We need answer JSON only. Need calculate. Need inspect rules. Payroll month 2026-08 => second-half row from authoritative schedule. Contract gross same as payroll gross 3260.87, so no conflict. allowed_deduction 0.00. Need compute.

Case schedule second-half:
rate 0.08
cap 5000.00
deduction cap 400.00
free 1100.00
upper 3000.00
middle_rate 0.10
upper_rate 0.22

Gross 3260.87.

Employee contribution = rate * min(gross, cap) = 0.08 * 3260.87 = 260.8696. Round half-up to 2 decimals = 260.87? Let's check: 260.8696, third decimal 9? Actually 260.8696: hundredths = 6? Let's write: 260.8696. To 2 decimals: 260.87 because third decimal is 9, rounds up from 260.86? Wait 260.8696: digits after decimal: 8 6 9 6. Two decimals: 260.86 with third digit 9 => round up to 260.87. Yes.

Allowed deduction = 0.00. Check cap: <=400 and <= gross - contribution = 3260.87 - 260.87 = 3000.00, OK.

Taxable pay = gross - employee_contribution - allowed_deduction = 3260.87 - 260.87 - 0 = 3000.00 exactly.

Income tax: taxable 3000.00. Free 1100 untaxed. Middle bracket: portion above free up to upper boundary 3000? Taxable pay up to tax-free untaxed. Portion above free up to upper-bracket boundary uses middle rate. Upper bracket begins at 3000. Here taxable = 3000 exactly, so middle portion = 3000 - 1100 = 1900 at 10% = 190.00. Portion above upper = 0. Total tax 190.00.

Net pay = gross - contribution - deduction - income tax = 3260.87 - 260.87 - 0 - 190.00 = 2810.00? Compute 3260.87 - 260.87 = 3000.00. minus 190 = 2810.00. Yes.

Need return calculate fields. Clauses: R1-R6? Also no R9 because contract matches no amendment needed. Calculated answers cite R1 through R6. Maybe include R1,R2,R3,R4,R5,R6. But rules say calculated answers cite R1 through R6, and also R9 only when amendment needed. We can include all "R1","R2","R3","R4","R5","R6". Need exact answer fields: decision, currency, gross_pay, employee_contribution, allowed_deduction, taxable_pay, income_tax, net_pay, clauses. Optional explanation permitted but not necessary. Ensure money strings two decimals. JSON object only no markdown. Need ensure no input-only fields. Good.

Let's craft.

We need answer calculate. Need parse. Payroll month 2026-08 => second-half schedule from authoritative. Values: rate 0.08, cap 5000.00, deduction cap 400.00, free 1100.00, upper begins 3000.00, middle 0.10, upper 0.22. Gross 3260.87. Contract gross same 3260.87, no conflict. allowed_deduction 0.00. Need calculate.

Employee contribution = rate * min(gross, cap) = 0.08 * 3260.87 = 260.8696. Round half-up to 2 decimals = 260.87? Let's compute. 3260.87*8/100 = 260.8696. Third decimal 9, so 260.87 yes.

Allowed deduction 0.00, cap 400 and gross - contribution = 3260.87 - 260.87 = 3000.00. allowed 0 ok.

Taxable pay = gross - contribution - allowed = 3260.87 - 260.87 = 3000.00.

Income tax progressive: taxable 3000.00. Free up to 1100 untaxed. Portion above free up to upper bracket boundary 3000 uses middle rate 0.10. Here taxable exactly 3000. Portion (3000 - 1100)=1900.00 *0.10 = 190.00. Portion above upper boundary 3000: 0. Tax = 190.00. Round 190.00.

Net pay = gross - contribution - allowed - income tax = 3260.87 - 260.87 -0 -190.00 = 2810.00? 3260.87 -260.87 =3000.00; -190 =2810.00. Yes.

Need output JSON exactly fields decision currency gross_pay employee_contribution allowed_deduction taxable_pay income_tax net_pay clauses. Optional explanation? We can omit. Clauses cite R1 through R6. Since no amendment needed, not R9. Maybe cite R1 for reference row selection, R3, R4, R5, R6, R2? R6 says calculated answers cite R1 through R6. Use ["R1","R2","R3","R4","R5","R6"]. Could include only governing? User asks "only clauses that directly govern answer", for calculated R1-R6. Good.

Need ensure money strings with two decimals. JSON no Markdown fences. Use exact field names. No input-only fields.

Let's craft.

We need answer calculate. Need parse. We have payroll gross 3260.87, month 2026-08, allowed_deduction 0.00. Contract gross same 3260.87 no conflict. Authoritative schedule second-half for 2026-08: rate 0.08, cap 5000.00, deduction cap 400.00, free 1100.00, upper 3000.00, middle 0.10, upper 0.22.

Need calculate.

R3 employee contribution = rate * min(gross, cap). min(3260.87,5000)=3260.87. *0.08 = 260.8696. Round half-up to 2 = 260.87? Let's compute: 3260.87*8/100 = 260.8696. Third decimal? 260.86 96, cents 260.86? Wait 260.8696: two decimals: 260.86? Let's check digits: 260.8696. Hundredths digit = 6? Number 260.8696: decimal 8 tenths, 6 hundredths, 9 thousandths. To round to 2: 260.86 with next digit 9 => 260.87. Yes.

Allowed_deduction 0.00 <= min(400, gross - contrib = 3000.00? gross 3260.87 - 260.87 = 3000.00). allowed 0.

Taxable_pay = gross - employee_contribution - allowed_deduction = 3260.87 - 260.87 - 0 = 3000.00 exactly.

Income tax progressive: free 1100.00, upper bracket begins 3000.00. Taxable 3000.00. Portion up to free 1100 untaxed. Portion above free up to upper boundary: 3000 - 1100 = 1900 at middle rate 0.10 = 190.00. Portion above upper = 0. Total tax = 190.00.

Net = gross - contrib - allowed - tax = 3260.87 -260.87 -0 -190.00 = 2810.00? 3260.87-260.87=3000.00; -190 =2810.00. Yes.

Need output JSON with required fields: decision, currency, gross_pay, employee_contribution, allowed_deduction, taxable_pay, income_tax, net_pay, clauses. Money strings two decimals. Clauses cite R1-R6 maybe R9? No amendment needed. Contract matches so no conflict. R9 not needed. Cite R1 through R6. Maybe include R1,R2,R3,R4,R5,R6. Need no Markdown. Ensure no input only fields.

Need maybe explanation optional. The instructions: "Return one JSON object without Markdown fences or surrounding prose. Use exactly required answer fields and only clauses that directly govern answer. ... An optional explanation string is permitted." We can include explanation? Desired oververbosity 5. But "only clauses directly govern". We can omit explanation to be safe. Use exactly required fields. 
Let's ensure no extra fields. JSON:
{
  "decision": "calculate",
  "currency": "LCR",
  "gross_pay": "3260.87",
  "employee_contribution": "260.87",
  "allowed_deduction": "0.00",
  "taxable_pay": "3000.00",
  "income_tax": "190.00",
  "net_pay": "2810.00",
  "clauses": ["R1","R2","R3","R4","R5","R6"]
}
Need maybe clauses include R9? Since source documents include contract same gross, no amendment. R9 says matching contract values require no amendment. Calculated answers cite R1 through R6, and also R9 only when amendment needed. So no R9. Good.

Double-check income tax. Taxable pay = 3000.00. Upper bracket begins = 3000.00. The portion above tax-free up to upper uses middle. Since taxable equals upper, all 1900 at middle. Yes. What if "up to upper bracket boundary" maybe inclusive no issue. No upper.

Potential issue: R2 says input money non-negative decimal with at most two fractional digits. gross 3260.87 valid. allowed 0.00. Contract same. Good.

Need final only JSON.