feat(emitter): first-class defn functions via cljFn wrapper

User-defined defn functions can now be passed as values to other
functions (e.g. bring/run-server, apply-fn, map, filter).

- Track function arities in definedFnArities table
- Register defn/defn- arities during emission
- Emit cljFn wrapper when a defn symbol is used as a value:
  * Multi-arity / rest: cljFn(procName)  (already seq[CljVal])
  * Single-arity: cljFn(proc(args): procName(args[0], ...))
- Direct calls remain unchanged (fast path)
- All existing emitter tests pass

src/emitter.nim

@@ -1,5 +1,5 @@
 # Bara Lang → Nim Emitter
-import strutils, sets, algorithm, sequtils
+import strutils, sets, algorithm, sequtils, tables
 import types
 import macros
 
@@ -10,13 +10,38 @@ var nsAliases*: seq[(string, string)] = @[]  # (alias, namespace)
 var scopeStack*: seq[HashSet[string]] = @[]
 var definedGlobals*: HashSet[string] = initHashSet[string]()
 var multiArityFns*: HashSet[string] = initHashSet[string]()
+var definedFnArities*: Table[string, int] = initTable[string, int]()  # -1 = multi-arity/rest
 var loopResultVar*: string = ""  # Set by loop handler when result capture is needed
 
 proc registerGlobal*(name: string) =
   definedGlobals.incl(name)
 
+proc mangleName*(name: string): string
+
+proc registerFn*(name: string, arity: int) =
+  definedFnArities[name] = arity
+
+proc emitFnWrapper*(name: string): string =
+  ## Emit a cljFn wrapper for a user-defined function when used as a value.
+  let mangled = mangleName(name)
+  if name in multiArityFns:
+    # Multi-arity / rest params already take seq[CljVal]
+    return "cljFn(" & mangled & ")"
+  elif definedFnArities.hasKey(name):
+    let arity = definedFnArities[name]
+    if arity == 0:
+      return "cljFn(proc(args: seq[CljVal]): CljVal = " & mangled & "())"
+    else:
+      var argRefs: seq[string] = @[]
+      for i in 0..<arity:
+        argRefs.add("args[" & $i & "]")
+      return "cljFn(proc(args: seq[CljVal]): CljVal = " & mangled & "(" & argRefs.join(", ") & "))"
+  else:
+    return mangled
+
 proc clearGlobals*() =
   definedGlobals = initHashSet[string]()
+  definedFnArities = initTable[string, int]()
 
 proc setNsAliases*(aliases: seq[(string, string)]) =
   nsAliases = aliases
@@ -807,6 +832,7 @@ proc emitSpecialForm(items: seq[CljVal], indent: int): string =
       # Rest params: generate proc with args: seq[CljVal]
       # Register so call sites wrap args in @[...]
       multiArityFns.incl(name.symName)
+      registerFn(name.symName, -1)
       let namedCount = restIdx
       var preambleLines: seq[string] = @[]
       for pi in 0..<restIdx:
@@ -824,6 +850,7 @@ proc emitSpecialForm(items: seq[CljVal], indent: int): string =
       popScope()
       let preamble = preambleLines.join("\n")
       return sp & "proc " & procName & exportMarker & "(args: seq[CljVal]): CljVal =\n" & preamble & "\n" & bodyCode
+    registerFn(name.symName, paramNames.len)
     if indent == 0:
       var bodyCode = ""
       if body.len == 0:
@@ -895,6 +922,7 @@ proc emitSpecialForm(items: seq[CljVal], indent: int): string =
     if hasRest:
       # Rest params: generate proc with args: seq[CljVal]
       multiArityFns.incl(name.symName)
+      registerFn(name.symName, -1)
       let namedCount = restIdx
       var preambleLines: seq[string] = @[]
       for pi in 0..<restIdx:
@@ -912,6 +940,7 @@ proc emitSpecialForm(items: seq[CljVal], indent: int): string =
       popScope()
       let preamble = preambleLines.join("\n")
       return sp & "proc " & procName & "(args: seq[CljVal]): CljVal {.used.} =\n" & preamble & "\n" & bodyCode
+    registerFn(name.symName, paramNames.len)
     var bodyCode = ""
     if body.len == 0:
       bodyCode = indentStr(indent + 1) & "cljNil()"
@@ -2196,6 +2225,10 @@ proc emitExpr*(v: CljVal, indent: int = 0): string =
     if isLocalVar(symName):
       return sp & mangleName(symName)
     if symName in definedGlobals:
+      # If the global is a user-defined function, emit a cljFn wrapper
+      # so it can be passed as a first-class value.
+      if symName in multiArityFns or definedFnArities.hasKey(symName):
+        return sp & emitFnWrapper(symName)
       return sp & mangleName(symName)
     return sp & "cljSymbol(\"" & symName & "\")"
   of ckList: