Fixed-10108 : should only advertise snap/1 in handshake if snapsync-server-enabled

[sagarkhandagre998]

PR description

p2p: only advertise snap/1 when snap server or snap sync is active

Problem

Besu unconditionally advertised snap/1 in its devp2p handshake regardless of --snapsync-server-enabled. Remote peers probed it, received empty responses, classified it as a non-server, and stopped sending snap requests to it — wasted connections with no operator warning.

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Approach Decision

The non-trivial part was that snap/1 serves two roles:

• Server role — Besu serves snap data to peers doing snap sync (--snapsync-server-enabled)
• Client role — Besu itself needs snap/1 negotiated to receive snap data from peers while doing snap sync (--sync-mode=SNAP)

In devp2p, both sides must advertise a capability for it to be active on a connection. Blindly removing snap/1 when the server is disabled would silently break snap sync for nodes still catching up.

So the fix gates advertisement on both conditions rather than just snapServerEnabled:

--snapsync-server-enabled	--sync-mode	Advertise snap/1?
false	non-SNAP	❌ — silent, DEBUG log
false	SNAP	✅ — WARN log (client-only, won't serve)
true	any	✅ — no warning

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Changes

• SnapProtocolManager — calculateCapabilities() now takes snapConfig and syncMode; applies the three-way logic above; logs WARN when advertising for client-only use
• BesuControllerBuilder — passes syncConfig.getSyncMode() into SnapProtocolManager
• SnapProtocolManagerTest — adds SyncMode.SNAP to keep the existing test exercising a snap-capable node

Fixed Issue(s)

Fixed #10108

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[sagarkhandagre998]

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