fix(desktop): retain distinct agent instances in autocomplete

[atishpatel]

Summary

• preserve each distinct agent pubkey in autocomplete even when agents share a persona or owner/name
• continue to collapse duplicate source rows for the same normalized pubkey
• show a truncated pubkey in the channel member-add picker so same-named instances are selectable

Validation

• pnpm --filter buzz test — 4,489 passed
• pnpm --filter buzz exec tsc --noEmit --pretty false
• pnpm --filter buzz exec biome check src/features/agents/lib/agentAutocompleteEligibility.ts src/features/agents/lib/agentAutocompleteEligibility.test.mjs src/features/channels/ui/MembersSidebar.tsx
• independent validation by Fast Fizz on 509cb8d97b82f9708e24d4d59ad17c7b39516643: typecheck, focused Biome, 22/22 focused tests, and git diff --check

Generated by Hardworking Honey.

[wesbillman]

Thorough review by Carl on Wes’s behalf at exact head 509cb8d97b82f9708e24d4d59ad17c7b39516643: this fix is needed, correctly scoped, and not covered by PR #4999. No code blocker found.

The existing coalescer treats personaId or (owner, display name) as an agent identity. That is false for managed instances: two distinct pubkeys can intentionally share both. The result is loss, not cosmetic duplication—one real agent becomes impossible to select in @mention, new-DM, and channel member-add autocomplete. This patch changes only agent coalescing to normalized pubkey identity while retaining source-row deduplication for the same pubkey and the existing preference ranking for duplicate representations.

#4999 is complementary, not duplicative. It syncs/rehydrates private managed-agent configuration and enumerates/materializes relay-only records keyed by agent pubkey. It does not modify agentAutocompleteEligibility.ts, MembersSidebar.tsx, or any autocomplete coalescing call site; its frontend changes are only usePersonaSync. Indeed, #4999 can make this bug more visible on fresh devices by surfacing multiple legitimate relay records that the current frontend then collapses by shared persona/name. #5202 is independently useful on current main and remains necessary if #4999 lands.

I traced all three helper consumers: mention autocomplete, new-message recipients, and member-add. Candidate assembly already deduplicates repeated source rows by normalized pubkey before this helper; the helper’s remaining role is now correctly “merge duplicate representations of one pubkey,” not “guess that two keys are one agent.” Existing mention UI already displays truncated npubs on same-name collisions, new-DM rows expose the pubkey on hover, and this PR adds an always-visible truncated key for agent member-add rows, so retained duplicates are distinguishable. Eligibility, archival, channel-membership, and reachability gates remain unchanged.

Focused validation: pnpm typecheck passed; all 22/22 eligibility tests passed; Biome on all three changed files passed; git diff --check passed; worktree clean; remote head unchanged. CI is still running, so merge remains gated on exact-head CI and the PR leaving draft.

One non-blocking cleanup opportunity: currentPubkey and getLabel are now compatibility-only arguments and are intentionally underscored. Removing them from the helper API and its three callers would reduce dead conceptual surface, but it is not worth delaying this bug fix if the author prefers the smaller call-site diff.