diff --git a/server/auth.ts b/server/auth.ts
index bdc4b17..edfe185 100644
--- a/server/auth.ts
+++ b/server/auth.ts
@@ -34,9 +34,12 @@ export function hasAdminClaim(req: Request) {
  * when the external handoff is wired — the `user_id` column stays the same.
  */
 export const DEVELOPMENT_TEST_USER_ID = 'osint-test-player'
-export function resolveUserId(req: Request): string {
+export function resolveUserId(req: Request): string | null {
   const sub = req.authClaims?.sub
-  return typeof sub === 'string' && sub.length > 0 ? sub : DEVELOPMENT_TEST_USER_ID
+  if (typeof sub === 'string' && sub.length > 0) return sub
+  // In production an absent token is anonymous (no shared identity); locally it
+  // resolves to a single dev user so the game is playable without an issuer.
+  return process.env.NODE_ENV === 'production' ? null : DEVELOPMENT_TEST_USER_ID
 }
 
 export function resolvePlayerName(req: Request): string {
diff --git a/server/index.ts b/server/index.ts
index e9a29e2..c0e4431 100644
--- a/server/index.ts
+++ b/server/index.ts
@@ -41,6 +41,18 @@ const STORY_NODE_TYPES: StoryNodeType[] = ['cutscene', 'dialogue', 'level', 'det
 function wantsEdit(req: express.Request) {
   return editingEnabled && req.query.edit === '1' && hasAdminClaim(req)
 }
+// Identity guards for player-scoped routes.
+function requireUser(req: express.Request, res: express.Response): string | null {
+  const userId = resolveUserId(req)
+  if (!userId) { res.status(401).json({ error: 'Sign in required' }); return null }
+  return userId
+}
+async function ownsPlaythroughOr403(req: express.Request, res: express.Response, playthroughId: string): Promise<string | null> {
+  const userId = requireUser(req, res)
+  if (!userId) return null
+  if (!await narrative.ownsPlaythrough(userId, playthroughId)) { res.status(403).json({ error: 'Not your playthrough' }); return null }
+  return userId
+}
 function slug(value: unknown, fallback: string) {
   return String(value || fallback).trim().toLowerCase().replace(/[^a-z0-9-]+/g, '-').replace(/^-+|-+$/g, '')
 }
@@ -156,7 +168,8 @@ app.post('/api/levels/:id/documents', upload.single('file'), async (req, res, ne
 })
 app.post('/api/levels/:id/documents/:documentId/judge', async (req, res, next) => {
   try {
-    if (!hasAdminClaim(req) && !await narrative.ownsActiveLevel(resolveUserId(req), String(req.params.id))) {
+    const levelUser = resolveUserId(req)
+    if (!hasAdminClaim(req) && (!levelUser || !await narrative.ownsActiveLevel(levelUser, String(req.params.id)))) {
       return res.status(403).json({ error: 'This level is not active for the current player' })
     }
     const result = await levels.judgeDocument(String(req.params.id), String(req.params.documentId))
@@ -503,13 +516,15 @@ app.post('/api/mysteries', requireAdmin, async (req, res, next) => {
 // New Game creates a playthrough bound to the caller's identity.
 app.post('/api/playthroughs', async (req, res, next) => {
   try {
-    const result = await narrative.createPlaythrough(resolveUserId(req), req.body?.mystery ? slug(req.body.mystery, req.body.mystery) : undefined)
+    const userId = requireUser(req, res); if (!userId) return
+    const result = await narrative.createPlaythrough(userId, req.body?.mystery ? slug(req.body.mystery, req.body.mystery) : undefined)
     result ? res.status(201).json(result) : res.status(404).json({ error: 'No mystery available' })
   } catch (error) { next(error) }
 })
 app.get('/api/playthroughs/current', async (req, res, next) => {
   try {
-    const result = await narrative.getCurrentPlaythrough(resolveUserId(req))
+    const userId = resolveUserId(req)
+    const result = userId ? await narrative.getCurrentPlaythrough(userId) : null
     result ? res.json(result) : res.status(204).end()
   } catch (error) { next(error) }
 })
@@ -517,7 +532,8 @@ app.get('/api/playthroughs/current', async (req, res, next) => {
 // gates; instantiates the board when entering a level node).
 app.post('/api/playthroughs/:id/advance', async (req, res, next) => {
   try {
-    const result = await narrative.advancePlaythrough(resolveUserId(req), String(req.params.id), req.body?.terminalKey)
+    const userId = requireUser(req, res); if (!userId) return
+    const result = await narrative.advancePlaythrough(userId, String(req.params.id), req.body?.terminalKey)
     result.ok ? res.json(result.state ?? null) : res.status(result.error === 'Playthrough not found' ? 404 : result.errorCode ? 409 : 400)
       .json({ error: result.error, errorCode: result.errorCode, pendingGoals: result.pendingGoals })
   } catch (error) { next(error) }
@@ -527,6 +543,7 @@ app.post('/api/playthroughs/:id/advance', async (req, res, next) => {
 // stand-in until the server-side achievement rule engine drives awards from play.
 app.get('/api/playthroughs/:id/achievements', async (req, res, next) => {
   try {
+    if (!await ownsPlaythroughOr403(req, res, String(req.params.id))) return
     const flags = await narrative.listAchievements(String(req.params.id))
     flags ? res.json(flags) : res.status(404).json({ error: 'Playthrough not found' })
   } catch (error) { next(error) }
@@ -534,6 +551,7 @@ app.get('/api/playthroughs/:id/achievements', async (req, res, next) => {
 app.post('/api/playthroughs/:id/achievements', async (req, res, next) => {
   try {
     if (process.env.NODE_ENV === 'production') return res.status(403).json({ error: 'Manual grants are disabled' })
+    if (!await ownsPlaythroughOr403(req, res, String(req.params.id))) return
     if (!req.body?.flagKey) return res.status(400).json({ error: 'A flagKey is required' })
     const result = await narrative.awardAchievement(String(req.params.id), String(req.body.flagKey), req.body.nodeId ? String(req.body.nodeId) : null)
     result.ok ? res.json({ earned: result.earned }) : res.status(result.error === 'Playthrough not found' ? 404 : 400).json({ error: result.error })
@@ -543,42 +561,52 @@ app.post('/api/playthroughs/:id/achievements', async (req, res, next) => {
 // server-side against the player's current node, so players can't forge flags).
 app.post('/api/playthroughs/:id/utterances/:uid/reach', async (req, res, next) => {
   try {
+    if (!await ownsPlaythroughOr403(req, res, String(req.params.id))) return
     const result = await narrative.reachUtterance(String(req.params.id), String(req.params.uid))
     result.ok ? res.json({ earned: result.earned ?? false }) : res.status(404).json({ error: 'Not found' })
   } catch (error) { next(error) }
 })
 // Field notebook: capture NPC lines during play, list them, and remove (on tear/discard).
 app.get('/api/playthroughs/:id/notebook', async (req, res, next) => {
-  try { res.json(await narrative.notebookPages(String(req.params.id))) }
-  catch (error) { next(error) }
+  try {
+    if (!await ownsPlaythroughOr403(req, res, String(req.params.id))) return
+    res.json(await narrative.notebookPages(String(req.params.id)))
+  } catch (error) { next(error) }
 })
 app.post('/api/playthroughs/:id/notebook', async (req, res, next) => {
   try {
+    if (!await ownsPlaythroughOr403(req, res, String(req.params.id))) return
     const page = await narrative.addNotebookPage(String(req.params.id), String(req.body?.text || ''), req.body?.utteranceId ? String(req.body.utteranceId) : null)
     page ? res.status(201).json(page) : res.status(400).json({ error: 'Empty text or unknown playthrough' })
   } catch (error) { next(error) }
 })
 app.delete('/api/playthroughs/:id/notebook/:pageId', async (req, res, next) => {
   try {
+    if (!await ownsPlaythroughOr403(req, res, String(req.params.id))) return
     const ok = await narrative.removeNotebookPage(String(req.params.id), String(req.params.pageId))
     ok ? res.json({ ok: true }) : res.status(404).json({ error: 'Not found' })
   } catch (error) { next(error) }
 })
 // The phone tool: the directory available on the current node, and dialing a number.
 app.get('/api/playthroughs/:id/phone', async (req, res, next) => {
-  try { res.json(await narrative.phoneDirectory(String(req.params.id))) }
-  catch (error) { next(error) }
+  try {
+    if (!await ownsPlaythroughOr403(req, res, String(req.params.id))) return
+    res.json(await narrative.phoneDirectory(String(req.params.id)))
+  } catch (error) { next(error) }
 })
 app.post('/api/playthroughs/:id/dial', async (req, res, next) => {
-  try { res.json(await narrative.dial(String(req.params.id), String(req.body?.number || ''))) }
-  catch (error) { next(error) }
+  try {
+    if (!await ownsPlaythroughOr403(req, res, String(req.params.id))) return
+    res.json(await narrative.dial(String(req.params.id), String(req.body?.number || '')))
+  } catch (error) { next(error) }
 })
 // Dev teleport: jump the playthrough to an explicit story node. Powers /node/:id.
 app.post('/api/playthroughs/:id/goto', async (req, res, next) => {
   try {
     if (process.env.NODE_ENV === 'production') return res.status(403).json({ error: 'Node teleport is disabled' })
+    const userId = requireUser(req, res); if (!userId) return
     if (!req.body?.nodeId) return res.status(400).json({ error: 'A nodeId is required' })
-    const result = await narrative.gotoNode(resolveUserId(req), String(req.params.id), String(req.body.nodeId))
+    const result = await narrative.gotoNode(userId, String(req.params.id), String(req.body.nodeId))
     result.ok ? res.json(result.state ?? null) : res.status(result.error === 'Playthrough not found' || result.error === 'Node not found' ? 404 : 400).json({ error: result.error })
   } catch (error) { next(error) }
 })
diff --git a/server/narrativeRepository.ts b/server/narrativeRepository.ts
index e8dfa60..74ffde7 100644
--- a/server/narrativeRepository.ts
+++ b/server/narrativeRepository.ts
@@ -65,6 +65,7 @@ export interface NarrativeRepository {
   phoneDirectory(playthroughId: string): Promise<{ available: boolean; numbers: { number: string; name: string }[] }>
   dial(playthroughId: string, number: string): Promise<{ outcome: 'connect' | 'voicemail' | 'unknown'; name?: string; state?: PlaythroughState }>
   gotoNode(userId: string, playthroughId: string, nodeId: string): Promise<{ ok: boolean; state?: PlaythroughState; error?: string }>
+  ownsPlaythrough(userId: string, playthroughId: string): Promise<boolean>
   listMysteries(): Promise<MysterySummary[]>
   listPlayableMysteries(): Promise<{ slug: string; title: string }[]>
   deleteMystery(id: string): Promise<boolean>
@@ -345,6 +346,10 @@ export function createNarrativeRepository(pool: Pool, objectStorage: ObjectStora
       return npc ? { outcome: 'voicemail', name: npc.name } : { outcome: 'unknown' }
     },
 
+    async ownsPlaythrough(userId, playthroughId) {
+      return ((await pool.query('SELECT 1 FROM osint.playthroughs WHERE id=$1 AND user_id=$2', [playthroughId, userId])).rowCount || 0) > 0
+    },
+
     async listAchievements(playthroughId) {
       if (!(await pool.query('SELECT 1 FROM osint.playthroughs WHERE id=$1', [playthroughId])).rowCount) return null
       const rows = (await pool.query<{ flag_key: string }>('SELECT flag_key FROM osint.achievements WHERE playthrough_id=$1 ORDER BY flag_key', [playthroughId])).rows
diff --git a/src/App.tsx b/src/App.tsx
index e7c8d8a..7ef7265 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -469,7 +469,7 @@ export function App() {
       if (!response.ok) { setStatus('OBJECTIVE COMPLETE · STORY ADVANCE UNAVAILABLE'); return }
       const next = await response.json() as PlaythroughState
       if (next.node?.kind === 'level' && next.node.levelSlug) window.location.assign(`/level/${encodeURIComponent(next.node.levelSlug)}`)
-      else window.location.assign('/')
+      else window.location.assign('/?resume=1') // resume straight into the next node, not the splash
     } finally { setAdvancing(false) }
   }