Await agent DB writes and handle cache failures gracefully

[realproject7]

Problem

Agent registration and management actions persist to DB via fire-and-forget fetch().catch(() => {}). If the DB write fails:

• On-chain tx succeeded but DB cache is out of sync
• User sees "success" but agent data isn't cached
• Subsequent page loads fall back to RPC or show stale data
• agent-register/route.ts has no 23505 conflict handling for rapid re-registration

Affected locations:

• `AgentRegister.tsx` lines 105-117 — agent-register fire-and-forget
• `AgentManage.tsx` — agent-update fire-and-forget after URI update, wallet bind/unbind
• `agents/page.tsx` line 89 — cacheAgentById fire-and-forget
• `AgentDashboard.tsx` line 106 — cacheAgentById fire-and-forget

Fix

1. Await the DB writes in AgentRegister and AgentManage — don't fire-and-forget
2. Show "on-chain OK, cache failed — will sync on next visit" if DB write fails (don't show full error, just a warning)
3. Add 23505 conflict handling in `agent-register/route.ts` — if row exists, update instead of failing
4. Add retry logic for `cacheAgentById` — retry once on failure before giving up

Files to modify

• `src/components/AgentRegister.tsx` — await DB write, show warning on failure
• `src/components/AgentManage.tsx` — await DB writes, show warning on failure
• `src/app/api/user/agent-register/route.ts` — add 23505 conflict handling
• `src/app/agents/page.tsx` — add retry for cacheAgentById
• `src/components/AgentDashboard.tsx` — add retry for cacheAgentById

Branch

`task/634-agent-cache-reliability`

Acceptance criteria

• Agent register awaits DB write and shows warning if it fails
• Agent manage actions await DB writes
• agent-register route handles 23505 conflicts gracefully
• cacheAgentById retries once on failure
• On-chain success is never blocked by DB failure
• Build passes

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Self-Verification (T3)

• Run npm run dev, register a new agent on /agents page
• Check browser console — no silent fetch failures
• Verify agent data appears in Supabase users table after registration
• On /agents Manage tab, update agent URI — verify success message appears
• Bind/unbind wallet — verify success message appears
• Temporarily break the DB endpoint (wrong URL) — verify UI shows warning, not false success
• Run npm run build — no errors

[realproject7]

T3 tools for verification: Use the donor wallet for agent registration. Use Chrome MCP to verify network requests and console output.