Phase 3d — Captcha solving (DEFERRED — sequenced last, non-MVP-blocking)

Part of Phase 3 — WebURL Crawler & Crawl Billing. See 00-umbrella-plan.md. Status: deferred. Build only after 03a/03b/03c ship and there's a real need. Depends on 03a (the StealthyFetcher tier) and the per-crawl proxy from 03b. Touches the crawl billing model from 03c.

Why deferred

Scrapling already solves Cloudflare Turnstile/Interstitial via solve_cloudflare=True on the StealthyFetcher tier (03a; references/Scrapling/scrapling/fetchers/stealth_chrome.py:38,90). That covers the most common interstitial. The remaining captcha types (reCAPTCHA v2/v3, hCaptcha, image) need a paid third-party solver, add latency (10–60s/solve), have <100% success, and carry target-ToS/legal considerations. None of that is MVP-blocking, so it's sequenced last.

Scope boundary

Challenge	Handled by	Where
Cloudflare Turnstile / Interstitial	Scrapling `solve_cloudflare=True`	`03a`, StealthyFetcher tier
reCAPTCHA v2/v3, hCaptcha, image	`captchatools` (this subplan)	StealthyFetcher `page_action`

Grounding (libraries verified)

captchatools is itself the provider registry. new_harvester(api_key, solving_site, sitekey, captcha_url, captcha_type="v2"|"v3"|"hcaptcha"|"image", ...) → .get_token(proxy=…, proxy_type=…, user_agent=…, b64_img=…) returns a token string (references/Captcha-Tools/README.md:28–47). solving_site ∈ {capmonster,2captcha,anticaptcha,capsolver,captchaai} (:113–127). Errors: ErrNoBalance, ErrWrongAPIKey, ErrWrongSitekey, … via captchatools.exceptions (:136–155). Implication: we do not rebuild a multi-provider class hierarchy (unlike 03b's proxy registry) — captchatools already dispatches across the 5 services. Our layer is thin: config resolution + page detection/injection glue.
captchatools only harvests a token; it does not inject it. The caller must drop the token into the page (g-recaptcha-response / h-captcha-response textarea, or invoke the JS callback) and submit.
Injection requires a browser page, so this only works on the StealthyFetcher tier. Scrapling exposes page_action: "a function that takes the page object, runs after navigation, and does the automation you need" (stealth_chrome.py:30,82). AsyncFetcher (HTTP) and DynamicFetcher cannot solve interactive captchas — a captcha hit there must escalate to StealthyFetcher.

Sketch (when built)

Config layer (app/utils/captcha/, mirroring app/utils/proxy/'s config resolution from 03b):
- CaptchaConfig = (enabled, solving_site, api_key), resolved from env defaults or per-connector config (same resolve_* pattern as proxy in 03b).
- Env: CAPTCHA_SOLVING_ENABLED (default FALSE), CAPTCHA_SOLVER_PROVIDER, CAPTCHA_SOLVER_API_KEY. Off by default → zero captcha attempts (and zero solver cost).
Detection + injection page_action factory — builds a callback passed to StealthyFetcher.async_fetch(..., page_action=…):
- Detect sitekey in DOM (.g-recaptcha[data-sitekey], .h-captcha[data-sitekey], reCAPTCHA-v3 via grecaptcha.execute).
- Harvest: new_harvester(solving_site, api_key, sitekey, captcha_url=page.url, captcha_type=…).get_token(proxy=<the 03b per-crawl proxy>, user_agent=<page UA>).
- Inject token + dispatch events / invoke callback; submit; wait for navigation.
Crawler escalation: only the StealthyFetcher tier attempts solving; a captcha detected on a lower tier escalates to StealthyFetcher (the ladder already ends there per 03a).
Dependency: add captchatools to pyproject.toml (build-time only).

The billing asymmetry (the hard part — decide at build time)

03c bills the workspace owner per successful crawl (CrawlOutcomeStatus.SUCCESS), and absorbs proxy cost into the flat $1/1000. Captcha is different: the solver charges per attempt (~$1–3 / 1000, type-dependent) regardless of whether the crawl ultimately succeeds. So a failed solve = real upstream cost with no billable success — proxy's absorb-it model doesn't transfer cleanly.

Options (resolve when this is actually built):

(a) Separate per-solve charge — meter each solve attempt as its own unit (e.g. web_crawl_captcha usage_type, its own *_MICROS_PER_* knob), independent of crawl SUCCESS. Most cost-honest; bills even on failed solves (matching the upstream charge).
(b) Higher crawl price when captcha enabled — absorb into a fatter flat rate; simplest UX, but cross-subsidizes failed solves and easy-vs-hard pages unevenly.
(c) Cost-plus pass-through — meter the solver's reported cost × margin.

Recommendation leaning (a) (separate per-attempt unit) because the upstream cost is per-attempt and significant, but defer the final call.

Risks / considerations

Solver-tier only. No captcha solving on the HTTP/DynamicFetcher tiers; must escalate to StealthyFetcher (slower, browser-backed).
Latency & flakiness. Solves take 10–60s and aren't guaranteed; tune timeouts and a max-attempts cap so a single URL can't burn unbounded solver credit.
Solver-account balance. ErrNoBalance/ErrWrongAPIKey (README.md:136–155) must surface clearly and disable solving rather than loop.
Proxy coherence. Pass the same per-crawl proxy (03b) to get_token(proxy=…) so the solve happens from the same IP as the crawl (some captchas IP-bind the token).
Policy / ToS. Automated captcha solving may violate a target site's terms; gate behind the explicit CAPTCHA_SOLVING_ENABLED flag and treat as an opt-in, owner-acknowledged capability.

Out of scope

Anything in 03a/03b/03c.
Cloudflare Turnstile (already handled by Scrapling in 03a).
Final captcha billing model — chosen at build time (see options above).

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