engine

Imported from matt-FFFFFF/agent-plugins (plugins/omo/skills/ultimate-browsing/engine/AGENTS.md). Install upstream with npx skills add matt-FFFFFF/agent-plugins --skill engine. Copyright stays with the author.

ultimate-browsing/engine — Generic WAF-Profile Fetch Chain (Python)

Generated: 2026-08-10 / 38d268995

UPSTREAM BASELINE AND VERSION POLICY

READ THIS BEFORE TOUCHING engine/** OR PROPOSING AN UPSTREAM SYNC.

This engine is NOT project-original code. It is a vendored-and-modified snapshot of fivetaku/insane-search, and the version we run on is a deliberate choice, not an accident of neglect.

The pin

We intentionally track a pinned baseline plus local divergence, not upstream HEAD. There is no submodule and no automated drift check for this engine (unlike the frontend skill's upstream submodules): the vendored files ARE the source of truth, and upstream is a reference we port FROM, deliberately, file by file.

Why we do not blind-rebase onto upstream HEAD

1. Upstream reset its public history. On 2026-08-06 upstream published a single squashed commit, 019ee16 refactor: reset public history at 0.14.0, discarding the prior public history through 0.13.x. There is no upstream commit graph to rebase onto and no way to cherry-pick an individual upstream change by sha — only whole-file diffing against a moving HEAD.
2. Upstream 0.14.0 REMOVED capability. The endpoint-mining / internal-API auto-derivation / site-recipe subsystems that upstream carried publicly between 0.12.0 and 0.14.0 are gone from upstream HEAD. Syncing to HEAD is therefore not strictly an upgrade: parts of it are a downgrade relative to the intermediate versions, and none of it is recoverable from the reset history.
3. Our tree diverged on purpose. The KEEP list below is functionality upstream never had. A wholesale overwrite with upstream HEAD would silently delete it.
4. Different threat model. Our engine ships inside a published npm package and a public marketplace mirror, under a CI no-site-name gate and a de-personalization deny-list. Upstream carries neither constraint, so upstream code is not drop-in-shippable here.

KEEP — our divergences a re-vendor MUST NOT regress

These exist only in our tree. Any upstream sync that removes or bypasses one of them is a regression, not an upgrade:

• Phase 2.5 surrogate retrieval (surrogate.py, surrogates.yaml) — archive / reader / proxy routes tried before paying for a browser spin-up, with per-entry last_verified staleness handling and --allow-proxy gating.
• Provenance / trust contract (result_schema.py) — Provenance and Trust literals on every result, so a snapshot can never be reported as the live page.
• Surrogate dead-end validation (L1.5 in validators.py) — interstitial titles and AMP-style redirect stubs rejected instead of returned as content.
• The no-site-name rule and its CI gate (bias_check.py) — zero hard-coded site names, brands, or target domains in engine/**.
• Module split of the fetch chain — curl_probe / referers / url_transforms / waf_detector / validators / executor / summary as separate modules rather than one monolith.
• The Python test suite under engine/tests/ with its HTML/JSON fixtures.
• De-personalization — no personal absolute paths, no personal auth token literals, no personal browser choice; enforced by depersonalization-gate.test.ts.
• Skill-level layering — the engine is Tier 1 under a router that also owns Tier 1.5 (agent-reach) and Tier 2 (CloakBrowser + agent-browser). Upstream has no such tiering.

WANT — upstream improvements worth porting forward

Our snapshot predates these; they are wanted, and each must be ported as a reviewed, site-agnostic change that preserves every KEEP item above. Port individually; never as a tree overwrite:

• Content quality: dedicated markdown conversion of fetched HTML, main-content extraction, PDF text extraction, and JSON-LD rescue when the HTML body is thin.
• Transient-failure retry and render-merge of statically fetched HTML with the browser-rendered DOM.
• Differential block classification — distinguishing a bot-detection block from an infrastructure or authentication failure, instead of collapsing both into challenge.
• Additional stealth fetch backends beyond the current Playwright templates, and additional WAF vendor profiles.
• Per-host route learning — remembering which route succeeded for a host, with a TTL and a bounded store. Must stay runtime state, never committed site knowledge (R4).
• Engine-level Phase 0 routing — the official-public-API preference is currently only a documented rule (R5) the agent can skip; upstream moved it into code so it cannot be skipped. Worth adopting.

OUT OF SCOPE

• The removed upstream endpoint-mining / internal-API auto-derivation / site-recipe subsystems. They are absent from upstream HEAD and are not reconstructed here. They also sit against R3/R4 and R7's anti-bias rule: discovered internal endpoints are runtime findings, never committed engine knowledge.
• Any upstream code carrying site-specific selectors, domains, or brand names. It fails bias_check.py at the door; re-derive it site-agnostically or leave it out.
• Automated upstream tracking. No submodule, no drift check, no auto-bump. Syncing is a deliberate, reviewed, human-initiated act.

THE SYNC RULE

Any future upstream sync preserves BOTH sides. Concretely:

1. Diff the specific upstream capability you want against our tree — do not overwrite files wholesale, and never git checkout upstream over engine/.
2. Port it as its own reviewed change, keeping every KEEP item intact.
3. Re-run python3 engine/bias_check.py and the engine/tests/ suite; a port that introduces a site name or breaks a fixture does not ship.
4. Update the pin table above (baseline, date, what was ported) in the same change, plus the provenance section of ../ATTRIBUTION.md.
5. If a port must drop a KEEP item, say so explicitly in the PR and get it agreed first — silent regressions of the KEEP list are the failure mode this policy exists to prevent.

OVERVIEW

A 17-module Python package embedded in the ultimate-browsing skill: a site-agnostic fetch chain that escalates from a cheap curl probe to a real browser, with declarative WAF and surrogate registries. Not "optional scripts" — it has its own CLI entry (python3 -m engine URL), two YAML config schemas, a 4-file test suite, and a standalone CI guard. Package exports (__init__.py): fetch, FetchResult, Attempt, Verdict, ValidationResult, validate, CHALLENGE_MARKERS, detect, TRANSFORMS, apply_transform.

THE NO-SITE-NAME RULE (enforced in CI)

engine/** must contain zero hard-coded site names, brands, or target domains. Site specifics belong to runtime hints or observations, never to code. bias_check.py is a standalone scanner enforcing this: a brand denylist, a URL regex scan, an allowlist for genuine infrastructure hosts (archive.org, r.jina.ai, google.com, httpbin.org, relay.invalid), and a # NOTE-BIAS-OK comment convention for legitimate exemptions such as test fixtures.

python3 engine/bias_check.py       # fails on any site-specific leak

FETCH CHAIN PHASES

fetch(url, ...)                                   # fetch_chain.py
  Phase 1  curl_probe.py    — curl_cffi TLS-impersonation probe
  Phase 2  grid             — referer/transform/device attempt grid
  Phase 2.5 surrogate.py    — third-party archive/reader/proxy routes
  Phase 3  executor.py      — capability-matched Playwright fallback

Ordering is not hardcoded: each waf_profiles.yaml profile carries a fallback_when_challenge list that drives the ladder. surrogate_wayback precedes browser executors in every profile, so archives are tried before paying for a browser spin-up.

PROVENANCE / TRUST CONTRACT

result_schema.py puts two literals on every FetchResult:

• Provenance = "live" | "snapshot" | "proxy"
• Trust = "origin" | "archive" | "untrusted"

A snapshot result carries snapshot_timestamp and must be cited with that timestamp — never presented as the live page. surrogates.yaml kind fixes these values: archive -> snapshot/archive, reader -> live, proxy -> proxy/untrusted.

SURROGATE REGISTRY (surrogates.yaml)

Site-agnostic infrastructure only. Every entry carries last_verified (ISO date); entries older than 90 days are deprioritized and flagged, because surrogate routes rot (a 2026-08 probe found 4 of 6 known routes dead or stubbed). proxy routes are MITM by construction: they require the explicit --allow-proxy flag and never receive Cookie or Authorization headers. Every surrogate response is re-validated with target_url set, so an interstitial or a redirect stub is rejected instead of returned as content.

VALIDATOR LAYERS (validators.py)

L1    challenge markers (CHALLENGE_MARKERS)
L1.5  surrogate dead ends — interstitial titles + AMP-style redirect stubs
      (is_redirect_stub(), needs target_url)
L2    size/shape fingerprints
L3+   content checks

CLI

python3 -m engine URL [--selector S] [--device auto|desktop|mobile]
                      [--timeout 25] [--max-attempts 12]
                      [--no-playwright] [--allow-proxy] [--json] [--trace]

TESTS

tests/ — test_surrogate.py (staleness, proxy gating, short-circuit), test_surrogate_validators.py, test_fetch_chain.py, test_playwright_templates.py, plus HTML/JSON fixtures under tests/fixtures/.

NOTES

• summary.py emits an R7 API-first hint after >=3 challenge verdicts against a known WAF profile: look for /api/, /graphql, or .json endpoints, which usually carry weaker WAF protection than the HTML surface.
• templates/ holds the Playwright JS templates (playwright_real_chrome.js, playwright_mobile_chrome.js) the executor drives.
• url_transforms.py transforms stay domain-agnostic (mobile_subdomain, am_prefix, drop_www).
• Parent: ../AGENTS.md (ultimate-browsing skill root).