fix(desktop): dedupe profile mention completions

[zhongwater123]

What / Why

Fixes #88915.

When Bot Mode is active, a profile can be offered twice in the Desktop @ autocomplete: once by the synchronous Bot plugin contribution and once by the gateway's core profile completion. Both rows insert the same mention, so the duplicate is not a distinct choice.

Product impact path

1. A user types @ in the main Desktop composer or the edit-message composer.
2. Both consumers call useAtCompletions.
3. Bot Mode contributes the roster handle through composer.atCompletions.
4. complete.path independently returns the same active profile handle.
5. The hook previously concatenated both arrays, and the adapter assigned index-distinct IDs.
6. The popover therefore rendered two selectable rows that insert the same @handle.

Root cause and scope

useAtCompletions had no identity reconciliation at the only merge seam between contributed and core completion rows.

This patch deduplicates case-insensitive bare @handle overlaps while preserving contribution order, so the richer Bot row wins. It deliberately does not collapse typed references such as @file:..., distinct multi-source handles such as @researcher-homelab, or the simple context actions @diff / @staged. The same merge is used for gateway success, no-gateway fallback, and request-error fallback.

Non-goals: changing backend profile enumeration, Bot roster/group behavior, path-reference formatting, databases, Langfuse, security behavior, or unrelated completion sources.

Commits

• Base (NousResearch/hermes-agent:main): e624e9fde561e1add9388384012b295fde669ade
• Head: b6b494493853006525a60939dfcedc6779044de3
• History: one commit by zhongwater123; two files changed; no commits from another PR.

Main / head comparison and mutation proof

Regression command:

node ../../node_modules/vitest/vitest.mjs run --project ui src/app/chat/composer/hooks/use-at-completions-contrib.test.tsx

• Latest base behavior plus the new regression test, with the production fix absent: failed, 1 failed / 3 passed. The popover returned ['@Researcher', '@researcher']; expected ['@Researcher'].
• PR head: passed, 4 / 4.
• Mutation proof: temporarily removed only the production merge fix from the PR head while retaining the regression test; the same assertion failed again, 1 failed / 3 passed. Restored the fix and reconfirmed 4 / 4 with a clean worktree.

Validation

Passed on the final head:

• Focused regression: 4 / 4.
• vitest run --project ui src/app/chat/composer/hooks: 87 / 87 across 14 files.
• node --test src/plugins/*/tests/*.test.mjs: 254 / 254.
• npm run typecheck: renderer, Electron, and E2E TypeScript configs passed.
• npm run build: production renderer (15,033 modules), Electron main/preload bundles, native dependency staging, and assert-dist-built passed.
• npm run lint: exit 0, 0 errors; 123 warnings are in unmodified repository files. The two touched files separately pass ESLint with --max-warnings=0.
• Prettier check for both touched files passed.
• python scripts/check-windows-footguns.py --all: passed, 983 files scanned.
• git diff --check: passed.

Checks that did not pass or could not run:

• npm run test:ui did not pass in this Windows environment. The captured run timed out in four unrelated files: src/app/skills/index.test.tsx, src/app/messaging/index.test.tsx, src/store/session-unread-tile.test.ts, and src/app/settings/gateway-settings.test.tsx. A single-worker rerun of exactly those files also failed 12 / 20 (mostly 15-second timeouts plus existing DOM/act() isolation symptoms). None imports or exercises the changed hook.
• HERMES_PYTHON=D:\python312\python.exe scripts/run_tests.sh tests/gateway/test_complete_path_at_filter.py reached pytest collection but could not collect because concurrent_log_handler is not installed. No Python production code is changed.

Platform

• Windows 11, case-sensitive NTFS checkout
• Node.js 24.19.0; npm 10.9.3
• Python 3.12.2 for the attempted backend test

Overlap audit

No open PR references #88915 or its exact symptom at publication time. #86814 touches the Bot plugin but is a stale/conflicting alternate feature implementation and does not reconcile contributed/core completion rows.

Prepared with Codex assistance; evidence verified against the stated commits.