feat(composer): plugin-contributed @ mentions in the picker (#43)

[BowmanStephen]

Problem

The composer's @ autocomplete only offered files/URLs/git refs — bot roster names were invisible, so users had to type the exact profile handle blind (Hermes-Bot-Mode issue #43).

Change

A new composer.mentions contribution surface, following the proven microActions registry pattern:

• ComposerMentionProvider / ComposerMentionEntry — resolve(ctx) returns entries with text (inserted on pick), display, meta, and optional group (rendered as a section header, e.g. "Bots").
• useAtCompletions accepts mentionEntries and merges matches into the @ picker payload alongside complete.path results, grouped by the provider's label.
• Mention items are tagged metadata.mention so the mid-message trigger keeps them alongside skills — a bot name is a legitimate inline reference, like a skill.
• Exported from @hermes/plugin-sdk.

The companion Hermes-Bot-Mode PR registers the roster as a Bots group (active profile excluded).

Tests

3 new in use-at-completions.test.ts: mention rides alongside path completions, display-name filtering, mention metadata tag. 342 composer/sdk tests pass, tsc --noEmit clean.

[Enough1122]

AI code review — automated review for reference, author can ignore or act on any point.

feat(composer): plugin-contributed @ mentions in the picker (#43)

No blocking issues found. A few minor observations:

1. apps/desktop/src/app/chat/composer/hooks/use-at-completions.ts (toItem) — the mention: true metadata tag is only attached when entry.group is truthy (...(entry.group ? { metadata: { ...metadata, mention: true } } : { metadata })). But ComposerMentionEntry.group is optional ("When absent, entries merge into the plain list"). A plugin-contributed mention without a group is therefore never tagged as a mention, and isSkillItem (the mid-message filter) will silently drop it mid-message even though it shows up in the picker. The mention tag should be derived from the entry source (or a dedicated flag), independent of the optional grouping field.

2. Same file, catch branch — when the gateway complete.path call throws, the fallback filters mentions by e.text only, while the success path matches both text and display (displayOf(e)). A mention whose display name matches the query (but whose raw text does not) disappears on gateway error but appears on success — inconsistent behavior for the same keystrokes. Consider hoisting the matching predicate so both paths use it.

3. composer-utils.ts isSkillItem — the name now reads as "skill item" but the predicate is "skill OR mention". Renaming to something like isMidMessageItem (or documenting the widened contract) would prevent future callers from misreading the intent.

4. Tests are good (picker ride-along, display-name filtering, mention tagging). The as never[] casts in use-at-completions.test.ts are slightly loose — a concrete CompletionEntry[] type would keep the tests honest if the interface changes.