Fix unnecessary RPC calls on /agents page for known non-agent users

[realproject7]

Bug

When a known PlotLink user (who is NOT an agent) visits /agents, the page fires 3+ RPC calls to base-rpc.publicnode.com (agentIdByWallet, balanceOf, tokenOfOwnerByIndex) even though the DB already knows this user has no agent registration. This defeats the purpose of PR #597 (agent DB cache).

Visible in network tab: multiple base-rpc.publicnode.com fetches on every page load.

Root Cause

In src/app/agents/page.tsx, the detection flow is:

1. Call getAgentUserFromDB(address) — this function (lib/actions.ts lines 186-231) queries the users table with agent_id IS NOT NULL filter on ALL queries
2. For a user who exists in DB but has agent_id = NULL → all queries exclude them → returns null
3. dbUser = null, dbDetected = false
4. needsRpcFallback = !dbLoading && !dbDetected && !!address → true
5. Three RPC calls fire unnecessarily

The function cannot distinguish between:

• "User exists in DB but is not an agent" (agent_id IS NULL) → should NOT make RPC calls
• "User has no DB record at all" (completely unknown wallet) → SHOULD make RPC calls (might be externally registered agent)

Fix

Change the detection to also check if the user exists in DB at all (regardless of agent status):

Option A: Two-step DB check in agents/page.tsx

// Step 1: Check if user has cached agent data
const { data: agentUser, isLoading: agentLoading } = useQuery({
  queryKey: ["db-agent", address],
  queryFn: () => getAgentUserFromDB(address!),
  enabled: !!address,
});

// Step 2: Check if user exists in DB at all (regardless of agent status)
const { data: regularUser, isLoading: userLoading } = useQuery({
  queryKey: ["db-user-exists", address],
  queryFn: () => getUserFromDB(address!),
  enabled: !!address && !agentLoading && agentUser === null,
});

const dbLoading = agentLoading || (agentUser === null && userLoading);
const dbDetected = agentUser?.agent_id != null;
const userExistsInDB = agentUser != null || regularUser != null;

// Only RPC if user has NO DB record at all (completely unknown wallet)
const needsRpcFallback = !dbLoading && !dbDetected && !userExistsInDB && !!address;

Option B: Single function that returns discriminated result

Create a new checkAgentStatus(address) server action that returns:

type AgentStatus = 
  | { status: "agent"; user: User }        // known agent
  | { status: "not-agent" }                 // known user, no agent_id  
  | { status: "unknown" }                   // no DB record at all

This is cleaner and avoids two separate DB round-trips.

Expected behavior after fix

Scenario	DB check	RPC calls	Result
Known user, no agent_id	getUserFromDB → user found, agent_id = NULL	None	Show registration form
Known agent	getAgentUserFromDB → agent found	None	Show management UI
Unknown wallet (no DB record)	Both return null	Yes (3 calls)	Check if externally registered
Unknown wallet, externally registered agent	Both return null, RPC finds agent	Yes, then auto-cache	Show management UI

Files to modify

• src/app/agents/page.tsx — fix needsRpcFallback logic
• lib/actions.ts — possibly add checkAgentStatus() helper

Branch

task/600-fix-agent-rpc-fallback

Acceptance criteria

• Known PlotLink users with no agent_id → zero RPC calls on /agents page
• Known agents → zero RPC calls (read from DB)
• Completely unknown wallets → RPC fallback fires (correct)
• Externally registered agents detected and auto-cached on first visit
• Build passes