir(),
+      },
     });
 
     forwardLines(child.stdout, 'info');

server/src/services/mediaMtxService/supervisor.test.js

@@ -0,0 +1,66 @@
+// MediaMTX Supervisor Tests
+// Purpose: Verifies that generated MediaMTX state and child hooks inherit the server's single data root.
+// Scope: Uses a child-process double and a temporary directory; no listener or background process is started.
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('fs');
+const os = require('os');
+const path = require('path');
+const EventEmitter = require('events');
+const { PassThrough } = require('stream');
+const { createMediaMtxSupervisor } = require('./supervisor');
+
+test('passes the resolved data root to MediaMTX runOnReady hooks', () => {
+  const temporaryDataDir = fs.mkdtempSync(path.join(os.tmpdir(), 'multirover-mediamtx-supervisor-'));
+  const generatedConfigPath = path.join(temporaryDataDir, 'mediamtx.yml');
+  const previousDataDir = process.env.SERVER_DATA_DIR;
+  let invocation = null;
+
+  process.env.SERVER_DATA_DIR = temporaryDataDir;
+
+  const spawnProcess = (command, args, options) => {
+    const child = new EventEmitter();
+    child.stdout = new PassThrough();
+    child.stderr = new PassThrough();
+    child.kill = (signal) => {
+      child.emit('exit', 0, signal);
+    };
+    invocation = { command, args, options };
+    return child;
+  };
+
+  const logger = {
+    info() {},
+    warn() {},
+    error() {},
+  };
+
+  try {
+    const supervisor = createMediaMtxSupervisor({
+      config: { media: { additionalHosts: ['media.example.test'] } },
+      serverPort: 8080,
+      logger,
+      mediaMtxBin: '/test/bin/mediamtx',
+      snapshotWriterPath: '/test/bin/rover-snapshot-writer',
+      configPath: generatedConfigPath,
+      spawnProcess,
+    });
+
+    supervisor.start();
+
+    assert.equal(invocation.command, '/test/bin/mediamtx');
+    assert.deepEqual(invocation.args, [generatedConfigPath]);
+    assert.equal(invocation.options.env.SERVER_DATA_DIR, temporaryDataDir);
+    assert.equal(fs.existsSync(generatedConfigPath), true);
+
+    supervisor.stop();
+  } finally {
+    /*
+      Restore process-global state and delete only the test-owned directory so a
+      failed assertion cannot alter later tests or leave generated YAML behind.
+    */
+    if (previousDataDir === undefined) delete process.env.SERVER_DATA_DIR;
+    else process.env.SERVER_DATA_DIR = previousDataDir;
+    fs.rmSync(temporaryDataDir, { recursive: true, force: true });
+  }
+});