Feature/fragmentation fixes (#453)

* Fix fragmentation + BLE long-write + padding

- Accumulate CBATTRequest long writes by offset and decode once per central
- Decode original packet after fragment reassembly (preserve flags/compression)
- Switch MessagePadding to strict PKCS#7 and validate before unpadding
- Make BinaryProtocol.decode robust: try raw first, then unpad fallback
- Unpad frames before BLE notify; fragment when exceeding centrals' max update length
- Skip notify path when max update length < 21 bytes (protocol minimum)

Verified large PMs and announces route without decode errors and peers show reliably.

* Tests: fix weak delegate lifetime, legacy constants, and unused vars; fragment unpadded frames

- BLEServiceTests: hold strong reference to MockBitchatDelegate
- IntegrationTests: fix inline comment braces; replace removed types with test-safe values; use numeric 0x06 for legacy handshake resp checks
- BinaryProtocolTests: remove unused minResult variable
- BLEService: fragment the unpadded frame so fragments are efficient

* tests: add Noise rehandshake recovery test; document in-memory test bus and autoFlood; stabilize large-network broadcast

* tests: align suite with current behavior (compression, padding, routing, nonce); deflake and stabilize

---------

Co-authored-by: jack <jackjackbits@users.noreply.github.com>

bitchatTests/README.md

@@ -0,0 +1,45 @@
+# Test Harness Guide
+
+This test suite uses an in-memory networking harness to make end-to-end and integration tests deterministic, fast, and race-free without touching production code.
+
+## In-Memory Bus
+
+- **File:** `bitchatTests/Mocks/MockBLEService.swift`
+- **Registry/Adjacency:** Global `registry` maps `peerID` to a `MockBLEService` instance; `adjacency` records simulated links between peers.
+- **Setup:** Call `MockBLEService.resetTestBus()` in `setUp()` to clear state between tests; use `_testRegister()` when creating a node to register immediately.
+- **Topology:** Use `simulateConnectedPeer(_:)` and `simulateDisconnectedPeer(_:)` to add/remove links. `connectFullMesh()` helpers in tests build larger topologies.
+- **Handlers:** Tests can observe data via `messageDeliveryHandler` (decoded `BitchatMessage`) and `packetDeliveryHandler` (raw `BitchatPacket`).
+- **De‑duplication:** A thread-safe `seenMessageIDs` prevents duplicate deliveries during flooding/relays.
+
+## Broadcast Flooding
+
+- **Flag:** `MockBLEService.autoFloodEnabled`
+- **Intent:** When `true`, public broadcasts propagate across the entire connected component (ignores TTL for reach) while still de‑duping to prevent loops.
+- **Usage:** Enabled in Integration tests (`setUp`) to simulate large-network broadcast; disabled in E2E tests to keep routing explicit and verify TTL behavior (see `PublicChatE2ETests.testZeroTTLNotRelayed`).
+
+## Rehandshake Flow (Noise)
+
+- **Why:** The legacy NACK recovery path was removed; recovery now relies on Noise session rehandshake after decrypt failure or desync.
+- **Manager:** `NoiseSessionManager` manages per-peer sessions.
+- **Pattern:** On decrypt failure, proactively clear the local session and re-initiate a handshake. The peer accepts and replaces their session.
+- **Test:** `IntegrationTests.testRehandshakeAfterDecryptionFailure`
+  - Corrupts ciphertext to induce a decrypt error.
+  - Calls `removeSession(for:)` on the initiator’s manager before `initiateHandshake(with:)` to avoid `alreadyEstablished`.
+  - Verifies encrypt/decrypt succeeds post-rehandshake.
+
+## Tips
+
+- **Determinism:** Add small async delays only where handler installation/topology changes could race the first send.
+- **Scoping:** Keep `autoFloodEnabled` toggled only within Integration tests; always reset in `tearDown()` to avoid cross-test contamination.
+- **Direct vs Relay:** Private messages target a specific peer when adjacent; otherwise they are surfaced to neighbors for relay and, if known, also delivered to the target.
+
+## Quick Start
+
+- Create nodes with `_testRegister()` and connect them:
+  - `let svc = MockBLEService(); svc.myPeerID = "PEER1"; svc._testRegister()`
+  - `svc.simulateConnectedPeer("PEER2")`
+- Observe messages:
+  - `svc.messageDeliveryHandler = { msg in /* asserts */ }`
+- Enable broadcast flooding for Integration suites only:
+  - `MockBLEService.autoFloodEnabled = true`
+