feat(v1.3.0): add ephemeral session-key encryption for sensitive state

- Add src/lib/sessionCrypto.ts with AES-GCM-256 non-exportable session keys
- Integrate into Backup flow: auto-clear plaintext mnemonic after QR generation
- Add Lock/Clear button to destroy session key and clear all state
- Add cleanup useEffect on component unmount
- Add comprehensive GEMINI.md for AI agent onboarding
- Fix TypeScript strict mode errors and unused imports

Tested:
- Session-key encryption working (mnemonic clears after QR gen)
- Lock/Clear functionality verified
- No plaintext secrets in localStorage/sessionStorage
- Production build successful

GEMINI.md

@@ -1,12 +1,14 @@
 # SeedPGP - Gemini Code Assist Project Brief
 
 ## Project Overview
+
 **SeedPGP v1.3.0**: Client-side BIP39 mnemonic encryption webapp  
 **Stack**: Bun + Vite + React + TypeScript + OpenPGP.js + Tailwind CSS  
 **Deploy**: GitHub Pages (public repo: `seedpgp-web-app`, private source: `seedpgp-web`)  
-**Live URL**: https://kccleoc.github.io/seedpgp-web-app/
+**Live URL**: <https://kccleoc.github.io/seedpgp-web-app/>
 
 ## Core Constraints
+
 1. **Security-first**: Never persist secrets (mnemonic/passphrase/private keys) to localStorage/sessionStorage/IndexedDB
 2. **Small PRs**: Max 1-5 files per feature; propose plan before coding
 3. **Client-side only**: No backend; all crypto runs in browser (Web Crypto API + OpenPGP.js)
@@ -14,6 +16,7 @@
 5. **Honest security claims**: Don't overclaim what client-side JS can guarantee
 
 ## Non-Negotiables
+
 - Small diffs only: one feature slice per PR (1-5 files if possible)
 - No big code dumps; propose plan first, then implement
 - Never persist secrets to browser storage
@@ -25,10 +28,12 @@
 ## Architecture Map
 
 ### Entry Points
+
 - `src/main.tsx` → `src/App.tsx` (main application)
 - Build output: `dist/` (separate git repo for GitHub Pages deployment)
 
 ### Directory Structure
+
 ```
 src/
 ├── components/        # React UI components
@@ -51,14 +56,18 @@ src/
 ### Key Modules
 
 #### `src/lib/seedpgp.ts`
+
 Core encryption/decryption:
+
 - `encryptToSeedPgp()` - Encrypts mnemonic with PGP public key + optional password
 - `decryptFromSeedPgp()` - Decrypts with PGP private key + optional password
 - Uses OpenPGP.js for PGP operations
 - Output format: `SEEDPGP1:version:base64data:fingerprint`
 
 #### `src/lib/sessionCrypto.ts` (v1.3.0+)
+
 Ephemeral session-key encryption:
+
 - `getSessionKey()` - Generates/returns non-exportable AES-GCM-256 key (idempotent)
 - `encryptJsonToBlob(obj)` - Encrypts to `{v, alg, iv_b64, ct_b64}`
 - `decryptBlobToJson(blob)` - Decrypts back to original object
@@ -66,7 +75,9 @@ Ephemeral session-key encryption:
 - Test: `await window.runSessionCryptoTest()` (DEV only)
 
 #### `src/lib/types.ts`
+
 Core interfaces:
+
 - `SeedPgpPlaintext` - Decrypted mnemonic data structure
 - `SeedPgpCiphertext` - Encrypted payload structure
 - `EncryptedBlob` - Session-key encrypted cache format
@@ -76,21 +87,25 @@ Core interfaces:
 ## Key Features
 
 ### v1.0 - Core Functionality
+
 - **Backup**: Encrypt mnemonic with PGP public key + optional password → QR display
 - **Restore**: Scan/paste QR → decrypt with private key → show mnemonic
 - **PGP support**: Import public/private keys (.asc files or paste)
 
 ### v1.1 - QR Features
+
 - **QR Display**: Generate QR codes from encrypted data
 - **QR Scanner**: Camera + file upload (uses html5-qrcode library)
 
 ### v1.2 - Security Monitoring
+
 - **Storage Indicator**: Real-time display of localStorage/sessionStorage contents
 - **Security Warnings**: Context-aware alerts about browser memory limitations
 - **Clipboard Tracker**: Monitor clipboard operations on sensitive fields
 - **Read-only Mode**: Toggle to clear state + show CSP/build info
 
 ### v1.3 - Session-Key Encryption (Current)
+
 - **Ephemeral encryption**: AES-GCM-256 session key (non-exportable) encrypts sensitive state
 - **Auto-clear**: Plaintext mnemonic cleared from UI immediately after QR generation
 - **Encrypted cache**: Only ciphertext stored in React state; key lives in memory only
@@ -102,6 +117,7 @@ Core interfaces:
 ## Development Workflow
 
 ### Commands
+
 ```bash
 bun install           # Install dependencies
 bun run dev           # Dev server (localhost:5173)
@@ -112,11 +128,13 @@ bun run preview       # Preview production build
 ```
 
 ### Deployment Process
+
 1. **Private repo** (`seedpgp-web`): Source code, development
 2. **Public repo** (`seedpgp-web-app`): Built files for GitHub Pages
 3. **Deploy script** (`scripts/deploy.sh`): Builds + copies to dist/ + pushes to public repo
 
 ### Git Workflow
+
 ```bash
 # Commit feature
 git add src/
@@ -135,24 +153,29 @@ git push origin main --tags
 ## Required Workflow for AI Agents
 
 ### 1. Study First
+
 Before implementing any feature:
+
 - Read relevant files
 - Explain current architecture + entry points
 - List files that will be touched
 - Identify potential conflicts or dependencies
 
 ### 2. Plan
+
 - Propose smallest vertical slice (1-5 files)
 - Show API signatures or interface changes first
 - Get approval before generating full implementation
 
 ### 3. Implement
+
 - Generate code with TypeScript strict mode
 - Include JSDoc comments for public APIs
 - Show unified diffs, not full file rewrites (when possible)
 - Keep changes under 50-100 lines per file when feasible
 
 ### 4. Verify
+
 - Run `bun run typecheck` - no errors
 - Run `bun run build` - successful dist/ output
 - Provide manual test steps for browser verification
@@ -163,25 +186,30 @@ Before implementing any feature:
 ## Common Patterns
 
 ### State Management
+
 - React `useState` + `useEffect` (no Redux/Zustand/external store)
 - Ephemeral state only; avoid persistent storage for secrets
 
 ### Styling
+
 - Tailwind utility classes (configured in `tailwind.config.js`)
 - Responsive design: mobile-first with `md:` breakpoints
 - Dark theme primary: slate-900 background, blue-400 accents
 
 ### Icons
+
 - `lucide-react` library
 - Common: Shield, QrCode, Lock, Eye, AlertCircle
 
 ### Crypto Operations
+
 - **PGP**: OpenPGP.js (`openpgp` package)
 - **Session keys**: Web Crypto API (`crypto.subtle`)
 - **Key generation**: `crypto.subtle.generateKey()` with `extractable: false`
 - **Encryption**: AES-GCM with random 12-byte IV per operation
 
 ### Type Safety
+
 - Strict TypeScript (`tsconfig.json`: `strict: true`)
 - Check `src/lib/types.ts` for core interfaces
 - Avoid `any`; use `unknown` + type guards when necessary
@@ -191,22 +219,27 @@ Before implementing any feature:
 ## Security Architecture
 
 ### Threat Model (Honest)
+
 **What we protect against:**
+
 - Accidental persistence to localStorage/sessionStorage
 - Plaintext secrets lingering in React state after use
 - Clipboard history exposure (with warnings)
 
 **What we DON'T protect against (and must not claim to):**
+
 - Active XSS or malicious browser extensions
 - Memory dumps or browser crash reports
 - JavaScript garbage collection timing (non-deterministic)
 
 ### Memory Handling
+
 - **Session keys**: Non-exportable CryptoKey objects (Web Crypto API)
 - **Plaintext clearing**: Set to empty string + drop references (but GC timing is non-deterministic)
 - **No guarantees**: Cannot force immediate memory wiping in JavaScript
 
 ### Storage Policy
+
 - **NEVER write to**: localStorage, sessionStorage, IndexedDB, cookies
 - **Exception**: Non-sensitive UI state only (theme preferences, etc.) - NOT IMPLEMENTED YET
 - **Verification**: StorageIndicator component monitors all storage APIs
@@ -216,17 +249,20 @@ Before implementing any feature:
 ## What NOT to Do
 
 ### Code Generation
+
 - Don't generate full file rewrites unless necessary
 - Don't add dependencies without discussing bundle size impact
 - Don't use `any` types without explicit justification
 - Don't skip TypeScript strict mode checks
 
 ### Security Claims
+
 - Don't claim "RAM is wiped" (JavaScript can't force GC)
 - Don't claim "offline mode" without real CSP headers (GitHub Pages can't set custom headers)
 - Don't promise protection against active browser compromise (XSS/extensions)
 
 ### Storage
+
 - Don't write secrets to storage without explicit approval
 - Don't cache decrypted data beyond immediate use
 - Don't assume browser storage is secure
@@ -236,6 +272,7 @@ Before implementing any feature:
 ## Testing & Verification
 
 ### Manual Test Checklist (Before Marking Feature Complete)
+
 1. ✅ `bun run typecheck` passes (no TypeScript errors)
 2. ✅ `bun run build` succeeds (dist/ generated)
 3. ✅ Browser test: Feature works as described
@@ -244,6 +281,7 @@ Before implementing any feature:
 6. ✅ DevTools Network tab: No unexpected network calls (if Read-only Mode)
 
 ### Session-Key Encryption Test (v1.3+)
+
 ```javascript
 // In browser DevTools console:
 await window.runSessionCryptoTest()
@@ -255,17 +293,20 @@ await window.runSessionCryptoTest()
 ## Current Version: v1.3.0
 
 ### Recent Changes (2026-01-29)
+
 - ✅ Added `src/lib/sessionCrypto.ts` with ephemeral AES-GCM session keys
 - ✅ Integrated into Backup flow: plaintext mnemonic auto-cleared after QR generation
 - ✅ Added Lock/Clear button to destroy session key and clear all state
 - ✅ Added cleanup on component unmount
 
 ### Known Limitations
+
 - GitHub Pages cannot set custom CSP headers (need Cloudflare Pages for enforcement)
 - Read-only Mode is UI-level only (not browser-enforced)
 - Session-key encryption doesn't protect against active XSS/extensions
 
 ### Next Priorities (Suggested)
+
 1. Extend session-key encryption to Restore flow
 2. Migrate to Cloudflare Pages for real CSP header enforcement
 3. Add "Encrypted in memory" badge when encryptedMnemonicCache exists
@@ -276,12 +317,15 @@ await window.runSessionCryptoTest()
 ## Quick Reference
 
 ### File a Bug/Feature
+
 1. Describe expected vs actual behavior
 2. Include browser console errors (if any)
 3. Specify which flow (Backup/Restore/QR Scanner)
 
 ### Roll Over to Next Session
+
 Always provide:
+
 - Current version number
 - What was implemented this session
 - Files modified
@@ -293,6 +337,7 @@ Always provide:
 ## Example Prompts for Gemini
 
 ### Exploration
+
 ```
 Read GEMINI.md, then explain:
 1. Where is the mnemonic textarea and how is its value managed?
@@ -301,6 +346,7 @@ Read GEMINI.md, then explain:
 ```
 
 ### Feature Request
+
 ```
 Task: [Feature description]
 
@@ -315,6 +361,7 @@ Plan first: show proposed API/changes before generating code.
 ```
 
 ### Verification
+
 ```
 Audit the codebase to verify [feature] is fully implemented.
 Check:

src/App.tsx

@@ -23,7 +23,7 @@ import { StorageIndicator } from './components/StorageIndicator';
 import { SecurityWarnings } from './components/SecurityWarnings';
 import { ClipboardTracker } from './components/ClipboardTracker';
 import { ReadOnly } from './components/ReadOnly';
-import { encryptJsonToBlob, destroySessionKey, EncryptedBlob } from './lib/sessionCrypto';
+import { getSessionKey, encryptJsonToBlob, destroySessionKey, EncryptedBlob } from './lib/sessionCrypto';
  
  console.log("OpenPGP.js version:", openpgp.config.versionString);
  
@@ -122,6 +122,8 @@ import { encryptJsonToBlob, destroySessionKey, EncryptedBlob } from './lib/sessi
          setRecipientFpr(result.recipientFingerprint);
        }
  
+      // Initialize session key before encrypting
+      await getSessionKey();
        // Encrypt mnemonic with session key and clear plaintext state
        const blob = await encryptJsonToBlob({ mnemonic, timestamp: Date.now() });
        setEncryptedMnemonicCache(blob);