fix(swift-sdk): cap the faucet captcha's aggregate proof-of-work

[QuantumExplorer]

Hardening for the TestnetFaucet client that merged in #4098: its per-field challenge bounds (c ≤ 256, d ≤ 6) still admit an aggregate of ~4.3B expected SHA-256 attempts, so a misbehaving or compromised same-domain faucet endpoint can pin the device's cores across 256 parallel solver tasks until the 30-second timeout on every faucet tap. Add an aggregate bound (c × 16^d ≤ 64M, ~10× the live faucet's actual soft challenge of c=100, d=4 ≈ 6.6M) so oversized challenges throw and route to the web-faucet fallback instead of burning CPU/battery.

Split out of #4049 when that PR was narrowed to the send_payment fee fix — this commit was originally review hardening there (ad29deae05) and was deliberately parked for a standalone PR rather than dropped. One hunk, comment-documented; Swift parse-checked.

Note: the faucet client's placement in the SDK package is itself under review (it may move back app-side); if #4098 is reverted, this rides along with the file.

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 25c9c949-f9a0-44d3-a2e1-ee4fc47c69cf

📥 Commits

Reviewing files that changed from the base of the PR and between d6ba78a and 7ab9aa6.

📒 Files selected for processing (1)

• packages/swift-sdk/Sources/SwiftDashSDK/Utils/TestnetFaucet.swift

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/faucet-captcha-pow-cap

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[thepastaclaw]

✅ Review complete (commit 7ab9aa6)

[thepastaclaw]

Code Review

This is a small, well-scoped hardening fix that adds an aggregate proof-of-work bound (c × 16^d ≤ 64M) after the existing per-field bounds check in TestnetFaucet.swift's solveCaptcha. Both agents verified the arithmetic against the stated live-faucet baseline (~6.6M) and worst-case (~4.3B) and confirmed the guard is correctly placed before any solver tasks spawn. Only one low-severity documentation nitpick was found; no correctness, security, or consensus-relevant issues.

Source (experiment sonnet-primary-opus-quarter-sample-20260710, cohort sonnet_primary, bucket 2, trigger new_pr, specialists none): reviewers codex/general=gpt-5.6-sol(completed); sonnet5/general=claude-sonnet-5(completed); verifier=verifier-sonnet5-4100-1783853670=claude-sonnet-5; orchestrator=openai/gpt-5.6-sol reasoning=high (orchestration-only, not a reviewer/verifier).

💬 1 nitpick(s)

[thepastaclaw]

Code Review

This new_push follow-up (b0f1ef1 → 7ab9aa6) makes exactly one change: the aggregate PoW-cap error message now reports the computed expectedWork value and the 64,000,000 threshold alongside c and d, directly resolving the sole prior nitpick. The guard's math and placement are unchanged and remain correct (c × 16^d ≤ 64M, checked before any solver tasks spawn). No new issues in this delta or across the cumulative PR.

Source (experiment sonnet-primary-opus-quarter-sample-20260710, cohort sonnet_primary, bucket 2, trigger new_push, specialists none): reviewers codex/general=gpt-5.6-sol(completed); sonnet5/general=claude-sonnet-5(completed); verifier=verifier-sonnet5-4100-1783854540=claude-sonnet-5; orchestrator=openai/gpt-5.6-sol reasoning=high (orchestration-only, not a reviewer/verifier).