an addition:
after checking the book, i suspect i saw a Greenish Warbler as well.
it was relatively large and its legs were dark, not as pale as yellow-browed's.
it flied between branches and twigs not high above the stony stream.
these match quite well with the description in the bird book.
in addition, i didn't hear it called.
if this is true, i had 4 ticks in around an hour just beside the construction sites!