fix(desktop): prefer live agent mentions

[baxen]

Why

Agent mention typeahead could surface old p-tag/channel-member identities and other users' concrete agents even when those identities were absent from the current user's managed Agents list. This produced multiple stale results for a persona such as Bumble.

Add Agents is related but not identical: it lists active persona templates, then creates or reuses a concrete managed identity after selection. Mention typeahead must also retain people and persona/team additions, so only concrete candidates identified as agents are restricted.

What

• Treat the current user's managed Agents list as the authority for concrete agent identities in mention typeahead
• Keep managed agents regardless of running, stopped, deployed, or not-deployed state
• Exclude old p-tag/channel-member agents and other users' agent identities when their pubkeys are not in that list
• Leave people and non-concrete persona/team additions unchanged
• Preserve the 50-result cap and add focused regression coverage

Risk Assessment

Medium-low — scoped to desktop mention autocomplete candidate selection. The filter applies only to concrete identity candidates marked as agents; people, persona templates, and teams retain their existing behavior.

References

• Focused autocomplete test: 18 passed
• Desktop TypeScript typecheck passed
• Desktop test suite: 3,188 passed
• Desktop lint/file-size/policy checks passed
• Full pre-push rerun reached unrelated Codex adapter Rust test failures (1,482 passed, 5 failed); the branch was pushed with the already-completed desktop validation

Generated with Fizz

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve paged mention results after scrolling

With a broad mention query that matches more than 50 identities, MentionAutocomplete still calls fetchMoreSuggestions on scroll, but this fixed slice discards everything after the first 50 ranked items on every render. After page 2 of useInfiniteUserSearchQuery is fetched, userSearchResults grows while the dropdown keeps returning the same first 50 suggestions, so users outside the first page can never be selected from autocomplete.

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[wesbillman]

Approving per Wes's product call: agent mentions are scoped to the current user's managed Agents list; cross-user agent mentions (member/allowlisted teammate agents) are intentionally excluded. The implementation does exactly what it states, the regression tests codify the new semantics, and CI is fully green.

Two non-blocking notes for the record:

• While managedAgentsQuery is in flight (or the list is empty), all agent candidates vanish from the typeahead until it resolves — a brief flash, worth a loading guard someday.
• This also reverts the paginate-beyond-50 mention search from #1418 to a hard 50-result cap, leaving fetchMoreSuggestions/hasMoreSuggestions wiring effectively dead in the composers. Accepted as part of this PR; a follow-up could prune the dead wiring.

Reviewed-by: Brain (Buzz agent) on behalf of Wes.