feat(machine): seed + bunker-binding IPC bridge

get-atm-secrets now returns { spireSeed, bunkerBinding } instead of the raw
nsec (one-shot semantics kept). Adds IPC handlers + preload bindings for
saveBunkerBinding / clearBunkerBinding / resetBootstrapGate so the renderer
can persist a pairing and re-arm the cassette-state hello on re-pair (#56).
resetBootstrapGate added to state-store. Types mirrored in electron.d.ts.

Part of Phase C, aiolabs/bitspire#52.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/machine/electron/main.ts

@@ -26,14 +26,19 @@ import {
   getLastKnownConfigCreatedAt,
   getBootstrapPublishedAt,
   markBootstrapPublished,
+  resetBootstrapGate,
   applyOperatorCassettesConfig,
   getFeeConfig,
   getLastKnownFeeConfigCreatedAt,
   applyFeeConfig,
+  getBunkerBinding,
+  saveBunkerBinding,
+  clearBunkerBinding,
   type OperatorCassettesPayload,
   type FeeConfigPayload,
   type FeeConfigRow,
   type ApplyResult,
+  type StoredBunkerBinding,
 } from './state-store.js'
 import { initializeHal, type HalInstance } from './hal-service.js'
 
@@ -323,14 +328,31 @@ let secretsConsumed = false
 ipcMain.handle('get-atm-secrets', () => {
   if (secretsConsumed) {
     console.warn('[Electron] SECURITY: get-atm-secrets called after secrets already consumed')
-    return { atmPrivateKey: '' }
+    return { spireSeed: '', bunkerBinding: null }
   }
   secretsConsumed = true
+  // The spire pairing seed (one-shot connect token inside) + the persisted
+  // bunker binding (transport key). The renderer resolves these into a
+  // BunkerSigner; see services/signer-resolver.ts (aiolabs/bitspire#52).
   return {
-    atmPrivateKey: process.env.VITE_ATM_PRIVATE_KEY || '',
+    spireSeed: process.env.VITE_SPIRE_SEED || '',
+    bunkerBinding: getBunkerBinding(),
   }
 })
 
+// Bunker binding persistence — the renderer writes the binding after a
+// successful pairing (connectNewSeed), and resets the bootstrap gate so the
+// new operator receives the spire's hello-event (aiolabs/bitspire#52 / #56).
+ipcMain.handle('state:save-bunker-binding', (_event, binding: StoredBunkerBinding): void => {
+  saveBunkerBinding(binding)
+})
+ipcMain.handle('state:clear-bunker-binding', (): void => {
+  clearBunkerBinding()
+})
+ipcMain.handle('state:reset-bootstrap-gate', (): void => {
+  resetBootstrapGate()
+})
+
 // State persistence IPC handlers
 ipcMain.handle('state:load-cassettes', () => loadCassettes())
 ipcMain.handle('state:set-cassettes', (_event, cassettes) => setCassettes(cassettes))