R - allocate a share of a number over different columns using an ifelse statement

I have the following data set:

observation <- c(1:10)
pop.d.rank  <- c(1:10)
cost  <- c(101:110)
all <- data.frame(observation,pop.d.rank,cost) 

And I want to allocate the following amount of money over three years:

annual.investment <- 500

I can do this for the first year with the following script:

library(dplyr)

all <- all %>%  
 mutate(capital_allocated.5G = diff(c(0, pmin(cumsum(cost), annual.investment)))) %>%
 mutate(capital_percentage.5G = capital_allocated.5G / cost * 100) %>%
 mutate(year = ifelse(capital_percentage.5G >= 50, "Year.1",0))

But when I try to do this for the second year, taking into account the previous year's investment, the code does not work. Here is my attempt at putting an ifelse statement in the mutate loop so that it does not overwrite the money allocated in the previous year:

all <- all %>%  
 mutate(capital_allocated.5G = ifelse(year == 0, diff(c(0, pmin(cumsum(cost), annual.investment))), 0) %>%
 mutate(capital_percentage.5G = capital_allocated.5G / cost * 100) %>%
 mutate(year = ifelse(capital_percentage.5G >= 50, "Year.2",0))

I want the data to look like the following, where the amount allocated goes first to any row that hasn't been 100% completed from the previous year.

capital_allocated.5G <- c(101, 102, 103, 104, 105, 106, 107, 108, 109, 55)
capital_percentage.5G <- c(100, 100, 100, 100, 100, 100, 100, 100, 100, 50)
year <- c("Year.1", "Year.1","Year.1", "Year.1","Year.1", "Year.2", "Year.2","Year.2", "Year.2","Year.2")
example.output <- data.frame(observation,pop.d.rank,cost,   capital_allocated.5G, capital_percentage.5G, year)