Parking Lot Philharmonic

[Johicopter]

The sun beams at me
A far-off candle’s spotlight seen  I would commit to either the candle or spotlight metaphor here
Via gradient of eyelid veins  Great way to tell us the narrator's eyes are closed
I am still
Breathing in silence, expectant
An afternoon’s overture begins to rise  The wording here is a little awkward. Overtures start, enter, or crescendo, but they don't necessarily "rise".
Car horns blare in opening
Wood winds play with flame-bright leaves  You imply in the first three lines that your eyes are closed, so it's jarring to have this singular visual of leaves
A snare drum rallentando of stranger’s steps  Rallentando refers to slowing down; is that what you are trying to convey?
The orchestra sits as audience
Performance in the round reversed
I am on stage, in spotlight center  Is the stage the parking lot? If so, does that mean the "orchestra" is on stage with you in the metaphor?
My nerves vibrate slowly, tugged by the breeze
A melodious harp of my own sinew
Harmonizes with muscles to ease their grip  I like this depiction of rest
A loosened breath
First of the day  Is it morning or afternoon? It feels unclear.
A note in a symphonic swell
Then

burbled

electronic trills.  I am not sure why the only period in the poem is here if you continue the thought on the next line. I think the space is doing enough to break up the text.

A notification from my responsible self
I return to the shade of the building
My fingers seek a warm portion of my pocket
Remaining heat from sunlight
Clings to the leather of my coat
As a folded program, or ticket stub
A reminder of peace
I find it, and hold it
Long after I can recall the tune
I find myself humming
Without knowing why

I think the ending is strong here and I think you are effective at capturing the moment in intimate detail. I noticed the metaphor of music shifted slightly in the first half, from the tangible sounds of the outside world to the internal vibrations that allow the narrator to relax and breathe. I find this second version of the metaphor much more novel and interesting. Perhaps it could be explored more.