merge system and user config in function calls

Note that we're removing explicit map sizing because
map size has become unpredictable

Author: qstearns

server/internal/gateway/env.go

@@ -84,6 +84,14 @@ func (c *CaseInsensitiveEnv) Set(key, value string) {
 	c.data[strings.ToLower(key)] = value
 }
 
+func (c *CaseInsensitiveEnv) All() map[string]string {
+	result := make(map[string]string, len(c.data))
+	for k, v := range c.data {
+		result[k] = v
+	}
+	return result
+}
+
 type ToolCallEnv struct {
 	SystemEnv  *CaseInsensitiveEnv
 	UserConfig *CaseInsensitiveEnv

server/internal/gateway/proxy.go

@@ -204,10 +204,17 @@ func (tp *ToolProxy) doFunction(
 		return oops.E(oops.CodeBadRequest, err, "failed to read request body").Log(ctx, logger)
 	}
 
-	payloadEnv := make(map[string]string, len(plan.Variables))
-	for _, v := range plan.Variables {
-		if val := env.Get(v); val != "" {
-			payloadEnv[v] = val
+	payloadEnv := make(map[string]string)
+
+	// Start with system environment variables
+	for k, v := range env.SystemEnv.All() {
+		payloadEnv[k] = v
+	}
+
+	// For each variable required by the function, allow user config to merge/override
+	for _, varName := range plan.Variables {
+		if val := env.UserConfig.Get(varName); val != "" {
+			payloadEnv[varName] = val
 		}
 	}