Look up indexed symbol definitions by exact or folded symbol name. Use this before
broad search when you already know a function, type, class, interface, constant,
or similar symbol name.
Inputs use SIFS vocabulary: `source` for a local path or Git URL, `profile` for
saved source/options, and `limit` for bounded output. Pass `kind` or `kinds` to
filter to symbol kinds such as `function`, `struct`, `class`, or `case`. Pass
`include_docs` or `extensions` for a one-off document/custom-extension index
scope. Paths in results are repository-relative indexed file paths. Symbol
postings include role, confidence, and origin metadata so agents can distinguish
indexed definitions from lower-confidence extraction sources.