budgets: normalize limit_amount to avoid scientific notation breaking UpdateBudget

[CorinneVerheyde]

Rollback Plan

Revert this change and publish a new provider release.

As this change only normalizes limit_amount when reading aws_budgets_budget, rollback risk is low and isolated to the Budgets resource.

Changes to Security Controls

No.

Description

Large limit_amount values are returned by the AWS Budgets API in scientific notation (e.g. 2.51E+7).

The provider stores this value directly in state during Read:

d.Set("limit_amount", budget.BudgetLimit.Amount)

This causes subsequent UpdateBudget calls to fail with:

ValidationException: Value at 'newBudget.budgetLimit.amount' failed to satisfy constraint

This change normalizes limit_amount to a plain decimal string during Read, so subsequent updates continue to send a valid value to AWS.

An acceptance test TestAccBudgetsBudget_largeLimitAmountUpdate was added to reproduce the issue:

• create a budget with a large limit_amount
• perform an in-place update by adding a notification
• verify the update succeeds

Before fix: fails on update
After fix: passes

Relations

Closes #47487

References

Output from Acceptance Testing

% make testacc TESTS=TestAccBudgetsBudget_largeLimitAmountUpdate PKG=budgets

make: Verifying source code with gofmt...
==> Checking that code complies with gofmt requirements...
make: Running acceptance tests on branch: 🌿 main 🌿...
TF_ACC=1 go1.26.2 test ./internal/service/budgets/... -v -count 1 -parallel 20 -run='TestAccBudgetsBudget_largeLimitAmountUpdate'  -timeout 360m -vet=off
2026/04/16 23:56:36 Creating Terraform AWS Provider (SDKv2-style)...
2026/04/16 23:56:36 Initializing Terraform AWS Provider (SDKv2-style)...
=== RUN   TestAccBudgetsBudget_largeLimitAmountUpdate
=== PAUSE TestAccBudgetsBudget_largeLimitAmountUpdate
=== CONT  TestAccBudgetsBudget_largeLimitAmountUpdate
--- PASS: TestAccBudgetsBudget_largeLimitAmountUpdate (67.31s)
PASS
ok      github.com/hashicorp/terraform-provider-aws/internal/service/budgets    67.635s

[github-actions]

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[github-actions]

✅ Thank you for correcting the previously detected issues! The maintainers appreciate your efforts to make the review process as smooth as possible.