example: an unshield pays the fee as a private note, and Max is what one payment can take

[sergeytimoshin]

Makes the example show a withdrawal with a private application fee, and a Max that one payment can actually take, with the API from #65.

• Example wallet_screen.dart: Unshield takes a recipient (this account by default) and pays the demo fee as a private output to the collector in the same spend; the balance line shows reserved and free amounts.
• Example action_sheet.dart: Max is the largest amount whose fee fits the payment's TokenBalance.limits entry, within the free balance; an amount past it reads "More than one payment can take now".
• Example spend_limit.dart: spendLimit picks the narrowest proof width for a spend's private outputs, largestAmount solves amount + fee(amount) <= limit; unit tests in spend_limit_test.dart.
• Example texts: a send no longer claims to hide its recipient, and the activity row for sent covers an unshield with a fee.

flutter analyze and flutter test pass in the example; the screens were not run on devnet (no API key here).

[github-actions]

Proof timing on phones

Before: main at 70becb6. After: this pull request at 0d9b2fc.

The proof, key loaded, of release builds in AWS Device Farm, by shape (notes → outputs): medians of each phone. Each phone's key load, witness and first runs are in its tables below.

by phone		1 → 2	2 → 2	4 → 2	8 → 2	16 → 2	24 → 2	merge 24 → 1
Samsung Galaxy A16 (low)	before	1.18 s	2.02 s	3.66 s	7.07 s	14.96 s	24.88 s	22.09 s
	after	1.21 s	2.02 s	3.66 s	7.02 s (-1 %)	14.93 s	25.04 s (+1 %)	21.91 s (-1 %)
Samsung Galaxy A56 (mid)	before	0.34 s	0.58 s	1.06 s	2.00 s	3.90 s	6.08 s	5.80 s
	after	0.35 s	0.59 s	1.07 s	1.98 s	3.75 s (-4 %)	6.05 s	5.79 s
Samsung Galaxy S25 (high)	before	0.20 s	0.32 s	0.58 s	1.12 s	2.22 s	3.47 s	4.65 s
	after	0.21 s	0.35 s	0.62 s	1.22 s (+8 %)	3.04 s (+37 % !)	4.15 s (+20 %)	3.79 s (-18 %)
iPhone 12 (low)	before	0.37 s	0.59 s	1.03 s	1.93 s	3.69 s	6.12 s	6.17 s
	after	0.37 s	0.60 s	1.11 s (+7 %)	2.05 s (+6 %)	3.93 s (+7 %)	6.36 s (+4 %)	6.44 s (+5 %)
iPhone 15 (mid)	before	0.36 s	0.59 s	1.04 s	1.96 s	3.70 s	5.70 s	5.59 s
	after	0.32 s	0.50 s (-14 %)	0.91 s (-13 %)	1.70 s (-13 %)	3.16 s (-14 %)	5.38 s (-6 %)	5.53 s (-1 %)
iPhone 17 Pro (high)	before	0.21 s	0.34 s	0.62 s	1.16 s	2.12 s	3.54 s	3.47 s
	after	0.21 s	0.37 s	0.63 s	1.19 s	2.18 s (+3 %)	3.56 s	3.51 s

Samsung Galaxy A16, Android 14, low tier

by scenario		1 → 2	2 → 2	4 → 2	8 → 2	16 → 2	24 → 2	merge 24 → 1
first run, including download	before	5.70 s (download: 2.93 s, 8.8 MiB)	11.62 s (download: 7.03 s, 15.6 MiB)	20.85 s (download: 12.52 s, 28.9 MiB)	35.07 s (download: 19.04 s, 55.9 MiB)	79.30 s (download: 47.51 s, 109.5 MiB)	124.29 s (download: 73.63 s, 171.6 MiB)	116.09 s (download: 68.53 s, 165.0 MiB)
	after	5.65 s (download: 2.76 s, 8.8 MiB) (-1 %)	11.47 s (download: 6.90 s, 15.6 MiB) (-1 %)	20.23 s (download: 11.95 s, 28.9 MiB) (-3 %)	41.17 s (download: 24.97 s, 55.9 MiB) (+17 %)	77.60 s (download: 47.67 s, 109.5 MiB) (-2 %)	131.49 s (download: 80.06 s, 171.6 MiB) (+6 %)	120.40 s (download: 72.70 s, 165.0 MiB) (+4 %)
warm	before	1.23 s	2.12 s	3.72 s	7.19 s	15.23 s	26.02 s	22.91 s
	after	1.28 s (+4 %)	2.09 s	3.72 s	7.16 s	15.37 s (+1 %)	25.67 s (-1 %)	22.33 s (-3 %)
first run after restart	before	1.15 s	2.18 s	3.80 s	7.49 s	15.63 s	25.46 s	23.25 s
	after	1.19 s	2.22 s	3.92 s (+3 %)	7.39 s (-1 %)	15.45 s (-1 %)	26.25 s (+3 %)	22.60 s (-3 %)
repeated after restart	before	1.23 s	2.07 s	3.76 s	7.17 s	15.24 s	25.41 s	21.93 s
	after	1.23 s	2.03 s	3.77 s	6.91 s (-4 %)	15.21 s	25.21 s (-1 %)	22.15 s (+1 %)

by stage		1 → 2	2 → 2	4 → 2	8 → 2	16 → 2	24 → 2	merge 24 → 1
key load	before	0.05 s	0.11 s	0.14 s	0.20 s	0.35 s	0.58 s	0.65 s
	after	0.08 s	0.11 s	0.15 s	0.24 s	0.33 s	0.50 s (-13 %)	0.67 s
witness	before	0.03 s	0.03 s	0.05 s	0.13 s	0.24 s	0.23 s	0.15 s
	after	0.02 s	0.04 s	0.08 s	0.11 s	0.21 s	0.36 s (+55 % !)	0.08 s (-46 % !)
prove	before	1.18 s	2.02 s	3.66 s	7.07 s	14.96 s	24.88 s	22.09 s
	after	1.21 s	2.02 s	3.66 s	7.02 s (-1 %)	14.93 s	25.04 s (+1 %)	21.91 s (-1 %)

Samsung Galaxy A56, Android 15, mid tier

by scenario		1 → 2	2 → 2	4 → 2	8 → 2	16 → 2	24 → 2	merge 24 → 1
first run, including download	before	7.69 s (download: 6.80 s, 8.8 MiB)	5.23 s (download: 3.78 s, 15.6 MiB)	9.34 s (download: 6.71 s, 28.9 MiB)	17.51 s (download: 12.56 s, 55.9 MiB)	27.23 s (download: 17.46 s, 109.5 MiB)	41.59 s (download: 25.96 s, 171.6 MiB)	40.64 s (download: 25.75 s, 165.0 MiB)
	after	2.43 s (download: 1.55 s, 8.8 MiB) (-68 % !)	3.72 s (download: 2.27 s, 15.6 MiB) (-29 % !)	7.06 s (download: 4.40 s, 28.9 MiB) (-24 % !)	13.04 s (download: 8.11 s, 55.9 MiB) (-26 % !)	26.17 s (download: 16.57 s, 109.5 MiB) (-4 %)	42.22 s (download: 26.98 s, 171.6 MiB) (+2 %)	41.34 s (download: 26.65 s, 165.0 MiB) (+2 %)
warm	before	0.34 s	0.59 s	1.05 s	2.01 s	3.90 s	6.14 s	5.79 s
	after	0.36 s	0.57 s	1.06 s	2.02 s	3.73 s (-4 %)	6.12 s	5.84 s (+1 %)
first run after restart	before	0.56 s	0.65 s	1.17 s	2.16 s	4.24 s	6.41 s	6.11 s
	after	0.59 s	0.67 s	1.14 s	2.16 s	4.15 s (-2 %)	6.52 s (+2 %)	6.17 s (+1 %)
repeated after restart	before	0.35 s	0.60 s	1.07 s	2.04 s	3.93 s	6.14 s	5.92 s
	after	0.35 s	0.60 s	1.08 s	2.00 s	3.77 s (-4 %)	6.11 s	5.86 s (-1 %)

by stage		1 → 2	2 → 2	4 → 2	8 → 2	16 → 2	24 → 2	merge 24 → 1
key load	before	0.08 s	0.03 s	0.06 s	0.09 s	0.17 s	0.21 s	0.18 s
	after	0.12 s	0.03 s	0.05 s	0.09 s	0.16 s	0.23 s	0.19 s
witness	before	0.00 s	0.01 s	0.01 s	0.02 s	0.05 s	0.06 s	0.05 s
	after	0.00 s	0.01 s	0.01 s	0.02 s	0.04 s	0.06 s	0.05 s
prove	before	0.34 s	0.58 s	1.06 s	2.00 s	3.90 s	6.08 s	5.80 s
	after	0.35 s	0.59 s	1.07 s	1.98 s	3.75 s (-4 %)	6.05 s	5.79 s

Samsung Galaxy S25, Android 15, high tier

by scenario		1 → 2	2 → 2	4 → 2	8 → 2	16 → 2	24 → 2	merge 24 → 1
first run, including download	before	1.70 s (download: 1.19 s, 8.8 MiB)	2.41 s (download: 1.63 s, 15.6 MiB)	4.35 s (download: 2.99 s, 28.9 MiB)	8.33 s (download: 5.80 s, 55.9 MiB)	16.14 s (download: 11.26 s, 109.5 MiB)	26.40 s (download: 18.61 s, 171.6 MiB)	25.67 s (download: 18.09 s, 165.0 MiB)
	after	1.56 s (download: 1.09 s, 8.8 MiB) (-8 %)	2.31 s (download: 1.52 s, 15.6 MiB) (-4 %)	4.19 s (download: 2.88 s, 28.9 MiB) (-4 %)	9.24 s (download: 6.79 s, 55.9 MiB) (+11 %)	15.71 s (download: 10.75 s, 109.5 MiB) (-3 %)	25.05 s (download: 17.09 s, 171.6 MiB) (-5 %)	23.41 s (download: 15.46 s, 165.0 MiB) (-9 %)
warm	before	0.20 s	0.32 s	0.57 s	1.09 s	2.14 s	3.43 s	3.31 s
	after	0.19 s	0.31 s	0.56 s	1.10 s	2.17 s	3.50 s (+2 %)	3.77 s (+14 %)
first run after restart	before	0.29 s	0.35 s	0.63 s	1.26 s	2.50 s	3.80 s	6.47 s
	after	0.35 s (+20 % !)	0.42 s (+19 %)	0.74 s (+18 %)	1.42 s (+12 %)	4.43 s (+78 % !)	5.17 s (+36 % !)	5.03 s (-22 % !)
repeated after restart	before	0.20 s	0.35 s	0.63 s	1.22 s	2.41 s	4.83 s	6.16 s
	after	0.24 s	0.41 s (+18 %)	0.75 s (+19 %)	1.38 s (+13 %)	4.04 s (+68 % !)	4.98 s (+3 %)	3.94 s (-36 % !)

by stage		1 → 2	2 → 2	4 → 2	8 → 2	16 → 2	24 → 2	merge 24 → 1
key load	before	0.04 s	0.01 s	0.02 s	0.05 s	0.09 s	0.13 s	0.28 s
	after	0.05 s	0.02 s	0.03 s	0.05 s	0.14 s (+68 % !)	0.17 s	0.14 s (-48 % !)
witness	before	0.00 s	0.01 s	0.01 s	0.03 s	0.05 s	0.08 s	0.08 s
	after	0.00 s	0.01 s	0.02 s	0.03 s	0.07 s	0.08 s	0.06 s
prove	before	0.20 s	0.32 s	0.58 s	1.12 s	2.22 s	3.47 s	4.65 s
	after	0.21 s	0.35 s	0.62 s	1.22 s (+8 %)	3.04 s (+37 % !)	4.15 s (+20 %)	3.79 s (-18 %)

iPhone 12, iOS 18.5, low tier

by scenario		1 → 2	2 → 2	4 → 2	8 → 2	16 → 2	24 → 2	merge 24 → 1
first run, including download	before	1.59 s (download: 0.56 s, 8.8 MiB)	2.26 s (download: 0.72 s, 15.6 MiB)	5.37 s (download: 2.81 s, 28.9 MiB)	9.40 s (download: 4.54 s, 55.9 MiB)	20.31 s (download: 10.84 s, 109.5 MiB)	24.74 s (download: 9.00 s, 171.6 MiB)	22.70 s (download: 7.18 s, 165.0 MiB)
	after	1.52 s (download: 0.55 s, 8.8 MiB) (-4 %)	2.14 s (download: 0.72 s, 15.6 MiB) (-6 %)	3.86 s (download: 1.26 s, 28.9 MiB) (-28 % !)	7.45 s (download: 2.42 s, 55.9 MiB) (-21 % !)	15.08 s (download: 5.03 s, 109.5 MiB) (-26 % !)	23.73 s (download: 7.33 s, 171.6 MiB) (-4 %)	23.28 s (download: 7.09 s, 165.0 MiB) (+3 %)
warm	before	0.33 s	0.56 s	0.94 s	1.78 s	3.37 s	5.71 s	6.03 s
	after	0.32 s	0.54 s	0.98 s	1.90 s (+6 %)	3.62 s (+7 %)	6.04 s (+6 %)	6.33 s (+5 %)
first run after restart	before	0.40 s	0.72 s	1.25 s	2.27 s	4.21 s	6.90 s	6.67 s
	after	0.40 s	0.71 s	1.25 s	2.34 s (+3 %)	4.41 s (+5 %)	7.32 s (+6 %)	7.00 s (+5 %)
repeated after restart	before	0.38 s	0.65 s	1.13 s	2.12 s	3.97 s	6.47 s	6.33 s
	after	0.41 s	0.68 s	1.21 s (+7 %)	2.23 s (+5 %)	4.85 s (+22 % !)	6.72 s (+4 %)	6.59 s (+4 %)

by stage		1 → 2	2 → 2	4 → 2	8 → 2	16 → 2	24 → 2	merge 24 → 1
key load	before	0.02 s	0.03 s	0.05 s	0.10 s	0.18 s	0.22 s	0.25 s
	after	0.02 s	0.03 s	0.06 s	0.11 s	0.18 s	0.26 s	0.25 s
witness	before	0.00 s	0.00 s	0.00 s	0.00 s	0.01 s	0.01 s	0.01 s
	after	0.00 s	0.00 s	0.00 s	0.01 s	0.01 s	0.01 s	0.01 s
prove	before	0.37 s	0.59 s	1.03 s	1.93 s	3.69 s	6.12 s	6.17 s
	after	0.37 s	0.60 s	1.11 s (+7 %)	2.05 s (+6 %)	3.93 s (+7 %)	6.36 s (+4 %)	6.44 s (+5 %)

iPhone 15, iOS 18.5, mid tier

by scenario		1 → 2	2 → 2	4 → 2	8 → 2	16 → 2	24 → 2	merge 24 → 1
first run, including download	before	1.44 s (download: 0.51 s, 8.8 MiB)	2.20 s (download: 0.68 s, 15.6 MiB)	3.93 s (download: 1.24 s, 28.9 MiB)	10.39 s (download: 5.45 s, 55.9 MiB)	14.24 s (download: 4.65 s, 109.5 MiB)	21.41 s (download: 7.19 s, 171.6 MiB)	21.11 s (download: 6.95 s, 165.0 MiB)
	after	1.27 s (download: 0.47 s, 8.8 MiB) (-12 %)	1.86 s (download: 0.67 s, 15.6 MiB) (-15 %)	3.37 s (download: 1.22 s, 28.9 MiB) (-14 %)	6.46 s (download: 2.33 s, 55.9 MiB) (-38 % !)	12.62 s (download: 4.55 s, 109.5 MiB) (-11 %)	21.15 s (download: 7.34 s, 171.6 MiB) (-1 %)	20.07 s (download: 6.91 s, 165.0 MiB) (-5 %)
warm	before	0.36 s	0.55 s	1.03 s	1.96 s	3.36 s	5.51 s	5.78 s
	after	0.30 s (-18 %)	0.46 s (-16 %)	0.85 s (-17 %)	1.61 s (-18 %)	3.02 s (-10 %)	5.18 s (-6 %)	5.12 s (-11 %)
first run after restart	before	0.39 s	0.63 s	1.09 s	1.98 s	4.20 s	6.37 s	5.80 s
	after	0.34 s	0.57 s (-11 %)	1.02 s (-7 %)	1.88 s (-5 %)	3.44 s (-18 %)	5.56 s (-13 %)	6.13 s (+6 %)
repeated after restart	before	0.35 s	0.59 s	1.06 s	2.17 s	4.11 s	5.93 s	5.64 s
	after	0.33 s	0.55 s	0.97 s (-8 %)	1.81 s (-17 %)	3.32 s (-19 %)	5.40 s (-9 %)	6.36 s (+13 %)

by stage		1 → 2	2 → 2	4 → 2	8 → 2	16 → 2	24 → 2	merge 24 → 1
key load	before	0.01 s	0.02 s	0.04 s	0.07 s	0.17 s	0.24 s	0.22 s
	after	0.01 s	0.02 s	0.03 s	0.06 s	0.10 s (-40 % !)	0.16 s (-32 % !)	0.17 s
witness	before	0.00 s	0.00 s	0.00 s	0.01 s	0.01 s	0.01 s	0.01 s
	after	0.00 s	0.00 s	0.00 s	0.00 s	0.01 s	0.01 s	0.01 s
prove	before	0.36 s	0.59 s	1.04 s	1.96 s	3.70 s	5.70 s	5.59 s
	after	0.32 s	0.50 s (-14 %)	0.91 s (-13 %)	1.70 s (-13 %)	3.16 s (-14 %)	5.38 s (-6 %)	5.53 s (-1 %)

iPhone 17 Pro, iOS 26.3.1, high tier

by scenario		1 → 2	2 → 2	4 → 2	8 → 2	16 → 2	24 → 2	merge 24 → 1
first run, including download	before	0.85 s (download: 0.31 s, 8.8 MiB)	4.51 s (download: 3.62 s, 15.6 MiB)	7.27 s (download: 5.62 s, 28.9 MiB)	9.10 s (download: 6.16 s, 55.9 MiB)	24.38 s (download: 18.77 s, 109.5 MiB)	12.56 s (download: 3.11 s, 171.6 MiB)	14.32 s (download: 5.07 s, 165.0 MiB)
	after	0.96 s (download: 0.45 s, 8.8 MiB) (+13 %)	1.62 s (download: 0.73 s, 15.6 MiB) (-64 % !)	2.79 s (download: 1.22 s, 28.9 MiB) (-62 % !)	5.60 s (download: 2.59 s, 55.9 MiB) (-38 % !)	10.37 s (download: 4.60 s, 109.5 MiB) (-57 % !)	16.51 s (download: 7.04 s, 171.6 MiB) (+31 % !)	16.12 s (download: 6.80 s, 165.0 MiB) (+13 %)
warm	before	0.20 s	0.33 s	0.58 s	1.12 s	2.05 s	3.50 s	3.44 s
	after	0.20 s	0.34 s	0.62 s	1.17 s	2.15 s (+5 %)	3.54 s	3.52 s (+2 %)
first run after restart	before	0.23 s	0.38 s	0.68 s	1.23 s	2.27 s	3.70 s	3.63 s
	after	0.23 s	0.39 s	0.68 s	1.24 s	2.32 s	3.74 s	3.63 s
repeated after restart	before	0.22 s	0.37 s	0.65 s	1.20 s	2.23 s	3.62 s	3.53 s
	after	0.22 s	0.37 s	0.65 s	1.21 s	2.23 s	3.62 s	3.55 s

by stage		1 → 2	2 → 2	4 → 2	8 → 2	16 → 2	24 → 2	merge 24 → 1
key load	before	0.01 s	0.01 s	0.02 s	0.03 s	0.06 s	0.09 s	0.09 s
	after	0.00 s	0.01 s	0.02 s	0.03 s	0.06 s	0.09 s	0.09 s
witness	before	0.00 s	0.00 s	0.00 s	0.01 s	0.01 s	0.01 s	0.01 s
	after	0.00 s	0.00 s	0.00 s	0.01 s	0.01 s	0.01 s	0.01 s
prove	before	0.21 s	0.34 s	0.62 s	1.16 s	2.12 s	3.54 s	3.47 s
	after	0.21 s	0.37 s	0.63 s	1.19 s	2.18 s (+3 %)	3.56 s	3.51 s