M4 Android stage 1 (trust). The client now presents a persistent self-signed identity on
every connect, pins host certs trust-on-first-use, and runs the SPAKE2 PIN pairing
ceremony — parity with the Apple/Linux clients. The Rust connector already exposed this;
this wires it through the JNI + a Keystore-backed Kotlin store + the connect UI.
- crates/punktfunk-android: nativeGenerateIdentity (mint), nativeConnect gains
certPem/keyPem/pinHex (identity + TOFU/pinned), nativeHostFingerprint, nativePair
(SPAKE2). hex32/parse_hex32 helpers.
- kit/security: IdentityStore (AndroidKeyStore AES-256-GCM-wrapped PEM blob; StrongBox
with TEE fallback; four-state load so a decrypt failure never shadow-mints), PinStore
(host-id -> fp-hex in SharedPreferences). obtainIdentity mints once on genuine first run.
- app: ConnectScreen loads/mints the identity, looks up the stored pin, and gates connect
on a trust decision — TOFU prompt (first connect), fingerprint-changed warning, PIN dialog.
- AndroidManifest: allowBackup=false (Keystore keys don't restore; a restored device
re-mints rather than carrying a dead blob).
Verified live (emulator -> home-worker-2, synthetic m3-host):
- identity: host logs the presented client fingerprint; stable across an app restart.
- TOFU: first-connect prompt -> Trust -> pins the observed host fp -> pinned reconnect
skips the prompt.
- SPAKE2: PIN ceremony -> "pairing complete — client trusted" -> auto-connect under
--require-pairing; wrong PIN / host down -> "Pairing failed".
Known follow-up: trust is keyed by mDNS instance id for discovered hosts but by
"host:port" for manually-typed ones, so pairing via one path isn't recognized by the other.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
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