[Bug]: MsgContext.canonicalKey() is not injective — distinct conversations can collapse to one gateway session key #3534

Description

io.agentscope.harness.agent.gateway.MsgContext#canonicalKey() joins the routing components with a bare | separator and does not escape that separator inside the components, so the key is not injective: two different routing contexts can produce the same canonical key.

new MsgContext("chatui", "team|r:room-1", null, null, null, Map.of()).canonicalKey();
// "chatui|g:team|r:room-1"
new MsgContext("chatui", "team", "room-1", null, null, Map.of()).canonicalKey();
// "chatui|g:team|r:room-1"   <-- same key, different conversation

extra keys and values are joined the same way, so a value may also forge structural fragments.

Impact

canonicalKey() is the gateway session key (session id derivation, per-key turn gate, session -> key wake-up map). A collision routes two distinct conversations to the same gateway session, so participants of one group/room can see the other's conversation state.

Reproduction

MsgContext groupOnly = new MsgContext("chatui", "team|r:room-1", null, null, null, Map.of());
MsgContext groupRoom = new MsgContext("chatui", "team", "room-1", null, null, Map.of());
assertNotEquals(groupOnly.canonicalKey(), groupRoom.canonicalKey());
// fails on main: expected: not equal but was: <chatui|g:team|r:room-1>

Proposed fix

Escape % (first) and | in every component before appending. Keys without reserved characters are unchanged, so existing session mappings are preserved.

I can open a PR for this if it looks reasonable.