Originate v2 source routes and wire fragmentIdFilter targeted resync (#1378)

* Originate v2 source routes and wire fragmentIdFilter targeted resync

Part A — source-route origination policy:
- Gate route application (BLESourceRouteOriginationPolicy): only packets we
  author, directed at a single peer, with TTL headroom, whose recipient is
  not directly connected. Relays no longer attach routes to (and re-sign)
  packets they merely forward.
- Version-gate paths: MeshTopologyTracker records the highest protocol
  version observed per peer; BFS routes require every intermediate hop and
  the recipient to be v2-observed, capped at 4 intermediate hops.
- Degrade on failure: BLESourceRouteFailureCache marks a routed send that
  sees no inbound traffic from the recipient within 10s as failed and floods
  for 60s before retrying routes.

Part B — REQUEST_SYNC fragmentIdFilter (TLV 0x06):
- Requester: BLEFragmentAssemblyBuffer reports stalled broadcast
  reassemblies (no new fragment for 5s, retried at most every 10s); the
  maintenance pass sends a types=fragment REQUEST_SYNC naming the stalled
  8-byte fragment stream IDs to each connected peer.
- Responder: GossipSyncManager restricts the fragment diff to exactly the
  named streams, bypassing the since-cursor while the GCS filter still
  excludes pieces the requester holds; RSR/TTL-0/rate-limit semantics
  unchanged and REQUEST_SYNC stays link-local.
- Bounds: at most 60 IDs per request (60*17-1 = 1019 bytes <= the 1024-byte
  decoder cap); oversized 0x06 values are ignored, not fatal.

Docs: SOURCE_ROUTING.md gains the iOS origination policy (§8);
REQUEST_SYNC_MANAGER.md documents 0x05/0x06 as implemented.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Fix stall-clock refresh on duplicates and overflow suppression in fragment resync

Two fixes to stalledBroadcastFragmentIDs bookkeeping in
BLEFragmentAssemblyBuffer:

- Duplicate fragments no longer reset the stall clock. Fragment packets
  bypass the packet deduplicator, so relayed duplicates of an
  already-held index arriving every few seconds kept lastFragmentAt
  fresh and suppressed the targeted REQUEST_SYNC indefinitely. Now
  lastFragmentAt only updates when the index is new (actual progress).

- Only the streams that will actually be encoded on the wire are
  rate-limited. Previously every stalled candidate got
  lastResyncRequestAt set, but encodeFragmentIdFilter serializes at most
  RequestSyncPacket.maxFragmentIdFilterCount (60) IDs, so overflow
  streams were suppressed for retryAfter without ever being requested.
  Selection now caps at that shared constant, oldest stall first, so
  overflow stays eligible and rotates fairly on the next pass.

Tests: duplicates arriving periodically still trigger the stall report;
70 stalled streams yield the 60 oldest on the first pass and the
remaining 10 on the next.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: jack <jackjackbits@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

docs/SOURCE_ROUTING.md

@@ -2,7 +2,7 @@
 
 This document specifies the Source-Based Routing extension (v2) for the BitChat protocol. This upgrade enables efficient unicast routing across the mesh by allowing senders to specify an explicit path of intermediate relays.
 
-**Status:** Implemented in Android and iOS. Backward compatible (v1 clients ignore routing data).
+**Status:** Implemented in Android and iOS: both decode routed packets, forward along routes, and originate routes. iOS origination is policy-gated (see §8). Backward compatible (v1 clients never receive routed frames from iOS: routes are only originated when every node on the path has been observed speaking v2).
 
 ---
 
@@ -144,3 +144,44 @@ When a node receives a packet **not** addressed to itself:
     *   **Fallback:** If the Next Hop is unreachable, **fall back to broadcast/flood** to ensure delivery.
 3.  **If NO (Standard):**
     *   Flood the packet to all connected neighbors (subject to TTL and probability rules).
+
+---
+
+## 8. iOS Origination Policy
+
+iOS attaches a route (upgrading the packet to v2 and re-signing it) only when
+**all** of the following hold at send time (`BLESourceRouteOriginationPolicy`):
+
+1.  **Authored locally.** The packet's `SenderID` is our own peer ID. Relays
+    never rewrite someone else's packet — adding a route would force a
+    re-sign under the wrong key. Relays only *follow* existing routes
+    (`BLERouteForwardingPolicy`).
+2.  **Directed.** The packet has a single-peer `RecipientID` (not the
+    broadcast ID). In practice this covers Noise-encrypted private traffic,
+    private file transfers, and their fragments (fragments inherit the
+    parent's route and version, per §5).
+3.  **TTL headroom.** `TTL > 1`. Link-local packets (e.g. `REQUEST_SYNC`,
+    always TTL 0) never carry routes.
+4.  **Recipient not directly connected.** A direct write already delivers in
+    one hop; a route would only add bytes.
+5.  **Complete v2 path exists.** BFS over the confirmed-edge mesh graph
+    (`MeshTopologyTracker`, built from verified announce `directNeighbors`
+    claims, entries expiring after 60 s) finds a path with **at most 4
+    intermediate hops** where every intermediate hop **and the recipient**
+    has been observed originating or relaying a v2 packet. Nodes never seen
+    speaking v2 are assumed v1-only and are excluded — a v1 client cannot
+    decode a v2 frame, so routing through it would silently drop the packet.
+6.  **No recent route failure.** See below.
+
+If any gate fails, behavior is exactly the pre-routing flood/direct-write
+path — v1 peers observe no change.
+
+### Failure Fallback
+
+A routed unicast rides one path; a broken hop loses the packet where a flood
+would heal around it. iOS keeps a small per-recipient health cache
+(`BLESourceRouteFailureCache`): a routed send that sees no inbound packet
+authored by the recipient within 10 s counts as a route failure, and directed
+sends to that recipient fall back to flooding for the next 60 s before
+routing is attempted again. Retransmission of the payload itself stays where
+it always was (MessageRouter and higher layers).