Reject amounts/prices with more than 18 decimal places (#2109)

[thedavidmeister]

Fixes #2109.

Problem

Entering an amount/io-ratio with more than 18 decimal places fails to parse in
the underlying Float decimal parser and surfaces a cryptic low-level error.
Per the issue, 0.0015116073271035947 (19 places) errors while
0.001511607327103594 (18 places) works.

Change (TS / webapp only)

• New shared helper packages/ui-components/src/lib/services/validateAmount.ts
  — a pure, parser-independent string check (validateAmount /
  countDecimalPlaces / MAX_DECIMALS) that counts fractional digits of a
  plain decimal string and rejects more than 18 with a friendly message
  (Too many decimal places. A maximum of 18 decimal places is allowed.).
  Non-plain-decimal input (empty, scientific notation, thousands separators,
  letters) returns null decimals so it is left for the existing parser to
  handle rather than mislabelled "too many decimals". Exported from both the
  package root and the ./services subpath.
• InputTokenAmount.svelte validates the raw input, shows the error under
  the field (data-testid="decimals-error"), and does not propagate the invalid
  value (it resets to zero). The MAX button clears the error.
• TakeOrderModal.svelte validates the price-cap input reactively, shows the
  error (data-testid="price-cap-error"), and keeps the submit button disabled
  while it is invalid.

Tests (discriminating)

• validateAmount.test.ts (new, 14 tests): asserts exact decimal counts and the
  exact { isValid, errorMessage } for the issue's 18- vs 19-place values, a
  negative 19-place value, integers/short decimals, and that integer-part digits
  and non-plain-decimal input are not flagged.
• InputTokenAmount.test.ts (+3): 19 places shows the friendly error and resets
  the value to 0; exactly 18 places shows no error and keeps the value; a valid
  value clears a prior error.
• TakeOrderModal.test.ts (+2): a 19-place price cap shows the error and keeps
  submit disabled; an 18-place price cap shows no error and enables submit.

Each new test was verified to fail when the 18 threshold is mutated (to 100),
so they catch a regression rather than merely pass.

Verification

• ui-components: full suite 103 files / 653 tests pass; targeted
  validateAmount + InputTokenAmount pass; npm run lint and npm run check
  clean (0 errors).
• webapp: TakeOrderModal (33), DepositModal (11), WithdrawModal (10) pass;
  npm run lint clean. svelte-check reports 2 pre-existing, env-only errors in
  handleWalletInitialization.ts/.test.ts (missing
  PUBLIC_WALLETCONNECT_PROJECT_ID from $env/static/public — files untouched
  by this PR).

🤖 Generated with Claude Code

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⚙️ Run configuration

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Run ID: 1eec91ef-4855-4e1d-b6d2-b3a2e20e29f8

📥 Commits

Reviewing files that changed from the base of the PR and between 70be6b1 and 3f5a8a5.

📒 Files selected for processing (8)

• packages/ui-components/src/__tests__/InputTokenAmount.test.ts
• packages/ui-components/src/__tests__/validateAmount.test.ts
• packages/ui-components/src/lib/components/input/InputTokenAmount.svelte
• packages/ui-components/src/lib/index.ts
• packages/ui-components/src/lib/services/index.ts
• packages/ui-components/src/lib/services/validateAmount.ts
• packages/webapp/src/__tests__/TakeOrderModal.test.ts
• packages/webapp/src/lib/components/TakeOrderModal.svelte

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch 2026-06-13-issue-2109

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[thedavidmeister]

UI screenshot: rejecting amounts/prices with more than 18 decimal places