Closes#26193
Adds ContextReferenceProvider ABC so plugins can register custom
@-prefixes (e.g. @issue:ENG-123) with autocomplete and expansion.
Plugin output flows through existing token-limit guards. Zero
breaking changes.
The `/` menu was a flat first-30 slice of the completer's output, and the
completer emits every registry command before the first skill. On a
230-skill install that meant a bare `/` filled all 30 rows with commands
and offered no skill at all, while `/p` cut off inside the alphabetical
skill block — dropping /proving-a-fix-works (471 invocations) and
/pr-update (160) but keeping /pretext (2).
Spend the limit per kind and rank the skill block by recorded usage
(the same .usage.json count Capabilities shows), most-used first and A-Z
within a tie. A bare `/` is browsing, so bundled skills that shipped with
Hermes and were never opened are dropped as noise; a typed query is a
search, and a search that hides a match is broken, so there nothing is
pruned and the ranking only reorders. An argument stage keeps the order
its own command chose.
zccyman
Teknium
Brooklyn Nicholson