fix(samples/frontend): floor default quote amount to corridor minimum

[pengying]

Corridor minimums vary widely (e.g. USD->EUR ~$23, USD->BRL ~$12, USD->MXN
~$1), so a fixed default still failed with AMOUNT_OUT_OF_RANGE on higher-min
corridors. The quote step now looks up the corridor's minSendingAmount via
the exchange-rates endpoint and floors the default amount to it (+5% buffer
for FX drift). maxSendingAmount is intentionally not used as it is unreliable
for some corridors in this environment.

Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com

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2 Skipped Deployments

Project	Deployment	Actions	Updated (UTC)
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[pengying]

• fix(samples/frontend): floor default quote amount to corridor minimum #605 👈 (View in Graphite)
• fix(samples/frontend): scale default quote amount by source currency decimals #604
• fix(samples/kotlin): select crypto network when funding a quote from USDC #603
• feat(samples/kotlin): add exchange-rates lookup flow #602
• feat(samples/kotlin): add USD → USDC wallet payout flow #593
• fix(samples/kotlin): send customer email for USDB embedded wallets #590
• feat(samples/kotlin): support GRID_API_BASE_URL override #589
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[greptile-apps]

Greptile Summary

This PR fixes AMOUNT_OUT_OF_RANGE errors in the sample frontend's quote step by fetching the corridor's minSendingAmount via the exchange-rates API before building the request body, then flooring the default amount to that minimum plus a 5% FX-drift buffer.

• A new useEffect fires on sourceCurrency/destCurrency change, calls /api/exchange-rates with a probe amount, and stores the max minSendingAmount across all returned exchange-rate records.
• The body-building useEffect now takes minSendingAmount as a dependency and raises lockedCurrencyAmount to Math.max(defaultAmount, Math.ceil(minSendingAmount * 1.05)) when the corridor minimum exceeds the fixed default.
• Cancellation via a cancelled flag is handled correctly for in-flight fetches on rapid corridor switches.

Confidence Score: 5/5

Safe to merge — the change is confined to the sample frontend's quote step and only affects how the default body amount is pre-populated; users can still edit the value manually before submitting.

The new exchange-rates prefetch is well-scoped: cancellation is handled correctly, the two-effect sequencing is idiomatic React, and Math.max over corridor minimums is the safe choice. The silent-failure path was already flagged in the previous review thread and is a known trade-off in this demo context. No data is persisted or mutated by this component.

No files require special attention beyond what was already discussed in the earlier review thread about the catch handler.

Important Files Changed

Filename	Overview
samples/frontend/src/steps/CreateQuote.tsx	Adds a preflight exchange-rates fetch to discover the corridor's minSendingAmount and floors the default quote amount to it (+ 5% buffer). Logic is correct for the happy path; the previously-flagged silent-failure case (catch resets to null, body falls back to un-floored default) remains unaddressed in this revision.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant U as User
    participant C as CreateQuote
    participant ER as /api/exchange-rates
    participant Q as /api/quotes

    U->>C: Change sourceCurrency / destCurrency (or mount)
    C->>C: setMinSendingAmount(null)
    C->>C: "body useEffect → lockedCurrencyAmount = defaultAmount (un-floored)"
    C->>ER: "GET /api/exchange-rates?sourceCurrency=...&destinationCurrency=...&sendingAmount=probe"
    alt Success
        ER-->>C: "{ data: [{ minSendingAmount }] }"
        C->>C: setMinSendingAmount(max of all mins)
        C->>C: "body useEffect → lockedCurrencyAmount = max(defaultAmount, ceil(min * 1.05))"
    else Failure (network / API error)
        ER-->>C: error
        C->>C: catch → setMinSendingAmount(null)
        C->>C: "body useEffect → lockedCurrencyAmount = defaultAmount (still un-floored)"
    end
    U->>C: Click Create Quote
    C->>Q: "POST /api/quotes { lockedCurrencyAmount, ... }"
    Q-->>C: Quote response
    C->>U: Display result

Loading

%%{init: {'theme': 'base', 'themeVariables': {"darkMode": true, "background": "#0d1117", "primaryColor": "#21262d", "primaryTextColor": "#e6edf3", "primaryBorderColor": "#8b949e", "lineColor": "#8b949e", "textColor": "#e6edf3", "edgeLabelBackground": "#161b22", "actorBkg": "#21262d", "actorBorder": "#8b949e", "actorTextColor": "#e6edf3", "actorLineColor": "#8b949e", "signalColor": "#8b949e", "signalTextColor": "#e6edf3", "noteBkgColor": "#373320", "noteBorderColor": "#d4a72c", "noteTextColor": "#f0e6c0", "labelBoxBkgColor": "#21262d", "labelBoxBorderColor": "#8b949e", "labelTextColor": "#e6edf3", "loopTextColor": "#e6edf3", "activationBkgColor": "#30363d", "activationBorderColor": "#8b949e"}}}%%
sequenceDiagram
    participant U as User
    participant C as CreateQuote
    participant ER as /api/exchange-rates
    participant Q as /api/quotes

    U->>C: Change sourceCurrency / destCurrency (or mount)
    C->>C: setMinSendingAmount(null)
    C->>C: "body useEffect → lockedCurrencyAmount = defaultAmount (un-floored)"
    C->>ER: "GET /api/exchange-rates?sourceCurrency=...&destinationCurrency=...&sendingAmount=probe"
    alt Success
        ER-->>C: "{ data: [{ minSendingAmount }] }"
        C->>C: setMinSendingAmount(max of all mins)
        C->>C: "body useEffect → lockedCurrencyAmount = max(defaultAmount, ceil(min * 1.05))"
    else Failure (network / API error)
        ER-->>C: error
        C->>C: catch → setMinSendingAmount(null)
        C->>C: "body useEffect → lockedCurrencyAmount = defaultAmount (still un-floored)"
    end
    U->>C: Click Create Quote
    C->>Q: "POST /api/quotes { lockedCurrencyAmount, ... }"
    Q-->>C: Quote response
    C->>U: Display result

Loading

_{Reviews (2): Last reviewed commit: "fix(samples/frontend): floor default quo..." | Re-trigger Greptile}

[greptile-apps]

Silent min-fetch failure leaves body at the un-floored default

When the exchange-rates request fails (transient network error, API error, non-ok response), the .catch() handler silently resets minSendingAmount to null. The body useEffect then fires with flooredToMin = 0, so lockedCurrencyAmount falls back to defaultAmount — potentially below the corridor minimum. There is no in-UI indication of this, so a developer would only discover the fallback by seeing the AMOUNT_OUT_OF_RANGE error after submitting the quote. Surfacing the error (e.g. via setError) or at least displaying a warning in the form header would make the failure visible before submission.

Prompt To Fix With AI

This is a comment left during a code review.
Path: samples/frontend/src/steps/CreateQuote.tsx
Line: 53

Comment:
**Silent min-fetch failure leaves body at the un-floored default**

When the exchange-rates request fails (transient network error, API error, non-`ok` response), the `.catch()` handler silently resets `minSendingAmount` to `null`. The body `useEffect` then fires with `flooredToMin = 0`, so `lockedCurrencyAmount` falls back to `defaultAmount` — potentially below the corridor minimum. There is no in-UI indication of this, so a developer would only discover the fallback by seeing the `AMOUNT_OUT_OF_RANGE` error after submitting the quote. Surfacing the error (e.g. via `setError`) or at least displaying a warning in the form header would make the failure visible before submission.

How can I resolve this? If you propose a fix, please make it concise.

[pengying]

Merge activity

• Jun 26, 12:16 AM UTC: A user started a stack merge that includes this pull request via Graphite.
• Jun 26, 12:28 AM UTC: Graphite rebased this pull request as part of a merge.
• Jun 26, 12:28 AM UTC: @pengying merged this pull request with Graphite.

The base branch was changed.

[restamp-bot]

8ec790d is a pure rebase onto c310a47. Approving based on @shreyav's previous approval of cd77ced.